JP7587355B2 - Transmission server, transmission device, receiving device, and program - Google Patents

Description

The present invention relates to the technical fields of satellite broadcasting, terrestrial broadcasting, fixed communication, and mobile communication, and in particular to a transmission server that links broadcasting and communication and uses communication to enable data retransmission in response to a retransmission request from the receiving side, a transmitting device and receiving device related to digital broadcasting, and a program.

In satellite and terrestrial digital broadcasting systems, error-correcting codes are used as a technique for improving transmission performance in the presence of white noise. For example, advanced wideband satellite digital broadcasting uses LDPC (Low Density Parity Check) codes, which are powerful error-correcting codes with performance approaching the Shannon limit, which is the theoretical upper limit of utilization efficiency for the signal-to-noise ratio (see, for example, non-patent documents 1 and 2). However, in digital broadcasting, transmission conditions can deteriorate to the point that the signal cannot be restored by error-correcting codes alone, such as attenuation due to rain in satellite digital broadcasting and fading in terrestrial digital broadcasting.

On the other hand, in digital wireless communication, data retransmission control using ARQ (Automatic Repeat reQuest) is known as a data compensation technique other than error correction code (see, for example, Patent Documents 1 and 2). In digital wireless communication, the use of Hybrid ARQ, which combines error correction code and ARQ, can improve transmission performance, making it possible to transmit data with fewer retransmissions than using ARQ alone, and under conditions that cannot be compensated for by error correction code alone. However, conventional prior art using Hybrid ARQ is limited to two-way communication such as FPU and mobile phone base station communication, and a technique for compensating data with Hybrid ARQ in conjunction with communication in one-way broadcast such as broadcasting has not been established.

Although this does not constitute Hybrid ARQ, a technology has been disclosed in which, when the transmission conditions of digital broadcasting deteriorate, ARQ is performed from the receiving side to the transmitting side via an IP (Internet Protocol) network, which is a communication path that allows two-way communication, and data is resent from the transmitting side (see, for example, Patent Document 3).

A typical IP network is assumed to have an erasure channel (PEC: Packet Erasure Channel) where information is lost due to some kind of failure such as line congestion. Therefore, in Hybrid ARQ in digital wireless communication, error correction codes dedicated to IP communication, which is an erasure channel, such as LDPC-CC (Convolutional Codes) (see, for example, Patent Document 4) and LDGM (Low-Density Generator Matrix) codes (see, for example, Patent Document 5) are used as error correction codes for data compensation. These LDPC-CC and LDGM codes are error correction codes based on LDPC codes, just like advanced broadband satellite digital broadcasting, but they are codes designed with only IP communication, which is an erasure channel, in mind, and it is necessary to prepare an encoder and decoder for error correction codes dedicated to IP communication.

JP 2014-050034 A International Publication No. 2007/069406 International Publication No. 2015/048569 International Publication No. 2010/001610 International Publication No. 2015/022910

R. G. Gallager, “Low-Density Parity-Check Codes,” in Research Monograph series Cambridge, MIT Press, December 1963. "Advanced Wideband Digital Satellite Broadcasting Transmission Method (ISDB-S3) Standard ARIB STD-B44 Version 2.1", [online], revised March 25, 2016, ARIB, [Retrieved April 13, 2020], Internet <URL: https://www.arib.or.jp/kikaku/kikaku_hoso/std-b44.html>

As described above, in digital wireless communications, the use of Hybrid ARQ, which combines error correction codes and ARQ, can improve transmission performance, making it possible to transmit data with fewer retransmissions than when using ARQ alone, and under conditions that cannot be compensated for by error correction codes alone.

However, there is no established technique for linking communications with one-way broadcasting and compensating for data using Hybrid ARQ.

Therefore, even in digital broadcasting, a technique for compensating data using Hybrid ARQ, which combines error correction codes and ARQ in cooperation with communication and combines digital broadcasting and communication, is desired. For example, when the transmission conditions of digital broadcasting deteriorate, transmission performance can be improved by constructing a transmission system in which ARQ is performed from the receiving side to the transmitting side via an IP network, which is a communication path that allows two-way communication, and the transmitting side retransmits the data. In other words, since current digital broadcasting only assumes data compensation using error correction codes, compensating data related to digital broadcasting using Hybrid ARQ can also respond to deterioration of transmission conditions that cannot be corrected by error correction codes. Also, even when an ARQ system is configured using only IP communication, the number of retransmissions related to ARQ can be reduced by configuring Hybrid ARQ, which combines error correction codes related to broadcasting and communication.

However, if an error correction code for IP communication, as disclosed in Patent Documents 4 and 5, etc., is applied to a system using ARQ as disclosed in Patent Document 3 in order to build a transmission system using Hybrid ARQ that combines broadcasting and communication, it becomes necessary to prepare an encoder and decoder for the error correction code for digital broadcasting and an encoder and decoder for IP communication, and to have a mechanism for cooperating them, which increases the scale of the equipment.

Therefore, there is a demand to efficiently combine "error correction codes used in digital broadcasting" with ARQ, and to build a transmission system that uses Hybrid ARQ by integrating broadcasting and communications.

In other words, there is a demand for improving the error correction capability of digital broadcasting by linking digital broadcasting with communication over an IP network without increasing the size of the encoder in the transmitting device and the decoder in the receiving device, and by configuring a transmission system that realizes Hybrid ARQ, for example, by combining concatenated error correction codes of LDPC codes and BCH codes with retransmission requests using IP communication.

In addition, in general IP networks, the probability of packet loss and the manner in which packets are lost vary depending on the time of day and the line used, for example when the line is congested. Therefore, when implementing Hybrid ARQ in digital broadcasting and communication networks without increasing the scale of equipment, it is necessary to focus on block codes among the error correcting codes used in digital broadcasting, and to make the data to be retransmitted via the IP network into coded data in the block code of digital broadcasting, and to implement variable control of this coded data according to the communication quality of the IP network, thereby improving the transmission efficiency via the IP network.

Therefore, there is a need for a technique for improving the error correction capability of digital broadcasting and realizing an efficient Hybrid ARQ by configuring a transmission system that links digital broadcasting and communication via an IP network without increasing the size of the encoder in the transmitting device for digital broadcasting and the decoder in the receiving device, and that combines block codes such as concatenated codes for error correction of LDPC codes and BCH codes, and retransmission according to the communication quality of the IP network in response to a retransmission request using IP communication.

In view of the above problems, the object of the present invention is to provide a transmission server, a transmission device and a reception device related to digital broadcasting, and a program that enable efficient data retransmission based on the encoded data of the error-correcting code used in digital broadcasting, in response to a retransmission request from the receiving side, using communication, in accordance with the communication quality of the IP network.

The transmission server of the present invention digitally modulates coded data that has been coded using an error correction code related to digital broadcasting, and transmits the digitally modulated coded data to a receiving device via a broadcast transmission path. The transmission server stores the coded data for a predetermined period of time and transmits the data to an IP (Internet a storage unit which sequentially inputs coded data generated by the transmitting device, manages the coded data in a time series manner by a synchronization signal based on a frame number or time information of an error correcting code frame constituting a code length of the error correcting code, and stores a predetermined time of the coded data managed in a time series manner while updating the coded data; and a receiving unit which receives a retransmission request packet generated when a bit error in the coded data cannot be corrected by the error correcting code at the receiving device via an IP network, and controls retransmission of the coded data related to the retransmission request to the receiving device, extracts communication quality information measured by the receiving device based on communication with the transmitting server and retransmission request information indicating the coded data of the error correcting code frame related to the retransmission request, which are stored in the retransmission request packet, and determines whether or not to change the coding rate of a block code of the coded data generated by the transmitting device according to a predetermined coding rate change criterion based on the communication quality information, and retransmits the coded data, and based on the retransmission request information according to a result of the determination, reads out the coded data related to the retransmission request from the storage unit, configures coded data with an adaptively changed coding rate, and transmits the coded data to the receiving device. a coding rate adaptive change unit that performs error correction coding processing for switching between changing and not changing a coding rate of a block code of the coded data generated by the transmitting device under the control of the retransmission request processing unit, and, when changing the coding rate, changing the coding rate by distinguishing whether to make the coding rate higher or lower than the coding rate of the coded data generated by the transmitting device and transmitted over a broadcast transmission path, based on the same coding method as the error correction coding method used by the transmitting device and among a predetermined number of coding rates that are made available to the transmitting device; and an IP packet generation unit that generates a coded data packet in an IP packet format that stores the coded data related to the retransmission request configured through the control of the retransmission request processing unit, and transmits the coded data to the receiving device via an IP network , wherein the retransmission request processing unit determines whether to change the coding rate of the coded data generated by the transmitting device and retransmit it in accordance with the predetermined coding rate change criterion, based on either or both of delay information and packet loss rate information of a communication line measured by the receiving device in predetermined period units, as the communication quality information .

In the transmission server of the present invention, the coding rate adaptive change unit, when changing the coding rate of the coded data generated by the transmission device under the control of the retransmission request processing unit, adds padding bits known to the receiving device to the information bits of the coded data according to the coding rate to be changed, replaces the parity added to the coded data generated by the transmission device with the parity of the block code with the coding rate changed obtained by performing the error correction coding process, and generates coded data for retransmission from which the padding bits have been removed, and when changing the coding rate to a lower coding rate than the coding rate before the change, divides the information bits of the coded data by a division method predetermined between the transmission and reception, adds padding bits known to the receiving device to each of the divided information bits according to the coding rate to be changed, replaces the parity added to the coded data generated by the transmission device with the parity of the block code with the coding rate changed obtained by performing the error correction coding process, and generates coded data for retransmission from which the padding bits have been removed.

In the transmission server of the present invention, the coding rate adaptive change unit is characterized in that, when changing the coding rate of the coded data generated by the transmission device under the control of the retransmission request processing unit, in addition to changing the coding rate of the block code, it further has a means for changing the correction capability of the error correction code connected to the block code while maintaining the frame length of the error correction code frame after the coding rate change.

In the transmission server of the present invention, the IP packet generation unit is characterized in that it has an interleaving unit that generates an encoded data packet of an IP packet sequence by constructing an interleaved frame using the multiple error correction code frames and adding an identification header to the payload obtained by interleaving each error correction code frame longitudinally, a sequence number that identifies which bit in each error correction code frame it represents, and an IP header that is the header of the encoded data packet.

Furthermore, the transmitting device of the present invention is a transmitting device related to digital broadcasting, and is characterized in that the transmitting server of the present invention is provided inside the device.

Further, a receiving device of the present invention is a receiving device that receives a modulated wave signal that is digitally modulated by a transmitting device using an error correction code related to digital broadcasting and transmitted via a broadcast transmission path, the receiving device including: a demodulator that receives and demodulates the modulated wave signal; an error correction decoder that reconstructs an error correction code frame that constitutes a code length of the error correction code from the coded data obtained by demodulation and performs a decoding process corresponding to the error correction code to generate and reproduce received data; a retransmission request packet generator that generates a retransmission request packet in an IP packet format that includes retransmission request information indicating coded data of the error correction code frame related to a retransmission request for requesting retransmission of corresponding coded data when a bit error in coded data cannot be corrected using the error correction code, and transmits the retransmission request packet to a transmitting server of the present invention; an IP packet receiver that receives an coded data packet in an IP packet format that stores coded data retransmitted from the transmitting server in response to the retransmission request in response to the retransmission request packet, and extracts the coded data retransmitted in response to the retransmission request; and a delay related to communication with the transmitting server and a packet loss rate based on an amount of packet loss related to communication with the transmitting server for a predetermined period of time. and a communication quality measurement unit which measures and updates/holds communication quality information at a desired position and sequentially outputs communication quality information including either one or both of delay information and packet loss rate information of the communication line to the retransmission request packet generation unit so as to include the communication quality information in the retransmission request packet, the error correction decoding unit comprising a decoding feasibility determination unit which determines whether or not error correction decoding is possible for encoded data obtained from the transmitting device, and generates the retransmission request packet when it determines that bit errors in the encoded data cannot be corrected and the encoded data cannot be decoded; and a decoding feasibility determination unit which, when the encoding rate of the encoded data retransmitted in response to the retransmission request is not changed, demodulates the encoded data obtained the coding rate of the coded data being changed, and when the coding rate has been changed, adding padding bits according to the coding rate, attempting a decoding process through a complementation process related to replacement of the likelihood ratio required for decoding, and repeatedly requesting retransmission of the corresponding coded data until decoding is possible within a predetermined time; and when the coded data related to the retransmission request has been changed to a lower coding rate and the information bits have been divided (divided into two equal parts in an example described in detail later), a data combining unit recombines the divided decoded information bits in accordance with a division method predetermined between the coding rate and the transmission server to generate received data.

In the receiving device of the present invention, the error correction code is a concatenated code in which an LDPC code is an inner code and a BCH code is an outer code, and the decoding feasibility determination unit determines that a bit error in the coded data obtained from the transmitting device could not be corrected when the coded data is not error-free in the decoding process of the BCH code.

The receiving device of the present invention further includes a reception quality measurement unit that measures the reception quality of the received modulated wave signal, and the reception quality measurement unit maintains the broadcast reception path when the reception path at the time when the reception data is generated based on the encoded data that can be decoded by the error correction decoding unit is not via an IP network but is a broadcast reception path, and when the reception path at the time when the reception data is generated based on the encoded data that can be decoded by the error correction decoding unit is via an IP network, determines whether the reception quality is equal to or greater than a predetermined value, switches to the broadcast reception path if the reception quality is equal to or greater than the predetermined value, and maintains the reception path via the IP network if the reception quality is less than the predetermined value, and has a means for instructing the error correction decoding unit to continue to request a retransmission of the encoded data via the IP network and obtain the next encoded data by continuing to do so even after the retransmission request for the encoded data.

In the receiving device of the present invention, the IP packet receiving unit is characterized in that it has a deinterleaving unit that receives coded data packets of an IP packet sequence that stores coded data retransmitted in response to a retransmission request from the transmitting server in response to the retransmission request packet, and performs a reverse process of the interleaving performed by the transmitting server to extract the coded data retransmitted in response to the retransmission request.

Furthermore, the program of the present invention is configured as a program for causing a computer to function as a transmission server of the present invention.

Furthermore, the program of the present invention is configured as a program for causing a computer to function as a receiving device of the present invention.

According to the present invention, when data loss cannot be prevented by broadcast reception alone, a retransmission request is made from the receiving side to the transmitting side via an IP network, and the transmitting side is enabled to retransmit the data, so that the receiving side can supplement the data. In particular, by making the data retransmitted by the transmitting side via the IP network into coded data in the block code of digital broadcasting, and by variably controlling the coding rate of this coded data according to the communication quality of the IP network, it is possible to reduce the number of retransmission requests, and further improve the transmission efficiency via the IP network and strengthen the resistance to packet loss. In addition, by making both the error correction code used for broadcast reception and the error correction code used for transmission via the IP network the same as the coding format of the error correction code specified in the broadcasting standard, it is possible to realize this by preparing only one error correction decoder on the receiving side, and the equipment scale can be reduced.

1 is a block diagram showing a schematic configuration of a transmission system including a transmission server, a transmitting device, and a receiving device according to an embodiment of the present invention. 1 is a block diagram showing a schematic configuration of a transmission server and a transmission device according to an embodiment of the present invention. 10 is a flowchart showing a control flow relating to a retransmission request packet between a transmission server and a receiving device in an embodiment of the present invention. 1A to 1D are diagrams illustrating a method of generating coded data when the coding rate is changed by a coding rate adaptive change unit in a transmission server of an embodiment of the present invention (when coded data related to a retransmission request is changed to a higher coding rate). 1A to 1E are diagrams illustrating a method of generating coded data when the coding rate is changed by a coding rate adaptive change unit in a transmission server of one embodiment of the present invention (when coded data related to a retransmission request is changed to a lower coding rate). 11 is an explanatory diagram regarding interleaving processing of an IP packet generating unit in a transmission server according to an embodiment of the present invention. FIG. 1 is a block diagram showing a schematic configuration of a receiving device according to an embodiment of the present invention. 5 is a flowchart showing a reception control flow in a receiving device according to an embodiment of the present invention. 1 is a block diagram showing a schematic configuration of a transmission system including a transmission server, a transmitting device, and a receiving device according to an embodiment of the present invention. 4 is a flowchart showing a reception control flow in an advanced wideband satellite digital broadcast receiving device according to an embodiment of the present invention. 1A to 1E are diagrams illustrating a method of generating coded data when the coding rate is changed by a coding rate adaptive change unit in a transmission server of one embodiment of the present invention (when coded data related to a retransmission request is changed to a lower coding rate). 11 is an explanatory diagram of an interleaving process of an IP packet generating unit in a transmission server according to an embodiment of the present invention; FIG. 11A to 11F are diagrams showing a method of generating coded data when the coding rate is changed by the coding rate adaptive change unit in the transmission server of an application example according to the present invention (when the coded data related to a retransmission request is changed to a lower coding rate). FIG. 13 is a block diagram showing a schematic configuration of a receiving device according to a modified example of the present invention. 10 is a flowchart showing a reception control flow in a receiving device according to a modified example of the present invention. 1 is a diagram illustrating an outline of an operation when a transmission server according to an embodiment of the present invention transmits to a receiving device a coded data packet in which the coded data related to a retransmission request has been changed to a lower coding rate.

[Transmission System]
Fig. 1 is a block diagram showing a schematic configuration of a transmission system 1 including a transmission server 6, transmission devices 2 and 3, and a receiving device 5 according to an embodiment of the present invention. The transmission system 1 shown in Fig. 1 includes the transmission devices 2 and 3, the receiving device 5, one or more transmission servers 6, and a load balancing device 7 that is provided when multiple transmission servers 6 are configured.

The transmitting device 2 is a device that generates coded data by applying an error correction coding process to transmission data related to digital broadcasting and adding an error correction code parity, digitally modulates the coded data using a predetermined modulation method to generate a modulated wave signal, and emits radio waves related to digital broadcasting via a satellite broadcast transmission path including a broadcast satellite 4 via a transmitting antenna 2a. For example, the transmitting device 2 can be a transmitting device for advanced wideband satellite digital broadcasting. The transmitting device 2 also has a function of managing the sequentially generated coded data as an error correction code frame, adding a frame number or time information that functions as a synchronization signal, and transmitting the data to one or more transmission servers 6 via a local area network.

The transmitting device 3 is a device that generates coded data by applying an error correction coding process to transmission data related to digital broadcasting and adding an error correction code parity, digitally modulates the coded data using a predetermined modulation method to generate a modulated wave signal, and emits radio waves related to digital broadcasting via a terrestrial broadcast transmission path via a transmitting antenna 3a. For example, the transmitting device 3 can be a transmitting device for current or next-generation terrestrial digital broadcasting. The transmitting device 3 also has a function of managing the sequentially generated coded data as an error correction code frame, adding a frame number or time information that functions as a synchronization signal, and transmitting the data to one or more transmission servers 6 via a local area network.

The receiving device 5 has the functions of receiving and demodulating the modulated wave signal radiated by radio waves from the transmitting device 2 via the receiving antenna 5a, reconstructing the error correction code frame that constitutes the code length of the error correction code, and performing a decoding process corresponding to the error correction coding process in the transmitting device 2 to generate and reproduce the received data, and receiving and demodulating the modulated wave signal radiated by radio waves from the transmitting device 3 via the receiving antenna 5b, reconstructing the error correction code frame that constitutes the code length of the error correction code, and performing a decoding process corresponding to the error correction coding process in the transmitting device 3 to generate and reproduce the received data.

In addition, the receiving device 5 has the function of determining whether or not error correction decoding is possible for the encoded data obtained from the transmitting device 2 (or transmitting device 3), and if it determines that decoding is possible, it decodes the encoded data as is to generate received data, and if it determines that bit errors in the encoded data cannot be corrected and the encoded data cannot be decoded, it generates a retransmission request packet in the form of an IP packet requesting retransmission of the corresponding encoded data, and includes communication quality information in this retransmission request packet and transmits it to the transmitting server 6 via the IP network 8. Furthermore, the receiving device 5 has a function of receiving an IP packet format encoded data packet that stores the encoded data retransmitted from the transmission server 6 in response to the retransmission request (the encoded data is reconstructed by adaptively changing the encoding rate by distinguishing whether the encoding rate is higher or lower than the encoding rate of the encoded data transmitted over the broadcast transmission path in response to the communication quality information at the transmission server 6 side), extracting the encoded data retransmitted in response to the retransmission request, performing complementation according to the encoding rate for use in the decoding process, and repeating a request for retransmission of the corresponding encoded data until the decoding process can decode the encoded data within a predetermined time, and a function of recombining the decoded information bits that have been divided according to a division method predetermined between the transmitting server 6 and the encoded data related to the retransmission request and the information bits that have been divided (divided into two equal parts in an example described in detail later) to generate received data. Note that when the receiving device 5 cannot decode the encoded data by the decoding process within a predetermined time, it generates the received data in a state that includes bit errors.

Each of one or more transmission servers 6 is configured as a computer that stores a predetermined amount of coded data from transmission device 2 (or transmission device 3) that digitally modulates coded data using error correction codes related to digital broadcasting and transmits the coded data to reception device 5 via a broadcast transmission path, and for coded data requested for retransmission from reception device 5, reconstructs the coded data by changing the coding rate of the coded data transmitted via the broadcast transmission path in accordance with communication quality information, and generates coded data packets of an IP packet sequence that has been subjected to interleaving processing in this example, and makes the coded data packets available for transmission to reception device 5 via IP network 8.

That is, the transmission server 6 has a function of sequentially inputting the encoded data generated by the transmitting device 2 (or transmitting device 3) via the local area network, managing it in chronological order using a synchronization signal based on the frame number of the error correction code frame that constitutes the code length of the error correction code or on time information, and storing it while updating it for a predetermined period of time, and a function of receiving a retransmission request packet for the encoded data together with communication quality information when a bit error in the encoded data cannot be corrected using the error correction code used by the transmitting device 2 (or transmitting device 3) at the receiving device 5 via the IP network 8, and adaptively determining whether to increase or decrease the coding rate of the encoded data transmitted over the broadcast transmission path according to the communication quality information for the receiving device 5. It has a function of controlling the retransmission of the encoded data by changing the encoding rate, and a function of forming m error correction code frames having consecutive synchronization signals (frame number or time information) starting with an error correction code frame constituting the encoded data having a synchronization signal (frame number or time information) related to the retransmission request at the same encoding rate as the encoded data having the synchronization signal (frame number or time information) related to the retransmission request to construct an interleaved frame, performing interleaving processing on the interleaved frame in a direction perpendicular to the m error correction code frames to generate encoded data packets of an IP packet sequence, and transmitting the encoded data packets to the receiving device 5 via the IP network 8.

In particular, when the transmission server 6 changes the coding rate of the encoded data generated by the transmission device 2 (or transmission device 3) and retransmits it, if the coding rate is converted to a higher coding rate than before the change, it has the function of adding padding bits known to the receiving device 5 to the information bits of the encoded data according to the changed coding rate, adding the parity of the block code with the changed coding rate obtained by performing error correction coding processing in place of the parity added to the encoded data generated by the transmission device 2 (or transmission device 3), and generating encoded data for retransmission from which the padding bits have been removed. In addition, when the transmission server 6 changes the coding rate of the coded data generated by the transmission device 2 (or transmission device 3) and retransmits it, if the coding rate is to be converted to a lower coding rate than before the change, the transmission server 6 divides the information bits of the coded data between the transmission and reception (between the transmission server 6 and the reception device 5) using a division method determined in advance (dividing into two equal parts in an example described in detail later), adds padding bits known to the reception device 5 side to each of the divided information bits according to the coding rate to be changed, replaces the parity added to the coded data generated by the transmission device 2 (or transmission device 3) with the parity of the block code with the changed coding rate obtained by performing error correction coding processing, and adds it, and generates coded data for retransmission with the padding bits removed.

In the example transmission system 1 shown in FIG. 1, the transmission system 1 has been described as including the transmission device 2 and the transmission device 3, but it may include only one of the transmission device 2 and the transmission device 3. In the example transmission system 1 shown in FIG. 1, the transmission device 2 (or the transmission device 3) and the transmission server 6 have been described as separate entities, but it may be configured such that the transmission device 2 (or the transmission device 3) includes the transmission server 6, and one or more transmission devices 2 (or the transmission devices 3) are connected by a simple signal cable instead of being connected by a local area network.

When multiple transmission servers 6 are configured, the load distribution device 7 is provided between the multiple transmission servers 6 and the IP network 8. When retransmission request packets are received from many receiving devices 5 via the IP network 8, the load distribution device 7 distributes the processing load of the multiple transmission servers 6 and transmits the encoded data packets related to the retransmission request in parts. In the transmission system shown in FIG. 1, the load distribution device 7 is interposed between multiple receiving devices 5 whose users have been registered in advance, so that even if the number of registered users increases, it is only necessary to add a transmission server 6. However, when the transmission servers 6 corresponding to the number of registered users allowed in advance are individually provided, the installation of the load distribution device 7 may be omitted and the transmission servers 6 may be directly connected to the IP network 8.

Below, we will explain in more detail the transmitting device 2 (or transmitting device 3), the transmitting server 6, and the receiving device 5 in that order.

[Transmitting device]
Fig. 2 is a block diagram showing a schematic configuration of the transmission server 6 and the transmission device 2 (or the transmission device 3) according to an embodiment of the present invention. Note that the transmission device 2 (or the transmission device 3) shown in Fig. 2 shows only the main components according to the present invention, and the description of other components such as energy (power) dispersal processing is omitted.

Transmitting device 2 and transmitting device 3 employ error correction coding processing and modulation methods suitable for their respective broadcast transmission paths (satellite broadcast transmission paths or terrestrial broadcast transmission paths), but as shown in FIG. 2, they will be described collectively as including an error correction coding unit 21 and a modulation unit 22.

The error correction coding unit 21 is an encoder that performs error correction coding processing on transmission data related to digital broadcasting, adds error correction code parity, generates coded data, and outputs the coded data to the modulation unit 22. The error correction coding unit 21 also has a function of managing the sequentially generated coded data as an error correction code frame, adding a frame number or time information that functions as a synchronization signal, and transmitting the data to the transmission server 6 via the local area network.

The modulation unit 22 digitally modulates the coded data obtained from the error correction coding unit 21 using a predetermined modulation method to generate a modulated wave signal, and emits radio waves related to digital broadcasting via the broadcast transmission path.

When transmitting data related to digital broadcasting via a terrestrial broadcasting transmission path, the data can be in MPEG2-TS format, which is described in ARIB STD-B31 and used in terrestrial digital broadcasting, and when transmitting data via a satellite broadcasting transmission path, the data can be in TLV (Type Length Value) format, which is described in ARIB STD-B44 and used in advanced wideband satellite digital broadcasting.

In current terrestrial digital broadcasting, error correction coding is performed using a concatenated code in which a convolutional code is used as the inner code and a Reed-Solomon code is used as the outer code. In the next generation of terrestrial digital broadcasting, it is being considered to perform error correction coding using a concatenated code in which an LDPC code is used as the inner code and a BCH (Bose-Chaudhuri-Hocquenghem) code is used as the outer code. In advanced wideband satellite digital broadcasting, error correction coding will be performed using a concatenated code in which an LDPC code is used as the inner code and a BCH code is used as the outer code.

[Sending server]
The transmission server 6 shown in Figure 2 is configured as a computer that sequentially inputs coded data from the transmission device 2 (or transmission device 3) that digitally modulates coded data encoded using error correction codes related to digital broadcasting and transmits the coded data to the receiving device 5 via a broadcast transmission path, stores the data while updating it for a predetermined period of time, and adaptively changes the coding rate of coded data requested for retransmission by the receiving device 5 by distinguishing whether to set the coding rate to be higher or lower than the coding rate of the coded data transmitted via the broadcast transmission path in accordance with communication quality information, and reconstructs the data so that it can be transmitted to the receiving device 5 via the IP network 8.The transmission server 6 shown in Figure 2 is configured as a computer that sequentially inputs coded data encoded using error correction codes related to digital broadcasting from the transmission device 2 (or transmission device 3), digitally modulates the coded data encoded using error correction codes related to digital broadcasting and transmits the coded data to the receiving device 5 via the IP network 8.The transmission server 6 includes a storage unit 61, an IP packet generation unit 62, a retransmission request processing unit 63, a coding rate adaptive change unit 64, and a communication quality management unit 65.

The storage unit 61 is a functional unit that sequentially inputs the coded data generated by the transmitting device 2 (or the transmitting device 3) via the local area network based on a synchronization signal (frame number or time information), and stores the error correction code frames that constitute the code length of the error correction code while updating them for a predetermined period of time by managing them in a chronological order using the synchronization signal (frame number or time information). The coded data obtained from the transmitting device 2 (or the transmitting device 3) is provided with a frame number or time information identified by a TMCC (Transmission and Multiplexing Configuration Control) signal, which is a control signal in digital broadcasting used in a broadcast transmission path, as a synchronization signal. For example, in a data transmission method using a broadcast transmission path, the storage unit 61 also receives time information (time information may also be embedded in the main signal) contained in the TMCC signal transmitted together with the coded data in units of error correction code frames, and can manage the coded data in units of error correction code frames sequentially obtained from the transmitting device 2 (or the transmitting device 3) using the frame number associated with the time information as a synchronization signal. In addition, the encoded data managed in time series by the storage unit 61 using a synchronization signal (frame number or time information) may be notified from the transmission server 6 via the IP network 8 while being received during digital broadcasting. In other words, in the transmission system 1 shown in FIG. 1, by using the time information or frame number contained in the TMCC signal or main signal as a synchronization signal, it is possible to ensure synchronization of the transmission devices 2 and 3, the reception device 5, one or more transmission servers 6, and the load distribution device 7 provided when multiple transmission servers 6 are configured.

The IP packet generator 62 is a functional unit that generates an encoded data packet in an IP packet format that stores encoded data related to a retransmission request from the receiver 5, and transmits the encoded data packet to the receiver 5 via the IP network 8. This encoded data packet is generated when the receiver 5 determines that bit errors in the encoded data cannot be corrected using the error correction code used by the transmitter 2 (or the transmitter 3). The IP packet generator 62 has an interleave unit 621 that performs interleave processing to rearrange bits across each error correction code frame based on a predetermined rule that separates the bits of the encoded data related to the retransmission request by a predetermined value or more after assigning an identification header that enables the receiver 5 to identify each interleave frame related to the interleave processing and a sequence number that specifies which bit is represented in each error correction code frame, as will be described in detail later.

When the retransmission request processing unit 63 receives a retransmission request packet from the receiving device 5 via the IP network 8, it extracts the communication quality information measured by the receiving device 5 stored in the retransmission request packet and the retransmission request information indicating the encoded data of the error correction code frame related to the retransmission request. Then, based on the communication quality information received this time, the retransmission request processing unit 63 judges whether to change the encoding rate of the encoded data transmitted over the broadcast transmission path and retransmit the data in accordance with the predetermined encoding rate change standard managed by the communication quality management unit 65. Then, based on the retransmission request information received this time, the retransmission request processing unit 63 searches for the location of the encoded data related to the retransmission request from the storage unit 61 according to the judgment result, reads out m frames of error correction code frames having consecutive synchronization signals (frame number or time information) starting from the error correction code frame constituting the encoded data, and controls the storage unit 61 to output them to the encoding rate adaptive change unit 64, and controls the encoding rate adaptive change unit 64 to adaptively change the encoding rate of the read encoded data, reconstruct it, and output it to the IP packet generation unit 62. An example of control related to this retransmission request processing unit 63 will be described later with reference to FIG. 3.

The coding rate adaptive change unit 64 is controlled by the retransmission request processing unit 63 and includes switching units 641, 642 that switch between changing and not changing the coding rate of the coded data generated by the transmitting device 2 (or transmitting device 3), and an error correction coding unit 643 that performs an error correction coding process that changes the coding rate based on the same coding method as the error correction coding method used by the transmitting device 2 (or transmitting device 3) and among a predetermined number of coding rates that are available to the transmitting device 2 (or transmitting device 3) when changing the coding rate, by distinguishing whether to make the coding rate higher or lower than the coding rate of the coded data generated by the transmitting device and transmitted over the broadcast transmission path.

More specifically, the switching units 641 and 642 are functional units that switch so that when the encoded data related to the retransmission request read from the storage unit 61 (encoded data transmitted over the broadcast transmission path) is to be retransmitted without changing the encoding rate, the switching units 641 and 642 output the encoded data as is to the IP packet generation unit 62, and when the encoded data is to be retransmitted after changing the encoding rate, the switching units 641 and 642 output the encoded data reconstructed by changing the encoding rate to the IP packet generation unit 62.

For example, when the coding rate for transmission via the broadcast transmission path is the same as that for transmission via the IP network 8, the coding rate adaptive change unit 64 outputs the coded data of the corresponding error correction code frame transmitted by the transmitting device 2 (or transmitting device 3) read from the storage unit 61 directly to the IP packet generation unit 62.

On the other hand, when retransmitting encoded data with a changed encoding rate from transmission via a broadcast transmission path, the encoding rate adaptive change unit 64 changes the encoding rate using the error correction encoding unit 643.

When the error correction coding unit 643 changes the coding rate of the coded data related to the retransmission request (the coded data transmitted through the broadcast transmission path) and retransmits it, it reads only the information bits (i.e., the main signal in the block code) excluding the predetermined parity in the coded data from the storage unit 61. Next, the error correction coding unit 643 uses the information bits of the coded data as they are when converting to a coding rate higher than the coding rate before the change, and when converting to a coding rate lower than the coding rate before the change, it uses the information bits of the coded data divided into two by a division method predetermined between the transmitter and the receiver, and adds padding bits consisting of bits known between the transmission server 6 and the receiver 5 (all bits of "0" or "1", or a regular bit pattern of "0" and "1") to an insertion position known between the transmitter and the receiver according to the coding rate to be changed. Then, the error correction coding unit 643 performs error correction coding processing on the specific information bits to which the padding bits have been added, based on the same coding method as the error correction coding method used by the error correction coding unit 21 in the transmitting device 2 (or transmitting device 3), and at a coding rate different from the coding rate transmitted over the broadcast transmission path that is available to the transmitting device 2 (or transmitting device 3) related to the broadcast. Finally, the error correction coding unit 643 replaces the parity added to the coded data generated by the transmitting device 2 (or transmitting device 3) with the parity of the block code whose coding rate has been changed for the coded data transmitted over the broadcast transmission path, and adds it to the information bits, and generates coded data for retransmission from which the padding bits have been removed. The method of generating coded data when the coding rate is changed by the error correction coding unit 643 of the coding rate adaptive change unit 64 will be described later with reference to Figures 4 and 5.

The communication quality management unit 65 is a functional unit that is controlled by the retransmission request processing unit 63 and that holds and manages, as information, a predetermined coding rate change criterion used to determine a coding rate according to communication quality information stored in a retransmission request packet received from the receiving device 5. Note that coding rate change criteria will be described later with some examples. In addition, this communication quality information is generated by the receiving device 5 and includes either or both of communication line delay information and packet loss rate information.

The communication line delay information is information that indicates the transmission delay estimated by the time difference between the transmission time of the retransmission request packet sent from the receiving device 5 to the transmission server 6 and the reception time of the encoded data packet retransmitted from the transmission server 6 in response to the retransmission.

The packet loss rate information indicates the packet loss rate measured based on the communication record with the transmission server 6 over a predetermined period of time, assuming that a packet loss has occurred when a corresponding encoded data packet cannot be received from the transmission server 6 even after a predetermined time has elapsed since the transmission time of the retransmission request packet.

(Control flow related to retransmission request packet)
FIG. 3 is a flowchart showing a control flow relating to a retransmission request packet between the transmission server 6 and the receiving device 5 in one embodiment of the present invention.

First, the transmission server 6 stores the encoded data transmitted over the broadcast transmission path for a predetermined period of time while updating it in the storage unit 61 (step S50). The encoded data transmitted over the broadcast transmission path is data that has been error correction encoded, and is composed of error correction code frames of block codes such as LDPC codes described in ARIB STD-B44.

The receiving device 5 receives and demodulates the digital broadcast transmitted over the broadcast transmission path, and attempts to determine whether or not bit errors in the encoded data can be corrected. If the transmission environment is good and reception is error-free, or if the effects of white noise, etc. are within the range that can be decoded using error correction coding, the error-corrected and decoded received data is output as is so that it can be reproduced. If the transmission environment is poor, such as due to rain attenuation, and bit errors in the encoded data received over the broadcast transmission path cannot be corrected, the receiving device 5 generates a retransmission request packet for the corresponding encoded data via the IP network 8 and makes a retransmission request to the transmission server 6 (step S51). This retransmission request packet contains retransmission request information and communication quality information, as described above.

Therefore, when the transmission server 6 receives a retransmission request packet from the receiving device 5 (step S52), the retransmission request processing unit 63 extracts the retransmission request information and communication quality information from the retransmission request packet (step S53).

Then, the retransmission request processing unit 63 determines whether or not to change the coding rate of the coded data transmitted over the broadcast transmission path and retransmit the coded data, based on the communication quality information received this time, in accordance with a predetermined coding rate change criterion managed by the communication quality management unit 65 (step S54). Note that the coding rate change criterion will be described later with some examples.

When the retransmission request processing unit 63 determines that the encoded data transmitted over the broadcast transmission path should be retransmitted without changing the encoding rate (step S54: No), it searches for and reads the location of the encoded data related to the retransmission request from the storage unit 61 based on the currently received retransmission request information, and controls the storage unit 61 and the encoding rate adaptive change unit 64 to retransmit the encoded data at the same encoding rate as the encoded data transmitted over the broadcast transmission path (step S55).

On the other hand, when the retransmission request processing unit 63 determines that the coding rate of the coded data transmitted over the broadcast transmission path is to be changed and retransmitted (step S54: Yes), it searches for the location of the coded data related to the retransmission request from the storage unit 61 based on the retransmission request information received this time, and reads out only the information bits (i.e., the main signal in the block code) excluding a predetermined parity in the coded data. Then, the retransmission request processing unit 63 changes the coding rate by distinguishing whether to make it higher or lower than the coding rate of the coded data transmitted over the broadcast transmission path. In other words, when converting to a coding rate higher than the coding rate before the change, the retransmission request processing unit 63 uses the information bits of the coded data as they are, and when converting to a coding rate lower than the coding rate before the change, it uses the information bits of the coded data divided into two by a division method predetermined between the transmitter and receiver. In other words, when converting to a coding rate lower than the coding rate before the change, the number of information bits becomes greater than the number of information bits for the coding rate after the change, so the information bits are divided into two and processed so that the same coding format as the error correction code standardized in the broadcast standard can be applied. After that, the storage unit 61 and the coding rate adaptive change unit 64 are controlled to add padding bits known on the receiving device 5 side using the relevant information bits (non-split when converting to a coding rate higher than the coding rate before the change) and split into two when converting to a coding rate lower than the coding rate before the change), add the parity of the block code whose coding rate has been changed from the coding rate of the coded data transmitted over the broadcast transmission path, and then generate coded data for retransmission with the padding bits removed (step S56).

Finally, the transmission server 6 uses the IP packet generator 62 to construct an interleaved frame using m error correction code frames, interleaves the m error correction code frames in a transverse (orthogonal) direction to generate an IP packet sequence (encoded data packets), and when the encoding rate is changed, generates and transmits an encoding rate change notification packet as a notification to that effect, and then transmits the encoded data packet to the receiving device 5 (step S57). Note that the transmission server 6 can also construct an encoded data packet including encoding rate information and transmit it to the receiving device 5. In this example, in order to increase the transmission efficiency of the encoded data packets, when the encoding rate is changed, an encoding rate change notification packet is notified in advance to the receiving device 5 as a notification to that effect.

The transmission server 6 may be configured to transmit the coding rate change notification packet multiple times, or may be configured to obtain a reception confirmation response for the coding rate change notification packet and repeatedly transmit the coding rate change notification packet until a reception confirmation response is received from the receiving device 5. Note that when the coding rate of the coded data transmitted via the IP network 8 is the same as the coding rate of the coded data transmitted over the broadcast transmission path, the receiving device 5 only needs to know the information on the coding rate over the broadcast transmission path, so the transmission server 6 may omit the advance notification of the coding rate change notification packet, but may transmit the coding rate change notification packet each time the coded data packet is retransmitted, regardless of whether the coding rate has been changed.

The communication quality information acquired from the receiving device 5 includes either or both of communication line delay information and packet loss rate information, and the coding rate to be changed based on this information is determined according to predetermined coding rate change criteria managed by the communication quality management unit 65.

The coding rate change criteria are based on the same coding method as the error correction coding method used by the error correction coding unit 21 in the transmitting device 2 (or transmitting device 3), and are set so that the coding rate is changed by distinguishing whether to change the coding rate to a higher or lower rate than the coding rate of the coded data transmitted over the broadcast transmission path, from among a predetermined number of coding rates that are available to the transmitting device 2 (or transmitting device 3) for broadcasting.

For example, the coding rate change criterion may be any one of the following (1) to (9).
(1) Taking into consideration only the delay, when the delay obtained from the receiving device 5 is within a specified range of a predetermined default value, the encoded data transmitted over the broadcast transmission path is retransmitted with the same encoding rate; when the delay obtained from the receiving device 5 is less than a specified range of a predetermined default value, the encoding rate is changed to a coding rate corresponding to the relevant delay among the multi-stage encoding rates determined according to an arbitrary delay, within a range higher than the encoding rate of the encoded data transmitted over the broadcast transmission path, thereby improving transmission efficiency; when the delay obtained from the receiving device 5 exceeds a specified range of a predetermined default value, the encoding rate is changed to a coding rate corresponding to the relevant delay among the multi-stage encoding rates determined according to an arbitrary delay, within a range lower than the encoding rate of the encoded data transmitted over the broadcast transmission path, thereby preventing in advance resistance to packet loss caused by the delay.
(2) Taking into consideration only the packet loss rate, when the packet loss rate obtained from the receiving device 5 is within a specified range of a predetermined default value, the encoded data transmitted over the broadcast transmission path is retransmitted with the encoding rate unchanged; when the packet loss rate obtained from the receiving device 5 is below a specified range of a predetermined default value, the encoding rate is changed to a coding rate corresponding to the relevant packet loss rate among multi-stage encoding rates determined according to an arbitrary packet loss rate within a range higher than the encoding rate of the encoded data transmitted over the broadcast transmission path, thereby improving transmission efficiency; when the packet loss rate obtained from the receiving device 5 exceeds a specified range of a predetermined default value, the encoding rate is changed to a coding rate corresponding to the relevant packet loss rate among multi-stage encoding rates determined according to an arbitrary packet loss rate within a range lower than the encoding rate of the encoded data transmitted over the broadcast transmission path, thereby improving tolerance to packet loss.
(3) Taking into consideration both the delay and the packet loss rate, when the delay obtained from the receiving device 5 is within a predetermined range of a predetermined default value or the packet loss rate obtained from the receiving device 5 is within a predetermined range of a predetermined default value, the encoded data transmitted over the broadcast transmission path is retransmitted with the encoding rate unchanged; when the delay obtained from the receiving device 5 is less than a predetermined range of a predetermined default value and the packet loss rate obtained from the receiving device 5 is less than a predetermined range of a predetermined default value, the encoding rate is changed to a coding rate corresponding to the relevant packet loss rate within a range higher than the encoding rate of the encoded data transmitted over the broadcast transmission path, among the multi-stage encoding rates determined according to an arbitrary packet loss rate, thereby improving transmission efficiency; when the delay obtained from the receiving device 5 exceeds a predetermined range of a predetermined default value and the packet loss rate obtained from the receiving device 5 exceeds a predetermined range of a predetermined default value, the encoding rate is changed to a coding rate corresponding to the relevant packet loss rate within a range lower than the encoding rate of the encoded data transmitted over the broadcast transmission path, among the multi-stage encoding rates determined according to an arbitrary packet loss rate, thereby improving resistance to packet loss.
(4) Taking into consideration only the delay, when the delay obtained from the receiving device 5 is within a specified range of a predetermined default value, the encoded data transmitted over the broadcast transmission path is retransmitted with the same encoding rate; when the delay obtained from the receiving device 5 is less than a specified range of a predetermined default value, the encoding rate is changed to a predetermined step (e.g., one step) higher within a range higher than the encoding rate of the encoded data transmitted over the broadcast transmission path, thereby improving transmission efficiency; when the delay obtained from the receiving device 5 exceeds a specified range of a predetermined default value, the encoding rate is changed to a predetermined step (e.g., one step) lower within a range lower than the encoding rate of the encoded data transmitted over the broadcast transmission path, thereby preventing in advance resistance to packet loss caused by the delay.
(5) Taking into consideration only the packet loss rate, when the packet loss rate obtained from the receiving device 5 is within a specified range of a predetermined default value, the encoded data transmitted over the broadcast transmission path is retransmitted at the same encoding rate. When the packet loss rate obtained from the receiving device 5 is below a specified range of a predetermined default value, the encoding rate is changed to a predetermined step (e.g., one step) higher within a range higher than the encoding rate of the encoded data transmitted over the broadcast transmission path, thereby improving transmission efficiency. When the packet loss rate obtained from the receiving device 5 exceeds a specified range of a predetermined default value, the encoding rate is changed to a predetermined step (e.g., one step) lower within a range lower than the encoding rate of the encoded data transmitted over the broadcast transmission path, thereby improving tolerance to packet loss.
(6) Taking into consideration both the delay and the packet loss rate, when the delay obtained from the receiving device 5 is within a specified range of a predetermined default value, or when the packet loss rate obtained from the receiving device 5 is within a specified range of a predetermined default value, the coding rate of the encoded data transmitted over the broadcast transmission path is retransmitted without change; when the delay obtained from the receiving device 5 is less than a specified range of a predetermined default value and the packet loss rate obtained from the receiving device 5 is less than a specified range of a predetermined default value, the coding rate is changed to a coding rate that is a specified step (e.g., one step) higher within a range that is higher than the coding rate of the encoded data transmitted over the broadcast transmission path, thereby improving transmission efficiency; when the delay obtained from the receiving device 5 exceeds a specified range of a predetermined default value and the packet loss rate obtained from the receiving device 5 exceeds a specified range of a predetermined default value, the coding rate is changed to a coding rate that is a specified step (e.g., one step lower) within a range that is lower than the coding rate of the encoded data transmitted over the broadcast transmission path, thereby improving resistance to packet loss.
(7) Taking into consideration only the delay, when the delay obtained from the receiving device 5 is within a specified range of a predetermined default value, the encoded data transmitted over the broadcast transmission path is retransmitted at the same encoding rate. When the delay obtained from the receiving device 5 is less than a specified range of a predetermined default value, the encoding rate is changed to the maximum value that can be used by the transmitting device 2 (or transmitting device 3) for the encoded data transmitted over the broadcast transmission path, thereby improving transmission efficiency. When the delay obtained from the receiving device 5 exceeds a specified range of a predetermined default value, the encoding rate is changed to the minimum value that can be used by the transmitting device 2 (or transmitting device 3) for the encoded data transmitted over the broadcast transmission path, thereby preventing in advance resistance to packet loss caused by the delay.
(8) Taking into consideration only the packet loss rate, when the packet loss rate obtained from the receiving device 5 is within a specified range of a predetermined default value, the coding rate of the encoded data transmitted over the broadcast transmission path is retransmitted with the same coding rate; when the packet loss rate obtained from the receiving device 5 is below a specified range of a predetermined default value, the coding rate is changed to the maximum coding rate that can be used by the transmitting device 2 (or transmitting device 3) for the encoded data transmitted over the broadcast transmission path, thereby improving transmission efficiency; when the packet loss rate obtained from the receiving device 5 exceeds a specified range of a predetermined default value, the coding rate is changed to the minimum coding rate that can be used by the transmitting device 2 (or transmitting device 3) for the encoded data transmitted over the broadcast transmission path, thereby improving tolerance to packet loss.
(9) Taking into consideration both the delay and the packet loss rate, when the delay obtained from the receiving device 5 is within a predetermined range of a predetermined default value, or when the packet loss rate obtained from the receiving device 5 is within a predetermined range of a predetermined default value, the coding rate of the encoded data transmitted over the broadcast transmission path is retransmitted without changing the coding rate; when the delay obtained from the receiving device 5 is less than a predetermined range of a predetermined default value and the packet loss rate obtained from the receiving device 5 is less than a predetermined range of a predetermined default value, the coding rate is changed to the maximum coding rate that can be used by the transmitting device 2 (or transmitting device 3) for the encoded data transmitted over the broadcast transmission path, thereby improving transmission efficiency; and when the delay obtained from the receiving device 5 exceeds a predetermined range of a predetermined default value and the packet loss rate obtained from the receiving device 5 exceeds a predetermined range of a predetermined default value, the coding rate is changed to the minimum coding rate that can be used by the transmitting device 2 (or transmitting device 3) for the encoded data transmitted over the broadcast transmission path, thereby improving resistance to packet loss.

(Method of generating encoded data when changing encoding rate: When changing to a higher encoding rate)
With reference to Fig. 4, an example will be described in which the retransmission request processing unit 63 controls the storage unit 61 and the coding rate adaptive change unit 64 in accordance with the coding rate change standard exemplified above when changing the coding rate of the coded data related to the retransmission request to a higher coding rate, to generate coded data when the coding rate is changed. Figs. 4(a) to 4(d) are diagrams showing a method of generating coded data when the coding rate is changed (when the coding rate of the coded data related to the retransmission request is changed to a higher coding rate) by the coding rate adaptive change unit 64 in the transmission server 6 according to an embodiment of the present invention.

First, FIG. 4(a) shows the structure of an error-correcting code frame of a block code indicating coded data transmitted over a broadcast transmission path. Normally, multiple types of selectable coding rates are predefined in digital broadcasting. For example, ARIB STD-B44 prescribes 11 types of coding rates for the LDPC code, which is a block code: 41/120 (≒1/3), 49/120 (≒2/5), 61/120 (≒1/2), 73/120 (≒3/5), 81/120 (≒2/3), 89/120 (≒3/4), 93/120 (≒7/9), 97/120 (≒4/5), 101/120 (≒5/6), 105/120 (≒7/8), and 109/120 (≒9/10).

Incidentally, the information on the coding rate of the coded data transmitted over the broadcast transmission path is usually transmitted by a TMCC (Transmission and Multiplexing Configuration Control) signal, which is a transmission control signal in digital broadcasting, but the transmission server 6 may be configured to notify the coding rate in advance via the IP network 8. As described above, when the coding rate of the coded data to be retransmitted in response to a retransmission request is changed, the transmission server 6 generates and transmits a coding rate change notification packet as a notification indicating that the coding rate has been changed by the IP packet generation unit 62, or transmits a coded data packet including the coding rate information to the receiving device 5. Here, when the coding rate of the coded data transmitted over the IP network 8 is the same as the coding rate of the coded data transmitted over the broadcast transmission path, the receiving device 5 only needs to know the information on the coding rate on the broadcast transmission path, so the transmission server 6 may omit the advance notification of the coding rate change notification packet.

As shown in FIG. 4(a), if the coding rate of the coded data in the block code with a code length of N bits transmitted through the broadcast transmission path is F _b , the information bits of the coded data (i.e., the main signal in the block code) are composed of N×F _b bits, and the parity is composed of N×(1-F _b ) bits. Usually, when using a block code in a broadcast transmission path, the number of bits of the code length of the error correction code frame is often constant regardless of the coding rate so that it is easy to handle in the broadcast transmission path. For example, in ARIB STD-B44, the code length N of the LDPC code, which is a block code, is constant at N=44880 bits regardless of the LDPC coding rate. Here, if the coding rate of the coded data retransmitted through the IP network 8 is F _i , when the coding rate F _i of the coded data retransmitted through the IP network 8 is changed to a higher value than the coding rate of the coded data transmitted through the broadcast transmission path, the information bits transmitted through the broadcast transmission path are used as they are and converted to the coding rate F _i .

Then, the transmission server 6, which has received a retransmission request packet from the receiving device 5, extracts the communication quality information contained in the retransmission request packet using the retransmission request processing unit 63, and based on the communication quality information, determines whether or not to change the coding rate by referring to the coding rate change criteria managed by the communication quality management unit 65.

Then, when the retransmission request processing unit 63 determines to change the coding rate of the coded data transmitted over the broadcast transmission path from _Fb to coding rate _Fi ( _Fb < _Fi ), it first reads out from the storage unit 61 only N x _Fb information bits (i.e., the main signal in the block code) of the coded data of code length N bits related to the retransmission request shown in Figure 4(a) (see Figure 4(b)).

Next, the retransmission request processing unit 63 controls the coding rate adaptive change unit 64 to add N×(F i -F b ₎ bits of padding bits with a value known between the transmitter and the receiver (for example, all 0 bits) to the N×F _b bits of information bits (i.e., the main signal in the block code) read from the storage unit ₆₁ by the error correction coding unit 643 at an insertion position known between the transmitter and the receiver, and perform error correction coding processing with a coding rate of F _i on the information bits and padding bits to generate a parity of N×(1-F _{i )} bits (see FIG. 4(c)). For example, the error correction coding unit 643 changes the coding rate from F _b to the maximum coding rate available to the transmitter 2 (or the transmitter 3) while using the N×F _b bits of information bits (i.e., the main signal in the block code) as the coding rate F i. In this example, the padding bits are illustrated as being added after the information bits, but the padding bits may be added before the information bits. In other words, the insertion positions of the padding bits may be determined in advance so as to be known between the transmitter and the receiver based on the value of the coding rate F _i after the change.

Then, the error correction coding unit 643 removes the padding bits, reconstructs the coded data for retransmission by adding N×(1−F _i )-bit parity to the N×F _b- bit information bits, and outputs the reconstructed coded data to the IP packet generating unit 62 (see FIG. 4(d)). Since the frame length of the reconstructed coded data for retransmission is shorter than the original code length of N bits, the transmission efficiency is higher than when coded data of the code length of N bits is retransmitted to the receiving device 5.

(Method of generating encoded data when changing encoding rate: When changing to a lower encoding rate)
Next, with reference to Fig. 5, an example will be described in which the retransmission request processing unit 63 controls the storage unit 61 and the coding rate adaptive change unit 64 in accordance with the coding rate change standard exemplified above when changing the coded data related to the retransmission request to a lower coding rate, thereby generating coded data when the coding rate is changed. Figs. 5(a) to 5(e) are diagrams showing a method of generating coded data when the coding rate is changed (when the coded data related to the retransmission request is changed to a lower coding rate) by the coding rate adaptive change unit 64 in the transmission server 6 according to an embodiment of the present invention.

As shown in Fig. 5(a), if the coding rate of the coded data in the block code with a code length of N bits transmitted through the broadcast transmission channel is _Fb , the information bits of the coded data (i.e., the main signal in the block code) are composed of N x _Fb bits, and the parity is composed of N x (1 - _Fb ) bits. Usually, when using a block code in a broadcast transmission channel, the number of bits of the code length of the error correction code frame is often constant regardless of the coding rate so that it is easy to handle in the broadcast transmission channel. For example, in ARIB STD-B44, the code length N of the LDPC code, which is a block code, is constant at N = 44880 bits regardless of the LDPC coding rate. Here, if the coding rate of the coded data to be retransmitted via the IP network 8 is F _i , normally the information bits of coding rate F _i would be N×F _i and the parity would be N×(1-F _i ) bits, but these would be excessive for the coding length of the error correcting code specified by the broadcasting standard. Therefore, in this embodiment, when the coding rate F _i of the coded data to be retransmitted via the IP network 8 is changed to less than the coding rate F _b of the coded data transmitted over the broadcast transmission path, the original information bits are divided in half to fit within the coding length of the error correcting code specified by the broadcasting standard, and then re-coded to reconstruct the coded data.

More specifically, the transmission server 6, which has received a retransmission request packet from the receiving device 5, first extracts the communication quality information contained in the retransmission request packet using the retransmission request processing unit 63, and then, based on the communication quality information, determines whether or not to change the coding rate by referring to the coding rate change criteria managed by the communication quality management unit 65.

For example, if the coding rate change criterion (9) above is followed, when the delay obtained from the receiving device 5 is less than a predetermined default value, or when the packet loss rate obtained from the receiving device 5 is less than a predetermined default value, the retransmission request processing unit 63 determines that the coding rate of the coded data transmitted over the broadcast transmission path should be left unchanged (F _b = F _i ), and controls the coding rate adaptive change unit 64 to read the coded data of code length N bits related to the retransmission request shown in Figure 5 (a) from the storage unit 61 and output it as is to the IP packet generation unit 62.

On the other hand, when the delay obtained from the receiving device 5 is equal to or greater than a predetermined default value and the packet loss rate obtained from the receiving device 5 is equal to or greater than a predetermined default value, the retransmission request processing unit 63 determines to change the coding rate of the coded data transmitted over the broadcast transmission path from _Fb to coding rate _Fi ( _Fb > _Fi ), and first reads out from the storage unit 61 only N x _Fb information bits (i.e., the main signal in the block code) of the coded data of code length N bits related to the retransmission request shown in Figure 5(a) (see Figure 5(b)).

Next, the retransmission request processing unit 63 controls the coding rate adaptive changing unit 64 to divide the N× _Fb information bits (i.e., the main signal in the block code) read from the storage unit 61 into two by the error correction coding unit 643 using a division method predetermined between the transmitter and the receiver ((N× _Fb )/2). Here, an example is shown in which the information bits are divided into two equal parts into the first half and the second half of the information bit position (see FIG. 5(c)), but other division methods may be used, such as dividing into two parts into odd bits and even bits.

Next, the retransmission request processing unit 63 controls the coding rate adaptive change unit 64 to add N×F _i - ((N×F _b )/2) bits of padding bits with a value known between the transmitter and the receiver (for example, all bits of 0) to an insertion position known between the transmitter and the receiver as padding bits to generate a parity of N×(1-F _{i )} bits (see FIG. 5(d)). For example, the error correction coding unit 643 changes the coding rate F _b to the minimum coding rate available in the transmitting device 2 ( _or transmitting device 3) while using N×F _b bits of information bits (i.e., the main signal in the block code) as the coding rate _{F i} . In this example, the padding bits are illustrated as being added after the information bits, but the padding bits may be added before the information bits. In other words, the insertion positions of the padding bits may be determined in advance so as to be known between the transmitter and the receiver based on the value of the coding rate F _i after the change.

Then, the error correction coding unit 643 removes the padding bits, reconstructs the coded data for retransmission by adding N×(1−F _i )-bit parity to the (N×F _b )/2-bit information bits, and outputs the reconstructed coded data for retransmission to the IP packet generating unit 62 (see FIG. 5(e)). The frame length of this reconstructed coded data for retransmission is shorter than the original code length of N bits, and is not excessive for the coding length of the error correction code specified by the broadcasting standard. Therefore, the coded data related to the retransmission request can be changed to a lower coding rate, and the correction ability is higher than when retransmitting without changing the coding rate.

In this way, when the transmission server 6 receives a retransmission request packet, it adaptively changes the coding rate of the coded data related to the retransmission request based on the communication quality information contained in the retransmission request packet to generate a coded data packet and transmits it to the receiving device 5.

(Method of generating encoded data packets)
When transmitting encoded data requested to be resent to the receiving device 5 via the IP network 8, the transmitting server 6 preferably constructs an n x m interleaved frame, which will be described later with reference to Figure 6, using the IP packet generating unit 62 to generate an IP packet sequence with an identification header, sequence number, and IP header, interleaves the sending order of the IP packets according to the sequence number, and transmits them as encoded data packets to the receiving device 5, in order to achieve high correction performance even in the case of burst packet losses that occur in the IP network 8.

More specifically, the method of generating IP packets by the IP packet generator 62 in the transmission server 6 will be described with reference to FIG. 6. Each of FIG. 6(a) to FIG. 6(d) is an explanatory diagram of the method of generating IP packets by the IP packet generator 62 in the transmission server 6 in one embodiment of the present invention.

First, the IP packet generating unit 62 inputs m frames of error correcting code frames having consecutive synchronization signals (frame number or time information) starting from an error correcting code frame constituting coded data having a synchronization signal (frame number or time information) related to a retransmission request, each of which is composed of a code length of n bits with the same coding rate _{F i} , from the coding rate adaptive changing unit 64, and forms an n×m interleaved frame. Note that m is a fixed value, but can be variably set from the outside, and is a value shared between the sender and the receiver. Also, n=N when the code length n bits of the coding rate F _i has not been changed from the code length N bits of the coding rate F _b used in the broadcast transmission path, and n<N when it has been changed from the code length N bits of the coding rate F _b .

Therefore, the IP packet generation unit 62 temporarily stores m error correction code frames, including the error correction code frame as the encoded data related to the retransmission request, in a vertically arranged memory unit (not shown) (see FIG. 6(a)).

Then, the IP packet generation unit 62 reads each bit from the beginning of the m-frame error correction code frame using the interleave unit 621, and generates n packets of m-bit IP payloads as the packet length excluding the header of the IP packet to be generated (see FIG. 6(b)). That is, the IP payload is m bits obtained by collecting the same bits from bits 1 to n of each error correction code frame by one bit each.

Then, the IP packet generation unit 62 adds an identification header to the IP payload of n packets generated by the interleaving unit 621, which enables the receiving device 5 to identify each interleaved frame involved in the interleaving process, a sequence number that specifies which bit in each error correction code frame it represents, and an IP header as the header of the encoded data packet, thereby generating n packets of IP packets (see FIG. 6(c)). Note that in this example, the sequence numbers are expressed as 1 to n for ease of understanding, but any expression form can be used as long as it allows the receiving device 5 to identify which bit in the error correction code frame each IP packet represents.

As shown in FIG. 6(b), one interleaved frame is composed of IP payloads for n packets generated from multiple error correction code frames. If the IP packet generator 62 assigns, for example, ID="1" to an identification header to be added to a certain interleaved frame, it assigns ID="2" to the identification header to be added to the next interleaved frame, and ID="3" to the identification header to be added to the next interleaved frame while incrementing, so that the interleaved frame to which the identification header belongs can be identified by its value. Therefore, as shown in FIG. 6(c), the identification header is added so that it has the same value within one interleaved frame. Therefore, the receiving device 5 can identify which interleaved frame the IP payload of the received encoded data packet belongs to by referring to the identification header.

Then, the IP packet generating unit 62 uses the interleaving unit 621 to interleave the generated n packets of IP packets based on the sequence numbers and a predetermined rule for the order of transmission to the IP network 8 (for example, the packets may be sent in ascending order of sequence numbers, or a different order of sequence numbers determined between the sender and the receiver), and transmits them as encoded data packets to the receiving device 5.

In this embodiment, the IP packet generation unit 62 requires m (m is an integer of 1 or more) error correction code frames including an error correction code frame as the encoded data related to the retransmission request. In other words, the interleaving unit 621 cannot perform interleaving until m error correction code frames are available. Therefore, if time loss is a problem, only a predetermined number of bits n1 (<n) as sequence numbers of the n-bit error correction code frames related to the retransmission request may be extracted from m (m is an integer of 1 or more) error correction code frames to reduce the total number of IP packets holding the corresponding sequence numbers. Furthermore, m and n are fixed values, but can be variably set from the outside, so that the packet length of each IP packet can be adjusted.

In addition, while the IP packets are generated by collecting one bit from each error correction code frame, it is also possible to collect multiple bits from each error correction code frame. Conversely, it is also possible to treat two error correction code frames as one frame, or to generate 2n packets of m bits. The IP payloads of n packets generated in this way are treated as one interleaved frame, and an identification header for making each interleaved frame identifiable on the receiving device 5 side and a sequence number for identifying each IP payload are assigned. In other words, other interleaving techniques can be applied as long as the order of sending each bit of the error correction code frame is rearranged so that packet loss in the IP network 8 can be predicted in advance and mitigated. In general, the longer the period (signal length) targeted for interleaving processing, the stronger the resistance to burst packet loss, so the interleaving unit 621 is configured to perform optimal interleaving processing within an allowable period for the entire transmission system 1.

[Receiving device]
7 is a block diagram showing a schematic configuration of a receiving device 5 according to an embodiment of the present invention. The receiving device 5 includes a demodulator 51, an error correction decoder 52, a retransmission request packet generator 53, an IP packet receiver 54, a switch 55, and a communication quality measurement unit 56.

The demodulation unit 51 receives and demodulates the modulated wave signal emitted from the transmitter 2 (or the transmitter 3) via the broadcast transmission path (satellite broadcast transmission path or terrestrial broadcast transmission path), and outputs the encoded data obtained by this demodulation process to the error correction decoding unit 52 via the switching unit 55.

The error correction decoding unit 52 is a decoder that calculates the log-likelihood ratio (LLR) of each bit of the encoded data obtained from the demodulation unit 51 prior to the decoding process of the error correction code, reconstructs the error correction code frame that constitutes the code length of the error correction code using this prior log-likelihood ratio (prior LLR), and performs a decoding process corresponding to the error correction encoding process in the transmitting device 2 (or transmitting device 3) to generate received data and output it externally in a reproducible manner.

Here, the error correction decoding unit 52 has a decoding feasibility determination unit 521, an encoded data completion unit 522, and a data combination unit 523.

The decoding possibility determination unit 521 determines whether the encoded data constituting the error correction code frame can be decoded for error correction, and when it is determined that the encoded data can be decoded, it decodes it as is to generate received data, and when it is determined that the bit error in the encoded data cannot be corrected and the encoded data cannot be decoded, it outputs retransmission request information for the encoded data constituting the error correction code frame to the retransmission request packet generation unit 53. In addition, in a data transmission method using a broadcast transmission path, the encoded data in units of error correction code frames obtained by the receiving device 5 receiving it sequentially via the demodulation unit 51 can be identified based on the time information included in the TMCC signal or main signal transmitted together, and can also be managed by a synchronization signal (frame number or time information) like the transmission server 6. Therefore, as a synchronization signal, this retransmission request information may include time information that makes it possible to identify the error correction code frame to be retransmitted, or may also include the frame number.

The encoded data complementation unit 522 is a functional unit that extracts encoded data related to a retransmission request from the encoded data packet received from the transmission server 6 in response to the transmission of the retransmission request packet by the retransmission request packet generation unit 53, and complements the extracted data for use in the decoding process of the encoded data in the error correction code frame.

The error correction decoding unit 52 is configured to complement the encoded data acquired via the IP network 8 for the encoded data in the error correction code frame by using the function of the encoded data complementing unit 522, and to repeatedly request retransmission of the selected encoded data in the error correction code frame until the data can be decoded by the error correction code decoding process within a predetermined time.

The data combining unit 523 is a functional unit that, when the coded data related to the retransmission request is changed to a lower coding rate and the information bits are divided, recombines the divided decoded information bits according to a division method predetermined between the data combining unit 523 and the transmission server 6 to generate received data.

If the error correction decoding unit 52 is unable to perform the decoding process within the specified time, it generates the received data with bit errors still included.

In addition, in this example, when the transmission server 6 changes the coding rate of the coded data to be retransmitted, it generates and transmits a coding rate change notification packet as a notification to that effect, and then transmits the coded data packet to the receiving device 5. Therefore, the error correction decoding unit 52 uses the function of the coded data complementing unit 522 to determine whether or not the coding rate of the coded data obtained via the IP network 8 is different from that at the time of broadcast reception based on the presence or absence of a coding rate change notification, and adds padding bits as appropriate according to the coding rate, and performs complementing processing related to the replacement of the likelihood ratio required for decoding.

The retransmission request packet generating unit 53 is a functional unit that generates a retransmission request packet in an IP packet format that includes retransmission request information indicating a request to retransmit the encoded data in the error correction code frame and communication quality information obtained from the communication quality measuring unit 56, in order to request the transmission server 6 to retransmit the encoded data in the error correction code frame when the decoding feasibility determining unit 521 determines that decoding is not possible, and transmits the retransmission request packet to the transmission server 6 via the IP network 8.

The IP packet receiving unit 54 is a functional unit that receives from the transmission server 6 an encoded data packet of an IP packet sequence that stores the encoded data resent in response to the resend request packet, acquires the encoded data related to the resend request, and outputs it to the error correction decoding unit 52 via the switching unit 55. The IP packet receiving unit 54 also has a deinterleaving unit 541 that uses the identification header and sequence number to perform the reverse process of the interleaving unit 621 on the transmission server 6 side and reconstructs the encoded data resent in response to the resend request.

The switching unit 55 controls the switching of the reception path of the encoded data by the reception path switching signal from the error correction decoding unit 52. That is, the switching unit 55 mainly operates to input the encoded data obtained by demodulation by the demodulation unit 51, which is transmitted via the broadcast transmission path, to the error correction decoding unit 52. However, when the decoding possibility determination unit 521 in the error correction decoding unit 52 determines that the encoded data obtained via the broadcast transmission path cannot be decoded, the switching unit 55 is controlled by the reception path switching signal from the error correction decoding unit 52 to input the encoded data retransmitted via the IP network 8 and obtained from the IP packet receiving unit 54 to the error correction decoding unit 52 until the encoded data can be decoded by the error correction code decoding process within a predetermined time. In addition, the error correction decoding unit 52 controls the switching unit 55 to input the encoded data obtained via the broadcast transmission path to the error correction decoding unit 52 when the encoded data can be decoded by the error correction code decoding process within the predetermined time, or after the predetermined time has elapsed, by the reception path switching signal.

The communication quality measurement unit 56 is a functional unit that measures and updates/retains either or both of the delay related to communication with the transmission server 6 and the packet loss rate based on the amount of packet loss occurring in communication with the transmission server 6 at a predetermined interval, and sequentially outputs communication quality information including either or both of the delay information and packet loss rate information of the communication line to the retransmission request packet generation unit 53.

As described above, the communication line delay information is information that indicates the transmission delay estimated by the time difference between the transmission time of the retransmission request packet sent from the receiving device 5 to the transmission server 6 and the reception time of the encoded data packet retransmitted from the transmission server 6 in response to the retransmission.

The packet loss rate information indicates the packet loss rate measured based on the communication performance over a predetermined period of time, assuming that a packet loss has occurred when a corresponding encoded data packet cannot be received from the transmission server 6 even after a predetermined time has elapsed since the transmission time of the retransmission request packet.

(Reception control flow in the receiving device)
FIG. 8 is a flowchart showing a reception control flow in the receiving device 5 according to an embodiment of the present invention.

First, the receiving device 5 receives and demodulates the modulated wave signal radiated from the transmitting device 2 (or transmitting device 3) via the broadcast transmission path (satellite broadcast transmission path or terrestrial broadcast transmission path) by the demodulation unit 51, and outputs the coded data obtained by this demodulation process to the error correction decoding unit 52 via the switching unit 55 (step S1). Note that the receiving path of the switching unit 55 is controlled by the error correction decoding unit 52 as described above.

Then, the receiving device 5 uses the error correction decoding unit 52 to calculate the pre-LLR for each bit of the encoded data obtained by the demodulation process, reconstruct the error correction code frame, and executes a decoding process corresponding to the error correction encoding process in the transmitting device 2 (or transmitting device 3) (step S2).

The error correction decoding unit 52 uses the decoding feasibility determination unit 521 to determine whether the encoded data obtained from the transmitting device 2 (or transmitting device 3) can be decoded for error correction (step S3), and when it is determined that the encoded data can be decoded, it decodes the encoded data as is to generate reproducible received data (step S3: No). Since the current receiving path does not go through the IP network 8 (step S9: No), it maintains the setting of the switching unit 55 as the receiving path for receiving broadcast as is, and proceeds to the demodulation and decoding process for the next encoded data in the time series. That is, the error correction decoding unit 52 attempts to decode the encoded data obtained from the transmitting device 2 (or transmitting device 3), and when there is no bit error or the bit error is within a correctable range, it decodes the encoded data as is to generate reproducible received data.

On the other hand, if the decoding possibility determination unit 521 determines that the encoded data constituting the error correction code frame cannot be decoded, the error correction decoding unit 52 generates retransmission request information for the encoded data constituting the error correction code frame, outputs it to the retransmission request packet generation unit 53, and instructs it to generate a retransmission request packet indicating a retransmission request for the encoded data (step S3: Yes). In addition, the decoding possibility determination unit 521 controls the switching unit 55 to switch to a receiving path that inputs the encoded data to the error correction decoding unit 52 via the IP network 8.

When the decoding feasibility determination unit 521 determines that decoding is not possible, the retransmission request packet generation unit 53 generates a retransmission request packet in an IP packet format including the retransmission request information and the communication quality information obtained from the communication quality measurement unit 56 to request the transmission server 6 to retransmit the encoded data in the error correction code frame, and transmits the packet to the transmission server 6 via the IP network 8 (step S4). Here, the communication quality information includes either or both of communication line delay information and packet loss rate information.

Therefore, when the transmission server 6 receives a retransmission request packet from the receiving device 5, it extracts the retransmission request information and communication quality information from the retransmission request packet, and determines, based on the communication quality information, according to a predetermined coding rate change criterion, whether to change the coding rate and, if so, to which coding rate. As described above, the coding rate change criterion is based on the same coding method as the error correction coding method used by the error correction coding unit 21 on the transmitting side, and, among a predetermined number of coding rates available to the transmitting device 2 for broadcasting, determines whether the coding rate is to be changed to a higher or lower one than the coding rate of the coded data transmitted over the broadcast transmission path. The transmission server 6 also forms an interleaved frame by forming m error correction code frames having consecutive synchronization signals (frame number or time information) starting from an error correction code frame constituting the encoded data having a synchronization signal (frame number or time information) related to the retransmission request at the same coding rate as the encoded data having the synchronization signal (frame number or time information) related to the retransmission request, and performs interleaving processing on the interleaved frame in a direction perpendicular to the m error correction code frames to generate encoded data packets of an IP packet string, which are then transmitted to the receiving device 5 via the IP network 8. When the encoding rate is changed, the transmission server 6 also generates and transmits an encoding rate change notification packet as a notification to that effect, and then transmits the encoded data packet. Therefore, the receiving device 5 can determine whether the encoding rate of the encoded data obtained via the IP network 8 is different from that at the time of broadcast reception by the IP packet receiving unit 54 and the error correction decoding unit 52.

Therefore, after transmitting a retransmission request packet to the transmission server 6, the receiving device 5 receives from the transmission server 6 an encoded data packet (IP packet sequence) of m error correction code frames including the encoded data to be decoded that was retransmitted in response to the retransmission request packet, and the deinterleaving unit 541 uses the identification header and sequence number assigned to the IP packet to perform the reverse process of the interleaving unit 621 on the transmission server 6 side to reconstruct the encoded data that was retransmitted in response to the retransmission request, and outputs it to the error correction decoding unit 52 (step S5).

Then, the receiving device 5 determines, by the encoded data complementation unit 522 in the error correction decoding unit 52, whether the encoding rate of the encoded data obtained via the IP network 8 is different from that at the time of broadcast reception (step S6). If the encoding rate of the encoded data obtained via the IP network 8 is different from that at the time of broadcast reception (step S6: Yes), in order to restore the error correction code frame with the changed encoding rate shown in Figure 4 (d) or Figure 5 (e), padding bits known between the sender and the receiver according to the encoding rate are added to an insertion position known between the sender and the receiver (step S7).

On the other hand, if the coding rate of the coded data obtained via the IP network 8 is the same as that at the time of broadcast reception (step S6: No), the coded data complementation unit 522 does not need to add padding bits.

Then, the coded data complementing unit 522 complements the coded data acquired via the IP network 8 so that it can be used in the decoding process of the coded data in the error correction code frame (step S8). More specifically, the error correction decoding unit 52 is configured as an error correction decoder for block codes and performs decoding using a log-likelihood ratio, so that the coded data complementing unit 522 complements the coded data acquired via the IP network 8 by replacing the log-likelihood ratio when the bit value is 0 with +∞ (the maximum value as the likelihood of the bit being "0"), the log-likelihood ratio when the bit value is 1 with -∞ (the maximum value as the likelihood of the bit being "1"), and by replacing the log-likelihood ratio with 0 if a packet loss occurs and a non-delivery bit occurs.

Then, the error correction decoding unit 52 repeatedly requests retransmission of the encoded data until the data can be decoded by the error correction code decoding process within a predetermined time (steps S2 to S8), and generates received data based on the decoded encoded data. If the current receiving path is via the IP network 8 (step S9: Yes), the switching unit 55 is controlled to switch the receiving path to receiving via the broadcast transmission path (step S10), and the process proceeds to demodulation and decoding of the next encoded data in the time series. Note that if the error correction decoding unit 52 cannot decode the data by the decoding process within the predetermined time, it generates received data that still contains bit errors, and proceeds to step S9, where it controls the switching unit 55 to switch the receiving path to receiving via the broadcast transmission path.

When the coded data related to the retransmission request is changed to a lower coding rate and the information bits are divided, the error correction decoding unit 52 repeats the request for retransmission of the coded data transmitted over the broadcast transmission path until both coded data pieces of the divided information bits can be decoded by the error correction code decoding process within a predetermined time. Then, when the error correction decoding unit 52 can decode both coded data pieces of the divided information bits, the data combining unit 523 recombines the divided decoded information bits according to a division method predetermined between the data combining unit 523 and the transmission server 6 to generate received data.

The retransmission request packet can be a non-delivery notification packet that is commonly used in IP packet format, and the encoded data packet is configured to be retransmitted in response to the non-delivery notification packet. Therefore, the error correction decoding unit 52 can replace the encoded data obtained from the demodulation unit 51 with the encoded data obtained by retransmission and perform decoding again. By repeatedly requesting retransmission until the received data can be restored within a specified time, it is possible to output the data in a reproducible manner.

In this way, in the transmission system 1 shown in FIG. 1, when transmission conditions deteriorate to the extent that data restoration using error correction codes is impossible due to attenuation or fading caused by rainfall, the receiving device 5 requests the transmission server 6 to resend the corresponding encoded data via the IP network 8. The transmission server 6 adaptively changes the encoding rate according to the communication quality information for the encoded data encoded by the same error correction code encoder (i.e., error correction encoder 21) as when it was transmitted via the broadcast transmission path by the transmitting device 2 (or transmitting device 3), and transmits the data to the receiving device 5 via the IP network 8.

The receiving device 5 uses the same error correction code decoder (i.e., error correction decoding unit 52) as was used when receiving the data via radio waves to complement the coded data that could not be decoded with the coded bits acquired via the IP network 8 and attempt to decode again to restore the received data. Even when a large amount of data is lost via radio waves or when the IP network 8 is also considered a lossy communication channel and some data is lost, the receiving device 5 can output the data in a reproducible manner by repeatedly making retransmission requests until it can restore the received data within a specified time.

In particular, by encoding the data retransmitted by the transmission server 6 via the IP network 8 as block code data for digital broadcasting, and by variably controlling the encoding rate of this encoded data to match the communication quality of the IP network 8, it is possible to reduce the number of retransmission requests and further improve the transmission efficiency via the IP network 8. In addition, by using the same standardized error correction code for the broadcasting error correction code and the error correction code used in transmission via the IP network 8, it is possible to realize this by providing only one error correction decoder in the receiving device 5, and the equipment scale can be reduced.

Example
A more specific embodiment in which the transmission system 1 is configured for advanced wideband satellite digital broadcasting will be described below.

Figure 9 is a block diagram showing a schematic configuration of a transmission system 1 including a transmission server 6, a transmission device 2, and a reception device 5 according to an embodiment of the present invention. Note that similar components will be described with the same reference numbers.

The transmission system 1 of one embodiment shown in FIG. 9 is an example of the advanced wideband satellite digital broadcasting described in ARIB STD-B44, and includes a transmission server 6, a transmission device 2, and a reception device 5 according to one embodiment of the present invention. Here, one transmission server 6 is used, and the installation of a load balancer 7 is omitted, but as described above, multiple transmission servers 6 may be used and connected to an IP network 8 via the load balancer 7.

In addition, in the transmission system 1 illustrated in FIG. 9, an example is described in which the sending device 2 and the sending server 6 are separate entities and connected via a local area network, but the sending device 2 may also be provided with the sending server 6, and instead of being connected via a local area network, they may be connected via a simple signal cable.

The transmitting device 2 illustrated in FIG. 9 is configured in the same manner as that illustrated in FIG. 2 described above, and generates encoded data by performing an error correction coding process on transmission data related to digital broadcasting and adding error correction code parity (LDPC parity and BCH parity), digitally modulates the encoded data using a predetermined modulation method to generate a modulated wave signal, and emits radio waves related to digital broadcasting via the transmission path of advanced wideband satellite digital broadcasting including the broadcasting satellite 4 via the transmitting antenna 2a. In advanced wideband satellite digital broadcasting, the number of bits per frame of encoded data is 44,880 bits, and the error correction coding process uses an LDPC code as an inner code and a BCH code as an outer code. In addition, the transmitting device 2 manages the sequentially generated encoded data as an error correction code frame, adds a synchronization signal (frame number or time information), and transmits it to the transmission server 6.

The receiving device 5 illustrated in FIG. 9 is configured in the same manner as in FIG. 7 described above, and receives and demodulates the modulated wave signal emitted by the transmitting device 2 via the receiving antenna 5a, and performs a decoding process corresponding to the error correction coding process in the transmitting device 2 to generate received data that can be reproduced.

The receiving device 5 also has the function of determining whether or not error correction decoding is possible for the encoded data obtained from the transmitting device 2, and if it determines that decoding is possible, it decodes the encoded data as is to generate received data, and if it determines that bit errors in the encoded data cannot be corrected and the data cannot be decoded, it generates a retransmission request packet in the form of an IP packet requesting retransmission of the corresponding encoded data, and includes communication quality information in this retransmission request packet and transmits it to the transmitting server 6 via the IP network 8. Furthermore, the receiving device 5 has a function of receiving an IP packet format encoded data packet that stores the encoded data retransmitted from the transmission server 6 in response to the retransmission request (the encoded data is reconstructed by adaptively changing the encoding rate by distinguishing whether the encoding rate is higher or lower than the encoding rate of the encoded data transmitted over the broadcast transmission path in response to the communication quality information at the transmission server 6 side), extracting the encoded data retransmitted in response to the retransmission request, performing complementation according to the encoding rate for use in the decoding process, repeating a request for retransmission of the corresponding encoded data until the data can be decoded by the decoding process within a predetermined time, and when the encoded data related to the retransmission request is changed to a lower encoding rate and the information bits are divided, recombining the divided decoded information bits according to a division method predetermined between the transmitting server 6 and the receiving device 5 to generate received data. Note that when the receiving device 5 cannot decode the data by the decoding process within the predetermined time, it generates the received data in a state including bit errors.

The transmission server 6 is configured in the same manner as in FIG. 2 described above, and has the functions of sequentially inputting the coded data generated by the transmission device 2, managing it in chronological order using the synchronization signal (frame number or time information) of the error correction code frame, and storing it while updating it for a specified period of time, and generating coded data packets in IP packet format that store the coded data related to the retransmission request in response to a retransmission request packet received from the reception device 5 via the IP network 8, and transmitting the coded data packets to the reception device 5 via the IP network 8.

Therefore, in this embodiment, the transmitting device 2 applies error correction coding processing for advanced wideband satellite digital broadcasting to the transmission data related to the digital broadcasting, generates a modulated wave signal, and transmits it via the transmitting antenna 2a and the broadcasting satellite 4. The receiving device 5 first demodulates the modulated wave signal of advanced wideband satellite digital broadcasting received from the receiving antenna 5a, and attempts to restore the received data using error correction decoding processing. If the transmission environment is good and reception is error-free, or if the effects of white noise, etc. are within the range that can be decoded using error correction coding, the receiving device 5 restores the received data from the encoded data as is and makes it possible to play it. If the transmission environment is poor, such as due to rain attenuation, and the encoded data has deteriorated to the extent that it cannot be decoded using error correction coding, the receiving device 5 requests a retransmission of the corresponding encoded data via the IP network 8 to the transmitting server 6 that works in cooperation with the transmitting device 2.

When a retransmission request is made from the receiving device 5 to the transmission server 6 via the IP network 8, the transmission server 6 variably controls the coding rate of the coded data after error correction coding processing in accordance with the communication quality information, and retransmits the data to the receiving device 5 via the IP network 8. The receiving device 5 generates coded data by complementing the coded data obtained from the IP network 8, executes error correction decoding processing, and restores the received data to make it playable.

(Example: Reception control flow in a receiver for advanced wideband digital satellite broadcasting)
Fig. 10 is a flow chart showing a reception control flow in the receiver 5 for the advanced wideband satellite digital broadcasting of the embodiment shown in Fig. 9. Note that the same step numbers as in Fig. 8 are given the same numbers.

First, the receiving device 5 receives and demodulates the modulated wave signal radiated from the transmitting device 2 via the broadcast transmission path of the advanced wideband digital satellite broadcasting using the demodulation unit 51, and outputs the coded data obtained by this demodulation process to the error correction decoding unit 52 via the switching unit 55 (step S1). Note that the receiving path of the switching unit 55 is controlled by the error correction decoding unit 52, as described above.

Then, in order to execute a decoding process corresponding to the error correction encoding process in the transmitting device 2 by the error correction decoding unit 52, the receiving device 5 first calculates the a priori LLR of each bit of the encoded data from the likelihood table and reconstructs the error correction code frame (step S2A). Since the number of bits per frame of encoded data in advanced wideband digital satellite broadcasting is 44,880 bits, and the error correction encoding process uses an LDPC code as the inner code and a BCH code as the outer code, the likelihood table is used to calculate a priori log-likelihood ratios indicating the likelihood that a bit is "0" and the likelihood that a bit is "1".

Then, the receiving device 5 performs LDPC decoding using a sum-product algorithm based on a log-likelihood ratio by the error correction decoding unit 52 (step S2B), and then performs power despreading processing and decoding processing of the BCH code (step S2C). ARIB STD-B44 specifies that if bit errors cannot be corrected completely during the decoding processing of the BCH code of the outer code and the data does not become error-free, the data is replaced with a null packet, a flag is set indicating that an error exists, etc.

The error correction decoding unit 52 determines whether the bit errors could not be completely corrected in the decoding process of the BCH code, or whether the errors were corrected in the decoding process but the number of BCH errors was a predetermined number, in order to determine whether the decoding feasibility determination unit 521 can perform error correction decoding on the encoded data obtained from the transmitting device 2 (step S3'). That is, in this embodiment, focusing on the fact that the correction capability of the LDPC code is uncertain and the correction capability of the BCH code is deterministic, an efficient retransmission request in Hybrid ARQ is realized by utilizing the presence or absence of an error-free BCH code connected to the LDPC code.

Here, the error correction decoding unit 52 determines whether the encoded data obtained from the transmitting device 2 can be decoded using the decoding feasibility determination unit 521. If it determines that the encoded data can be decoded, it decodes the data as is and generates the received data in a playable form (step S3': No). Since the current receiving path does not go through the IP network 8 (step S9: No), it maintains the setting of the switching unit 55 as the receiving path for receiving the broadcast as is, and proceeds to the demodulation and decoding process for the next encoded data in the chronological order.

On the other hand, if the error correction decoding unit 52 determines by the decoding possibility determination unit 521 that the encoded data constituting the error correction code frame cannot be decoded, the error correction decoding unit 52 generates retransmission request information for the encoded data constituting the error correction code frame, outputs it to the retransmission request packet generation unit 53, and instructs the retransmission request packet generation unit 53 to generate a retransmission request packet indicating a retransmission request for the encoded data (step S3': Yes). That is, if the error correction decoding unit 52 cannot restore the received data from the encoded data due to deterioration of the transmission conditions or the like, it instructs the retransmission request packet generation unit 53 to make a retransmission request to the transmission server 6 by ARQ. In addition, the decoding possibility determination unit 521 controls the switching unit 55 to switch to a receiving path that inputs the encoded data to the error correction decoding unit 52 via the IP network 8.

In response to an instruction from the decoding feasibility determination unit 521, the retransmission request packet generation unit 53 generates a retransmission request packet in the form of an IP packet, which includes retransmission request information indicating a request for retransmission of the encoded data that the decoding feasibility determination unit 521 has determined to be undecodable, and communication quality information obtained from the communication quality measurement unit 56, and transmits the packet to the transmission server 6 via the IP network 8 (step S4). Here, the communication quality information includes either or both of communication line delay information and packet loss rate information.

When the transmission server 6 receives a retransmission request packet from the receiving device 5, it extracts the retransmission request information and communication quality information from the retransmission request packet, and determines, based on the communication quality information, according to a predetermined coding rate change criterion, whether to change the coding rate and, if so, to which coding rate. As described above, the coding rate change criterion is based on the same coding method as the error correction coding method used by the error correction coding unit 21 on the transmitting side, and among a predetermined number of coding rates available to the transmitting device 2 for broadcasting, determines whether the coding rate is to be changed to a higher or lower one than the coding rate of the coded data transmitted over the broadcast transmission path.

Then, the transmission server 6 forms an interleaved frame by forming m error correction code frames having consecutive synchronization signals (frame number or time information) starting from an error correction code frame constituting the encoded data having a synchronization signal (frame number or time information) related to the retransmission request at the same coding rate as the encoded data having the synchronization signal (frame number or time information) related to the retransmission request, and performs interleaving processing on the interleaved frame in a direction perpendicular to the m error correction code frames to generate encoded data packets of an IP packet string, which are then transmitted to the receiving device 5 via the IP network 8. When the encoding rate is changed, the transmission server 6 generates and transmits an encoding rate change notification packet as a notification to that effect, and then transmits the encoded data packet. Therefore, the receiving device 5 can determine whether the encoding rate of the encoded data obtained via the IP network 8 is different from that at the time of broadcast reception by the IP packet receiving unit 54 and the error correction decoding unit 52. An example of the encoding rate change by the transmission server 6 (when the encoded data related to the retransmission request is changed to a lower encoding rate, which will be described as a representative example) will be described later with reference to FIG. 11. An example of how the transmission server 6 generates a retransmission request packet in IP packet format (when changing the encoded data related to the retransmission request to a lower encoding rate) will be described later with reference to FIG. 12.

Therefore, after transmitting a retransmission request packet to the transmission server 6, the receiving device 5 receives from the transmission server 6 an encoded data packet (IP packet sequence) of m error correction code frames including the encoded data to be decoded that was retransmitted in response to the retransmission request packet, and the deinterleaving unit 541 uses the identification header and sequence number assigned to the IP packet to perform the reverse process of the interleaving unit 621 on the transmission server 6 side to reconstruct the encoded data that was retransmitted in response to the retransmission request, and outputs it to the error correction decoding unit 52 (step S5).

Then, the receiving device 5 determines, by the encoded data complementation unit 522 in the error correction decoding unit 52, whether the encoding rate of the encoded data obtained via the IP network 8 is different from that at the time of broadcast reception (step S6). If the encoding rate of the encoded data obtained via the IP network 8 is different from that at the time of broadcast reception (step S6: Yes), in order to restore the error correction code frame with the changed encoding rate shown in Figure 4 (d) or Figure 5 (e), padding bits known between the sender and the receiver according to the encoding rate are added to an insertion position known between the sender and the receiver (step S7).

On the other hand, if the coding rate of the coded data obtained via the IP network 8 is the same as that at the time of broadcast reception (step S6: No), the coded data complementation unit 522 does not need to add padding bits.

Then, the coded data complementing unit 522 complements the coded data acquired via the IP network 8 so that it is used in the decoding process of the coded data in the error correction code frame (step S8'). The IP network 8 is assumed to be a lost communication channel, and the error correction decoding unit 52 determines the correct bit value for the coded data received via the IP network 8, and assumes that the correct bit value is unknown for packets lost due to packet loss or the like in the communication channel on the way to the IP network 8. More specifically, the error correction decoding unit 52 is configured as an error correction decoder for block codes and performs decoding using a log likelihood ratio, so that the coded data complementing unit 522 complements the coded data acquired via the IP network 8 by replacing the log likelihood ratio with +∞ (the maximum value as the likelihood of "0") when the bit value is 0, with -∞ (the maximum value as the likelihood of "1") when the bit value is 1, and by replacing the log likelihood ratio with 0 if a packet loss occurs and a non-delivery bit occurs.

The error correction decoding unit 52 then repeatedly requests retransmission of the encoded data until the data can be decoded by the error correction code decoding process within a predetermined time (steps S2 to S8'), and generates received data based on the decoded encoded data. If the current reception path is via the IP network 8 (step S9: Yes), the switching unit 55 is controlled to switch the reception path to reception via the broadcast transmission path (step S10), and the demodulation and decoding process for the next encoded data in the time series is started. Here, the error correction decoding unit 52 can be configured to completely restore the received data by repeatedly requesting retransmission until there are no more bit errors in the BCH code decoding process, but it is preferable to set a limit of within a predetermined time to avoid infinite loop processing.

When the coded data related to the retransmission request is changed to a lower coding rate and the information bits are divided, the error correction decoding unit 52 repeats the request for retransmission of the coded data transmitted over the broadcast transmission path until both coded data pieces of the divided information bits can be decoded by the error correction code decoding process within a specified time. Then, when the error correction decoding unit 52 can decode both coded data pieces of the divided information bits, the data combining unit 523 recombines the divided decoded information bits according to a division method predetermined between the data combining unit 523 and the transmission server 6 to generate received data.

The retransmission request packet can be a non-delivery notification packet that is commonly used in IP packet format, and the encoded data packet is configured to be retransmitted in response to the non-delivery notification packet. Therefore, the error correction decoding unit 52 can replace the encoded data obtained from the demodulation unit 51 with the encoded data obtained by retransmission and perform decoding again. By repeatedly requesting retransmission until the received data can be restored within a specified time, it is possible to output the data in a reproducible manner.

(Method of generating encoded data when changing encoding rate in one embodiment: when changing to a lower encoding rate)
As explained with reference to Figures 4 and 5, the transmission server 6 adaptively changes the coding rate of the coded data related to the retransmission request, distinguishing whether to set the coding rate to be higher or lower than the coding rate of the coded data transmitted over the broadcast transmission path depending on the communication quality information, and reconstructs the coded data.

That is, the only difference between the coded data related to the retransmission request generated by the transmission server 6 is that when changing to a higher coding rate, the information bits are not divided, and when changing to a lower coding rate, the information bits are divided. Therefore, here, as a representative example of changing the coded data related to the retransmission request to a lower coding rate, reference is made to FIG. 11, and an example of generating coded data when the coding rate is changed is described, in which the retransmission request processing unit 63 in the transmission server 6 controls the storage unit 61 and the coding rate adaptive change unit 64 in accordance with the coding rate change standard (9) above, in this example, within the range of the number of types of LDPC coding rates that comply with ARIB STD-B44.

In the example shown in Figures 11(a) to 11(e), the transmission server 6 receives coded data with the highest LDPC coding rate (109/120 (≒ 9/10) within the range of LDPC coding rate types conforming to ARIB STD-B44, stores the data in the storage unit 61, and when the radio wave reception conditions deteriorate from the receiving device 5, the transmission server 6 changes the coding rate of the coded data requested for retransmission via the IP network 8 to 61/120 (≒ 1/2) and retransmits the data.

As shown in FIG. 11(a), here, the coding rate of the coded data in the LDPC code with code length N=44880 bits transmitted through the broadcast transmission path is F _b =109/120 (≈9/10). In ARIB STD-B44, one error correcting code frame has a constant code length of 44880 bits regardless of the LDPC coding rate, and is configured in slot units based on the set partitioning method, so that the information bits to be coded by the LDPC code are the "slot header", "main signal (data to be transmitted)", "BCH code parity", and "stuff bit" that have been power-dispersed, and one error correcting code frame is configured by adding the parity of the LDPC code. Then, in the storage unit 61 in the transmission server 6, the coded data in units of one error correcting code frame shown in FIG. 11(a) is managed in chronological order with a synchronization signal (frame number or time information) added, and is stored while updating for a predetermined time. The LDPC code parity at an LDPC coding rate of 109/120 (≈9/10) is composed of 44880×(1−109/120)=4114 bits.

Then, the transmission server 6, which has received a retransmission request packet from the receiving device 5, extracts the communication quality information contained in the retransmission request packet using the retransmission request processing unit 63, and based on the delay and packet loss rate information contained in the communication quality information, determines whether or not to change the coding rate by referring to the coding rate change criteria managed by the communication quality management unit 65.

If the coding rate change criteria in (9) above are followed, when the delay obtained from the receiving device 5 is less than a predetermined default value, or when the packet loss rate obtained from the receiving device 5 is less than a predetermined default value, the retransmission request processing unit 63 determines that the LDPC coding rate of the coded data transmitted over the broadcast transmission path should remain unchanged at 109/120 (≒ 9/10), and controls the coding rate adaptive change unit 64 to read the coded data with a code length of N bits related to the retransmission request shown in FIG. 11(a) from the storage unit 61 and output it as is to the IP packet generation unit 62.

On the other hand, when the delay obtained from the receiving device 5 is equal to or greater than a predetermined default value and the packet loss rate obtained from the receiving device 5 is equal to or greater than a predetermined default value, the retransmission request processing unit 63 determines to change the LDPC coding rate _Fb = 109/120 (≈ 9/10) of the coded data transmitted over the broadcast transmission path to the LDPC coding rate _Fi = 61/120 (≈ 1/2) ( _Fb > _Fi ), and first reads out from the storage unit 61 only the information bits to be coded with the LDPC code of N x _Fb = 40766 bits (i.e., the BCH coded bits that have been power dispersed) of the coded data with a code length of 44,880 bits related to the retransmission request shown in Figure 11 (a) (see Figure 11 (b)).

Next, the error correction coding unit 643 controls the coding rate adaptive change unit 64, and the error correction coding unit 643 divides the 40766 information bits (i.e., the BCH coded bits after power dispersal) read from the storage unit 61 into two bits ((N×F _b )/2=20383 bits) using a division method determined in advance between the transmitter and the receiver. Here, an example is shown in which the information bits are divided into two parts at the first half and the second half of the information bit position (see FIG. 11(c)), but other division methods may be used, such as dividing into two parts at odd bits and even bits.

Next, the retransmission request processing unit 63 controls the coding rate adaptive change unit 64 to add N×F i - ((N×F _b )/2) = 2431 bits of padding _bits with a value known between the transmitter and the receiver (for example, all 0 bits) to the first and second halves of each of the two divided information bits to an insertion position known between the transmitter and the receiver, and performs LDPC coding processing with a coding rate F _i = 109/120 (≈ 9/10) on these information bits and padding bits to generate a parity of N× (1 - F _i ) = 4114 bits (see FIG. 11 (d)). Note that in this example, the padding bits are illustrated as being added to the rear of the information bits, but the padding bits may be added to the front of the information bits, that is, the insertion position of the padding bits may be determined in advance so as to be known between the transmitter and the receiver according to the value of the coding rate F _i after the change.

Then, the error correction coding unit 643 removes the padding bits, reconstructs the coded data for retransmission (42,449 bits) by adding 22,066 bits of parity to the 20,383 bits of information bits, and outputs it to the IP packet generating unit 62 (see FIG. 11(e)). The frame length of this reconstructed coded data for retransmission, 42,449 bits, is shorter than the original code length of 44,880 bits and is not excessive for the coding length of the error correction code specified in the broadcasting standard. Therefore, the coded data related to the retransmission request can be changed to a lower coding rate, and the correction ability is higher than when retransmitting without changing the coding rate.

In this way, when the transmission server 6 of this embodiment receives a retransmission request packet, it adaptively changes the LDPC coding rate of the coded data related to the retransmission request based on the communication quality information contained in the retransmission request packet to generate a coded data packet and transmits it to the receiving device 5.

(How an embodiment of a transmitting server generates encoded data packets in the form of IP packets)
The encoded data packet is composed of one or more IP packets, and in this example, the packet length excluding the IP header of the IP packet is set to a fixed length of 1000 bytes. However, in reality, the packet length can be set to a variable length that is determined arbitrarily within a range that does not exceed the MTU (Maximum Transmission Unit) of the assumed IP network 8.

As described above, the only difference between the coded data related to the retransmission request generated by the transmission server 6 is that when changing to a higher coding rate, the information bits are not divided, and when changing to a lower coding rate, the information bits are divided. Therefore, here, as a representative example of changing to a lower coding rate for coded data related to a retransmission request, reference is made to FIG. 12, and an example is described in which an n×m interleaved frame is constructed for the coded data, and then a coded data packet (IP packet sequence) is generated and transmitted to the receiving device 5.

Figures 12(a) to 12(d) are explanatory diagrams showing how the IP packet generator 62 in the transmission server 6 generates IP packets in one embodiment of the present invention.

First, the IP packet generating unit 62 inputs m frames of error correcting code frames having consecutive synchronization signals (frame number or time information) starting from an error correcting code frame constituting coded data having a synchronization signal (frame number or time information) related to a retransmission request, each of which is composed of a code length of n bits with the same coding rate _{F i} , from the coding rate adaptive changing unit 64, and forms an n×m interleaved frame. Note that m is a fixed value, but can be variably set from the outside, and is a value shared between the sender and the receiver. Also, n=N when the code length n bits of the coding rate F _i has not been changed from the code length N bits of the coding rate F _b used in the broadcast transmission path, and n<N when it has been changed from the code length N bits of the coding rate F _b .

The IP packet generator 62 temporarily stores m error correction code frames (LDPC frames) including an error correction code frame as the encoded data related to the retransmission request in a vertically aligned manner in a storage unit (not shown) (see FIG. 12(a)). In FIG. 12(a), when the encoded data obtained from the encoding rate adaptive change unit 64 is an LDPC frame whose encoding rate has been changed to a lower encoding rate, the IP packet generator 62 temporarily stores the first and second halves of the information bits in a pair in a vertically aligned manner, such as LDPC frame #1 (first half of information bits), LDPC frame #2 (second half of information bits), LDPC frame #3 (first half of information bits), ..., LDPC frame #m (second half of information bits).

As described above with reference to FIG. 6, the IP packet generation unit 62 reads each bit from the beginning of the error correction code frame of m frames by the interleave unit 621, generates n packets of m-bit IP payloads as the packet length excluding the header of the generated IP packet (see FIG. 12(b)), and adds an identification header for enabling the receiver 5 to identify each interleaved frame related to the interleaving process, a sequence number that specifies which bit in each error correction code frame is represented, and an IP header as the header of the encoded data packet to generate n packets of IP packets (see FIG. 12(c)). Then, the IP packet generation unit 62 interleaves the generated n packets of IP packets by the interleave unit 621 based on a predetermined rule for the order of sending to the IP network 8 according to the sequence numbers (for example, the packets may be sent in ascending order of sequence numbers, or the order of sending of different sequence numbers determined between the sender and the receiver may be used), and transmits them to the receiver 5 as encoded data packets.

By transmitting the IP packet sequence of the coded data that has been subjected to the interleaving process in this manner as a coded data packet from the transmission server 6 to the receiving device 5, the IP network 8 becomes more resistant to burst packet loss (i.e., the packet loss correction capability is improved).

(Application example: changing the coding rate of LDPC code and changing the correction ability of BCH code)
When changing the coding rate of the coded data related to a retransmission request (coded data transmitted over a broadcast transmission path) and retransmitting the coded data, the error correction coding unit 643 in the coding rate adaptive change unit 64 may not only change the coding rate of the LDPC code, but also change the correction capability of the BCH code to be enhanced from 12 bits to 23 bits, and reconstruct the coded data.

Figures 13(a) to 13(f) are diagrams showing a method of generating coded data when the coding rate is changed by the coding rate adaptive change unit 64 in the transmission server 6 of an application example according to the present invention (when the coded data related to the retransmission request is changed to a lower coding rate). In addition, in order to be able to compare with the example shown in Figure 11, Figure 13 shows an example in which the retransmission request processing unit 63 in the transmission server 6 receives coded data with the highest LDPC coding rate (109/120 (≒ 9/10) within the range of the number of types of LDPC coding rates conforming to ARIB STD-B44, stores it in the storage unit 61, and when the radio wave reception situation deteriorates from the receiving device 5, the coding rate of the coded data requested for retransmission via the IP network 8 is changed to 61/120 (≒ 1/2) to generate coded data.

First, in FIG. 13(a), similarly to FIG. 11(a), the coding rate of the coded data in the LDPC code with the code length N=44880 bits transmitted through the broadcast transmission path is shown as F _b =109/120 (≈9/10). As described above, in ARIB STD-B44, one error correcting code frame has a constant code length of 44880 bits regardless of the LDPC coding rate, and is configured in slot units based on the set partitioning method, so that the information bits to be coded by the LDPC code are the "slot header", "main signal (data to be transmitted)", "BCH code parity", and "stuff bit" that have been power-dispersed, and one error correcting code frame is configured by adding the parity of the LDPC code. Then, in the storage unit 61 in the transmission server 6, the coded data in units of one error correcting code frame shown in FIG. 13(a) is managed in chronological order with a synchronization signal (frame number or time information) added, and is stored while updating for a predetermined time. The LDPC code parity at an LDPC coding rate of 109/120 (≈9/10) is composed of 44880×(1−109/120)=4114 bits.

Then, the transmission server 6 that receives the retransmission request packet from the receiving device 5 extracts the communication quality information contained in the retransmission request packet by the retransmission request processing unit 63, in the same manner as in the embodiment described with reference to FIG. 11 above, and determines whether or not to change the coding rate based on the delay and packet loss rate information contained in the communication quality information and by referring to the coding rate change criteria managed by the communication quality management unit 65.

If the coding rate change criteria in (9) above are followed, when the delay obtained from the receiving device 5 is less than a predetermined default value, or when the packet loss rate obtained from the receiving device 5 is less than a predetermined default value, the retransmission request processing unit 63 determines that the LDPC coding rate of the coded data transmitted over the broadcast transmission path should remain unchanged at 109/120 (≒ 9/10), and controls the coding rate adaptive change unit 64 to read the coded data with a code length of N bits related to the retransmission request shown in FIG. 13(a) from the storage unit 61 and output it as is to the IP packet generation unit 62.

On the other hand, when the delay obtained from the receiving device 5 is equal to or greater than a predetermined default value and the packet loss rate obtained from the receiving device 5 is less than a predetermined default value, the retransmission request processing unit 63 determines to change the LDPC coding rate _Fb = 109/120 (≈ 9/10) of the coded data transmitted over the broadcast transmission path to the LDPC coding rate _Fi = 61/120 (≈ 1/2) ( _Fb > _Fi ), and first reads out from the storage unit 61 only the information bits to be coded with the LDPC code of N x _Fb = 40766 bits (i.e., the BCH coded bits that have been power diffused) of the coded data with a code length of 44,880 bits related to the retransmission request shown in Figure 13(a) (see Figure 13(b)).

In this application example, the retransmission request processing unit 63 controls the coding rate adaptive change unit 64, and the error correction coding unit 643 performs a power despreading process on the 40,766 information bits (i.e., the power-spread BCH-coded bits) read from the storage unit 61, to restore the bit sequence of the "slot header", "main signal (data to be transmitted)", "BCH code parity with 12-bit correction capability", and "stuff bits", deletes the "slot header", and assigns the deleted bit area to the BCH code parity (see FIG. 13(c)). Therefore, the bit sequence of the "main signal (data to be transmitted)", "BCH code parity with 23-bit correction capability", and "stuff bits" is obtained without changing the overall information bit length. This allows the configuration to strengthen the correction capability from the 12-bit correction BCH code described in ARIB STD-B44 to a 23-bit correction BCH code while maintaining the frame length of the error correction code frame after changing the LDPC coding rate (for information on the BCH code with 23-bit correction capability, see, for example, "Yoichi Suzuki, Akira Hashimoto, Takafumi Matsuzaki, Shoji Tanaka, Takeshi Kimura, Kenichi Tsuchida, "Improvement of the performance of set-partitioned 8PSK coding modulation using concatenated codes of LDPC codes and BCH codes," IEICE Transactions on Electronics, Information and Communication Engineers, Vol. 97, no. 8, PP. 648-659, August 1, 2014").

Next, the error correction coding unit 643 performs power dispersion processing again on the information bits of the bit arrangement of "signal (data to be transmitted)", "BCH code parity with 23-bit correction capability", and "stuff bits" shown in Fig. 13(c), and then divides the information bits into two by a division method predetermined between the transmitter and the receiver ((N x _Fb )/2 = 20383 bits), as in the embodiment described above with reference to Fig. 11. Here, an example is shown in which the information bits are divided into two equal parts at the first half and the second half of the information bit position (see Fig. 13(d)), but other division methods may be used, such as dividing into two parts at odd bits and even bits.

Next, the retransmission request processing unit 63 controls the coding rate adaptive change unit 64 to add N×F i -(N×F _b )=2431 _bits as padding bits to the first and second halves of each of the two divided information bits with a value known between the transmitter and the receiver (for example, all bits of 0), and performs LDPC coding processing with a coding rate of F _i =61/120 (≒1/2) on these information bits and padding bits to generate a parity of N×(1-F _i )=22066 bits (see FIG. 13(e)). Note that, in this example, the padding bits are illustrated as being added to the rear of the information bits, but the padding bits may be added to the front of the information bits, that is, the insertion position of the padding bits may be determined in advance so as to be known between the transmitter and the receiver according to the value of the coding rate F _i after the change.

Then, the error correction coding unit 643 removes the padding bits, reconstructs the coded data for retransmission (42,449 bits) by adding 22,066 bits of parity to the 20,383 bits of information bits, and outputs it to the IP packet generating unit 62 (see FIG. 13(f)). The frame length of this reconstructed coded data for retransmission, 42,449 bits, is shorter than the original code length of 44,880 bits and is not excessive for the coding length of the error correction code specified in the broadcasting standard. Therefore, the coded data related to the retransmission request can be changed to a lower coding rate, and the correction ability is higher than when retransmitting without changing the coding rate.

In addition, by improving the correction capability of the BCH code, it is possible to improve the tolerance to packet loss in the IP network 8. The change in the BCH code may be determined in advance between the transmitter and receiver so that the correction capability of the BCH code is always changed when the LDPC coding rate is changed, or a criterion for changing the correction capability of the BCH code that is determined arbitrarily may be added to the coding rate change criteria described above so that the correction capability of the BCH code is switched depending on either or both of the delay and the packet loss rate, and the receiving device 5 may be notified in advance of the change in the coding rate and before the encoded data to be retransmitted.

In this way, when the transmission server 6 of this application example receives a retransmission request packet, it can be configured to adaptively change the LDPC coding rate and the correction capability of the BCH code of the coded data related to the retransmission request based on the communication quality information contained in the retransmission request packet to generate a coded data packet and transmit it to the receiving device 5.

As described above, according to the transmission system 1 of the present embodiment, when data loss cannot be prevented by broadcast reception alone, a retransmission request is made from the receiving device 5 to the transmission server 6 via the IP network 8, and the transmission server 6 is enabled to retransmit the data, so that the data can be supplemented on the receiving device 5 side. In particular, by making the data retransmitted by the transmission server 6 via the IP network 8 into coded data in the block code of digital broadcasting, and by variably controlling the coding rate of this coded data according to the communication quality of the IP network 8, it is possible to reduce the number of retransmission requests and further improve the transmission efficiency via the IP network. In addition, by making both the error correction code used for broadcast reception and the error correction code used in transmission via the IP network the same as the coding format of the error correction code specified by the broadcast standard, the receiving device 5 can be realized with just one error correction decoder, and the equipment scale can be reduced.

(Modification)
Fig. 14 is a block diagram showing a schematic configuration of a modified receiving device 5 according to the present invention. In Fig. 14, the same components as those shown in Fig. 7 are given the same reference numbers. The modified receiving device 5 shown in Fig. 14 is different from that shown in Fig. 7 in that it further includes a reception quality measuring unit 57 and the switching unit 55 is controlled so that the reception path is switched by a first reception path switching signal from the error correction coding unit 52 and a second reception path switching signal from the reception quality measuring unit 57. The other configurations are the same.

As in the above-described embodiment, the switching unit 55 mainly operates to input the coded data transmitted via the broadcast transmission path and obtained by demodulation by the demodulation unit 51 to the error correction decoding unit 52. However, when the decoding feasibility determination unit 521 in the error correction decoding unit 52 determines that the coded data obtained via the broadcast transmission path cannot be decoded, the switching unit 55 is controlled by the first reception path switching signal from the error correction decoding unit 52 to input the coded data retransmitted via the IP network 8 and obtained from the IP packet receiving unit 54 to the error correction decoding unit 52 until the coded data can be decoded by the error correction code decoding process within a predetermined time.

In addition, in this modified example, once the receiving path is controlled to be switched to via the IP network 8, the switching unit 55 maintains the receiving path via the IP network 8 unless it is controlled by a second receiving path switching signal from the reception quality measurement unit 57, and operates to continue receiving the next encoded data following the encoded data for which a retransmission request has been made via the IP network 8 even after a retransmission request for the encoded data.

The reception quality measurement unit 57 measures the reception quality (e.g., MER (Modulation Error Ratio)) of the received modulated wave signal, determines whether the reception quality is equal to or greater than a predetermined value, and controls the switching unit 55 and the error correction decoding unit 52.

More specifically, when the reception quality of the received modulated wave signal is equal to or greater than a predetermined value and the reception path of the switching unit 55 is via the IP network 8, the reception quality measuring unit 57 controls the switching unit 55 to switch by a second reception path switching signal so that the encoded data obtained via the broadcast transmission path is input to the error correction decoding unit 52.

In addition, when the reception quality of the received modulated wave signal is less than a predetermined value and the receiving path of the switching unit 55 is via the IP network 8, the reception quality measurement unit 57 does not perform switching control of the switching unit 55 to keep the receiving path of the switching unit 55 via the IP network 8, but instead instructs the error correction decoding unit 52 by a continuation instruction signal to continue to request a retransmission of the next encoded data via the IP network 8 and obtain it, even after the retransmission request for the encoded data.

(Modification of Reception Control Flow in Receiving Device)
15 is a flow chart showing a reception control flow in the receiving device 5 according to a modified embodiment of the present invention. Note that the same step numbers as in FIG. 8 are given the same numbers.

Steps S1 to S8 shown in FIG. 15 are the same as steps S1 to S8 shown in FIG. 8, and further explanation is omitted.

In other words, even in the receiving device 5 of this modified example, the encoded data transmitted via the broadcast transmission path and obtained by demodulation by the demodulation unit 51 is input to the error correction decoding unit 52 via the switching unit 55, and when the decoding feasibility determination unit 521 in the error correction decoding unit 52 determines that the encoded data obtained via the broadcast transmission path cannot be decoded, the switching unit 55 is controlled to switch and request and obtain the encoded data again via the IP network 8, and the request for retransmission of the encoded data is repeated until the encoded data can be decoded by the error correction code decoding process within a predetermined time (steps S1 to S8).

Then, in the receiving device 5 of this modified example, the error correction decoding unit 52 generates received data based on the decoded encoded data, and if the current receiving route is not via the IP network 8 but is a receiving route for receiving broadcasts (step S9: No), the switching unit 55 maintains the setting of the receiving route for receiving broadcasts as is, and proceeds to the demodulation and decoding process for the next encoded data in the chronological order.

On the other hand, in the receiving device 5 of this modified example, after the error correction decoding unit 52 generates received data based on the decoded encoded data, if the current receiving path is via the IP network 8 (step S9: Yes), the receiving quality measuring unit 57 determines whether the receiving quality of the received modulated wave signal is equal to or greater than a predetermined value (step S10A).

When the reception quality of the received modulated wave signal is equal to or greater than a predetermined value and the reception path of the switching unit 55 is via the IP network 8 (step S10A: Yes), the reception quality measurement unit 57 controls the switching unit 55 to switch so that the coded data obtained via the broadcast transmission path is input to the error correction decoding unit 52 by the second reception path switching signal, and proceeds to the demodulation and decoding process for the next coded data in the chronological order (step S10B).

However, when the reception quality is less than the predetermined value and the receiving path of the switching unit 55 is via the IP network 8 (step S10A: No), the reception quality measurement unit 57 does not control the switching unit 55 to keep the receiving path via the IP network 8, but instead instructs the error correction decoding unit 52 by a continuation instruction signal to continue to request and obtain the encoded data via the IP network 8 even after the retransmission request for the encoded data (step S10C), and proceeds to step S4 and operates in the same manner thereafter. Note that when the error correction decoding unit 52 cannot decode the data by the decoding process within the predetermined time, it generates received data that still contains bit errors and proceeds to step S9.

Therefore, once the receiving device 5 of this modified example shown in Figures 14 and 15 switches the receiving path to via the IP network 8, if the receiving quality of the received modulated wave signal is below a predetermined value, it predicts that the receiving conditions will continue to deteriorate to the point where bit errors cannot be corrected by the error correction decoding process, and requests and obtains retransmission of the encoded data to be encoded by the error correction decoding unit 52 via the IP network 8 until the receiving quality reaches or exceeds the predetermined value.

Therefore, the transmission system 1 equipped with the receiving device 5 of this modified example also includes all the advantages of the above-mentioned embodiment, and in addition, the operation takes into account the reception quality of the received modulated wave signal, making it possible to receive stable digital data.

[Outline of operation when changing the coding rate of coded data related to a retransmission request to a lower coding rate and retransmitting the data]
For better understanding, referring to Figure 16, an overview of the operation will be described in which the encoded data related to a retransmission request is changed to a lower encoding rate and retransmitted in one embodiment of the transmission system 1 including the example and one modified example shown in Figures 1 to 15 described above.

Figure 16 is a diagram illustrating an overview of the operation when a transmission server 6 in one embodiment of the present invention transmits to a receiving device 5 an encoded data packet in which the encoded data related to a retransmission request has been changed to a lower encoding rate.

For example, assume that the coding rate (LDPC coding rate) of the coded data related to the retransmission request transmitted over the broadcast transmission path is 9/10 (109/120) in accordance with ARIB STD-B44 (see Figure 16 (a)).

First, the transmission server 6 adaptively changes the coding rate by distinguishing whether to set the coding rate higher or lower than the coding rate of the coded data transmitted over the broadcast transmission path according to the communication quality information, and reconstructs the coded data. Here, an example is described in which the coding rate of the coded data related to the retransmission request is changed from 9/10 to a lower coding rate of 1/2.

When the transmission server 6 changes the coding rate of the coded data related to the retransmission request from 9/10 to a lower coding rate of 1/2, the transmission server 6 divides the information bits of the coded data related to the retransmission request into two (here, into an equal first half and a second half) according to a division method predetermined between the sender and the receiver (the transmission server 6 and the receiver 5) (see FIG. 16(b)).

Next, the transmission server 6 performs re-encoding to change the coding rate to 1/2 using padding bits, and generates coded data with parity bits for the coding rate of 1/2 added (see FIG. 16(c)).

The transmission server 6 then generates an error-correcting code frame (LDPC frame) of the encoded data by deleting the padding bits from the encoded data to which the parity bits have been added, and then assembles an interleaved frame to form an interleaved encoded data packet (IP packet sequence), which it then transmits to the receiving device 5 via the IP network 8 (see FIG. 16(d)).

After receiving the encoded data packets, the receiving device 5 performs deinterleaving, which is the reverse process of the transmitting server 6, adds padding bits, and then performs packet loss correction by decoding the encoded data at a coding rate of 1/2 (see FIG. 16(e)).

Then, the receiving device 5 can generate received data in which the information bits related to the encoded data requested to be resent are restored by concatenating the first half of the decoded information bits of the error-correcting code frame #1 and the second half of the decoded information bits of the error-correcting code frame #2 (see FIG. 16(f)).

Therefore, according to the transmission system 1 of the present invention, when data loss cannot be prevented by broadcast reception alone, a retransmission request is made from the receiving device 5 to the transmission server 6 via the IP network 8, and the transmission server 6 is enabled to retransmit the data, so that the data can be supplemented on the receiving device 5 side. In particular, by making the data retransmitted by the transmission server 6 via the IP network 8 into coded data in the block code of digital broadcasting, and by variably controlling the coding rate of this coded data according to the communication quality of the IP network 8, it is possible to reduce the number of retransmission requests, and further improve the transmission efficiency via the IP network 8 and strengthen the resistance to packet loss. In addition, by making both the error correction code used for broadcast reception and the error correction code used in transmission via the IP network 8 the same as the coding format of the error correction code specified by the broadcast standard, it is possible to realize this by preparing only one error correction decoder on the receiving device 5 side, and the equipment scale can be reduced.

In the above embodiment, a program for making each means of a computer functioning as the transmission server 6 function can be preferably used. Also, a program for making each means of a computer functioning as the receiving device 5 function can be preferably used. Specifically, a control unit for controlling each means can be configured with a central processing unit (CPU) in a computer, and a storage unit for appropriately storing a program required to operate each means can be configured with at least one memory. That is, the function of each of the above-mentioned means can be realized by having the CPU execute the program in such a computer. Furthermore, a program for making each of the means function can be stored in a predetermined area of the above-mentioned storage unit (memory). Such a storage unit can be configured with a RAM or ROM inside the device, or can be configured with an external storage device (for example, a hard disk). Also, such a program can be configured as part of the software on the OS used by the computer (stored in the ROM or external storage device). Furthermore, a program for making such a computer function as each means can be recorded on a computer-readable recording medium. Also, each of the above-mentioned means can be configured as part of hardware or software, and can be realized by combining each of them.

The above-mentioned examples, applications, and modifications of one embodiment have been described as representative examples, but it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. For example, an example has been described in which the transmission server 6 inputs encoded data directly from the transmission device 2 (or transmission device 3), but in relay broadcasting, etc., the receiver may first receive modulated waves from the transmission device 2 (or transmission device 3) and demodulate them, and then input the encoded data obtained by demodulation. Therefore, the present invention should not be construed as being limited by the above-mentioned examples, but is limited only by the scope of the claims.

The present invention makes it possible to efficiently combine error correction codes used in digital broadcasting with retransmission requests, making it useful for data compensation related to digital broadcasting.

REFERENCE SIGNS LIST 1 Transmission system 2 Transmitter for satellite broadcast transmission path 2a Transmitting antenna for satellite broadcast transmission path 3 Transmitter for terrestrial broadcast transmission path 3a Transmitting antenna for terrestrial broadcast transmission path 4 Broadcasting satellite 5 Receiving device 5a Receiving antenna for satellite broadcast transmission path 5b Receiving antenna for terrestrial broadcast transmission path 6 Transmission server 7 Load balancing device 8 IP network 21 Error correction coding unit 22 Modulation unit 51 Demodulation unit 52 Error correction decoding unit 53 Retransmission request packet generation unit 54 IP packet receiving unit 55 Switching unit 56 Communication quality measurement unit 57 Reception quality measurement unit 61 Storage unit 62 IP packet generation unit 63 Retransmission request processing unit 64 Coding rate adaptive change unit 521 Decoding feasibility determination unit 522 Coding data complementation unit 523 Data combination unit 541 Deinterleaving unit 621 Interleaving unit 641, 642 Switching unit 643 Error correction coding unit

Claims (11)

A transmission server that digitally modulates coded data that has been coded using an error correction code related to digital broadcasting, and transmits the digitally modulated coded data to a receiving device via a broadcast transmission path, stores the coded data for a predetermined period of time, and enables the data to be transmitted to the receiving device via an IP (Internet Protocol) network,
a storage unit which sequentially receives the coded data generated by the transmitting device, manages the coded data in a time series manner by a synchronization signal based on frame numbers of error correction code frames constituting a code length of the error correction code or on time information, and stores the coded data managed in a time series manner for a predetermined time while updating the coded data;
a retransmission request processing unit that receives, via an IP network, a retransmission request packet generated when the receiving device is unable to correct bit errors in the encoded data using the error correction code, and when controlling retransmission of the encoded data related to the retransmission request to the receiving device, extracts communication quality information measured by the receiving device based on communication with the transmission server and retransmission request information indicating the encoded data of the error correction code frame related to the retransmission request, which are stored in the retransmission request packet, determines whether or not to change the encoding rate of the block code of the encoded data generated by the transmitting device according to a predetermined encoding rate change criterion based on the communication quality information, reads out the encoded data related to the retransmission request from the storage unit based on the retransmission request information in accordance with a result of the determination, configures encoded data with an adaptively changed encoding rate, and controls retransmission of the encoded data to the receiving device;
a coding rate adaptive change unit that switches between changing and not changing a coding rate of a block code of the coded data generated by the transmitting device under the control of the retransmission request processing unit, and when changing the coding rate, performs an error correction coding process that changes the coding rate based on the same coding method as the error correction coding method used by the transmitting device and among a predetermined number of coding rates that are available for the transmitting device, by distinguishing whether the coding rate is higher or lower than the coding rate of the coded data generated by the transmitting device and transmitted over a broadcast transmission path;
an IP packet generating unit that generates an encoded data packet in an IP packet format that stores encoded data related to a retransmission request configured through control by the retransmission request processing unit, and transmits the encoded data packet to the receiving device via an IP network;
The retransmission request processing unit is characterized in that it determines whether to change the coding rate of the encoded data generated by the transmitting device and retransmit it in accordance with the predetermined coding rate change criterion based on either or both of communication line delay information and packet loss rate information measured by the receiving device on a predetermined period basis as the communication quality information. The coding rate adaptive change unit, when changing the coding rate of the coded data generated by the transmitting device under the control of the retransmission request processing unit,
When converting to a coding rate higher than the coding rate before the change, padding bits known to the receiving device are added to information bits of the coded data according to the coding rate to be changed, and the parity of the block code obtained by performing the error correction coding process and having the coding rate changed is added to replace the parity added to the coded data generated by the transmitting device, and coded data for retransmission is generated from which the padding bits have been removed;
2. The transmission server according to claim 1, characterized in that, when converting to a coding rate lower than the coding rate before the change, information bits of the coded data are divided by a division method predetermined between a transmitter and a receiver, padding bits known to the receiver are added to each of the information bits divided according to the coding rate to be changed, the parity of the block code with the coding rate changed obtained by performing the error correction coding process is added in place of the parity added to the coded data generated by the transmitter, and coded data for retransmission is generated with the padding bits removed. The transmission server according to claim 1 or 2, characterized in that, when the coding rate adaptive change unit changes the coding rate of the coded data generated by the transmission device under the control of the retransmission request processing unit, in addition to changing the coding rate of the block code, it further has a means for changing the correction capability of the error correction code connected to the block code while maintaining the frame length of the error correction code frame after the coding rate change. The transmission server according to any one of claims 1 to 3, characterized in that the IP packet generation unit has an interleaving unit that generates an encoded data packet of an IP packet sequence by constructing an interleaved frame using the multiple error correction code frames and adding an identification header for making the interleaved frame identifiable, a sequence number that specifies which bit in each error correction code frame is represented, and an IP header that is the header of the encoded data packet to the payload obtained by performing interleaving across each error correction code frame. A transmitting device for digital broadcasting,
A transmission device comprising the transmission server according to any one of claims 1 to 4 therein. A receiving device receives a modulated wave signal transmitted via a broadcast transmission path by digitally modulating coded data that has been coded by a transmitting device using an error correction code related to digital broadcasting, the receiving device comprising:
A demodulation unit that receives and demodulates the modulated wave signal;
an error correction decoding unit that reconstructs an error correction code frame constituting a code length of the error correction code from the encoded data obtained by demodulation and performs a decoding process corresponding to the error correction code to generate received data so that the data can be reproduced;
a retransmission request packet generator that generates a retransmission request packet in an IP packet format including retransmission request information indicating coded data of an error correcting code frame related to a retransmission request for requesting retransmission of corresponding coded data when a bit error in the coded data cannot be corrected using the error correcting code, and transmits the retransmission request packet to a transmission server according to any one of claims 1 to 4;
an IP packet receiving unit that receives an encoded data packet in an IP packet format that stores encoded data retransmitted in response to the retransmission request from the transmission server in response to the retransmission request packet, and extracts the encoded data retransmitted in response to the retransmission request;
a communication quality measuring unit that measures, for each predetermined period, and updates and holds either or both of a delay related to communication with the transmission server and a packet loss rate based on an amount of packet loss occurring in communication with the transmission server, and sequentially outputs communication quality information including either or both of delay information and packet loss rate information of the communication line to the retransmission request packet generating unit so as to be included in the retransmission request packet,
The error correction decoding unit
a decoding possibility determination unit that determines whether or not error correction decoding is possible for the encoded data obtained from the transmitting device, and generates the retransmission request packet when it determines that bit errors in the encoded data cannot be corrected and the encoded data cannot be decoded;
an encoded data complementation unit which, for the encoded data retransmitted in response to the retransmission request, adds padding bits according to the encoding rate obtained by demodulation when the encoding rate has not been changed, and when the encoding rate has been changed, attempts decoding processing through complementation processing related to replacement of a likelihood ratio required for decoding, and repeats a request for retransmission of the corresponding encoded data until decoding is possible within a predetermined time;
a data combining unit which, when the coded data related to the retransmission request is changed to a lower coding rate and information bits are divided, recombines the divided decoded information bits according to a division method predetermined between the data combining unit and the transmission server to generate received data;
A receiving device comprising: The receiving device according to claim 6, characterized in that the error correction code is a concatenated code in which an LDPC code is an inner code and a BCH code is an outer code, and the decoding feasibility determination unit determines that bit errors in the encoded data obtained from the transmitting device could not be corrected when the encoded data is not error-free in the decoding process of the BCH code. Further comprising a reception quality measuring unit that measures the reception quality of the received modulated wave signal,
The reception quality measurement unit
When the reception route at the time when the reception data is generated based on the encoded data that has been decoded by the error correction decoding unit is not via an IP network but is a reception route for receiving broadcasts, the reception route for receiving broadcasts is maintained;
The receiving device according to claim 6 or 7, further comprising a means for determining whether the reception quality is equal to or greater than a predetermined value when the reception data is generated based on the encoded data decoded by the error correction decoding unit via an IP network, and for switching to a reception path for broadcast reception if the reception quality is equal to or greater than the predetermined value, and for maintaining the reception path via the IP network if the reception quality is less than the predetermined value, and for instructing the error correction decoding unit to continue to request a retransmission of the next encoded data via the IP network and obtain it even after a retransmission request for the encoded data. The receiving device according to any one of claims 6 to 8, characterized in that the IP packet receiving unit has a deinterleaving unit that receives an encoded data packet of an IP packet sequence that stores encoded data retransmitted in response to a retransmission request from the transmitting server in response to the retransmission request packet, and performs a reverse process of the interleaving by the transmitting server to extract the encoded data retransmitted in response to the retransmission request . A program for causing a computer to function as a transmission server according to any one of claims 1 to 4. A program for causing a computer to function as a receiving device according to any one of claims 6 to 9.