JP7614875B2 - 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 specification ARIB STD-B44 version 2.1", [online], revised March 25, 2016, ARIB, [searched February 8, 2021], 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 is desired that works in conjunction with communications to compensate for data using Hybrid ARQ, which combines error correcting codes and ARQ, by integrating digital broadcasting and communications. For example, when the transmission conditions for 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 resends the data. In other words, since current digital broadcasting only assumes data compensation using error correcting codes, compensating for digital broadcasting data using Hybrid ARQ can also handle deterioration of transmission conditions that cannot be corrected using error correcting codes.

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, when retransmission is performed using IP communication, if the number of packets to be retransmitted increases, the load on the communication line will increase and the line will become congested. Therefore, a technique is desired that minimizes the number of packets requested for retransmission and efficiently realizes data compensation using Hybrid ARQ.

Therefore, there is a need for a technique to improve the error correction capability of digital broadcasting and realize efficient Hybrid ARQ by configuring a transmission system that links digital broadcasting and communication via an IP network, for example, by combining error correction concatenated codes of LDPC codes and BCH codes with retransmission requests using IP communications, without increasing the size of the encoder in the transmitting device for digital broadcasting and the decoder in the receiving device, and by minimizing the number of packets requested for retransmission.

Therefore, in view of the above problems, the first object of the present invention is to provide a transmission server, a transmitting device and a receiving device related to digital broadcasting, and a program that enable a transmission technology with improved error correction capabilities by linking digital broadcasting and communication via an IP network without increasing the size of the error correction decoding unit in the receiving device, and by realizing Hybrid ARQ that combines error correction using LDPC codes and retransmission requests using IP communication.

The second object of the present invention is to provide a transmission server, a transmitting device and a receiving device for digital broadcasting, and a program that can reduce the number of retransmitted packets as much as possible and improve transmission efficiency by selecting an appropriate coding rate according to the correction capability of the error correction code used in digital broadcasting and the line quality of the IP network.

The third object of the present invention is to provide a transmission server, a transmitting device and a receiving device for digital broadcasting, and a program that can improve transmission efficiency by puncturing packets at positions that minimize loss of error correction capability when changing the coding rate by puncturing processing in the transmission server.

The fourth object of the present invention is to provide a transmission server, a transmission device and a reception device for digital broadcasting, and a program that, when the packet loss rate occurring in an IP network measured on the reception device side is lower than the bit error rate assumed in digital satellite broadcasting, reduces the number of packets transmitted in the IP network by using an error correction code with a higher coding rate than that used in digital satellite broadcasting, thereby realizing a more efficient Hybrid ARQ.

The transmission server of the present invention is a transmission server that stores a predetermined time of encoded data from a transmission device that digitally modulates encoded data encoded using an error correction code related to digital broadcasting and transmits the digitally modulated encoded data to a receiving device via a broadcast transmission path, and enables transmission to a receiving device via an IP (Internet Protocol) network, and includes a storage unit that sequentially inputs encoded data generated by the transmission device, manages the data in a time series using a synchronization signal based on the frame number or time information of an error correction code frame that constitutes the code length of the error correction code, and stores the predetermined time of the encoded data managed in a time series while updating it, a retransmission request processing unit that receives a retransmission request packet generated when the receiving device determines that a bit error in the encoded data cannot be corrected using the error correction code via the IP network, extracts packet loss rate information measured by the receiving device stored in the retransmission request packet and retransmission request information indicating the encoded data of the error correction code frame related to the retransmission request, and controls reading of the corresponding encoded data from the storage unit based on the retransmission request information, an IP packet generation unit that converts the encoded data read from the storage unit into IP packets, and a retransmission request processing unit that converts the packet loss rate information into an IP packet. Based on this, the system is equipped with a coding rate determination unit that refers to a predetermined erasure correction performance table as a coding rate conversion standard and determines the highest coding rate capable of erasure correction within a range equal to or higher than the coding rate of the coded data transmitted over the broadcast transmission path, and a coding rate conversion unit that converts the coding rate of the IP packetized coded data by a puncturing process that thins out only the parity of the coded data when converting the coding rate so that the coding rate becomes the coding rate determined by the coding rate determination unit, and forms a coded IP packet in which the coding rate has been adaptively converted by a puncturing process so that the coding rate of the coded data is not converted as it is, and can be output to the outside. The coding rate of the coded data to be retransmitted as the coded IP packet can be improved by the puncturing process, and the receiving device can decode it in the same error correction code format as the coded data transmitted over the broadcast transmission path.

In the transmission server of the present invention, the coding rate determination unit determines to use one of a plurality of coding rates predetermined in the erasure correction performance table for retransmission via an IP network, regardless of the coding rate used for transmitting coded data via a broadcast transmission path.

In the transmission server of the present invention, the coding rate conversion unit converts the coding rate by deleting the parity area at the position of the value obtained by dividing the number of packets in the parity area before puncturing by the number of packets to be deleted by puncturing, by using an equal interval thinning method based on the ratio between the number of bits before puncturing and the number of bits to be deleted by puncturing, and rounding down the decimal points of an integer multiple of the average puncturing interval to an integer.

In the transmission server of the present invention, the erasure correction performance table indicates required packet erasure rates indicating the highest erasure correctable coding rates of 44.4%, 38.1%, 34.0%, 28.5%, 22.3%, 18.6%, 15.2%, 11.3%, and 2.16% for at least coding rates of 1/2, 0.56, 0.61, 0.66, 0.73, 0.76, 0.8, 0.85, and 0.95, and the coding rate conversion unit has a function of converting the coding rate of 1/2 of the ISDB-S3 compliant LDPC code coded data transmitted via the broadcast transmission path to any one of the coding rates of 0.56, 0.61, 0.66, 0.73, 0.76, 0.8, 0.85, and 0.95 by the puncturing process.

In the transmission server of the present invention, the IP packet generation unit is configured to construct an interleaved frame using the multiple error correction code frames, and to add at least 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 to the payload obtained by traversing each error correction code frame, thereby generating a predetermined number of IP packets, and further includes an interleaving processing unit that performs interleaving processing on the predetermined number of encoded IP packets formed by the encoding rate conversion unit according to a predetermined interleaving standard.

The transmitting device of the present invention is a transmitting device related to digital broadcasting, and is characterized in that it includes the transmitting server of the present invention.

The 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, and includes a demodulation unit that receives and demodulates the modulated wave signal, an error correction decoding unit that reconstructs an error correction code frame that constitutes the 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 and reproduce received data, and a retransmission request information indicating the encoded data of the error correction code frame related to a retransmission request for requesting retransmission of the corresponding encoded data when it is determined that a bit error in the encoded data cannot be corrected using the error correction code, and a packet loss rate indicating the packet loss rate of an IP network. The present invention is characterized in that it comprises a retransmission request packet generation unit that generates a retransmission request packet in an IP packet format containing information and transmits it to the transmission server of the present invention, an IP packet reception unit that receives an encoded IP packet in an IP packet format that stores encoded data retransmitted from the transmission server in response to the retransmission request packet and extracts the encoded data retransmitted in response to the retransmission request, and a communication quality measurement unit that measures at least the packet loss rate of the IP network based on the retransmission request packet received by the IP packet reception unit, and the error correction decoding unit uses the encoded data retransmitted in response to the retransmission request in the decoding process and repeats a request for retransmission of the corresponding encoded data until the data can be decoded by the decoding process within a predetermined time.

The receiving device of the present invention is also characterized in that the communication quality measurement unit has a function of measuring the packet loss rate of the IP network by counting the number of packets lost from the sequence number of the IP packet.

The receiving device of the present invention is 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 error correction decoding unit determines that bit errors in the coded data obtained from the transmitting device could not be corrected when bit errors could not be completely corrected in the decoding process of the BCH code, or when errors could be corrected in the decoding process but a predetermined number of BCH errors have occurred.

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.

According to the present invention, when data loss cannot be prevented by broadcast reception alone, a retransmission request is sent from the receiving side to the transmitting side via an IP network, and the transmitting side can retransmit the data, thereby enabling the receiving side to supplement the data. In addition, according to the present invention, the number of retransmission requests can be reduced by configuring the system to simultaneously perform error correction coding and retransmission requests. In addition, by changing the error correction coding rate according to the quality of the IP network, transmission efficiency can be improved. In addition, according to the present invention, when changing the coding rate, the transmitting side punctures the data so as not to degrade the performance of the error correction code as much as possible, and the receiving side decodes the punctured IP packets by assuming that the packets have been lost in the IP network. This makes it possible to easily decode the data using a check matrix with the same coding rate as the satellite broadcast channel without preparing a new LDPC coding table.

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. 1 is an explanatory diagram of a method of generating IP packets based on construction of an interleaved frame by an IP packet generating unit in a transmission server according to an embodiment of the present invention; FIG. 11 is a diagram showing an example of an erasure correction performance table used at the time of coding rate conversion by a coding rate conversion unit in a transmission server according to an embodiment of the present invention. 10 is a flowchart showing a coding rate conversion process for an IP packet in a coding rate conversion unit of a transmission server according to an embodiment of the present invention. 1A to 1D are diagrams illustrating how coded data after coding rate conversion is reconstructed by a coding rate conversion unit in a transmission server according to an embodiment of the present invention. 1A and 1B are explanatory diagrams of an IP packet generation process by an IP packet generation unit in a transmission server according to an embodiment of the present invention, and a puncturing process on an IP packet by a coding rate conversion unit, respectively. 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.

[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.

The receiving device 5 also has the function of determining whether the encoded data obtained from the transmitting device 2 (or transmitting device 3) can be decoded for error correction, and if it is determined that the encoded data can be decoded, it decodes the encoded data as is to generate received data, and if it is determined that the bit error 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 a retransmission of the corresponding encoded data, includes packet loss rate information in this retransmission request packet, and transmits it to the transmitting server 6 via the IP network 8. That is, the receiving device 5 is configured to demodulate the digital broadcast received from the receiving antenna 5a (or 5b) and reproduce the received data, and reproduces the received data as is when the transmission environment is good and the data can be received without errors, or when the influence of white noise, etc. is within the range that can be decoded by error correction code, but when the transmission environment is poor due to rain attenuation, fading, etc. and the signal has deteriorated to the extent that it cannot be decoded by error correction code, it requests the transmitting server 6 to retransmit the corresponding encoded data via the IP network 8.

Furthermore, the receiving device 5 has a function of receiving an encoded IP packet in an IP packet format (an IP packet in which the encoding rate has been adaptively converted by puncturing within a range equal to or greater than the encoding rate of the encoded data transmitted over the broadcast transmission path in response to the packet loss rate information at the transmitting server 6 side) that stores the encoded data retransmitted in response to the retransmission request packet from the transmitting server 6 in response to the retransmission request, 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 data can be decoded by the decoding process within a specified time. Note that when the receiving device 5 cannot decode the data by the decoding process within the specified time, it generates received data that still contains 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 encoded using error correction codes related to digital broadcasting and transmits the coded data to reception device 5 via a broadcast transmission path, and transmits coded IP packets in an IP packet format (IP packets in which the coding rate has been adaptively converted by puncturing processing within a range equal to or higher than the coding rate of the coded data transmitted via the broadcast transmission path in accordance with packet loss rate information on the transmission server 6 side) that store coded data requested for retransmission by reception device 5 via IP network 8 to reception device 5.

That is, the transmission server 6 has a function of sequentially inputting the coded data generated by the transmission device 2 (or the transmission device 3) via the local area network, managing the coded data in a time series manner by a synchronization signal based on the frame number of the error correction code frame constituting the code length of the error correction code or on time information, and storing the data while updating the data for a predetermined period of time; receiving a retransmission request packet indicating a retransmission request for the coded data together with packet loss rate information when a bit error in the coded data could not be corrected by the error correction code used by the transmission device 2 (or the transmission device 3) via the IP network 8, and adaptively determining whether or not to increase the coding rate of the coded data transmitted over the broadcast transmission path to the reception device 5 according to the packet loss rate information; and a function of controlling the retransmission of the coded IP packet having the coding rate converted by the puncturing process, and of forming, when retransmitting the coded IP packet, m error correcting code frames having consecutive synchronization signals (frame number or time information), starting with an error correcting code frame constituting the coded data having a synchronization signal (frame number or time information) related to a retransmission request, at the same coding rate as the coded data having the synchronization signal (frame number or time information) related to the retransmission request, to construct an interleaved frame, reading out the interleaved frame bit by bit in a direction orthogonal to the m error correcting code frames to temporarily generate N packets of IP packets, forming N ₂ (N ₂ ≦N) packets of coded IP packets having the coding rate converted by the puncturing process, performing interleaving as necessary, and transmitting the resulting coded IP packet to the receiving device 5 via the IP network 8.

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 the transmission device 2 (or the transmission device 3) may include the transmission server 6 inside the device, and one or more transmission devices 2 (or the transmission devices 3) may be 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 coded IP 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 error correction code frames, adding frame numbers, 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 Fig. 2 is configured as a computer that sequentially inputs from the transmission device 2 (or transmission device 3) that digitally modulates the coded data that uses the error correction code related to digital broadcasting and transmits it to the receiving device 5 via broadcast transmission line, updates and saves it for a predetermined time, and for the coded data that is requested to be retransmitted from the receiving device 5 among the coded data, determines the highest coding rate that can be erased and corrected within the range that is equal to or higher than the coding rate of the coded data that is transmitted via broadcast transmission line according to packet erasure rate information, adaptively forms the coded IP packet that converts the coding rate by puncturing, and can transmit it to the receiving device 5 via IP network 8, and comprises a storage unit 61, an IP packet generation unit 62, a retransmission request processing unit 63, a coding rate determination unit 64, an erase correction performance table storage unit 65, a coding rate conversion unit 66 and an interleave processing unit 67.

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.

When the IP packet generation unit 62 receives coded data having a synchronization signal (frame number or time information) related to a retransmission request read from the storage unit 61, the IP packet generation unit 62 constructs an interleaved frame by forming m error correction code frames having consecutive synchronization signals (frame number or time information) starting from the error correction code frame constituting the coded data, at the same coding rate as the coded data having the synchronization signal (frame number or time information) related to the retransmission request, reads the interleaved frame bit by bit in a direction orthogonal to the m error correction code frames, generates N packets of IP packets, and outputs them to the coding rate conversion unit 66.

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 packet loss rate information measured by the receiving device 5 and 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. The retransmission request processing unit 63 then outputs the packet loss rate information to the encoding rate determination unit 64, and based on the retransmission request information, controls the retransmission request processing unit 63 to read the encoded data related to the retransmission request input from the transmitting device 2 (or transmitting device 3) and stored in the storage unit 61, and output it to the IP packet generation unit 62.

The coding rate determination unit 64 is a functional unit that, based on the packet loss rate information obtained from the retransmission request processing unit 63, refers to the loss correction performance table stored in the loss correction performance table storage unit 65 as a coding rate conversion standard, determines the highest coding rate that is capable of loss correction within a range equal to or greater than the coding rate of the coded data transmitted over the broadcast transmission path, and notifies the coding rate conversion unit 66 of the determined coding rate information.

The coding rate conversion unit 66, in accordance with coding rate information determined by distinguishing whether or not to make the coding rate higher than that of the coded data transmitted over the broadcast transmission path in accordance with packet loss rate information notified by the coding rate determination unit 64 for N packets of IP packets obtained from the IP packet generation unit 62, converts the coding rate by a puncturing process that thins out only the parity of the coded data when converting the coding rate, and forms N ₂ (N ₂ ≦ N) packets of coded IP packets whose coding rate has been adaptively converted by a puncturing process and outputs them to the interleaving processing unit 67.

The interleave processing unit 67 performs interleaving processing by bit swapping on the N ₂ (N ₂ ≦N) packets of coded IP packets obtained from the coding rate conversion unit 66 in accordance with a predetermined interleaving standard among the N ₂ packets, and transmits the N ₂ packets of coded IP packets after interleaving processing to the receiving device 5 via the IP network 8 as a response to the retransmission request.

The erasure correction performance table storage unit 65 stores an erasure correction performance table as a coding rate conversion standard. The erasure correction performance table indicates the maximum packet loss rate that can be achieved error-free for each coding rate that is determined in advance by computer simulation, and is referenced by the coding rate determination unit 64 so that it can determine the highest coding rate (which minimizes packets including parity bits) among the coding rates at which packets can be lost.

(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, by the storage unit 61, the encoded data transmitted over the broadcast transmission path while updating it for a predetermined period of time (step S1). 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 receiving device 5 outputs the received data that has been error-corrected and decoded 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 transmitting server 6 (step S2). As described above, this retransmission request packet contains retransmission request information and packet loss rate information.

When the transmission server 6 receives a retransmission request packet from the receiving device 5 (step S3), the retransmission request processing unit 63 extracts the retransmission request information and packet loss rate information from the retransmission request packet, outputs the packet loss rate information to the coding rate determination unit 64, and, based on the retransmission request information, reads out the coded data related to the retransmission request input from the transmitting device 2 (or transmitting device 3) and stored in the storage unit 61, and controls the data to be output to the IP packet generation unit 62 (step S4).

Next, transmission server 6, based on the packet loss rate information obtained from retransmission request processing unit 63, refers to the loss correction performance table stored in loss correction performance table storage unit 65 as coding rate conversion criterion, determines the highest coding rate F _i that can be lost correction within the range that is equal to or higher than the coding rate of the coded data transmitted on broadcast transmission line, and notifies coding rate conversion unit 66 of the information of determined coding rate F _i (step S5).

Then, the transmission server 6 uses the IP packet generator 62 to IP packetize the coded data with coding rate _Fb read from the storage unit 61 based on the retransmission request information (step S6). Here, the IP packet generator 62 forms m error correction code frames having consecutive synchronization signals (frame number or time information) starting from the error correction code frame constituting the coded data at the beginning, at the same coding rate as the coded data having the synchronization signal (frame number or time information) related to the retransmission request, to construct an interleaved frame, reads the interleaved frame bit by bit in a direction orthogonal to the m error correction code frames, temporarily generates IP packets for N packets, and outputs them to the coding rate converter 66.

Next, the transmission server 6 causes the coding rate conversion unit 66 to perform coding rate conversion processing on the N IP packets to form N ₂ (N ₂ ≦N) coded IP packets, and outputs them to the interleave processing unit 67 (step S7).

Finally, the transmitting server 6 forms coded IP packets by interleaving N ₂ packets according to a predetermined interleaving standard using the interleaving processing unit 67, and transmits the interleaved N ₂ packets of coded IP packets as a response to the retransmission request via the IP network 8 to the receiving device 5, after transmitting a coding rate change notification packet as necessary (step S8).

Instead of notifying by using the coding rate change notification packet, information indicating the coding rate change may be embedded in the header or payload of the _N2 packets of coded IP packets.

The transmission server 6 may be configured to transmit the coding rate conversion notification packet multiple times, or may be configured to obtain a reception confirmation response for the coding rate conversion notification packet and repeatedly transmit the coding rate conversion notification packet until a reception confirmation response is received from the receiving device 5. Furthermore, 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 information about the coding rate over the broadcast transmission path, and therefore the transmission server 6 may omit prior notification of the coding rate conversion notification packet.

In addition, when the interleaving process in the interleave processing unit 67 is omitted, the coding rate conversion unit 66 may output one IP packet of the coded data related to the retransmission request. However, from the viewpoint of increasing the resistance to burst packet losses occurring in the IP network 8, it is preferable to execute the interleaving process in the interleave processing unit 67. Therefore, in this example, the IP packet generation unit 62 generates N packets of IP packets, and the interleave processing unit 67 can perform interleaving while the coding rate conversion unit 66 performs coding rate conversion.

(IP Packet Generation Method in IP Packet Generation Unit)
Here, a method for generating IP packets according to this embodiment will be described with reference to Fig. 4. Fig. 4 is an explanatory diagram relating to a method for generating IP packets based on construction of interleaved frames by the IP packet generating unit 62 in the transmission server 6 according to an embodiment of the present invention.

In this example, when the transmission server 6 transmits the encoded IP data requested for retransmission to the receiving device 5 via the IP network 8, in order to achieve high correction performance even in the case of burst packet losses occurring in the IP network 8, the IP packet generating unit 62 generates IP packets based on the construction of an interleaved frame so that the subsequent interleaving processing unit 67 can perform interleaving processing.

First, as shown in Fig. 4(a), the IP packet generator 62 reads out from the storage unit 61, and inputs m frames of error correcting code frames having consecutive sync signals (frame number or time information ₎ starting from an error correcting code frame constituting coded data having a sync 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 Fb used in the broadcast transmission path, to compose an N x 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 transmitter and the receiver.

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. 4(a)).

Next, as shown in FIG. 4(b), the IP packet generator 62 reads each bit in the m-frame error correction code frame from the beginning, and generates N packets of m-bit IP payloads as the packet length excluding the header of the IP packet to be generated. In other words, the IP payload is m bits obtained by collecting the same bits from bits 1 to N of each error correction code frame, one bit at a time.

Next, as shown in FIG. 4(c), the IP packet generator 62 generates N packets of IP packets by adding a sequence number that identifies which bit in each error correction code frame it represents and an IP header as the header of the encoded IP packet to the generated IP payload for N packets. If necessary, an identification header that allows the receiving device 5 to identify the interleaved frame may be inserted between the IP header and the sequence number. The identification header may be assigned a number that can be distinguished in synchronization with the time series of the encoded data read from the storage unit 61. This makes it possible to identify the interleaved frame when the receiving device 5 receives the encoded IP packet, even if multiple interleaved frames are configured. 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.

In this way, the IP packet generation unit 62 generates N packets worth of IP packets based on the construction of an interleaved frame so that they can be interleaved by the subsequent interleave processing unit 67.

In addition, the interleave processing unit 67 in this embodiment needs 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 interleave unit 621 cannot execute the interleave process until m error correction code frames are available. Therefore, when time loss is a problem, only a predetermined number of bits N ₁ (<N) as sequence numbers of the N _2- 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. And, m, N ₁ , and N ₂ are fixed values but can be variably set from the outside, so that the packet length of each IP packet can be adjusted.

The IP packet generator 62 generates IP packets by collecting one bit from each error correction code frame, but 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 the multiple packets thus generated are treated as one interleaved frame, and the interleaving processor 67 rearranges the order in which the bits of the error correction code frame are sent so as to anticipate and mitigate burst packet losses in the IP network 8, and any interleaving technique can be applied. In general, the longer the period (signal length) targeted by the interleaving process, the stronger the resistance to burst packet losses, so the interleaving processor 67 is configured to perform optimal interleaving within an allowable period for the entire transmission system 1.

(Method of determining the coding rate in the coding rate determination unit)
Based on the packet loss rate information obtained from retransmission request processing unit 63, coding rate determining unit 64 of this embodiment refers to the loss correction performance table stored in loss correction performance table storage unit 65 as coding rate conversion criterion, determines the highest coding rate F _i that can be lost correction within the range that is equal to or higher than the coding rate of the coded data transmitted through broadcast transmission line, and notifies coding rate conversion unit 66 of the information of determined coding rate F _i .

Here, as one example of the transmission system 1 of this embodiment shown in FIG. 1, the coding rate _Fb of the error correction code used for transmission via the broadcast transmission path is 1/2, 3/5 (=0.6), 2/3 (≈0.67), 3/4 (=0.75), 4/5 (=0.8), 5/6 (≈0.83), 7/8 (≈0.88), or 9/10 (=0.9) that are used in digital satellite broadcasting. However, regardless of these coding rates, the coding rate determination unit 64 determines to use for retransmission one of a plurality of coding rates optimized for retransmission via the IP network 8.

As an example, the coding rate _Fb of the satellite broadcasting channel is 1/2, and the coding rate F _i when retransmitting the retransmission request data to the IP network is selected from the coding rates 1/2, 0.56, 0.61, 0.66, 0.73, 0.76, 0.8, 0.85, and 0.95 according to the communication quality of the IP network 8. It is also possible to flexibly change to other coding rates of 1/2 or more according to the number of punctures. The transmission method including the error correction code is based on ARIB STD-B44 (ISDB-S3).

Figure 5 is a diagram showing an example of an erasure correction performance table used when the coding rate conversion unit 64 in the transmission server 6 of one embodiment of the present invention converts the coding rate. The erasure correction performance table shown in Figure 5 contains values obtained in advance by computer simulation, and holds the maximum packet loss rate (required packet loss rate) that can be achieved error-free for each of 1/2, 0.56, 0.61, 0.66, 0.73, 0.76, 0.8, 0.85, and 0.95 as the coding rate (shortened coding rate) used when retransmitting via the IP network 8.

For example, when the coding rate F _b of the error correcting code used for transmission via broadcast transmission line is 1/2, and the packet loss rate of the IP network 8 related to the retransmission request obtained from the receiving device 5 is 25%, coding rate conversion unit 64 refers to the erasure correction performance table shown in Fig. 5, and as the coding rate F _i of retransmission to the receiving device 5 via IP network 8, it determines the maximum coding rate F _i = 0.66 that can be erasure corrected within the range that is equal to or higher than the coding rate of the coded data transmitted via broadcast transmission line.That is, coding rate conversion unit 64 refers to the erasure correction performance table as the coding rate F _i that can be transmitted error-free in the IP network 8 with packet loss rate of 25%, and 1/2, 0.56, 0.61, 0.66 are candidates, but in order to suppress the line congestion of IP network 8 and improve transmission efficiency, it selects the maximum coding rate that contains the least number of parity bits, and notifies coding rate conversion unit 66 of coding rate F _i = 0.66 in this example.

In this way, when the IP network 8 of the Internet line is used for retransmission, the coding rate determination unit 64 determines the coding rate F i so that the packet loss rate during retransmission can be suppressed low in the case where the packet loss rate varies greatly depending on the usage state of the line, or when the IP transmission is performed using the bandwidth guarantee _control in the closed network.In particular, it is assumed that the packet loss rate in the IP network 8 varies within a range smaller than the range that can be corrected with coding rate 1/2 for a long time, so by making the coding rate of the error correction code for the IP network 8 higher than 1/2 available, the packet containing parity bit can be reduced, and the coding data can be retransmitted by correcting packet loss efficiently.

(Encoding rate conversion process of IP packets in encoding rate conversion unit)
Next, the coding rate conversion process of the IP packet in the coding rate conversion unit 66 according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a flowchart showing the coding rate conversion process of the IP packet in the coding rate conversion unit 66 of the transmission server 6 according to an embodiment of the present invention.

When the coding rate conversion unit 66 receives an IP packet storing coded data with coding rate _Fb generated by the IP packet generation unit 62, the coding rate conversion unit 66 compares the coding rate _Fb in the IP packet with the coding rate F _i determined by the coding rate determination unit 64 (step S71).

If F _b < F _i is satisfied (step S72: Yes), the coding rate conversion unit 66 performs puncturing on the IP packet to form an encoded IP packet with the coding rate changed to F _i (step S73); if F _b < F _i is not satisfied (i.e., F _b = F _i ) (step S72: No), the coding rate conversion unit 66 forms an encoded IP packet with the coding rate of F _b unchanged for the IP packet (step S74), and outputs the encoded IP packet to the interleaving processing unit 63.

Figures 7(a) to (d) are diagrams showing how the coding rate conversion unit 66 in the transmission server 6 of one embodiment of the present invention reconstructs coded data after coding rate conversion.

First, Fig. 7(a) is a diagram showing the configuration of an error correction frame of a block code showing coded data of code length N bits transmitted through a broadcast transmission line. Normally, a plurality of selectable coding rates are predefined in digital broadcasting. For example, in the transmission system 1 of this embodiment, the coding rate _Fb of the error correction code used for transmission through the broadcast transmission line can be 1/2, 3/5 (=0.6), 2/3 (≒0.67), 3/4 (=0.75), 4/5 (=0.8), 5/6 (≒0.83), 7/8 (≒0.88), 9/10 (=0.9) used in digital satellite broadcasting.

As shown in FIG. 7(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 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 to be retransmitted via the IP network 8 is F _i , the parity of the coding rate F _i may be changed from the coding rate F _b by using the information bits of N×F _b bits (i.e., the main signal in the block code) and may be set to a block code with a code length of N ₂ bits. Therefore, it is sufficient if the coding rate is within a range equal to or higher than the coding rate of the coded data transmitted through the broadcast transmission path.

Therefore, as mentioned above, transmission server 6 updates and stores the coded data of coding rate F _b transmitted on broadcast transmission path for a predetermined time in storage unit 61, and when retransmission request packet is received from receiving device 5 by retransmission request processing unit 63, extracts retransmission request information and packet loss rate information from retransmission request packet, outputs packet loss rate information to coding rate determination unit 64, and controls to read the coded data related to retransmission request stored in storage unit 61 based on retransmission request information, and output to IP packet generation unit 62.Then, coding rate determination unit 64 refers to the erasure correction performance table stored in erasure correction performance table storage unit 65 as coding rate conversion standard based on the packet loss rate information obtained from retransmission request processing unit 63, and determines the highest coding rate that can be erased and corrected within the range that is equal to or higher than the coding rate of the coded data transmitted on broadcast transmission path as F _i , and notifies coding rate conversion unit 66 of the information of determined coding rate F _i .

As shown in FIG. 7B, the encoded data read from the storage unit 61 consists of N×F _b information bits and N×(1−F _b ) parity bits, and is IP packetized by the IP packet generator 62 .

Then, as shown in FIG. 7( c), when F _b < F _{i is satisfied, the transmission server 6 performs coding rate conversion of the coded data by performing puncturing processing in which only the parity bits of the coded data are thinned out to a coding rate of F i using} an equal-interval thinning method based on the ratio between the number of bits before puncturing in the parity area and the number of bits to be deleted by puncturing, using the equal-interval thinning method.

Then, when the transmission server 6 forms a coded IP packet with a converted coding rate by the coding rate conversion unit 66, the frame length of the coded data transmitted by the coded IP packet at this time becomes _N2 (=N× _Fb / _Fi ) as shown in Fig. 7(d), and the coded data is reconstructed to consist of _N2 × _Fi (=N× _Fb ) information bits and _N2 ×(1- _Fi ) parity bits. Since the frame length _N2 of this reconstructed coded data for retransmission is shorter than the original code length N bits, the transmission efficiency is higher than when coded data of the code length N bits is retransmitted to the receiving device 5.

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 packet loss rate information contained in the retransmission request packet to form a coded IP packet and transmit it to the receiving device 5.

(An embodiment in which a transmission system is configured for advanced wideband satellite digital broadcasting)
The operation of an embodiment in which the transmission system 1 of this embodiment is configured for advanced wideband digital satellite broadcasting will be described with reference to Figure 3 again. First, the transmission server 6 uses the storage unit 61 to store, while updating, a predetermined period of coded data transmitted by the transmitting device 2 over the broadcast transmission path of advanced wideband digital satellite broadcasting (step S1).

When the signal has deteriorated to the extent that it cannot be decoded using error correction code due to rain attenuation or the like, when errors cannot be corrected using BCH code, or when a certain number of bit errors has been reached, the receiving device 5 generates a retransmission request packet including retransmission request information indicating the LDPC frame (44,880 bits) that needs to be retransmitted in association with a synchronization signal such as time information contained in the TMCC, and packet loss rate information of the IP network 8 measured on the receiving device 5 side, and makes a retransmission request to the transmitting server 6 (step S2).

When the transmission server 6 receives the retransmission request packet sent from the receiving device 5 at the retransmission request processing unit 63 (step S3), it extracts the retransmission request information and packet loss rate information from the retransmission request packet, and based on the retransmission request information indicating the LDPC frame that needs to be retransmitted, controls the storage unit 61 to read the LDPC frame related to the retransmission request stored therein and output it to the IP packet generation unit 62, and outputs the packet loss rate information to the coding rate determination unit 64 (step S4).

Then, transmission server 6, based on the packet loss rate information obtained from retransmission request processing unit 63, refers to the loss correction performance table stored in loss correction performance table storage unit 65 as a coding rate conversion standard by coding rate determination unit 64, determines the highest coding rate F _i that can be lost and corrected within the range that is equal to or higher than the coding rate of the coded data transmitted on broadcast transmission line, and notifies coding rate conversion unit 66 of the information of determined coding rate F _i (step S5).The loss correction performance table shows the maximum packet loss rate (required packet loss rate) that can be achieved error-free for each coding rate 1/2, 0.56, 0.61, 0.66, 0.73, 0.76, 0.8, 0.85, 0.95 shown in above-mentioned Figure 5, which is obtained in advance by computer simulation.

For example, when the packet loss rate of the IP network 8 notified by the receiving device 5 is 40%, the coding rate determining unit 64 refers to the erasure correction performance table and determines the coding rate F _i of retransmitting to the receiving device 5 via the IP network 8 to be 1/2. Here, the coding rate F i that can be transmitted error-free in the IP network 8 with a packet loss rate of 40% is only 1/2. In this case, the coding rate determining unit 64 notifies the coding rate conversion unit 66 of the determined coding _{rate F i =} F _b = 1/2. At this time, the coding rate of the broadcast transmission line of satellite broadcasting and the coding rate of the IP network 8 are the same (F _i = F _b = 1/2), so as described with reference to Fig. 6, the coding rate conversion unit 66 forms the coding IP packet that has the coding rate of the IP packet that stores the corresponding LDPC frame that is coded by the transmitting device 2 and is generated by the IP packet generating unit 62 as it is, and outputs it to the interleaving processing unit 67. The IP packet generation unit 62 constructs an interleaved frame as described with reference to Figure 4, and in this example generates IP packets worth N = 44,880 packets each with sequence numbers from 1 to 44,880 and IP headers added, and outputs the packets to the coding rate conversion unit 66.

On the other hand, for example, when the packet loss rate of IP network 8 notified by receiving device 5 is 25%, coding rate determination unit 64 refers to erasure correction performance table and determines the coding rate F _i of retransmitting to receiving device 5 via IP network 8 to be 0.66.That is, the coding rate F _i that can transmit error-free in IP network 8 with packet loss rate of 25% is referred to from erasure correction performance table as 1/2, 0.56, 0.61, 0.66, but in order to suppress the line congestion of IP network 8 and improve transmission efficiency, coding rate determination unit 64 selects the maximum coding rate that contains the least number of packets with parity bits.In this case, coding rate determination unit 64 notifies coding rate conversion unit 66 of the determined coding rate F _i = 0.66. At this time, since the coding rate of the satellite broadcast transmission path and the IP network 8 are different ( _Fb < _Fi ), as described with reference to FIG. 6, the coding rate conversion unit 66 performs puncturing on the IP packet that stores the corresponding LDPC frame that was generated by the IP packet generation unit 62 and coded by the transmitting device 2 to form a coded IP packet with a coding rate of _Fi = 0.66, and outputs the coded IP packet to the interleave processing unit 67.

Figures 8(a) and (b) are explanatory diagrams of the IP packet generation process of the IP packet generation unit 62 in the transmission server 6 of one embodiment of the present invention, and the puncturing process on the IP packet by the coding rate conversion unit 66.

As illustrated in FIG. 8(a), the IP packet generation unit 62 constructs an N (=44,880 bits) x m (=1,000 bytes) interleaved frame, and in this example, reads each bit from the beginning of m error correction code frames with coding rate F _b = 1/2, and generates N packets of IP packets with m-bit IP payloads as the packet length excluding the headers of the IP packets to be generated, that is, N = 44,880 packets of IP packets with sequence numbers from 1 to 44,880 and IP headers added.

Then, as shown in Fig. 8(b), the coding rate conversion unit 66 deletes (punctures) 10472 packets from the IP packet group with coding rate F _b = 1/2 arranged in the order of information bits (22814 bits) and LDPC parity bits (22066 bits) so as to convert to coding rate F _i = 0.66. Due to the structure of the LDPC check matrix, it is possible to convert the coding rate without extremely deteriorating the error correction performance by puncturing at equal intervals in the parity area. In the example shown in Fig. 8(b), first, the coding rate conversion unit 66 calculates the average puncture interval using an equal interval thinning method based on the ratio between the number of bits before puncturing and the number of bits deleted by puncturing, that is, the number of packets before puncturing in the parity area (22066) ÷ the number of packets deleted by puncturing (10472) ≈ 2.11. If the packet position numbers of the parity area before puncturing are defined as 1, 2, 3, ..., 22066 from the side closest to the information bit, the coding rate conversion unit 66 deletes (punctures) the parity area parts of the numbers obtained by rounding down the decimal points of the average puncturing interval (=2.11) x i (i is an integer that increments from 1 up to the number of punctured packets, 1, 2, 3, ..., 10472) and converting it into integers. For example, the integer multiples of 2.11 are 2.11, 4.22, 6.33, 8.44, 10.55, 12.66, 14.77, 16.88, 18.99, 21.1, ..., so the puncture positions are the 2nd, 4th, 6th, 8th, 10th, 12th, 14th, 16th, 18th, 21st ... packets from the beginning of the parity area. This equal interval thinning method makes it possible to puncture the parity area as evenly as possible according to the number of punctures.

Finally, the transmitting server 6 uses the interleave processing unit 67 to form coded IP packets that have been interleaved according to a predetermined interleaving standard among N ₂ = 34,418 (= 22,814 information bits + parity bits after puncturing (22,066 - 10,462)) packets as necessary, and after sending a coding rate change notification packet as necessary, transmits the interleaved N ₂ = 34,418 coded IP packets to the receiving device 5 via the IP network 8 as a response to the retransmission request (step S8).

[Receiving device]
9 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, and a communication quality measurement unit 55.

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.

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 before or after the decoding process of the error correction code, uses this LLR to reconstruct the error correction code frame that constitutes the code length of the error correction code, 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 judges whether the encoded data constituting the error correction code frame can be decoded for error correction, and if it judges that the encoded data can be decoded, it decodes it as is to generate received data, and if it judges 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 generating unit 53. Note that 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 frame number as with the transmission server 6, so 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 error correction decoding unit 52 also has a function of extracting coded data related to the retransmission request from the coded IP 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 complementing the extracted data for use in the decoding process of the coded data in the error correction code frame.

The error correction decoding unit 52 is configured to complement the encoded data in the error correction code frame acquired via the IP network 8 (bit complementation corresponding to the inverse process of the puncturing process in the encoding rate conversion unit 66 on the transmitting side, and complementation for conversion to a log-likelihood ratio), 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. 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.

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 IP packet to the receiving device 5. Therefore, the error correction decoding unit 52 determines whether 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 appropriately performs bit complementation corresponding to the inverse process of the puncturing process according to the coding rate, and performs complementation 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 and packet loss rate information obtained from the communication quality measuring unit 55, in order to request the transmission server 6 to retransmit the encoded data in the error correction code frame when the error correction decoding unit 52 determines that the encoded data cannot be decoded, and transmits the packet to the transmission server 6 via the IP network 8.

The IP packet receiving unit 54 is a functional unit that receives an encoded IP packet in an IP packet format that stores the retransmitted encoded data from the transmission server 6 in response to the retransmission request packet, reconstructs the interleaved frame, and then performs the reverse process of the interleaving processing unit 67 in the transmission server 6, i.e., sorting according to the sequence numbers of the IP packets (for example, sorting the sequence numbers in ascending order), converting them into a data format acceptable to the error correction decoding unit 52, obtains the encoded data related to the retransmission request, and outputs it to the error correction decoding unit 52.

The communication quality measurement unit 55 is a functional unit that measures and updates the packet loss rate related to communication with the transmission server 6 in units of a predetermined period, and sequentially outputs the packet loss rate information to the retransmission request packet generation unit 53. More specifically, the communication quality measurement unit 55 has a function of measuring the packet loss rate of the IP network by counting the number of packets lost from the sequence number of the IP packet.

(Reception control flow in the receiving device)
FIG. 10 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 emitted 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 encoded data obtained by this demodulation process to the error correction decoding unit 52 (step S21).

Next, 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 S22).

Here, the error correction decoding unit 52 determines whether the encoded data obtained from the transmitting device 2 (or transmitting device 3) can be decoded for error correction (step S23), and if it is determined that the encoded data can be decoded, the data is decoded as is to generate reproducible received data (step S23: No), and the unit moves 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 if there is no bit error or if the bit error is within a correctable range, the unit decodes the data as is to generate reproducible received data. For example, in one embodiment, when the error correction code of the encoded data transmitted via the broadcast transmission path is a concatenated code in which an LDPC code is used as the inner code and a BCH code is used as the outer code, the error correction decoding unit 52 can be configured to determine that the bit errors in the encoded data obtained from the transmitting device 2 (or transmitting device 3) could not be corrected when the bit errors could not be corrected in the decoding process of the BCH code, or when the errors could be corrected in the decoding process but a predetermined number of BCH errors have occurred.

On the other hand, if the error correction decoding unit 52 determines that it cannot decode the encoded data that constitutes the error correction code frame, it generates retransmission request information for the encoded data that constitutes the error correction code frame, and outputs this to the retransmission request packet generating unit 53 to instruct it to generate a retransmission request packet indicating a retransmission request for the encoded data (step S23: Yes).

When the error correction decoding unit 52 determines that decoding is not possible, the retransmission request packet generating unit 53 generates a retransmission request packet in an IP packet format that includes the retransmission request information and the packet loss rate information obtained from the communication quality measuring unit 55 in order 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 S24).

When the transmission server 6 receives a retransmission request packet from the receiving device 5, it extracts the retransmission request information and the packet loss rate information from the retransmission request packet, and determines whether to change the coding rate and, if so, to which coding rate according to a predetermined coding rate conversion criterion based on the packet loss rate information. As described above, the coding rate conversion criterion refers to a predetermined loss correction performance table shown in FIG. 5 as an example, and determines the highest coding rate capable of loss correction within a range equal to or higher than the coding rate of the coded data transmitted on the broadcast transmission path. Note that it determines which of a plurality of coding rates optimized for retransmission via the IP network 8 is used for retransmission, regardless of the coding rate of the error correction coding method used by the error correction coding unit 21 on the transmitting side.

Then, based on the retransmission request information, the transmission server 6 reads out the coded data related to the retransmission request for the corresponding error correction code frame from the storage unit 61, forms a coded IP packet with adaptive coding rate conversion, and transmits it to the receiving device 5 via the IP network 8.

The receiving device 5 receives an encoded IP packet in IP packet format that stores the retransmitted encoded data from the transmitting server 6 in response to the retransmission request packet, reconstructs the interleaved frame, and then performs the reverse process of the interleaving processing unit 67 in the transmitting server 6, i.e., rearranges the IP packets according to their sequence numbers (for example, rearranges them in ascending order of sequence numbers), converts them into a data format acceptable to the error correction decoding unit, obtains the encoded data related to the retransmission request, and outputs it to the error correction decoding unit 52 (step S25).

In this example, when the transmission server 6 changes the coding rate, it generates and transmits a coding rate conversion notification packet as a notification to that effect, and then transmits the encoded IP packet to the receiving device 5. Therefore, the receiving device 5 can determine, by the error correction decoding unit 52, whether or not the coding rate of the encoded data obtained via the IP network 8 is different from that at the time of broadcast reception (step S26).

If the coding rate of the coded data obtained via the IP network 8 is different from that at the time of broadcast reception (step S26: Yes), the error correction decoding unit 52 performs bit complementation (addition of a specified bit that makes it possible to identify that a log-likelihood ratio of 0 is assigned to the position that was deleted by the puncturing process) corresponding to the inverse process of the puncturing process performed by the coding rate conversion unit 66 on the transmitting side for the coded data in the error correction code frame obtained via the IP network 8 (step S27).

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 S26: No), the error correction decoding unit 52 does not need to perform bit complementation processing.

Then, the error correction decoding unit 52 performs a complementation by converting the encoded data acquired via the IP network 8 into a log-likelihood ratio for use in the decoding process of the encoded data in the error correction code frame (step S28). 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 for the encoded data acquired via the IP network 8, the log-likelihood ratio is complemented by replacing the log-likelihood ratio with +∞ (the maximum value as the likelihood of a "0") when the bit value is 0, the log-likelihood ratio with -∞ (the maximum value as the likelihood of a "1") when the bit value is 1, and by replacing the log-likelihood ratio with 0 when a packet loss occurs and a non-delivery bit occurs or when a packet is lost in the IP network 8 and the received bit is unknown.

Then, the error correction decoding unit 52 repeatedly requests retransmission of the encoded data until it can be decoded by the error correction code decoding process within a predetermined time (steps S22 to S28), generates received data based on the decoded encoded data, and then reproduces the received data while proceeding to the demodulation and decoding process for the next encoded data in the chronological order.

In addition, in the error correction decoding unit 52, when the coding rate is different between via the broadcast transmission path and via the IP network 8, the punctured portion of the coded IP packet is regarded as a packet lost in the IP network 8, and the received data is decoded. As a specific example, in the case where the coding rate F _b =2/1 of the coded data received via the broadcast transmission path and the coding rate F _i =0.66 of the coded data received via the IP network 8, since 10472 bits are punctured on the transmitting side, the error correction decoding unit 52 regards the packet at the punctured position as having been lost in the transmission path, sets the logarithmic likelihood ratio to 0, performs LDPC decoding with a 1/2 parity check matrix, and then performs power despreading and BCH decoding to regenerate the received data.

The retransmission request packet can be a non-delivery notification packet that is commonly used in IP packet format, and the encoded IP packet is configured to be retransmitted in response to that 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, and by repeatedly requesting retransmission until the received data can be restored within a specified time, it can be output in a reproducible manner.

(Modification of Erasure Correction Performance Table)
In the above example, the coding rate determination unit 64 in the transmission server 6 acquires packet loss rate information from the receiving device 5, but it may acquire communication quality information including delay information of communication line in addition to packet loss rate information. That is, the communication quality measurement unit 55 in the receiving device 5 can be configured to measure delay information of communication line in addition to packet loss rate information.

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

The communication line delay information is information that indicates the transmission delay estimated from 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 IP packet retransmitted from the transmission server 6 in response to the retransmission.

Therefore, a coding rate conversion standard is determined by performing a computer simulation by adding communication line delay information to the packet loss rate information, and then creating an erasure correction performance table similar to the example shown in FIG. 5 and storing it in the erasure correction performance table storage unit 65, so that the coding rate determination unit 64 can refer to the erasure correction performance table.

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 side to the transmitting side via the IP network, and the transmitting side is enabled to retransmit the data, so that the receiving side can supplement the data. Also, according to the transmission system 1 of the present embodiment, the number of retransmission requests can be reduced by configuring the system to simultaneously perform error correction coding and retransmission requests. Also, by changing the error correction coding rate according to the communication quality of the IP network, it is possible to improve the transmission efficiency. Also, according to the transmission system 1 of the present embodiment, when changing the coding rate, the transmitting side punctures the data so as not to degrade the performance of the error correction code as much as possible, and the receiving side decodes the punctured IP packets by assuming that the packets have been lost in the IP network, so that it is possible to easily decode the data using a check matrix with the same coding rate as the satellite broadcast channel without preparing a new LDPC coding table.

In particular, according to the transmission system 1 of this embodiment, it is possible to determine the coding rate of the retransmission data using one of a number of coding rates that are suited to the characteristics of the IP network, without being limited to the coding rate used in the broadcast transmission path, depending on the communication quality of the IP network. Furthermore, according to the transmission system 1 of this embodiment, when the packet loss rate of the IP network is small, the coding rate can be easily increased by puncturing, and it is possible to improve transmission efficiency without transmitting redundant parity to the IP network.

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.

LIST OF SYMBOLS 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 Broadcast 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 Communication quality measurement unit 61 Storage unit 62 IP packet generation unit 63 Retransmission request processing unit 64 Coding rate determination unit 65 Erasure correction performance table storage unit 66 Coding rate conversion unit 67 Interleaving processing unit

Claims (10)

A transmission server that stores a predetermined amount of coded data for a predetermined period of time from a transmission device that digitally modulates coded data using an error correction code related to digital broadcasting and transmits the digitally modulated coded data to a reception device via a broadcast transmission path, and enables the data to be transmitted to the reception 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 a retransmission request packet generated when it is determined in the receiving device that a bit error in the encoded data cannot be corrected using the error correction code via an IP network, extracts packet loss rate information measured by the receiving device and retransmission request information indicating encoded data of an error correction code frame related to the retransmission request, which are stored in the retransmission request packet, and controls reading of the corresponding encoded data from the storage unit based on the retransmission request information;
an IP packet generator for converting the encoded data read from the storage unit into an IP packet;
A coding rate determination unit, which refers to a predetermined erasure correction performance table as a coding rate conversion standard based on the packet erasure rate information, and determines the highest coding rate that can be erased and corrected within the range that is equal to or higher than the coding rate of the coded data transmitted through the broadcast transmission line;
a coding rate conversion unit which converts the coding rate of the IP packetized coded data by a puncturing process that thins out only the parity of the coded data when the coding rate is to be converted so that the coding rate becomes the coding rate determined by the coding rate determination unit, and which forms a coded IP packet whose coding rate has been adaptively converted by a puncturing process so as to be output to an external device, while leaving the coding rate of the coded data unchanged when the coding rate is not to be converted;
Equipped with
A transmission server characterized in that the coding rate of the coded data to be retransmitted as the coded IP packet can be improved by the puncturing process, and the coded data can be decoded by the receiving device in the same error correction code format as the coded data transmitted via the broadcast transmission path. The transmission server according to claim 1, characterized in that the coding rate determination unit determines to use one of a plurality of coding rates predetermined in the erasure correction performance table for retransmission via an IP network, regardless of the coding rate used for transmission of coded data via a broadcast transmission path. The transmission server according to claim 1 or 2, characterized in that the coding rate conversion unit converts the coding rate by deleting the parity area at the position of the value obtained by dividing the number of packets before puncturing in the parity area by the number of packets to be deleted by puncturing, by using an equal interval thinning method based on the ratio between the number of bits before puncturing and the number of bits to be deleted by puncturing, and rounding down the decimal points of an integer multiple of the value of the average puncturing interval obtained by dividing the number of packets before puncturing in the parity area by the number of packets to be deleted by puncturing, to obtain an integer. The erasure correction performance table shows required packet erasure rates indicating the highest erasure correctable coding rates of 44.4%, 38.1%, 34.0%, 28.5%, 22.3%, 18.6%, 15.2%, 11.3%, and 2.16% for at least coding rates of 1/2, 0.56, 0.61, 0.66, 0.73, 0.76, 0.8, 0.85, and 0.95,
The transmission server according to any one of claims 1 to 3, characterized in that the coding rate conversion unit has a function of converting a coding rate of 1/2 of coded data of an ISDB-S3 compliant LDPC code transmitted via a broadcast transmission path into any one of coding rates of 0.56, 0.61, 0.66, 0.73, 0.76, 0.8, 0.85, and 0.95 by the puncturing process. the IP packet generation unit is configured to generate a predetermined number of IP packets by forming an interleaved frame using the plurality of error correction code frames, and adding at least a sequence number specifying which bit in each error correction code frame is represented and an IP header which is a header of an encoded data packet to a payload obtained by traversing each error correction code frame,
The transmission server according to any one of claims 1 to 4, further comprising an interleaving processing unit that performs interleaving processing on a predetermined number of coded IP packets formed by the coding rate conversion unit in accordance with a predetermined interleaving criterion. A transmitting device for digital broadcasting,
A transmission device comprising the transmission server according to any one of claims 1 to 5 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 generating unit that generates a retransmission request packet in an IP packet format, the retransmission request packet including retransmission request information indicating coded data of an error correcting code frame related to a retransmission request for requesting retransmission of the corresponding coded data when it is determined that bit errors in the coded data cannot be corrected using the error correcting code, and packet loss rate information indicating a packet loss rate of an IP network, and transmits the retransmission request packet to a transmission server according to any one of claims 1 to 5;
an IP packet receiving unit that receives an encoded IP 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 measurement unit that measures at least a packet loss rate of an IP network based on the retransmission request packet received by the IP packet receiving unit,
The receiving device is characterized in that the error correction decoding unit uses the encoded data retransmitted in response to the retransmission request in the decoding process, and repeatedly requests retransmission of the corresponding encoded data until the encoded data can be decoded by the decoding process within a specified time. The receiving device according to claim 7, characterized in that the communication quality measurement unit has a function of measuring the packet loss rate of the IP network by counting the number of packets lost from the sequence numbers of the IP packets. The error correction code is a concatenated code in which an LDPC code is concatenated as an inner code and a BCH code is concatenated as an outer code,
The receiving device according to claim 7 or 8, characterized in that the error correction decoding unit determines that bit errors in the encoded data obtained from the transmitting device could not be corrected when the decoding process of the BCH code could not completely correct bit errors, or when errors could be corrected in the decoding but a predetermined number of BCH errors have been detected. A program for causing a computer to function as a transmission server according to any one of claims 1 to 5.