JP7564665B2 - Receiving device - 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 digital data transmission device and a reception device.

In digital transmission systems, multi-level modulation methods are often used so that more information can be transmitted within the frequency bandwidth available for each service. Increasing the number of bits allocated per symbol of the modulated signal (modulation order) is an effective way to increase frequency efficiency, but the relationship between the upper limit of the information speed that can be transmitted per 1 Hz frequency and the signal-to-noise ratio is restricted by the Shannon limit. One example of information transmission using a satellite transmission path is satellite digital broadcasting.

In currently used digital satellite broadcasting, information correction is performed in the receiving device using error correction codes. By adding a redundant signal called a parity bit to the information to be transmitted, it is possible to control the signal redundancy (coding rate) and increase resistance to noise. Error correction codes and modulation methods are closely related, and the theoretical upper limit of frequency utilization efficiency relative to the signal-to-noise ratio is called the Shannon limit. Gallagher proposed the LDPC (Low Density Parity Check) code in 1962 as one of the powerful error correction codes with performance approaching the Shannon limit (see, for example, Non-Patent Document 1).

An LDPC code is a linear code defined by a very sparse check matrix H (the elements of the check matrix consist of 0s and 1s, and the number of 1s is very small).

LDPC codes are powerful error-correcting codes that can achieve transmission characteristics approaching the Shannon limit by increasing the code length and using an appropriate check matrix, and LDPC codes are also adopted in ARIB STD-B44 (hereinafter referred to as the advanced satellite broadcasting system; see Non-Patent Document 2, for example), which specifies the transmission system for 4K/8K Super Hi-Vision satellite broadcasting, the next-generation broadcasting service. By combining multi-level modulation with powerful error-correcting codes such as LDPC codes, it is becoming possible to achieve transmission with higher frequency utilization efficiency.

Taking the advanced satellite broadcasting system as an example, the LDPC code in this system is composed of forward error correction (FEC) frames and has a code length of 44,880 bits, and has been shown to have a performance within approximately 1 dB of the BPSK limit (theoretical upper limit of frequency utilization efficiency relative to the signal-to-noise ratio when the signal point arrangement is BPSK) (see, for example, Non-Patent Document 3).

In addition, for the advanced satellite broadcasting system, 11 types of LDPC coding rates are defined: 41/120 (≒1/3), 49/120 (≒2/5), 61/120 (≒1/2), 73/120 (≒3/5), 81/120 (≒2/3), 89/120 (≒3/4), 93/120 (≒7/9), 97/120 (≒4/5), 101/120 (≒5/6), 105/120 (≒7/8), and 109/120 (≒9/10).

As a countermeasure against rain attenuation in 21 GHz band satellite broadcasting, there have been reports on the study of a diverse reception system based on route diversity that utilizes communication complementation via a public IP (Internet Protocol) network (see, for example, Non-Patent Document 4).

R. G Gallager, “Low Density Parity Check Codes,” in Research Monograph series Cambridge, MIT Press, 1963 "Advanced Wideband Satellite Digital Broadcasting Transmission Method Standard ARIB STD-B44 Version 2.1", [online], formulated on March 25, 2016, ARIB, [searched on July 13, 2020], Internet <URL: https://www.arib.or.jp/kikaku/kikaku_hoso/std-b44.html> Suzuki et al., "Design of LDPC Codes for Advanced BS Digital Broadcasting," Journal of the Institute of Image Information and Television Engineers, Institute of Image Information and Television Engineers, vol. 62, No. 12, December 1, 2008, pp. 1997-2004 Suzuki et al., "Rain attenuation compensation by communication complementation for 21 GHz band satellite broadcasting - Basic study of a diverse reception system using LDPC codes for British paper picture broadcasting", Technical Report of the Institute of Electronics, Information and Communication Engineers, IEICE Technical report SAT2019-71(2020-02), pp.25-28

In recent years, in addition to the current 2K services via satellite and terrestrial broadcasting, and 4K/8K Super Hi-Vision via satellite broadcasting, there are high expectations for the new provision of 4K/8K Super Hi-Vision via terrestrial broadcasting. However, when we look at the 12 GHz band used for satellite broadcasting, available frequencies are tight, and it is difficult to secure sufficient frequency bandwidth for the transmission of next-generation content that goes beyond 4K/8K services.

Another band that can be used for satellite broadcasting is the 21 GHz band. The 21 GHz band has a bandwidth of 600 MHz allocated for satellite broadcasting, making it a promising transmission band for achieving large-capacity transmission.

However, the 21 GHz band is more affected by rain attenuation than the 12 GHz band, so in order to ensure a sufficient C/N margin, technical solutions to the transmission method are required, such as the application of powerful error correction codes such as the LDPC code mentioned above, or reducing the number of modulation levels.

In addition, with the recent convergence of broadcasting and communications, the diversification of transmission formats that go beyond the boundaries of radio waves is progressing, with the standardization of IP-based transmission methods in particular progressing. The integration of next-generation communications networks such as 5G with satellite transmission paths is also being considered, and it is expected that the standardization of IP-based transmission methods will accelerate even further in the future.

As disclosed in the above-mentioned non-patent document 4, a diverse reception system based on route diversity that utilizes communication supplementation via a public IP network has been reported as a countermeasure against rain attenuation in 21 GHz band satellite broadcasting. In this diverse reception system, when satellite broadcasting cannot be received due to rain attenuation, it is possible to avoid the interruption of broadcast signals in rainy areas by retransmitting the received signal via satellite that was normally received from a clear area not affected by rain via communication via a public IP network.

To achieve this kind of communication complementation by combining satellite broadcasting and public IP networks, it is desirable to apply a common error correction code or transmission frame to both transmission paths, and a stable transmission technology for synchronization signals that can achieve early frame synchronization is required. Furthermore, stable transmission of synchronization signals requires a transmission technology with sufficient noise resistance that takes into account the effects of rain attenuation, particularly in 21 GHz band satellite broadcasting.

In view of the above problems, the object of the present invention is to provide a transmitting device and a receiving device that have excellent noise resistance and stabilize the frame synchronization of the transmission signal between the transmitting device and the receiving device in a transmission system that transmits signals using broadcasting and a public IP network.

First, the transmitting device and receiving device in the transmission system according to the present invention use a transmission frame that is consistent with an LDPC code with a code length of 44,880 bits as the basic transmission unit. That is, the transmitting device and receiving device of the present invention use an LDPC code with a strong error correction capability, particularly an LDPC code with a code length of 44,880 bits that has a proven performance record in advanced satellite broadcasting systems, as the basic transmission unit, and further apply a BCH code as the outer code to mitigate the effects of rain attenuation that occurs in the 21 GHz band. Then, when the transmitting device of the present invention orthogonally modulates the transmission frame using a specified modulation method and transmits it, the size of the transmission frame has an integer multiple relationship with the packet size of MPEG-2TS excluding the TS synchronization byte. This enables efficient transmission without excess or deficiency for MPEG-2TS excluding the TS synchronization byte.

In particular, the transmitting device of the present invention intermittently and periodically multiplexes a time signal symbol frame by π/2 shift BPSK modulation, which can realize stable synchronization with excellent noise resistance, to a transmission frame including a main signal, a BCH code parity, and an LDPC code parity. The transmitting device of the present invention constantly acquires time information (bit string) generated inside the transmitting device, or time information (bit string) conforming to an NTP (Network Time Protocol) packet in an IP network corresponding to the generation time of the transmission frame related to the transmission of the main signal. Here, the time signal symbol frame includes a predetermined number of identical time signals (symbols) that have been converted by π/2 shift BPSK modulation after energy diffusion processing for each time information (bit string) defined by a predetermined bit string used in a common format for signal transmission of broadcasting and public IP networks. The time information conforming to the NTP packet is only the timestamp (mode 1) out of the timestamp (64 bits) and delta (32 bits), or both the timestamp and delta (mode 2). The transmitting device of the present invention performs energy diffusion on time information (bit string) to generate a time signal (symbol) that has been subjected to π/2 shift BPSK modulation processing, and repeatedly multiplexes the same time signal multiple times within a time signal symbol frame. In addition, the transmitting device of the present invention multiplexes and transmits the time signal symbol frame once for each transmission frame of the main signal.

On the other hand, the receiving device of the present invention receives a received signal via broadcast corresponding to a transmission signal sent from the transmitting device of the present invention, performs orthogonal demodulation based on a predetermined modulation method, performs LDPC decoding and BCH decoding on the orthogonally demodulated signal using the same error correction code as the transmitting device, restores the received data (video, audio, etc.) and outputs it to the outside. The receiving device of the present invention also has a function of acquiring received data (video, audio, etc.) by receiving an IP packet sequence that stores the data of the main signal in the transmission signal via broadcast from the transmitting device of the present invention as a synchronously transmitted transmission signal via an IP network. The receiving device of the present invention also has a function of acquiring received data (video, audio, etc.) by transmitting a transmission signal retransmission request in IP packet format requesting retransmission of a desired transmission signal via an IP network to the transmitting device of the present invention, and receiving a transmission signal corresponding to the retransmission request in IP packet format from the transmitting device of the present invention. The receiving device of the present invention also has the function of transmitting a received signal retransmission request in IP packet format to another receiving device with a set IP address, requesting retransmission of a received signal corresponding to a desired transmitted signal via an IP network, and acquiring received data (video, audio, etc.) by receiving the received signal corresponding to the retransmission request in IP packet format from the other receiving device.

In this way, when the receiving device of the present invention receives a broadcast reception signal, for example, via multiple receiving antennas, it is possible to obtain a diversity effect that provides resistance to rain attenuation. Furthermore, by acquiring a transmission signal transmitted synchronously via an IP network, the receiving device of the present invention can obtain a diversity effect that provides resistance to rain attenuation by combining it with a broadcast reception signal to complement data through communication, even if there is packet loss. Furthermore, by acquiring a signal retransmitted from another receiving device, it is possible to obtain a diversity effect that provides resistance to rain attenuation by combining it with a broadcast reception signal to complement data through communication, even if there is packet loss.

In particular, the receiving device of the present invention demodulates the signal of a time signal symbol frame configured as a phase reference burst signal transmitted once per transmission frame of a main signal from a broadcast received signal prior to LDPC decoding and BCH decoding, establishes phase synchronization, extracts a predetermined number of time signals (symbols) that are the same signal section within the time signal symbol frame, averages them, and performs symbol judgment to generate a time signal (bit string) from which noise components have been removed. More specifically, each of the multiple time signals (symbols) demodulated for the time signal symbol frame corresponds to time information of a timestamp (mode 1), or both timestamp and delta (mode 2). Furthermore, the receiving device of the present invention performs symbol judgment by averaging once, or preferably multiple times, for the signal section (same signal section) of the time signal (symbol) indicating the same time, and performs energy despreading on the bit string from which noise components have been removed obtained by the symbol judgment to obtain time information of a timestamp (mode 1), or both timestamp and delta (mode 2). This time information is embedded in the transmission signal retransmission request and the received signal retransmission request transmitted in IP packet format via an IP network. The time information according to the present invention is defined by the transmitting device according to the present invention and is commonly used throughout the transmission system according to the present invention. The time information according to the present invention is also added as auxiliary information to the IP packet sequence that constitutes the transmission signal synchronously transmitted from the transmitting device according to the present invention via an IP network, the retransmitted transmission signal, and the transmission signal retransmitted from another receiving device. This can be realized, and a transmission system with excellent noise resistance to rain attenuation in 21 GHz band satellite broadcasting used as an advanced satellite broadcasting system can be configured.

Furthermore, a receiving device of the present invention is a receiving device that receives a transmission signal transmitted from a transmitting device using broadcasting and a public IP network, and the transmitting device, in order to transmit a signal to the receiving device using broadcasting and a public IP network, applies a BCH code as an outer code, and uses a transmission frame that is matched with an LDPC code of a predetermined code length as an inner code as a basic transmission unit, generates a transmission signal that has been orthogonally modulated by a predetermined modulation method in units of the transmission frame, and transmits the transmission signal via broadcasting, and applies energy dispersion processing to each piece of time information defined by a predetermined bit string used in a common format for signal transmission in broadcasting and the public IP network, converts it into a time signal by π/2 shift BPSK modulation, and transmits the same The present invention is configured to include a time signal symbol frame generating means for generating a time signal symbol frame including a predetermined number of the time signals, and intermittently and periodically multiplexing the time signal symbol frame as a phase reference burst signal into the transmission frame, and a transmitting device side IP signal transmitting/receiving means for connecting to a public IP network so as to be able to communicate with a receiving device with an IP address set, and to synchronously transmit data of a main signal in the transmission signal via broadcast specified based on the time information to the receiving device in IP packet format, or to retransmit data in response to a request from the receiving device, the transmitting signal via broadcast being received as a received signal, and performing quadrature demodulation based on the predetermined modulation method, and a demodulation and decoding means for performing LDPC decoding and BCH decoding on a signal using the same error correction code as that of the transmitting device to restore received data; a time signal symbol averaging and symbol determination means for demodulating a signal of a time signal symbol frame constituted as the phase reference burst signal multiplexed and transmitted from the received signal received by broadcast to a transmission frame of a main signal prior to the LDPC decoding and BCH decoding, establishing phase synchronization, extracting a predetermined number of the time signals which are in the same signal section within the time signal symbol frame, averaging them, performing symbol determination, and generating a bit string of the time signal from which noise components have been removed; and a receiving device-side IP signal transmitting/receiving means for communicating with a public IP network so as to enable reception of the main signal data synchronously transmitted from the transmitting device in IP packet format based on the time information in order to restore the main signal data in the received signal with high accuracy, enable a retransmission request to the transmitting device or another receiving device in IP packet format for the main signal data in the received signal specified based on the time information, and enable retransmission of the main signal data in the received signal in response to a retransmission request from another receiving device having the same function as the receiving device.

In the receiving device of the present invention, the time signal symbol frame has either one or both of a first mode in which the time information is a bit string of a timestamp, out of the timestamp and delta conforming to the NTP packet in a public IP network, and a second mode in which the time information is a bit string of both the timestamp and delta, and is configured to include a predetermined number of identical time signals in a frame size corresponding to each mode according to the mode determined between the transmitter and receiver, and the time signal symbol averaging/symbol determination means generates a bit string of a time signal that has been averaged and symbol-determined for a predetermined number of time signals that are the same signal section within the time signal symbol frame corresponding to the time information corresponding to each mode.

The receiving device of the present invention is also characterized in that it further comprises a means for receiving the broadcast-received received signal via multiple receiving antennas and performing diversity synthesis, or a means for performing data complementation for the broadcast-received received signal using data of the main signal in the received signal obtained via a public IP network.

According to the present invention, when realizing a diverse reception system, which is a countermeasure against rain attenuation for 21 GHz band satellite broadcasting, for example, it is possible to realize stable frame synchronization between satellite broadcasting and communications, and in particular, it is possible to configure a transmitting device and a receiving device that have excellent noise resistance to rain attenuation for 21 GHz band satellite broadcasting.

1 is a block diagram showing a schematic configuration of a transmission system according to an embodiment of the present invention; 1 is a block diagram showing a schematic configuration of a transmitting device according to an embodiment of the present invention; 1 is a diagram showing a configuration of a transmission frame and an LDPC code check matrix in a transmitting device according to an embodiment of the present invention; 1 is a diagram showing transmission frame configuration bits for each LDPC coding rate in a transmitting device according to an embodiment of the present invention. FIG. FIG. 2 is a diagram showing an example of a BCH code generating polynomial in a transmitting device according to an embodiment of the present invention. 1 is a block diagram showing a schematic configuration of a main signal energy dispersal circuit in a transmitting device according to an embodiment of the present invention; FIG. 2 is a diagram showing a schematic configuration of a bit interleaver for 8PSK in a transmitting device according to an embodiment of the present invention. A diagram showing the data structure of timestamp and delta in a transmitting device of one embodiment according to the present invention. 1 is a block diagram showing a schematic configuration of a time signal generating section and a time signal symbol frame generating section which receive time signal data as input in a transmitting device according to an embodiment of the present invention; A figure showing the frame structure of a time signal symbol frame (mode 1) in a transmitting device of one embodiment according to the present invention. A figure showing the frame structure of a time signal symbol frame (mode 2) in a transmitting device of one embodiment according to the present invention. 2 is a diagram showing a modulation symbol frame structure in a transmitting device according to an embodiment of the present invention; FIG. 2 is a diagram showing bit mapping of π/2 shift BPSK modulation in a transmitting device according to an embodiment of the present invention. FIG. 2 is a diagram showing bit mapping of QPSK modulation in a transmitting device according to an embodiment of the present invention. FIG. 2 is a diagram showing bit mapping of 8PSK modulation in a transmitting device according to one embodiment of the present invention. 1 is a block diagram showing a schematic configuration of a receiving device according to an embodiment of the present invention; 1 is a diagram showing a schematic configuration of a bit deinterleaver in a receiving device according to an embodiment of the present invention; 1 is a block diagram showing a circuit configuration of an energy despreading unit that receives an averaged bit string of a time signal symbol as input in a receiving device according to an embodiment of the present invention; A figure showing the C/N vs. BER characteristics when symbol determination is performed after averaging processing of time signal symbols based on a time signal symbol frame (mode 1, mode 2) in a receiving device of an embodiment of a transmission system according to the present invention, and when symbol determination is performed without averaging processing of the time signal symbols.

(Transmission System)
An example of the configuration of a transmission system 1 including a transmitting device 11 and a receiving device 16 according to an embodiment of the present invention will now be described.

FIG. 1 is a block diagram showing a schematic configuration of a transmission system 1 according to an embodiment of the present invention.
The transmission system 1 of this embodiment shown in Figure 1 comprises a signal source device 10, a transmitting device 11, an NTP server 12, a transmitting antenna 13 for a broadcasting satellite 14, n receiving antennas 15-n (n is an integer greater than or equal to 1) for the broadcasting satellite 14, m receiving antennas 15-m (m is an integer greater than or equal to 1) for the broadcasting satellite 14, a receiving device 16, and a retransmission receiving device 17.

The signal source device 10 is a device that supplies the original data (video, audio, etc.) to the transmitting device 11 for transmission to the receiving device 16.

The transmitting device 11 has the function of performing coding and modulation processing according to the broadcast transmission path (i.e., the broadcast transmission path of the advanced satellite broadcasting system) on the original data (video, audio, etc.) input from the signal source device 10, applying a BCH code as an outer code, generating a broadcast transmission signal with an LDPC code of a code length of 44,880 bits as the basic transmission unit, and transmitting the signal from the transmitting antenna 13 to the broadcast satellite 14, the function of synchronously transmitting an IP packet sequence that stores the data of the main signal in the broadcast transmission signal as a transmission signal via a public IP network (IP network 18) to a receiving device 16 with a preset IP address, and the function of, in response to a transmission signal retransmission request in IP packet format from the receiving device 16, retransmitting the transmission signal corresponding to the retransmission request in IP packet format to the receiving device 16 as a transmission signal via the IP network 18.

In particular, the transmitting device 11, which will be described in detail later, has a function of intermittently and periodically multiplexing a time signal symbol frame modulated by π/2 shift BPSK modulation to a transmission frame including a main signal, BCH code parity, and LDPC code parity constituting the transmission signal via the broadcast. The transmitting device 11 constantly acquires data of time information (bit string) generated within the transmitting device 11, or data of time information (bit string) conforming to an NTP packet transmitted from the NTP server 12 corresponding to the generation time of the transmission frame related to the transmission of the main signal via the IP network 18. Here, the time signal symbol frame includes a predetermined number of identical time signals (symbols) that have been converted by π/2 shift BPSK modulation after energy diffusion processing for each time information (bit string) defined by a predetermined bit string used in a common format for signal transmission of broadcast and public IP network. The time information conforming to the NTP packet is only the timestamp (mode 1) of the timestamp (64 bits) and delta (32 bits) or both the timestamp and delta (mode 2). The transmitting device 11 performs energy diffusion on the time information (bit sequence) to generate a time signal (symbol) that has been subjected to π/2 shift BPSK modulation processing, and repeatedly multiplexes the same time signal multiple times within the time signal symbol frame. The transmitting device 11 also multiplexes and transmits the time signal symbol frame once for each transmission frame of the main signal.

The NTP server 12 is a device that transmits NTP packets containing a timestamp (64 bits) and a delta (32 bits) to the transmitting device 11 via the IP network 18.

The transmitting antenna 13 is a transmitting antenna for transmitting the broadcasting transmission signal generated by the transmitting device 11 to the broadcasting satellite 14.

Broadcast satellite 14 is configured as a broadcast satellite of the existing advanced satellite broadcasting system that receives and amplifies the broadcast transmission signal generated by transmitter 11 and radiates it to the ground.

The n receiving antennas 15-n for the broadcasting satellite 14 are transmitting antennas that receive signals emitted from the broadcasting satellite 14 and transmit them as received signals to the receiving device 16.

The m receiving antennas 15-m for the broadcasting satellite 14 are transmitting antennas that receive signals emitted from the broadcasting satellite 14 and transmit them as received signals to the receiving device 16.

The receiving device 16 has the functions of inputting a received signal via broadcast corresponding to a transmission signal sent from the transmitting device 11 via the receiving antenna 15-n, performing orthogonal demodulation based on a predetermined modulation method, performing LDPC decoding and BCH decoding processes on the orthogonally demodulated signal using the same error correction code as the transmitting device 11, restoring the received data (video, audio, etc.) and outputting it externally, receiving an IP packet sequence that stores the data of the main signal in the transmission signal via broadcast from the transmitting device 11 as a transmission signal that is transmitted synchronously via the IP network 18 to obtain the received data (video, audio, etc.), and transmitting the desired transmission signal via the IP network 18. It has a function of transmitting a transmission signal retransmission request in IP packet format to the transmitting device 11, requesting retransmission of the desired transmission signal, and acquiring received data (video, audio, etc.) by receiving the transmission signal corresponding to the retransmission request in IP packet format from the transmitting device 11, and a function of transmitting a received signal retransmission request in IP packet format to another receiving device (i.e., retransmission receiving device 17) with a set IP address, via the IP network 18, requesting retransmission of the received signal corresponding to the desired transmission signal, and acquiring received data (video, audio, etc.) by receiving the received signal corresponding to the retransmission request in IP packet format from the retransmission receiving device 17.

In this way, when the receiving device 16 receives a broadcast reception signal, for example, via multiple receiving antennas 15-n, it can obtain a diversity effect that provides resistance to rain attenuation. Furthermore, by acquiring a transmission signal transmitted synchronously via the IP network 18, the receiving device 16 can obtain a diversity effect that provides resistance to rain attenuation by combining the broadcast reception signal with data complementation through communication, even if there is packet loss. Furthermore, by acquiring a signal retransmitted from another receiving device (i.e., retransmission receiving device 17), it can obtain a diversity effect that provides resistance to rain attenuation by combining the broadcast reception signal with data complementation through communication, even if there is packet loss.

In particular, the receiving device 16 of the present invention demodulates the signal of a time signal symbol frame constituted as a phase reference burst signal transmitted once per transmission frame of a main signal from a broadcast received signal prior to LDPC decoding and BCH decoding, establishes phase synchronization, extracts a predetermined number of time signals (symbols) that are the same signal section within the time signal symbol frame, averages them, performs symbol determination, and generates a time signal (bit string) from which noise components have been removed. More specifically, each of the multiple time signals (symbols) demodulated for the time signal symbol frame corresponds to time information of a timestamp (mode 1) or both timestamp and delta (mode 2). Furthermore, the receiving device 16 of the present invention averages the signal section (same signal section) of the time signal (symbol) indicating the same time once, preferably multiple times, to perform symbol determination, and performs energy despreading of the time signal (bit string) from which noise components have been removed to obtain time information of a timestamp (mode 1) or both timestamp and delta (mode 2). This time information is embedded in the transmitted signal retransmission request and the received signal retransmission request transmitted in IP packet format via the IP network 18. The time information according to the present invention is defined by the transmitting device 11 according to the present invention, and is used commonly throughout the transmission system 1 according to the present invention. The time information according to the present invention is also added as auxiliary information to the IP packet sequence that constitutes the transmitted signal synchronously transmitted from the transmitting device 11 via the IP network 18, the retransmitted transmitted signal, and the transmitted signal retransmitted from the retransmission receiving device 17.

This makes it possible to realize communication complementation that combines satellite broadcasting and public IP networks, as well as stable frame synchronization, and to configure a transmission system 1 that has excellent noise resistance to rain attenuation in 21 GHz-band satellite broadcasting, which is used as an advanced satellite broadcasting system.

The retransmission receiving device 17 has the functions of receiving a broadcast-based received signal corresponding to the transmission signal sent from the transmitting device 11 via the receiving antenna 15-m, performing orthogonal demodulation based on a predetermined modulation method, performing LDPC decoding and BCH decoding processes on the orthogonally demodulated signal using the same error correction code as the transmitting device 11, restoring the received data (video, audio, etc.) and storing it for a certain period of time, and, when a request to retransmit the received signal is received from the receiving device 16 via the IP network 18, retransmitting the received signal corresponding to the retransmission request to the receiving device 16 in IP packet format.

The retransmission receiving device 17 is not limited to one, and may be multiple devices. For convenience of explanation, in FIG. 1, the retransmission receiving device 17 is described as being distinct from the receiving device 16. However, the retransmission receiving device 17 may be configured to have all the functions of the receiving device 16, and similarly, the receiving device 16 may be configured to have all the functions of the retransmission receiving device 17, and the retransmission receiving device 17 and the receiving device 16 may be configured in the same manner without distinction.

Therefore, the transmission system 1 of this embodiment shown in FIG. 1 has a signal system (satellite loopback) in which the transmitting device 11 sends a transmission signal via broadcast to the broadcast satellite 14 via the transmitting antenna 13, and the receiving device 16 acquires a reception signal received via the receiving antenna 15-n. In addition, the transmission system 1 of this embodiment receives the IP signal of the NTP packet from the NTP server 12 via the IP network 18 by the transmitting device 11 to acquire time information, associates the time information with the transmission signal via broadcast, and transmits it multiplexed to the transmission signal via broadcast. Furthermore, by using the time information, the transmitting device 11 can synchronously transmit a transmission signal in the form of an IP packet to the receiving device 16 via the IP network 18 in response to the transmission signal via broadcast, or can retransmit in response to a retransmission request from the receiving device 16. In addition, the receiving device 16 can transmit a retransmission request to another receiving device (retransmission receiving device 17) with an IP address set, and the other receiving device (retransmission receiving device 17) can retransmit and acquire the reception signal received via broadcast.

In this way, the transmission system 1 of this embodiment shown in FIG. 1 is realized as a diverse receiving system that is a countermeasure against rain attenuation in 21 GHz band satellite broadcasting, and has a system that transmits the same transmission signal as the satellite broadcasting or the same reception signal as the transmission signal between multiple receiving devices even via the IP network 18. In addition, if the NTP server 12 is not used, it is also possible to generate information equivalent to an NTP packet based on time information generated inside the transmitting device 11. In addition, in the transmission system 1 of this embodiment, the receiving device 16 can receive the reception signal broadcast and received in a broadcast manner via the broadcasting satellite 14 by multiple receiving antennas 15-n. As an example of this, when the receiving device 16 connected to the receiving antenna 15-1 cannot directly receive broadcasts from the broadcasting satellite 14 due to rain attenuation, etc., a reception signal retransmission request is transmitted to a retransmission receiving device 17 connected to another point that is not affected by rain attenuation, for example, the receiving antenna 15-m, and the reception signal received by the retransmission receiving device 17 is retransmitted in IP packet format and acquired. In this way, the transmission system 1 of this embodiment can synchronously receive a common signal via satellite broadcasting and IP, and by using common time information throughout the system, it is possible to establish synchronization early. Below, we will explain in more detail the configuration and operation of the transmitting device 11 and receiving device 16 of this embodiment in order.

(Transmitting device)
2 is a block diagram showing a schematic configuration of a transmitting device 11 according to an embodiment of the present invention. The transmitting device 11 includes a transmission path coding unit 111, a time signal generating unit 112, a time information generating unit 113, a time signal symbol frame generating unit 114, a modulation symbol frame generating unit 115, an orthogonal modulation unit 116, an IP signal transmitting/receiving unit 117, a retransmission transmission signal DB (database) 118, and a retransmission processing unit 119.

First, the transmission path coding unit 111 sequentially stores the bit string of the original data (video, audio, etc.) input from the signal source device 10 as the main signal in a predetermined position of a transmission frame of 44,880 bits per frame, performs error correction coding processing, energy diffusion processing, and bit interleaving processing according to the coding modulation processing on a transmission frame basis, and outputs the result to the modulation symbol frame generation unit 115.

The error correction coding process in the transmission line coding unit 111 uses a concatenated code configuration with an LDPC code as the inner code and a BCH code as the outer code, and the code length of the LDPC code is 44,880 bits. Figure 3 is a diagram showing the configuration of a transmission frame and an LDPC code check matrix in a transmitting device 11 according to an embodiment of the present invention. Also, Figure 4 is a diagram showing the transmission frame configuration bits for each LDPC coding rate in a transmitting device 11 according to an embodiment of the present invention.

As shown in FIG. 3, one transmission frame is composed of a frame header (176 bits), a main signal, a BCH code parity (192 bits), a stuff bit (6 bits), and an LDPC code parity, and in all cases of LDPC coding rates available in the advanced satellite broadcasting system (see FIG. 4), one transmission frame is 44,880 bits. This transmission frame configuration makes it possible to easily maintain synchronization between the transmitting device 11 and the receiving device 16 while appropriately changing the strength of the error correction code. Also, as shown in FIG. 4, since all main signals are composed of an integer multiple of 187 bytes, it is possible to create a highly consistent frame for information such as 188-byte long MPEG-2TS minus the TS synchronization byte. Note that the configuration of the transmission frame and the LDPC code check matrix shown in FIG. 3 is the same as that of the advanced satellite broadcasting system, so further detailed explanation is omitted. However, it is also possible to combine the frame header (176 bits) and stuff bits (6 bits) into 182 bits within one transmission frame.

Figure 5 is a diagram showing an example of a BCH code generation polynomial in a transmitting device according to an embodiment of the present invention. In the example shown in Figure 5, it is possible to correct any 12 bits in one transmission frame. Furthermore, by applying 17th-order energy spreading processing to the bit string after BCH encoding (frame header, main signal, BCH parity, stuff bits), it is possible to flatten the modulation spectrum.

Figure 6 is a block diagram showing a schematic configuration of a main signal energy dispersal circuit that performs energy dispersal processing in the transmission line coding unit 111 in the transmission device 11 according to an embodiment of the present invention. As shown in Figure 6, the energy dispersal processing for the main signal in the transmission line coding unit 111 includes a shift register 1111 that periodically shifts out a 17th-order spreading code (PN code) having an initial value shown in the figure, one bit at a time, and exclusive OR circuits (XOR) 1112, 1113 for performing MOD2 addition between the bit string of the shift register 1111 and the data (bit string) of the main signal to be spread. By performing this 17th-order energy dispersal processing on the data (bit string) of the main signal to be spread, it is possible to obtain the data of the main signal after energy dispersal that is flattened as a modulation spectrum.

In addition, the advanced satellite broadcasting system also specifies modulation methods of 16APSK and 32APSK, which are orders higher than 8PSK, but in this embodiment, 8PSK is the maximum order modulation method, and the modulation method used for transmitting the main signal is either QPSK modulation or 8PSK modulation. Therefore, the bit interleave processing in the transmission line coding unit 111 is applied when the modulation method of the main signal is 8PSK. Figure 7 is a diagram showing a schematic configuration of the bit interleaver 1114 at the time of 8PSK in the transmitting device 11 of one embodiment of the present invention. The bit interleaver 1114 at the time of 8PSK shown in Figure 7 is an example of "forward reading" in which only the main signal (187 x 80 symbols) is written from top to bottom in the column direction in block units of 14960 rows and 3 columns, and read from left (MSB) to right (LSB) in the row direction. It is also possible to perform "backward reading" from right (LSB) to left (MSB), and which one to use is determined in advance based on the LDPC coding rate. In this way, by performing bit interleaving in the case of the 8PSK modulation method, the decoding performance of the LDPC code can be improved.

The time signal generating unit 112 shown in FIG. 2 acquires time information (bit string) data generated by itself by the time information generating unit 113 provided inside the transmitting device 11, or constantly acquires timestamp and delta conforming to the NTP packet used in the IP network 18 as time information (bit string) data, performs energy diffusion processing on the acquired time information (bit string), and then converts it into a time signal (symbol) by performing π/2 shift BPSK modulation, and outputs it to the time signal symbol frame generating unit 114.

Figure 8 shows the data structure of timestamp and delta in the transmitting device 11 of one embodiment of the present invention. Here, timestamp indicates the relative time in seconds based on 0:00 on January 1, 1900. The upper 32 bits indicate the integer part, and the lower 32 bits indicate the decimal point. If the MSB of the upper 32 bits is 0, the year 2036 is the reference. Delta indicates the expected transmission delay in seconds from the internal time of the transmitting device 11 to a general receiving terminal. It is a 32-bit signed fixed point, with the upper 16 bits indicating the integer part and the lower 16 bits indicating the decimal point. Timestamp and delta can be obtained by the IP signal transmitting/receiving unit 117 from the NTP packet generated by the NTP server 12 via the IP network 18.

The IP signal transmission/reception unit 117 is a functional unit that is communicatively connected to the IP network 18 and transmits and receives IP signals of IP packet strings. In this embodiment, the IP signal transmission/reception unit 117 has a function of acquiring an NTP packet, extracting time information, and outputting it to the time signal generation unit 112, and a function of communicating with a receiving device 16 (the retransmission receiving device 17 can have the same configuration as the receiving device 16) in which an IP address has been set.

The time information generating unit 113 is a functional unit that outputs self-generated time information to the time signal generating unit 112 in the same format as the timestamp and delta, and in this example is used when the NTP packets generated by the NTP server 12 cannot be obtained via the IP network 18.

In addition, in the transmitting device 11 of this embodiment, a transmitting signal can be synchronously transmitted to the receiving device 16 with an IP address set via the IP network 18, in addition to the transmitting signal via broadcast. The transmission path coding unit 111 transmits the data of the main signal in the transmitting signal via broadcast together with the multiplexing time information in the subsequent modulation symbol frame generating unit 115 to the IP signal transmitting/receiving unit 117, and the time signal generating unit 112 transmits the time information (bit string) corresponding to the generated time signal (symbol) to the IP signal transmitting/receiving unit 117. Then, when the IP signal transmitting/receiving unit 117 receives the data of the main signal and the time information (bit string), it generates an IP packet string that stores the data of the main signal and the time information (bit string) corresponding to the multiplexing time information, and transmits the IP transmitting signal synchronously to the receiving device 16 via the IP network 18 as a transmitting signal via IP.

In addition, in the transmitting device 11 of this embodiment, a transmission signal retransmission request from the receiving device 16 is accepted, and the corresponding transmission signal can be retransmitted to the receiving device 16 via the IP network 18. The transmission path coding unit 111 transmits the main signal data in the transmission signal via broadcast to the retransmission transmission signal DB 118 together with multiplexing time information in the downstream modulation symbol frame generating unit 115, and the time signal generating unit 112 transmits time information (bit string) corresponding to the generated time signal (symbol) to the retransmission transmission signal DB 118.

The retransmission transmission signal DB 118 links the main signal data in the broadcast transmission signal obtained from the transmission path coding unit 111 with the time information (bit string) corresponding to the multiplexed time information obtained from the time signal generation unit 112, and temporarily stores it for a specified period of time.

The retransmission processing unit 119 then monitors whether or not the IP signal transmission/reception unit 117 has received a transmission signal retransmission request, and when a transmission signal retransmission request has been received, reads out the main signal data in the transmission signal via broadcast that is temporarily stored in the retransmission transmission signal DB 118 based on the time information indicated in the transmission signal retransmission request. The retransmission processing unit 119 then outputs the read main signal data and the corresponding time information (bit string) to the IP signal transmission/reception unit 117. The IP signal transmission/reception unit 117 generates an IP packet string that stores the main signal data and time information (bit string) obtained from the retransmission processing unit 119, and retransmits the IP packet string to the receiving device 16 that is the source of the transmission signal retransmission request via the IP network 18, with the source of the transmission signal retransmission request as the destination.

In this way, the transmitting device 11 of this embodiment has a system that can transmit, via the IP network 18, an IP signal that stores data with the same content as the data of the main signal in the transmission signal via broadcast. At this time, in the modulation symbol frame generating unit 115 described later, the transmission frame in the transmission path coding unit 111 and the time signal of the multiplexing time in the time signal generating unit 112 correspond uniquely through multiplexing to the phase reference burst signal, so similarly, for the IP signal transmitted via the IP network 18, it is desirable to transmit the time information of the transmission signal and the multiplexing time with a predetermined unique IP packet structure while maintaining a unique relationship. Note that the time information in the IP signal transmitted via the IP network 18 can be expressed by a time signal (bit string) of the same format between broadcasting and communication.

The IP signal transmitting/receiving unit 117, the retransmission transmission signal DB 118, and the retransmission processing unit 119 are configured as a transmitting device-side IP signal transmitting/receiving means that communicates with a receiving device 16 (the retransmission receiving device 17 can be configured the same as the receiving device 16) that has an IP address set, and is configured to transmit the main signal data in the transmission signal via the broadcast, identified based on the time information, synchronously to the receiving device 16 in IP packet format, or to retransmit it upon request from the receiving device 16.

Figure 9 is a block diagram showing the schematic configuration of a time signal generator 112 and a time signal symbol frame generator 114 that receive time signal data as input in a transmitting device 11 according to an embodiment of the present invention. Also, Figure 10 shows the frame structure of a time signal symbol frame (mode 1) in a transmitting device 11 according to an embodiment of the present invention, and Figure 11 shows the frame structure of a time signal symbol frame (mode 2).

As shown in FIG. 9, the time signal generation unit 112 includes an 11th-order time signal energy dispersal circuit 112a and a π/2 shift BPSK modulation unit 112b.

The 11th-order time signal energy dispersal circuit 112a includes a shift register 1121 that periodically shifts out an 11th-order spreading code (PN code) having an initial value as shown, one bit at a time, and exclusive OR circuits (XOR) 1122, 1123 for performing MOD2 addition between the bit string of the shift register 1121 and the time signal (bit string) to be spread. By performing 11th-order time signal energy dispersal processing on the bit string (time information) of the time signal to be spread, it is possible to obtain a time signal (bit string) after energy dispersal that is flattened as a modulation spectrum.

As described above, the time signal (bit string) has two modes, mode 1 and mode 2, and the time signal energy dispersal circuit 112a performs 11th order energy dispersal processing as shown in FIG. 9 on the signal section of a 64-bit (timestamp bit string) time signal in mode 1, and a 96-bit (timestamp and delta bit string) time signal in mode 2. The π/2 shift BPSK modulation unit 112b then performs π/2 shift BPSK modulation processing on the time signal (bit string) after the energy dispersal processing, generates a time signal (symbol) for each mode, and outputs it to the time signal symbol frame generation unit 114. Since the time signal (bit string) is π/2 shift BPSK modulated, the number of bits and the number of symbols are expressed equivalently.

Next, the time signal symbol frame generating unit 114 generates a time signal symbol frame by repeatedly multiplexing the same time signal multiple times, and outputs it to the modulation symbol frame generating unit 115. In the case of mode 1, the time signal symbol frame generating unit 114 copies the π/2 shift BPSK symbol section of 64 symbols corresponding to the energy-dispersed time signal (64 bits) 15 times to generate the time signal symbol frame (mode 1) shown in FIG. 10. In addition, in the case of mode 2, the time signal symbol frame generating unit 114 copies the π/2 shift BPSK symbol section of 96 symbols corresponding to the energy-dispersed time signal (96 bits) five times to generate the time signal symbol frame (mode 2) shown in FIG. 11. In this way, the time signal symbol frame generating unit 114 repeatedly multiplexes the same time signal multiple times within the time signal symbol frame for the time signal (symbol) that has been subjected to energy diffusion and π/2 shift BPSK modulation processing by the time signal generating unit 112. This allows the receiver 16 to average multiple time signals in the same symbol interval, improving reception C/N degradation caused by rain attenuation, etc.

Therefore, the time signal generating unit 112, the time information generating unit 113, and the time signal symbol frame generating unit 114 are configured as a time signal symbol frame generating means that performs energy diffusion processing for each piece of time information defined by a predetermined bit sequence used in a common format for signal transmission in broadcasting and the public IP network (IP network 18), converts it into a time signal modulated by π/2 shift BPSK modulation, generates a time signal symbol frame containing a predetermined number of identical time signals, and intermittently and periodically multiplexes the same time signals into the transmission frame as a phase reference burst signal.

Then, the modulation symbol frame generating unit 115 uses the transmission frame signal obtained from the transmission path coding unit 111 as the main signal, generates a modulation symbol frame by multiplexing this main signal with a unique word and a phase reference burst signal, and outputs it to the orthogonal modulation unit 116. Here, the phase reference burst signal is composed of one time signal symbol frame (mode 1 or mode 2) indicating the time (multiplexing time) when the modulation symbol frame obtained from the time signal symbol frame generating unit 114 was generated.

Figure 12 shows the modulation symbol frame structure in a transmitter 11 according to an embodiment of the present invention. Figures 13 to 15 show bit mapping for π/2 shift BPSK modulation, QPSK modulation, and 8PSK modulation, respectively.

The modulation symbol frame shown in FIG. 12 is composed of the first 26 symbols of π/2 shift BPSK of a unique word, followed by 187 symbols of main signal modulation symbols and X symbols of repeated π/2 shift BPSK for phase reference. The unique word is selected from (18D2E82 (hexadecimal notation)), bit-inverted (272D17D (hexadecimal notation)), all "0", or all "1", and the corresponding bit is modulated by π/2 shift BPSK (see FIG. 13). The modulation symbol of the main signal shown in FIG. 12 is a signal section in which the signal of the transmission frame obtained from the transmission line coding unit 11 is modulated by QPSK shown in FIG. 13 or 8PSK shown in FIG. 14. As shown in FIG. 12, since the LDPC code length (transmission frame length) is 44880 bits, the modulation symbol length of the main signal is 187×120 symbols in the case of QPSK and 187×80 symbols in the case of 8PSK. In addition, X symbols of the phase reference burst signal are inserted for every 187 symbols of the main signal. As shown in FIG. 12, the symbol length of the phase reference burst signal in the modulation symbol frame is 120 x X symbols for QPSK and 80 x X symbols for 8PSK. Furthermore, since the phase reference burst signal is composed of one time signal symbol frame, there are 960 symbols in mode 1, so X = 8 for QPSK and X = 12 for 8PSK. Furthermore, there are 480 symbols in mode 2, so X = 4 for QPSK and X = 6 for 8PSK (see FIG. 12).

Therefore, the transmission frame obtained from the transmission line coding unit 111 and the time signal symbol frame used as the phase reference burst signal can maintain a unique relationship by forming a modulation symbol frame by the modulation symbol frame generation unit 115. In addition, since the time signal symbol frame used as the phase reference burst signal of π/2 shift PBSK modulation equivalent to the time signal 15 times in mode 1 and 5 times in mode 2 is repeatedly transmitted within the modulation symbol frame, the receiving device 16 can average the time signals (symbols) indicating the same time within the modulation symbol frame and each time signal symbol frame, thereby improving the noise resistance of the time signal (symbol).

Then, the orthogonal modulation unit 116 inputs the modulation symbol frame from the modulation symbol frame generation unit 115, performs orthogonal modulation processing on the symbol sequence of each signal section in the modulation symbol frame using the modulation method shown in FIG. 12, generates a modulated signal that has been waveform-shaped using a roll-off filter, and outputs the signal to the transmission antenna 13 as a transmission signal via broadcasting.

The transmission path coding unit 111, the modulation symbol frame generation unit 115, and the orthogonal modulation unit 116 are configured as a coding and modulation means that uses a BCH code as an outer code, a transmission frame that is consistent with an LDPC code of a predetermined code length (44,880 bits) as an inner code as a basic transmission unit, generates a transmission signal that has been orthogonally modulated by a predetermined modulation method (in this example, QPSK or 8PSK) in units of that transmission frame, and transmits it via broadcasting.

(Receiving device)
16 is a block diagram showing a schematic configuration of a receiving device 16 according to an embodiment of the present invention. The receiving device 16 includes an orthogonal demodulator 161, a transmission path decoder 162, a time signal symbol averaging/symbol decision unit 163, an energy despreading unit 164, a time information acquisition unit 165, an IP signal transmitter/receiver 166, a retransmission request/retransmission processor 167, and a retransmission received signal DB 168.

The orthogonal demodulation unit 161 inputs a received signal via broadcasting corresponding to a transmission signal sent from the transmitter 11 via the receiving antenna 15-n, and performs filtering on this received signal using the same roll-off filter as the transmitter 11 and adaptive equalization processing to correct waveform distortion occurring in the satellite transmission path, and then performs orthogonal demodulation based on the same modulation method as the transmitter 11. During this orthogonal demodulation process, the orthogonal demodulation unit 161 obtains the main signal (transmission frame signal) in FIG. 12 by performing phase synchronization using π/2 shift BPSK for phase reference and detection of a unique word consisting of 26 symbols previously specified between the transmitter and receiver (the transmitter 11 and the receiver 16) shown in FIG. 12.

The orthogonal demodulation unit 161 concatenates 187 main signal symbols connected to a unique word 120 times when QPSK modulation is used for transmitting the main signal (transmission frame signal), and concatenates 187 main signal symbols 80 times when 8PSK modulation is used, and performs demapping to obtain a transmission frame having the same length as a 44,880-bit LDPC code (see FIG. 3). In addition, in the case of 8PSK, since bit interleaving is performed in the transmitting device 11, the receiving device 16 also performs bit deinterleaving, which is the reverse process, to maintain bit consistency.

Figure 17 is a diagram showing a schematic configuration of a bit deinterleaver 161a in a receiving device 16 according to one embodiment of the present invention. The bit deinterleaver 161a shown in Figure 17 is configured to perform the inverse process of the bit interleaver 1114 shown in Figure 7, thereby making it possible to maintain the bit consistency of the main signal regardless of the modulation method.

In addition, in the demapping, the orthogonal demodulation unit 161 performs a calculation process to increase the probability value based on the likelihood that the information bit is 0 or 1 in LDPC decoding, so the signal after demapping usually uses likelihood information corresponding to the C/N of the received signal. For this reason, the orthogonal demodulation unit 161 outputs the likelihood information that constitutes the transmission frame to the transmission path decoding unit 162.

Next, the transmission path decoding unit 162 shown in Fig. 16 performs LDPC decoding, energy despreading (reverse processing using the same PN code as the energy spreading processing shown in Fig. 6), and BCH decoding on the likelihood information constituting the transmission frame obtained from the orthogonal demodulation unit 161, to restore the data of the main signal (see Fig. 3) in the transmission frame after error correction decoding, and further, if the MPEG-2TS synchronization byte has been removed in advance on the transmitting device 11 side, adds an MPEG-2TS synchronization byte (1 byte) to the restored data, and outputs it to an external device such as a display device or recording device (not shown) as received data. The transmission path decoding unit 162 also outputs the data of the main signal (see Fig. 3) in the restored transmission frame to the retransmission received signal DB 168. However, if a bit error remains in the main signal as a result of the decoding process of the main signal in the transmission path decoding unit 162, or if the decoding process itself cannot be performed, the transmission path decoding unit 162 outputs a message to the retransmission received signal DB 168 instead of outputting the signal to the outside.

The orthogonal demodulation unit 161 and the transmission path decoding unit 162 are therefore configured as demodulation and decoding means that receive a transmission signal via broadcast as a received signal, perform orthogonal demodulation based on a predetermined modulation method, and perform LDPC decoding and BCH decoding on the transmission frame signal after orthogonal demodulation using the same error correction code as the transmitting device 11, thereby restoring the received data.

The time signal symbol averaging and symbol determination unit 163 first selects and extracts the phase reference burst signal (symbol section of the time signal symbol frame) shown in FIG. 12 from the received symbols obtained from the orthogonal demodulation unit 121, and performs orthogonal demodulation. Here, the time signal symbol averaging and symbol determination unit 163 predetermines between the transmitter and receiver (between the transmitter 11 and the receiver 16) which of the time signal modes 1 and 2 will be used when selecting and extracting the phase reference burst signal (symbol section of the time signal symbol frame). In the case of mode 1, the condition is set to X=8 for QPSK and X=12 for 8PSK, and in the case of mode 2, the condition is set to X=4 for QPSK and X=6 for 8PSK. This allows the time signal symbol averaging and symbol determination unit 163 to identify the symbol section of the time signal symbol frame in each mode related to the time signal.

In addition, in mode 1, the time signal symbol averaging/symbol determination unit 163 extracts the phase reference burst signal (symbol section of the time signal symbol frame) multiplexed from the beginning of the modulation symbol frame shown in FIG. 12 15 times for every 64 symbols, and performs symbol averaging processing 15 times for the same symbol section. With this processing, for the 64-symbol time signal symbol frame (mode 1), noise averaging is performed 15 times for each symbol, improving the received C/N ratio.

In addition, in mode 2, the time signal symbol averaging/symbol determination unit 163 extracts the phase reference burst signal (symbol section of the time signal symbol frame) multiplexed from the beginning of the modulation symbol frame shown in FIG. 12 five times for every 96 symbols, and performs symbol averaging processing five times for the same symbol section. With this processing, for the 96-symbol time signal symbol frame (mode 2), noise averaging is performed five times for each symbol, improving the received C/N ratio.

Finally, the time signal symbol averaging/symbol decision unit 163 performs symbol decision on the time signal symbol from which the noise components have been removed after averaging, and outputs the time signal bit sequence obtained by the symbol decision to the energy despreading unit 164.

In this way, the time signal symbol frame has either or both of mode 1, in which the timestamp bit string is used as time information, and mode 2, in which the timestamp and delta bit strings are used as time information, of the timestamp and delta conforming to the NTP packet in the public IP network (IP network 18), and is configured to include a predetermined number of identical time signals in a frame size corresponding to each mode, depending on the mode determined between the sender and receiver. For this reason, the time signal symbol averaging/symbol determination unit 163 performs symbol averaging on a predetermined number of time signals that are considered to be the same signal section within the time signal symbol frame and correspond to the time information corresponding to each mode, and generates a bit string of the time signal that has been symbol-determined. Therefore, the time signal symbol averaging/symbol determination unit 163 is configured as a time signal symbol averaging/symbol determination means that demodulates the signal of the time signal symbol frame, which is configured as a phase reference burst signal that is multiplexed and transmitted from the received broadcast signal to the transmission frame of the main signal, extracts a predetermined number of time signals that are the same signal section within the time signal symbol frame, establishes phase synchronization, and averages them to generate a bit string of the time signal that has been subjected to symbol determination.

Then, the energy despreading unit 164 inputs the bit string of the time signal determined by the time signal symbol averaging/symbol determination unit 163, and performs energy despreading processing of the same PN code, which is the inverse processing of the time signal energy dispersal circuit 112a shown in FIG. 9, to restore a received time signal corresponding to the time signal of the original bit string before flattening on the transmitting device 11 side, and outputs the restored signal to the time signal acquisition unit 165.

Figure 18 is a block diagram showing the circuit configuration of the energy despreading unit 164, which receives as input a bit string obtained by symbol determination of a time signal in the receiving device 11 according to an embodiment of the present invention. As shown in Figure 18, the circuit configuration of the energy despreading unit 164 is configured in the same manner as the time signal energy dispersal circuit 112a shown in Figure 9, and includes a shift register 1641 that periodically shifts and outputs an 11th-order PN code having an initial value shown in the figure, one bit at a time, and exclusive OR circuits (XOR) 1642, 1643 for performing MOD2 addition between the bit string of the shift register 1641 and the time signal (bit string) to be despread. By performing 11th-order time signal energy despreading processing on the bit string of the time signal determined by the time signal symbol averaging/symbol determination unit 163, it is possible to restore the received time signal corresponding to the time signal of the original bit string before flattening on the transmitting device 11 side.

In addition, in the case of mode 1 related to the time signal, the energy despreading unit 164 inputs a bit string of 64 bits each, and outputs a received time signal (64 bits) to the time signal acquisition unit 165. In the case of mode 2 related to the time signal, the energy despreading unit 164 inputs a bit string of 96 bits each, and outputs a received time signal (96 bits) to the time signal acquisition unit 165.

When the time signal acquisition unit 165 receives a mode 1 reception time signal from the energy despreading unit 164, it acquires time information of the timestamp (64 bits) indicated by the mode 1 reception time signal. When the time signal acquisition unit 165 receives a mode 2 reception time signal from the energy despreading unit 164, it acquires time information of the timestamp (64 bits) and delta (96 bits) indicated by the mode 2 reception time signal, synchronizes it with the data of the main signal (see Figure 3) in the transmission frame restored by the transmission path decoding unit 162, and outputs it to the retransmission reception signal DB 168.

Therefore, the energy despreading unit 164 and the time signal acquisition unit 165 are configured as a time information acquisition means that performs energy despreading processing on the bit string of the time signal to acquire time information.

The retransmission received signal DB 168 temporarily stores a predetermined period of data of the main signal (see FIG. 3) in the transmission frame restored by the transmission path decoder 162, by linking it to time information (bit string) obtained from the time signal acquirer 165. The retransmission received signal DB 168 also temporarily stores the data by linking it to time information (bit string) obtained from the time signal acquirer 165 when a bit error remains in the main signal as a result of the decoding process of the main signal in the transmission path decoder 162, or when information indicating that the decoding process itself cannot be performed is input.

The IP signal transmission/reception unit 166 is a functional unit that is connected to the IP network 18 and transmits and receives IP signals in the form of IP packets. The IP signal transmission/reception unit 166 in this embodiment has the following functions: a transmission signal synchronously transmitted from the transmission device 11 in IP packet format, a reception signal retransmission request is transmitted to the transmission device 11, a transmission signal retransmitted from the transmission device 11 based on the transmission signal retransmission request is received, and output to the transmission line decoding unit 162; a reception signal retransmission request is transmitted to another reception device (in this example, the retransmission reception device 17), a reception signal retransmitted from the other reception device (in this example, the retransmission reception device 17) based on the reception signal retransmission request is received, and output to the transmission line decoding unit 162; and a reception signal retransmission request is received from another reception device having the same configuration as the reception device 16 in this embodiment, and a reception signal received by the reception device 16 in this embodiment corresponding to the reception signal retransmission request is retransmitted to the other reception device.

The retransmission request/retransmission processing unit 167 monitors the results of the decoding process of the main signal temporarily stored in the retransmission received signal DB 168, and when a bit error remains in the decoding process result or when information is input indicating that the decoding process itself cannot be performed, it notifies the IP signal transmission/reception unit 166 to transmit either a transmission signal retransmission request with time information to the transmitting device 11 requesting retransmission of the data of the main signal (see Figure 3) or a reception signal retransmission request with time information to another receiving device (in this example, the retransmission receiving device 17), or both, as predetermined, and performs retransmission request processing to generate and transmit the corresponding IP packet.

The retransmission request/retransmission processing unit 167 also monitors the reception of a received signal retransmission request from another receiving device having the same configuration as the receiving device 16 of this embodiment in the IP signal transmitting/receiving unit 166, and when a received signal retransmission request is received, reads the received signal received by the receiving device 16 of this embodiment that corresponds to the received signal retransmission request from the received signal retransmission DB 168, notifies the IP signal transmitting/receiving unit 166 to retransmit it to the other receiving device, and performs retransmission processing to generate and transmit the corresponding IP packet. As a result, the receiving device 16 of this embodiment can be configured to have all the functions of the receiving device for retransmission 17.

The IP signal transmitting/receiving unit 166, the retransmission request/retransmission processing unit 167, and the retransmission received signal DB 168 are configured as a receiving device side IP signal transmitting/receiving means communicatively connected to a public IP network (IP network 18) so as to enable reception of the main signal data synchronously transmitted from the transmitting device 11 in IP packet format based on time information in order to restore the main signal data in the received signal received by broadcast with a high degree of accuracy, enable a retransmission request in IP packet format to the transmitting device 11 or another receiving device (in this example, the retransmission device 17) for the main signal data in the received signal identified based on the time information, and enable retransmission of the main signal data in the received signal in response to a retransmission request from another receiving device having the same function as the receiving device 16.

The orthogonal demodulation unit 161 shown in FIG. 16 can input multiple broadcast-received signals corresponding to the transmission signals sent from the transmitting device 11 via multiple receiving antennas 15-n, and perform orthogonal demodulation on each signal based on a predetermined modulation method. The transmission path decoding unit 162 can then perform LDPC decoding and BCH decoding on each orthogonally demodulated signal using the same error correction code as the transmitting device 11, restore multiple received data (video, audio, etc.), and perform diversity combining to provide resistance to rain attenuation.

The transmission path decoding unit 162 can also be configured to receive an IP packet sequence that stores the data of the main signal in the transmission signal via broadcast from the transmitting device 11 via the IP network 18 as a transmission signal to be synchronously transmitted or retransmitted, and further obtain a signal retransmitted from another receiving device (i.e., the retransmission receiving device 17), to substitute for or complement the received data based on the received signal received via broadcast, thereby providing resistance to rain attenuation.

Therefore, when the receiving device 16 of this embodiment receives a broadcast reception signal, for example, via multiple receiving antennas 15-n, it can obtain a diversity effect that can provide resistance to rain attenuation. Furthermore, by acquiring a transmission signal transmitted synchronously via the IP network 18, the receiving device 16 can obtain a diversity effect that can provide resistance to rain attenuation by combining it with the broadcast reception signal, even if there is packet loss, and can perform data complementation by communication. Furthermore, by acquiring a signal retransmitted from another receiving device (i.e., retransmission receiving device 17), it can obtain a diversity effect that can provide resistance to rain attenuation by combining it with the broadcast reception signal, even if there is packet loss.

In particular, the time information in this transmission system 1 has a unique relationship between the transmitting device 11 and the receiving device 16 (including the retransmission receiving device 17), making it possible to easily compare and match transmission frames or received data at the same time obtained via broadcast and via the IP network 18. In particular, in the receiving device 16, since the time signal is obtained by averaging, it is possible to obtain extremely accurate time information, making it possible to easily maintain frame synchronization at the time of a retransmission request via the IP network 18 with high accuracy.

(Effectiveness check)
As an effect confirmation of the transmission system 1 of this embodiment, Fig. 19 shows the C/N vs. BER characteristics when symbol determination after averaging processing of the time signal symbol based on the time signal symbol frame (mode 1, mode 2) in the receiving device 16 of the transmission system 1 of one embodiment according to the present invention and when symbol determination is performed without averaging processing of the time signal symbol. From Fig. 19, it can be seen that at a bit error rate (BER) of 1.E-7, compared to the case where averaging is not performed, there is a gain of 11.71 dB in the case of mode 1 and a gain of 7.1 dB in the case of mode 2. As described above, the transmitting device 11 and the receiving device 16 according to the present invention can realize stable frame synchronization and can obtain reception performance with excellent noise resistance to rain attenuation in 21 GHz band satellite broadcasting in the realization of communication complementation combining satellite broadcasting and public IP network.

In the above-mentioned embodiment, a computer that functions as the transmitting device 11 or the receiving device 16 can be configured, and a program for making each means of the transmitting device 11 or the receiving device 16 function can be suitably 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 that appropriately stores 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 on 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). Furthermore, such a program can be configured as a part of the software on the OS used by the computer (stored in a ROM or an external storage device). Furthermore, a program for making such a computer function as each means can be recorded on a computer-readable recording medium. Furthermore, 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 embodiments 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, in transmission methods other than advanced satellite broadcasting, it is possible to achieve the same functions as the present invention by using error correction codes having similar code lengths. In addition, it is also possible to configure a transmission system that time-division multiplexes multiple types of digital modulation methods, including other modulation methods not included in the above-mentioned embodiments. Therefore, the present invention should not be construed as being limited by the above-mentioned embodiments, but is limited only by the scope of the claims.

The transmitting device and receiving device according to the present invention have a configuration with excellent noise resistance, making them useful for use in transmission systems that achieve stable frame synchronization between broadcasting and communications.

REFERENCE SIGNS LIST 1 Transmission system 10 Signal source device 11 Transmitting device 12 NTP server 13 Transmitting antenna 14 Broadcasting satellite 15-1, 15-n, 15-m Receiving antenna 16 Receiving device 17 Retransmission receiving device 18 IP network 111 Transmission path coding unit 112 Time signal generating unit 112a Time signal energy dispersal circuit 112b π/2 shift BPSK modulation unit 113 Time information generating unit 114 Time signal symbol frame generating unit 115 Modulation symbol frame generating unit 116 Orthogonal modulation unit 117 IP signal transmitting/receiving unit 118 Retransmission transmission signal DB (database)
119 Retransmission processing unit 161 Orthogonal demodulation unit 161a Bit deinterleaver 162 Transmission path decoding unit 163 Time signal symbol averaging/symbol decision unit 164 Energy despreading unit 165 Time information acquisition unit 166 IP signal transmission/reception unit 167 Retransmission request/retransmission processing unit 168 Retransmission received signal DB (database)
1111 Shift register 1112, 1113 Exclusive OR circuit (XOR)
1114 Bit interleaver 1121 Shift register 1122, 1123 Exclusive OR circuit (XOR)
1641 Shift register 1642, 1643 Exclusive OR circuit (XOR)

Claims (3)

A receiving device that receives a transmission signal transmitted from a transmitting device using broadcast and a public IP network,
The transmitting device is configured to include: a coding and modulation means for applying a BCH code as an outer code, and using a transmission frame that is matched with an LDPC code of a predetermined code length as an inner code as a basic transmission unit, generating a transmission signal that has been orthogonally modulated by a predetermined modulation method in units of the transmission frame, and transmitting the signal via broadcasting, in order to transmit a signal to the receiving device using broadcasting and a public IP network; a time signal symbol frame generating means for performing energy diffusion processing for each time information defined by a predetermined bit string used in a common format for signal transmission in broadcasting and the public IP network, converting the time information into a time signal by π/2 shift BPSK modulation, generating a time signal symbol frame including a predetermined number of identical time signals, and intermittently and periodically multiplexing the time signal symbol frame as a phase reference burst signal; and a transmitting device-side IP signal transmitting and receiving means for communicating with a receiving device with an IP address set, and for communicating with a public IP network so as to synchronously transmit data of a main signal in the transmission signal via broadcasting specified based on the time information to the receiving device in an IP packet format, or to retransmit the data in response to a request from the receiving device.
a demodulation and decoding means for receiving a transmission signal via broadcast as a reception signal, performing orthogonal demodulation based on the predetermined modulation method, and performing LDPC decoding and BCH decoding on the transmission frame signal after orthogonal demodulation using the same error correction code as that of the transmission device, thereby restoring reception data;
a time signal symbol averaging/symbol determination means for demodulating a signal of a time signal symbol frame constituted as the phase reference burst signal that is multiplexed and transmitted from the received signal received by broadcasting to a transmission frame of a main signal prior to the LDPC decoding and BCH decoding, establishing phase synchronization, extracting a predetermined number of the time signals that are in the same signal section within the time signal symbol frame, averaging the extracted time signals, and generating a bit string of the time signal that has been subjected to symbol determination;
a time information acquiring means for acquiring time information by performing an energy inverse diffusion process on the bit string of the time signal;
a receiving device-side IP signal transmitting/receiving means for communicating with a public IP network so as to receive the main signal data synchronously transmitted from the transmitting device in IP packet format based on the time information for highly accurate restoration of the main signal data in the received signal, to request the transmitting device or another receiving device to retransmit the main signal data in the received signal specified based on the time information in IP packet format, and to retransmit the main signal data in the received signal in response to a retransmission request from another receiving device having the same function as the receiving device;
A receiving device comprising: the time signal symbol frame has either one or both of a first mode in which a bit string of a timestamp is used as the time information, and a second mode in which bit strings of both the timestamp and the delta are used as the time information, among the timestamp and delta conforming to an NTP packet in a public IP network, and is configured to include a predetermined number of identical time signals in a frame size corresponding to each mode according to a mode determined between a transmitter and a receiver;
The receiving device according to claim 1, characterized in that the time signal symbol averaging/symbol decision means generates a bit string of a time signal by averaging a predetermined number of time signals that are the same signal section within the time signal symbol frame corresponding to the time information according to each mode and performing symbol decision. The receiving device according to claim 1 or 2, further comprising a means for receiving the received signal received via broadcast via a plurality of receiving antennas and performing diversity combining, or a means for performing data complementation for the received signal received via broadcast using data of a main signal in the received signal obtained via a public IP network.