JP2021177611A - Transmission server, transmission device, reception device, and program - Google Patents

Abstract

To provide a transmission server, a transmission device and a reception device for digital broadcasting, and a program that efficiently enable data retransmission in response to a retransmission request from a receiving side using communication based on coded data of an error correction code used in digital broadcasting.SOLUTION: A transmission server 6 of the present invention is supplied with coded data of an error correction code related to digital broadcasting generated by a transmission device 2 (3), stores the coded data for a predetermined time, receives, through an IP network 8, a retransmission request packet generated when a reception device 5 cannot correct a bit error of the coded data, changes a coding rate of the coded data related to the retransmission request while determining, according to communication quality, whether the coding rate is to be increased or decreased, and re-transmits it to the reception device 5 by IP packet formation. The transmission device 2 (3) of the present invention sequentially outputs the coded data to the transmission server 6. The reception device 5 of the present invention repeats the retransmission request until decoding within a predetermined time by using the coded data obtained through the retransmission request.SELECTED DRAWING: Figure 1

Description

The present invention relates to the technical fields of satellite broadcasting, terrestrial broadcasting, fixed communication and mobile communication, and in particular, it is possible to retransmit data in response to a retransmission request from the receiving side by linking broadcasting and communication. It relates to a transmission server, a transmission device and a reception device related to digital broadcasting, and a program.

In the digital broadcasting system of satellite broadcasting and terrestrial broadcasting, an error correction code is used as a technique for improving transmission performance under white noise. For example, in advanced broadband satellite digital broadcasting, the LDPC (Low Density Parity Check) code, which is a powerful error correction code having performance approaching the Shannon limit, which is the theoretical upper limit of utilization efficiency for the signal-to-noise ratio, is used ( For example, see Non-Patent Documents 1 and 2). However, in satellite digital broadcasting, attenuation due to rainfall, fading in terrestrial digital broadcasting, etc., in digital broadcasting, the transmission conditions may deteriorate to the extent that the signal cannot be recovered only by the error correction code.

On the other hand, in digital wireless communication, data retransmission control by ARQ (Automatic Repeat reQuest) is known as a data compensation technique other than an error correction code (see, for example, Patent Documents 1 and 2). In digital wireless communication, transmission performance can be improved by using Hybrid ARQ that combines an error correction code and ARQ, the number of retransmissions is smaller than that using ARQ alone, and conditions that cannot be compensated by the error correction code alone. Data transmission is possible. However, the conventional prior technology using Hybrid ARQ is limited to two-way communication such as FPU and mobile phone base station communication, and cooperates with communication in one-way broadcasting such as broadcasting, and data is transmitted by Hybrid ARQ. No compensation technique has been established.

Although it does not constitute a Hybrid ARQ, when the transmission conditions of digital broadcasting deteriorate, the ARQ is directed from the receiving side to the transmitting side via the IP (Internet Protocol) network, which is a communication path capable of bidirectional communication. (For example, see Patent Document 3).

A general IP network is assumed to be a binary erasure channel (PEC) in which information is lost due to some kind of failure such as line congestion. Therefore, in Hybrid ARQ in digital wireless communication, LDPC-CC (Convolutional Codes) (see, for example, Patent Document 4) and LDGM (Low-Density Generator Matrix) codes (for example, Patent Document 5) are used as error correction codes for data compensation. An error correction code dedicated to IP communication, which is a lost communication path such as (see), is used. These LDPC-CC and LDGM codes are error correction codes based on the LDPC code as in the case of advanced broadband satellite digital broadcasting, but are designed in consideration of only IP communication, which is a lost communication path. It is necessary to prepare an error correction code encoder and decoder dedicated to IP communication.

Japanese Unexamined Patent Publication No. 2014-050034 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 "Transmission method for advanced broadband satellite digital broadcasting (ISDB-S3) Standard ARIB STD-B44 2.1 version", [online], revised on March 25, 2016, ARIB, [search on April 13, 2016] , Internet <URL: https://www.arib.or.jp/kikaku/kikaku_hoso/std-b44.html>

As described above, in digital wireless communication, improvement of transmission performance can be realized by using Hybrid ARQ that combines an error correction code and ARQ, and the number of retransmissions is smaller than that using only ARQ, and only the error correction code is used. Data can be transmitted under conditions that cannot be compensated for.

However, a technique for coordinating with communication in one-way broadcasting such as broadcasting and compensating for data with Hybrid ARQ has not been established.

Therefore, also in digital broadcasting, a technique of compensating data with Hybrid ARQ by fusing digital broadcasting and communication in which an error correction code and ARQ are combined in cooperation with communication is desired. For example, when the transmission conditions of digital broadcasting deteriorate, by constructing a transmission system that performs ARP from the receiving side to the transmitting side via the IP network, which is a communication path capable of bidirectional communication, and retransmits data from the transmitting side. , Transmission performance can be improved. In other words, since the current digital broadcasting only assumes data compensation using an error correction code, by compensating the data related to digital broadcasting with Hybrid ARQ, it is possible to deal with the deterioration of transmission conditions that cannot be corrected by the error correction code. .. Further, even when the ARQ system is configured only by IP communication, the number of retransmissions related to ARQ can be reduced by configuring Hybrid ARQ that combines the error correction code related to broadcasting and communication.

However, in order to construct a transmission system using Hybrid ARQ by fusing broadcasting and communication, an error dedicated to IP communication disclosed in Patent Documents 4 and 5 and the like is added to the system using ARQ disclosed in Patent Document 3. When the correction code is applied and configured, a mechanism for preparing and coordinating an error correction code encoder and a decoder for digital broadcasting and an IP communication encoder and a decoder, respectively, is required. The scale of equipment will increase.

Therefore, it is required to efficiently combine "error correction code used in digital broadcasting" and ARQ, and to construct a transmission system using Hybrid ARQ by fusing broadcasting and communication.

That is, without increasing the encoder of the transmitting device and the decoder of the receiving device related to digital broadcasting, the digital broadcasting and the communication by the IP network are linked, for example, the concatenated code and IP of error correction of the LDPC code and the BCH code. It is desired to improve the error correction capability related to digital broadcasting by constructing a transmission system that realizes Hybrid ARQ that combines retransmission requests using communication.

Further, in a general IP network, the probability of packet loss and the appearance of packet loss vary depending on the time zone and line used, such as when the line is congested. Therefore, when realizing hybrid ARQ in digital broadcasting and communication networks without increasing the scale of equipment, pay attention to the block code among the error correction codes used in digital broadcasting, and digitally broadcast the data retransmitted via the IP network. It is required to use the coded data in the block code of the above, and to realize variable control according to the communication quality of the IP network to improve the transmission efficiency via the IP network.

Therefore, without increasing the encoder of the transmitting device and the decoder of the receiving device related to digital broadcasting, the digital broadcasting and the communication by the IP network are linked, for example, by the concatenated code of error correction of the LDPC code and the BCH code. By constructing a transmission system that realizes Hybrid ARQ that combines block code and retransmission according to the communication quality of the IP network in response to a retransmission request using IP communication, the error correction capability related to digital broadcasting is improved, and moreover, Therefore, a technique for realizing efficient Hybrid ARQ is desired.

In view of the above problems, an object of the present invention is to efficiently use communication to communicate with an IP network in response to a retransmission request from a receiving side based on coded data of an error correction code used in digital broadcasting. It is an object of the present invention to provide a transmission server capable of retransmitting data according to quality, a transmission device and a reception device related to digital broadcasting, and a program.

The transmission server of the present invention digitally modulates the encoded data encoded by using the error correction code related to digital broadcasting, and transmits the digitally modulated encoded data to the receiving device via the broadcasting transmission path. A transmission server that stores a predetermined time of the coded data from the device and enables transmission to the receiving device via the IP (Internet Protocol) network, and sequentially inputs the coded data generated by the transmitting device. It is managed in time series by a synchronization signal based on the frame number or time information of the error correction code frame constituting the code length of the error correction code, and the coded data managed in time series is saved while being updated for a predetermined time. The retransmission request packet generated when the bit error of the coded data cannot be corrected by the receiving device using the error correction code is received via the storage unit and the IP network, and the retransmission request packet is used as the retransmission request packet. The communication quality information measured by the receiving device and the retransmission request information indicating the coded data of the error correction code frame related to the retransmission request are extracted, and a predetermined coding rate based on the communication quality information is extracted. It is determined whether or not to change the coding rate of the block code of the coded data generated by the transmitting device according to the change standard and retransmit the data, and based on the determination result, the storage unit is based on the retransmit request information. With a retransmission request processing unit that reads the encoded data related to the retransmission request from, constructs the encoded data in which the encoding rate is adaptively changed, and controls the retransmission of the encoded data toward the receiving device. When the coding rate of the block code of the coded data generated by the transmitting device is changed or not changed by the control of the retransmission request processing unit, and the coding rate is changed, It is generated by the transmission device transmitted on the broadcast transmission line among a predetermined number of coding rates that are based on the same coding method as the error correction coding method used by the transmission device and that can be used by the transmission device. It is configured through control by a coding rate adaptive change unit that performs error correction coding processing that changes the coding rate by distinguishing whether it is higher or lower than the coding rate of the coded data, and the retransmission request processing unit. It is characterized by including an IP packet generation unit that generates an IP packet format encoded data packet for storing the encoded data related to the retransmission request and transmits the encoded data packet to the receiving device via the IP network.

Further, in the transmission server of the present invention, when the coding rate adaptive change unit changes the coding rate of the coded data generated by the transmission device under the control of the retransmission request processing unit, the code before the change is used. When converting to a coding rate higher than the coding rate, a padding bit known on the receiving device side is added to the information bit of the coded data according to the coded rate to be changed, and the error correction coding is performed. For retransmission, the parity of the block code obtained by changing the coding rate obtained by processing is replaced with the parity added to the coded data generated by the transmission device, and the padding bit is removed. When the coded data is generated and converted to a coding rate lower than the coding rate before the change, the information bits of the coded data are divided between transmission and reception by a predetermined division method and changed. The parity of the block code obtained by adding a padding bit known on the receiving device side to each of the information bits divided according to the rate and changing the coding rate obtained by performing the error correction coding process is obtained. It is characterized in that the encoded data for retransmission is generated by replacing the parity added to the encoded data generated by the transmitting device with the parity and removing the padding bit.

Further, in the transmission server of the present invention, the retransmission request processing unit uses either one or both of the communication line delay information and the packet loss rate information measured by the receiving device as the communication quality information. It is characterized in that it determines whether or not to change the coding rate of the coded data generated by the transmitting device and retransmit it according to the predetermined code rate changing standard.

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

Further, in the transmission server of the present invention, the IP packet generation unit is obtained by forming an interleave frame using the plurality of error correction code frames and performing interleaving so as to longitudinally cross each error correction code frame. An identification header for making the interleaved frame identifiable, a sequence number for specifying which bit is represented in each error correction code frame, and an IP header which is a header of the coded data packet are added to the payload. It is characterized by having an interleave part for generating an encoded data packet of an IP packet string.

Further, the transmitting device of the present invention is a transmitting device related to digital broadcasting, and means for sequentially outputting coded data encoded by using the error correction code related to the digital broadcasting to the transmitting server of the present invention. It is characterized by having.

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

Further, the receiving device of the present invention is a receiving device that digitally modulates encoded data encoded by a transmitting device using an error correction code related to digital broadcasting and receives a modulated wave signal transmitted via a broadcasting transmission path. The error correction code is obtained by reconstructing the demodulator that receives and demolishes the modulated wave signal and the error correction code frame that constitutes the code length of the error correction code from the coded data obtained by demodulating the error correction code. An error-correcting decoding unit that performs decoding processing corresponding to Error correction for error correction request for requesting Retransmission request packet generation unit that generates a retransmission request packet in IP packet format including the retransmission request information indicating the coded data of the code frame and transmits it to the transmission server of the present invention. Then, in response to the retransmission request packet, the transmission server receives an IP packet format encoded data packet that stores the encoded data retransmitted in response to the retransmission request, and the encoding is retransmitted in response to the retransmission request. A predetermined period of either or both of the delay related to the communication between the IP packet receiving unit for extracting data and the transmitting server and the packet loss rate based on the amount of packet loss generated related to the communication with the transmitting server. The retransmission request packet is generated so as to sequentially measure and update and hold the data in units, and sequentially include the communication quality information including one or both of the delay information and the packet loss rate information of the communication line in the retransmission request packet. A communication quality measuring unit for outputting to a unit is provided, and the error correction / decoding unit can determine whether or not error correction / decoding is possible for the coded data obtained from the transmission device, and can correct bit errors in the coded data. The coding rate has not been changed for the decoding passability determination unit that generates a retransmission request packet including the retransmission request bit position information when it is determined that decoding is not possible, and the coded data retransmitted in response to the retransmission request. When the coding rate of the coded data is obtained by demodulation, when the coding rate is changed, a padding bit corresponding to the coding rate is added to supplement the replacement of the likelihood ratio required for decoding. The coded data complement section that attempts the decoding process through the processing and repeats the request for retransmission of the corresponding coded data until it can be decoded within a predetermined time, and the coded data related to the retransmission request is changed to a lower coding rate and information. Bits are divided (divided into two equal parts in the example described in detail later) When it is, it is characterized by having a data binding unit that generates received data by recombination of the divided information bits after decoding with the transmission server according to a predetermined division method. ..

Further, in the receiving device of the present invention, the error correction code is composed of a concatenated code in which an LDPC code is concatenated as an internal code and a BCH code is concatenated as an external code, and the decoding possibility determination unit is a coding obtained from the transmitting device. The data is characterized in that when the BCH code decoding process does not make it error-free, it is determined that the bit error of the coded data could not be corrected.

Further, the receiving device of the present invention further includes a receiving quality measuring unit for measuring the receiving quality of the received modulated wave signal, and the receiving quality measuring unit can obtain the coded data decoded by the error correction decoding unit. When the reception path at the time when the reception data is generated is the reception path for broadcasting reception instead of via the IP network, the reception path for broadcasting reception is maintained, and the encoded data that can be decoded by the error correction decoding unit is used as the basis. When the reception route at the time of generating the reception data is via the IP network, it is determined whether or not the reception quality is equal to or higher than the predetermined value, and if the reception quality is equal to or higher than the predetermined value, the reception route for broadcasting reception is received. If the reception quality is less than a predetermined value, the reception path via the IP network is maintained, and even after the error correction / decoding unit is requested to retransmit the encoded data, the next is continued via the IP network. It is characterized by having a means for instructing to retransmit and acquire the encoded data.

Further, in the receiving device of the present invention, the IP packet receiving unit receives a coded data packet of an IP packet string that stores coded data retransmitted in response to a retransmission request from the transmitting server in response to the retransmission request packet. It is characterized by having a deinterleave unit that receives the data, performs reverse processing of the interleave by the transmission server, and extracts the encoded data retransmitted in response to the retransmission request.

Further, the program of the present invention is configured as a program for operating the computer as the transmission server of the present invention.

Further, the program of the present invention is configured as a program for operating the computer as the receiving device of the present invention.

According to the present invention, for data loss that cannot be prevented only by broadcast reception, data can be retransmitted on the receiving side by executing a retransmission request from the receiving side to the transmitting side via an IP network and enabling data retransmission from the transmitting side. Can be complemented. In particular, the data retransmitted by the transmitting side via the IP network is used as the coded data in the block code of digital broadcasting, and the encoded data is variably controlled to the coding rate according to the communication quality of the IP network to retransmit the data. It is possible to reduce the number of requests, improve the transmission efficiency via the IP network, and enhance the resistance to packet loss. Further, by making both the error correction code used for broadcast reception and the error correction code used for transmission via the IP network the same as the code format of the error correction code standardized by the broadcasting standard, one error correction decoding is performed on the receiving side. This can be achieved simply by preparing a vessel, and the scale of the equipment can be reduced.

It is a block diagram which shows the schematic structure of the transmission system including the transmission server, the transmission device and the receiving device of one Embodiment by this invention. It is a block diagram which shows the schematic structure of the transmission server and the transmission device of one Embodiment by this invention. It is a flowchart which shows the control flow which concerns on the retransmission request packet between the transmission server and the receiving device of one Embodiment by this invention. Each of (a) to (d) is when the coding rate is changed by the coding rate adaptation changing unit in the transmission server of one embodiment according to the present invention (when the coding data related to the retransmission request is changed to a higher coding rate). It is a figure which shows the generation method of the coded data of. Each of (a) to (e) is when the coding rate is changed by the coding rate adaptation changing unit in the transmission server of one embodiment according to the present invention (when the coding data related to the retransmission request is changed to a lower coding rate). It is a figure which shows the generation method of the coded data of. It is explanatory drawing concerning the interleaving process of the IP packet generation part in the transmission server of one Embodiment by this invention. It is a block diagram which shows the schematic structure of the receiving device of one Embodiment by this invention. It is a flowchart which shows the reception control flow in the receiving apparatus of one Embodiment by this invention. It is a block diagram which shows the schematic structure of the transmission system including the transmission server, the transmission device and the receiving device of one Example according to this invention. It is a flowchart which shows the reception control flow in the receiving apparatus of the advanced wideband satellite digital broadcasting of one Example by this invention. Each of (a) to (e) is when the coding rate is changed by the coding rate adaptation changing unit in the transmission server of the one embodiment according to the present invention (when the coding data related to the retransmission request is changed to a lower coding rate). It is a figure which shows the generation method of the coded data of. It is explanatory drawing about the interleave processing of the IP packet generation part in the transmission server of one Example by this invention. In each of (a) to (f), when the coding rate is changed by the coding rate adaptation changing unit in the transmission server of the application example according to the present invention (when the coding data related to the retransmission request is changed to a lower coding rate). It is a figure which shows the generation method of the coded data. It is a block diagram which shows the schematic structure of the receiving device of the modified example by this invention. It is a flowchart which shows the reception control flow in the receiving apparatus of the modified example by this invention. It is a figure explaining the operation outline at the time of transmitting the coded data packet which changed the coded data which concerns on a retransmission request to a lower code rate by the transmission server of one Example by this invention to a receiving apparatus.

[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 reception device 5 according to an embodiment of the present invention. The transmission system 1 shown in FIG. 1 includes transmission devices 2 and 3, a reception device 5, one or a plurality of transmission servers 6, and a load balancer 7 provided when a plurality of transmission servers 6 are configured. ..

The transmission device 2 generates coded data by performing error correction coding processing on the transmission data related to digital broadcasting and imparting error correction code parity, and digitally modulates the coded data by a predetermined modulation method. This is a device that generates a modulated wave signal and emits radio waves related to digital broadcasting via a satellite broadcasting transmission line including a broadcasting satellite 4 via a transmitting antenna 2a. For example, the transmitter 2 can be a transmitter for advanced wideband satellite digital broadcasting. Further, the transmission device 2 manages the sequentially generated coded data as an error correction code frame, assigns a frame number or time information that functions as a synchronization signal, and adds one or a plurality of coded data via the local area network. It has a function of transmitting to the transmission server 6.

The transmission device 3 generates coded data by performing error correction coding processing on the transmission data related to digital broadcasting and imparting error correction code parity, and digitally modulates the coded data by a predetermined modulation method. This is a device that generates a modulated wave signal and radiates a radio wave related to digital broadcasting via a transmission antenna 3a and a terrestrial broadcasting transmission line. For example, the transmitting device 3 can be a transmitting device for current or next-generation terrestrial digital broadcasting. Further, the transmission device 3 manages the sequentially generated coded data as an error correction code frame, assigns a frame number or time information that functions as a synchronization signal, and adds one or a plurality of coded data via the local area network. It has a function of transmitting to the transmission server 6.

The receiving device 5 receives the modulated wave signal radiated from the transmitting device 2 via the receiving antenna 5a, demodulates the signal, reconstructs the error correction code frame constituting the code length of the error correction code, and reconstructs the error correction code frame in the transmitting device 2. A function that performs decoding processing corresponding to error correction coding processing to generate received data so that it can be reproduced, and a modulated wave signal radiated from the transmitting device 3 via the receiving antenna 5b is received and demodulated. This device has a function of reconstructing an error correction code frame constituting the code length of the error correction code and performing decoding processing corresponding to the error correction coding process in the transmission device 3 to generate received data and make it playable.

Further, the receiving device 5 determines whether or not the coded data obtained from the transmitting device 2 (or the transmitting device 3) can be error-corrected and decoded, and when it is determined that the coded data can be decoded, the coded data is decoded as it is to generate the received data. If it is determined that the bit error of the encoded data cannot be corrected and cannot be decoded, a retransmission request packet in the form of an IP packet requesting retransmission of the corresponding encoded data is generated, and the retransmission request packet includes communication quality information. , Has a function of transmitting data to the transmission server 6 via the IP network 8. Further, the receiving device 5 receives the encoded data retransmitted from the transmitting server 6 in response to the retransmission request in response to the retransmission request packet (encoding data transmitted on the broadcast transmission line according to the communication quality information on the transmitting server 6 side). (Reconstructed by changing the coding rate adaptively by distinguishing whether it is higher or lower than the coding rate of), the encoded data packet in the IP packet format is received, and the retransmission request is made. The coded data retransmitted according to the above is extracted and complemented according to the coding rate so as to be used for the decoding process, and the request for retransmitting the corresponding coded data is repeated until the decoding process can perform decoding within a predetermined time. When the coded data related to the function and the retransmission request is changed to a lower coding rate and the information bits are divided (divided into two equal parts in the example described in detail later), the divided data is used after decoding. It has a function of recombining the information bits with the transmission server 6 according to a predetermined division method to generate received data. If the receiving device 5 cannot decode the data within a predetermined time by the decoding process, the receiving device 5 generates the received data in a state including a bit error.

Each of one or a plurality of transmission servers 6 digitally modulates the encoded data encoded by using the error correction code related to digital broadcasting and transmits the encoded data to the receiving device 5 via the broadcasting transmission line (transmission device 2 (). Alternatively, the coding rate of the coded data transmitted on the broadcast transmission line according to the communication quality information for the coded data requested to be retransmitted from the receiving device 5 after storing a predetermined time of the coded data from the transmitting device 3). Is changed to reconstruct the encoded data, and in this example, the encoded data packet of the interleaved IP packet string is generated and configured as a computer that can be transmitted to the receiving device 5 via the IP network 8. NS.

That is, the transmission server 6 sequentially inputs the coded data generated by the transmission device 2 (or the transmission device 3) via the local area network, and the frame number of the error correction code frame constituting the code length of the error correction code. Alternatively, a function of managing in time series by a synchronization signal based on time information and saving while updating a predetermined time, error correction used in the transmitting device 2 (or transmitting device 3) in the receiving device 5 via the IP network 8. When the bit error of the coded data cannot be corrected by using the code, the retransmission request packet related to the coded data is received together with the communication quality information, and the packet is sent to the receiving device 5 according to the communication quality information on the broadcast transmission line. A function that distinguishes between higher and lower coding rates of the transmitted coded data and adaptively changes the coding rate to control the retransmission of the coded data, and synchronization related to the retransmission request. An error correction code frame of m frames having a continuous synchronization signal (frame number or time information) starting from an error correction code frame constituting the coded data having a signal (frame number or time information) is related to the retransmission request. An interleaved frame is constructed by forming the interleaved frame with the same coding rate as the coded data having a synchronization signal (frame number or time information), and the interleaved frame is interleaved in a direction orthogonal to the error correction code frame of the m frame. It has a function of generating an encoded data packet of an IP packet string and transmitting it to the receiving device 5 via the IP network 8.

In particular, when the transmission server 6 changes the coding rate of the coded data generated by the transmitting device 2 (or the transmitting device 3) and retransmits the data, the transmission server 6 converts the coded data into a code rate higher than the code rate before the change. In the case, a padding bit known on the receiving device 5 side is added to the information bit of the coded data according to the coded rate to be changed, and the coded rate obtained by performing the error correction coding process is changed. The parity of the block code is replaced with the parity added to the coded data generated by the transmitting device 2 (or the transmitting device 3), and the padding bit is removed to generate the coded data for retransmission. Has a function. Further, when the transmission server 6 changes the coding rate of the coded data generated by the transmitting device 2 (or the transmitting device 3) and retransmits the data, the transmission server 6 converts the coded data into a code rate lower than the code rate before the change. In this case, the information bit of the coded data is divided between transmission and reception (between the transmission server 6 and the reception device 5) by a predetermined division method (divided into two equal parts in the example described in detail later), and the code is changed. A padding bit known on the receiving device 5 side is added to each of the information bits divided according to the conversion rate, and the parity of the block code obtained by performing error correction coding processing and changing the coding rate is transmitted. It has a function of replacing the parity added to the coded data generated by the device 2 (or the transmitting device 3) and adding the coded data, and removing the padding bit to generate the coded data for retransmission.

Although the transmission system 1 illustrated in FIG. 1 has been described as including the transmission device 2 and the transmission device 3, only one of the transmission device 2 and the transmission device 3 may be used. In the transmission system 1 illustrated in FIG. 1, the transmission device 2 (or the transmission device 3) and the transmission server 6 are described as separate bodies, but the transmission device 2 (or the transmission device 3) is provided with the transmission server 6. One or a plurality of transmission devices 2 (or transmission devices 3) may be connected by a simple signal cable instead of being connected by a local area network.

When a plurality of transmission servers 6 are configured, the load distribution device 7 is provided between the plurality of transmission servers 6 and the IP network 8, and retransmit request packets are received from many reception devices 5 via the IP network 8. Is a device that distributes the processing load of each of the plurality of transmission servers 6 and divides and transmits the encoded data packet related to the retransmission request. In the transmission system shown in FIG. 1, a plurality of receiving devices 5 registered in advance as users are targeted, and by interposing a load balancing device 7, it is sufficient to add a transmitting server 6 even when the number of registered users increases. It becomes a thing. However, when the transmission servers 6 corresponding to the number of registered users allowed in advance are individually arranged, the installation of the load balancer 7 may be omitted, and the transmission server 6 and the IP network 8 may be directly connected. good.

Hereinafter, the transmission device 2 (or the transmission device 3), the transmission server 6, and the reception device 5 will be described more specifically in this order.

[Transmission device]
FIG. 2 is a block diagram showing a schematic configuration of a transmission server 6 and a transmission device 2 (or a transmission device 3) according to an embodiment of the present invention. The transmitter 2 (or transmitter 3) shown in FIG. 2 shows only the main components according to the present invention, and the description of other components such as energy (electric power) diffusion processing will be omitted.

The transmission device 2 and the transmission device 3 employ an error correction coding process and a modulation method suitable for their respective broadcast transmission lines (satellite broadcast transmission line or terrestrial broadcast transmission line), but as shown in FIG. 2, errors It will be comprehensively described as including the correction coding unit 21 and the modulation unit 22.

The error correction coding unit 21 is an encoder that generates coded data by performing error correction coding processing on transmission data related to digital broadcasting and imparting error correction code parity, and outputs the coded data to the modulation unit 22. be. Further, the error correction coding unit 21 manages the sequentially generated coded data as an error correction code frame, assigns a frame number or time information that functions as a synchronization signal, to the transmission server 6 via the local area network. It has a function to transmit.

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

The transmission data related to digital broadcasting can be, for example, MPEG2-TS described in ARIB STD-B31 and used in terrestrial digital broadcasting when transmitted via a terrestrial broadcasting transmission line, for example, a satellite broadcasting transmission line. When transmitting via the data, it can be TLV (Type Length Value) format data described in ARIB STD-B44 and used in advanced broadband satellite digital broadcasting.

In the current terrestrial digital broadcasting, error correction coding processing is performed using a convolutional code as an internal code and a Reed-Solomon code as an external code. In the next-generation terrestrial digital broadcasting, it is being studied to perform error correction coding processing with a concatenated code in which an LDPC code is used as an internal code and a BCH (Bose-Chaudhuri-Hocquenghem) code is used as an external code. Further, in advanced broadband satellite digital broadcasting, error correction coding processing is performed using a concatenated code in which an LDPC code is concatenated as an internal code and a BCH code is concatenated as an external code.

[Sending server]
The transmission server 6 shown in FIG. 2 digitally modulates the encoded data encoded by using the error correction code related to digital broadcasting and transmits the encoded data to the receiving device 5 via the broadcasting transmission line (or the transmitting device 3). ), And saves while updating the predetermined time, and among the coded data, the coded data requested to be retransmitted from the receiving device 5 is the coded data transmitted on the broadcast transmission line according to the communication quality information. It is configured as a computer that can be transmitted to the receiving device 5 via the IP network 8 by selectively changing the coding rate and reconfiguring it by distinguishing whether it is higher or lower than the coding rate of the storage unit. It includes 61, an IP packet generation unit 62, a retransmission request processing unit 63, a coding rate adaptation change unit 64, and a communication quality control unit 65.

The storage unit 61 sequentially inputs the coded data generated by the transmission device 2 (or the transmission device 3) based on the synchronization signal (frame number or time information) via the local area network, and the code of the error correction code. It is a functional unit that manages error correction code frames constituting the length in time series with synchronization signals (frame numbers or time information) and saves them while updating a predetermined time. The coded data obtained from the transmission device 2 (or the transmission device 3) includes a frame number identified by a TMCC (Transmission and Multiplexing Configuration Control) signal, which is a control signal in digital broadcasting used in a broadcast transmission line. Time information is attached as a synchronization signal. For example, the storage unit 61 embeds time information (also embedding time information in the main signal) included in the TMCC signal transmitted together with the coded data in the error correction code frame unit in the data transmission method using the broadcast transmission line. The coded data of the error correction code frame unit sequentially obtained from the transmission device 2 (or the transmission device 3) by receiving the coded data in units of the error correction code frame, the frame number associated with the time information is used as the synchronization signal, and the synchronization signal is used. Can be managed with. Further, the coded data managed in time series by the storage unit 61 by the synchronization signal (frame number or time information) may be notified from the transmission server 6 via the IP network 8 while being received during the digital broadcasting. That is, in the transmission system 1 shown in FIG. 1, by using the time information and the frame number included in the TMCC signal or the main signal as the synchronization signal, the transmitting devices 2, 3 and the receiving devices 5, one or a plurality of units can be used. It is possible to secure the synchronization of the transmission server 6 and the load balancer 7 provided when a plurality of transmission servers 6 are configured.

The IP packet generation unit 62 is a functional unit that generates an IP packet format encoded data packet that stores the encoded data related to the retransmission request from the receiving device 5 and transmits the encoded data packet to the receiving device 5 via the IP network 8. Is. This coded data packet is generated when it is determined by the receiving device 5 that the bit error of the coded data cannot be corrected by using the error correction code used by the transmitting device 2 (or the transmitting device 3). Although the details will be described later, the IP packet generation unit 62 represents an identification header for making each interleave frame related to the interleave processing identifiable on the receiving device 5 side, and a bit number in each error correction code frame. After assigning a sequence number that specifies whether or not, the bits are rearranged so as to traverse each error correction code frame based on a predetermined rule that the bits of the coded data related to the retransmission request are separated by a predetermined value or more. It has an interleaving unit 621 that executes the interleaving process to be performed.

When the retransmission request processing unit 63 receives the retransmission request packet from the receiving device 5 via the IP network 8, the communication quality information measured by the receiving device 5 stored in the retransmission request packet and the error correction related to the retransmission request. The retransmission request information indicating the coded data of the code frame is extracted. Then, the retransmission request processing unit 63 encodes the coded data transmitted on the broadcast transmission line according to the predetermined coding rate change standard managed by the communication quality management unit 65 based on the communication quality information received this time. Determine whether to change the rate and resend. Then, the retransmission request processing unit 63 searches for the location of the encoded data related to the retransmission request from the storage unit 61 based on the retransmission request information received this time according to the determination result, and configures the encoded data. The storage unit 61 is controlled so as to read the error correction code frame for m frames having a continuous synchronization signal (frame number or time information) starting from the error correction code frame and output the error correction code frame to the coding rate adaptation change unit 64. The coding rate adaptation changing unit 64 is controlled so as to adaptively change and reconstruct the coding rate of the read coded data and output it to the IP packet generation unit 62. A control example related to the retransmission request processing unit 63 will be described later with reference to FIG.

The code rate adaptation change unit 64 is controlled by the retransmission request processing unit 63, and switches between changing and not changing the code rate of the coded data generated by the transmission device 2 (or the transmission device 3). When the switching units 641 and 642 and the coding rate are changed, the transmission device 2 (or the transmission device 3) is based on the same coding method as the error correction coding method used in the transmission device 2 (or the transmission device 3). Of the predetermined number of coding rates that can be used in 3), coding is performed by distinguishing whether the coding rate is higher or lower than the coding rate of the coded data generated by the transmission device transmitted on the broadcast transmission line. An error correction coding unit 643 that performs an error correction coding process for changing the rate is provided.

More specifically, when the switching units 641 and 642 retransmit the coded data (encoded data transmitted on the broadcast transmission line) related to the retransmission request read from the storage unit 61 without changing the coding rate. When the data is output to the IP packet generation unit 62 as it is, the code rate is changed and the data is retransmitted, the coded data reconstructed by changing the code rate by the error correction coding unit 643 is output to the IP packet generation unit 62. It is a functional part that switches so as to do.

For example, when the coding rate of the transmission via the broadcast transmission line and the transmission via the IP line 8 are the same, the coding rate adaptation changing unit 64 is the transmission device 2 (or the transmission device 3) read from the storage unit 61. The coded data of the corresponding error correction code frame transmitted in 1 is output to the IP packet generation unit 62 as it is.

On the other hand, when the code rate adaptation change unit 64 retransmits the coded data whose code rate has been changed from the transmission via the broadcast transmission line, the error correction coding unit 643 changes the code rate.

When the error correction coding unit 643 changes the coding rate of the coded data (coded data transmitted on the broadcast transmission line) related to the retransmission request and retransmits the data, the storage unit 61 determines the coded data in the coded data. Only the information bits (that is, the main signal in the block code) excluding the parity of are read. Subsequently, the error correction coding unit 643 uses the information bits of the coded data as they are when converting to a coding rate higher than the coding rate before the change, and the coding rate is lower than the coding rate before the change. When converting to a rate, the information bit of the coded data is divided into two by a predetermined division method between transmission and reception, and it is known between the transmission server 6 and the reception device 5 according to the coding rate to be changed. A padding bit consisting of (all "0" or "1" bits, or a regular bit pattern of "0" and "1") is added to a known insertion position between transmission and reception. Then, the error correction coding unit 643 is the same as the error correction coding method used by the error correction coding unit 21 in the transmission device 2 (or the transmission device 3) for the predetermined information bit to which the padding bit is added. The error correction coding process is performed based on the coding method of the above, and at a coding rate different from the coding rate transmitted on the broadcasting transmission line that can be used by the transmitting device 2 (or the transmitting device 3) related to broadcasting. Finally, the error correction coding unit 643 encodes the parity of the block code whose coding rate is changed for the coded data transmitted on the broadcast transmission line by the transmission device 2 (or the transmission device 3). Encoded data for retransmission is generated by replacing the parity added to the data with the information bit and removing the padding bit. Error correction of the coding rate adaptation changing unit 64 The method of generating the coded data when the coding rate is changed by the coding unit 643 will be described later with reference to FIGS. 4 and 5.

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

The delay information of the communication line is the time difference between the transmission time of the retransmission request packet transmitted from the receiving device 5 to the transmitting server 6 and the receiving time of the encoded data packet retransmitted from the transmitting server 6 in response to the transmission time. Information indicating an estimated transmission delay.

The packet loss rate information considers that packet loss has occurred when the corresponding encoded data packet cannot be received from the transmission server 6 even after a predetermined time has elapsed from the transmission time of the retransmission request packet, and the transmission server in units of a predetermined period. This is information indicating the packet loss rate measured based on the communication record with 6.

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

First, the transmission server 6 stores the coded data transmitted on the broadcast transmission line by the storage unit 61 while updating the coded data for a predetermined time (step S50). The coded data transmitted on the broadcast transmission line is error-correction-encoded data, and is composed of an error-correction code frame of a block code such as the LDPC code described in ARIB STD-B44.

The receiving device 5 receives and demodulates the digital broadcast transmitted on the broadcast transmission line, and attempts to correct the bit error of the encoded data. If the transmission environment is good and the data can be received without error, or if the influence of white noise or the like is within the range that can be decoded by the error correction code, the received data that has been error-corrected and decoded is output reproducibly. When the transmission environment is bad such as rainfall attenuation and the bit error of the coded data received via the broadcast transmission line cannot be corrected, the receiving device 5 generates a retransmission request packet for the corresponding coded data through the IP network 8. A retransmission request is made to the transmission server 6 (step S51). As described above, the retransmission request packet includes the retransmission request information and the communication quality information.

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

Subsequently, the retransmission request processing unit 63 encodes the coded data transmitted on the broadcast transmission line based on the communication quality information received this time according to a predetermined coding rate change standard managed by the communication quality management unit 65. It is determined whether or not to change the conversion rate and resend (step S54). The coding rate change standard will be described later with some examples.

Then, when the retransmission request processing unit 63 determines that the encoded data transmitted on the broadcast transmission line is to be retransmitted without changing the coding rate (step S54: No), the retransmission request processing unit 63 saves the data based on the retransmission request information received this time. The storage unit 61 and the coding rate adaptation change so that the location of the coded data related to the retransmission request is searched and read from the unit 61 and retransmitted at the same coding rate as the coding rate of the coded data transmitted on the broadcast transmission line. The unit 64 is controlled (step S55).

On the other hand, when the retransmission request processing unit 63 changes the coding rate of the coded data transmitted on the broadcast transmission line and determines that the data is to be retransmitted (step S54: Yes), the storage unit 63 is based on the retransmission request information received this time. The location of the coded data related to the retransmission request is searched from 61, and only the information bits (that is, the main signal in the block code) excluding the predetermined parity in the coded data are read out. Then, the retransmission request processing unit 63 changes the coding rate by distinguishing whether the coding rate is higher or lower than the coding rate of the coded data transmitted on the broadcast transmission line. That is, when the retransmission request processing unit 63 converts to a coding rate higher than the coding rate before the change, the information bit of the coded data is used as it is, and the coding rate is lower than the coding rate before the change. When converting, the information bit of the coded data is divided into two by a predetermined division method between transmission and reception. That is, when converting to a coding rate lower than the coding rate before the change, the number of information bits is larger than the number of information bits with respect to the changed coding rate, so the information bits are divided into two. Process so that the same code format as the error correction code standardized by the broadcasting standard can be applied. After that, when converting to a coding rate higher than the coding rate before the change, undivided, and when converting to a coding rate lower than the coding rate before the change, the information bits divided into two are used. For retransmission in which the padding bit known on the receiving device 5 side is added, the parity of the block code whose coding rate is changed from the coding rate of the coded data transmitted on the broadcast transmission line is added, and then the padding bit is removed. The storage unit 61 and the coding rate adaptation change unit 64 are controlled so as to generate the coded data of (step S56).

Finally, the transmission server 6 configures an interleave frame by the IP packet generation unit 62 using the error correction code frames for m frames, and interleaves in the direction of vertically traversing (orthogonal) the error correction code frames for m frames. Processes to generate an IP packet string (encoded data packet), and when the encoding rate is changed, a coding rate change notification packet is generated as a notification to that effect, and after transmission, the encoded data packet is received. Transmission to the device 5 (step S57). The transmission server 6 may be in a form of forming a coded data packet including the code rate information and transmitting the coded data packet to the receiving device 5. In this example, in order to improve the transmission efficiency of the coded data packet, when the code rate is changed, the receiving device 5 is notified in advance of the code rate change notification packet as a notification to that effect. ..

Further, the transmission server 6 may be configured to transmit the coding rate change notification packet a plurality of times, or may be configured to obtain a reception confirmation response of the coding rate change notification packet and receive a reception confirmation response from the receiving device 5. The code rate change notification packet may be repeatedly transmitted until it is received. 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 on the broadcasting transmission line, the receiving device 5 only has information on the coding rate on the broadcasting transmission line. The transmission server 6 may omit the advance notification of the coding rate change notification packet as long as it can grasp it, but regardless of whether the coding rate is changed or not, each time the coded data packet is retransmitted, the transmission server 6 may omit the advance notification. The coding rate change notification packet may be transmitted.

Here, the communication quality information acquired from the receiving device 5 includes one or both of the delay information of the communication line and the packet loss rate information, and which coding rate is based on these information. Whether to change to is performed according to a predetermined coding rate change standard managed by the communication quality control unit 65.

The coding rate change standard is based on the same coding method as the error correction coding method used by the error correction coding unit 21 in the transmission device 2 (or transmission device 3), and is based on the transmission device 2 (or transmission device 3) related to broadcasting. Of the predetermined number of coding rates that can be used in 3), the coding rate is changed by distinguishing whether the coding rate is higher or lower than the coding rate of the coded data transmitted on the broadcast transmission line. It has established.

For example, one of the following (1) to (9) can be used as the coding rate change criterion.
(1) Considering only the delay, when the delay obtained from the receiving device 5 is within the predetermined range of the predetermined default value, the data is retransmitted at the coding rate of the coded data transmitted on the broadcast transmission line. When the delay obtained from the receiving device 5 is less than the predetermined range of the predetermined default value, the code of the coded data transmitted on the broadcast transmission line among the multi-step coding rates determined according to the arbitrary delay. Change to the coding rate corresponding to the corresponding delay within the range higher than the conversion rate to improve the transmission efficiency, and if the delay obtained from the receiving device 5 exceeds the predetermined range of the predetermined default value, an arbitrary delay Of the multi-step coding rates determined according to the above, the delay is changed to the coding rate corresponding to the corresponding delay within the range lower than the coding rate of the coded data transmitted on the broadcast transmission line. Try to prevent resistance to packet loss due to it in advance.
(2) Considering only the packet loss rate, when the packet loss rate obtained from the receiving device 5 is within a predetermined range of a predetermined default value, the data is retransmitted with the coding rate of the coded data transmitted on the broadcast transmission line. When the packet loss rate obtained from the receiving device 5 is less than the predetermined range of the predetermined default value, the broadcast transmission line is among the multi-step coding rates determined according to the arbitrary packet loss rate. The packet loss rate obtained from the receiving device 5 is predetermined by changing to a coding rate corresponding to the corresponding packet loss rate within a range higher than the coding rate of the coded data transmitted in 1 to improve the transmission efficiency. When it exceeds the predetermined range of the default value, it corresponds within the range of the multi-step coding rate determined according to the arbitrary packet loss rate, which is lower than the coding rate of the coded data transmitted on the broadcast transmission line. Change the coding rate to correspond to the packet loss rate to increase the resistance to packet loss.
(3) Considering both the delay and the packet loss rate, the delay obtained from the receiving device 5 is within a predetermined range of a predetermined default value, or the packet loss rate obtained from the receiving device 5 is predetermined. When it is within the predetermined range of the default value, it shall be retransmitted with the coding rate of the coded data transmitted on the broadcast transmission line, and the delay obtained from the receiving device 5 is less than the predetermined range of the preset value and the reception is received. When the packet loss rate obtained from the device 5 is less than the predetermined range of the predetermined default value, the coding transmitted on the broadcast transmission line among the multi-step coding rates determined according to the arbitrary packet loss rate. The transmission efficiency is improved by changing to the coding rate corresponding to the corresponding packet loss rate within the range higher than the data coding rate, and the delay obtained from the receiving device 5 exceeds the predetermined range of the predetermined default value. And, when the packet loss rate obtained from the receiving device 5 exceeds the predetermined range of the predetermined default value, it is transmitted on the broadcast transmission line among the multi-step coding rates determined according to the arbitrary packet loss rate. Change to the coding rate corresponding to the corresponding packet loss rate within the range lower than the coding rate of the coded data to increase the resistance to packet loss.
(4) Considering only the delay, when the delay obtained from the receiving device 5 is within the predetermined range of the predetermined default value, the coded data transmitted on the broadcast transmission line shall be retransmitted at the coding rate. When the delay obtained from the receiving device 5 is less than the predetermined range of the predetermined default value, the coding is set higher by a predetermined step (for example, one step) within a range higher than the coding rate of the coded data transmitted on the broadcast transmission line. The transmission efficiency is improved by changing to a rate, and when the delay obtained from the receiving device 5 exceeds a predetermined range of a predetermined default value, it is within a range lower than the coding rate of the coded data transmitted on the broadcast transmission line. The coding rate is changed to a predetermined stage (for example, one stage) lower to prevent the resistance to packet loss due to the delay in advance.
(5) Considering only the packet loss rate, when the packet loss rate obtained from the receiving device 5 is within a predetermined range of a predetermined default value, the coded data transmitted on the broadcast transmission line is retransmitted at the coding rate. When the packet loss rate obtained from the receiving device 5 is less than a predetermined range of a predetermined default value, a predetermined stage (for example, a predetermined stage) is set within a range higher than the coding rate of the coded data transmitted on the broadcast transmission line. 1 step) Change to a higher coding rate to improve transmission efficiency, and when the packet loss rate obtained from the receiving device 5 exceeds the predetermined range of the preset default value, the code of the coded data transmitted on the broadcast transmission line. The coding rate is changed to a predetermined step (for example, one step) lower within the range lower than the conversion rate to increase the resistance to packet loss.
(6) Considering both the delay and the packet loss rate, the delay obtained from the receiving device 5 is within a predetermined range of a predetermined default value, or the packet loss rate obtained from the receiving device 5 is predetermined. When it is within the predetermined range of the default value, it shall be retransmitted with the coding rate of the coded data transmitted on the broadcast transmission line as it is, and the delay obtained from the receiving device 5 is less than the predetermined range of the preset value and the reception is received. When the packet loss rate obtained from the device 5 is less than the predetermined range of the predetermined default value, the code is one step higher (for example, one step) higher than the coding rate of the coded data transmitted on the broadcast transmission line. The transmission efficiency is improved by changing to the conversion rate, the delay obtained from the receiving device 5 exceeds the predetermined range of the predetermined default value, and the packet loss rate obtained from the receiving device 5 is the predetermined default value. When the range is exceeded, the coding rate is changed to a predetermined stage (for example, one stage) lower than the coding rate of the coded data transmitted on the broadcast transmission line to increase the resistance to packet loss.
(7) Considering only the delay, when the delay obtained from the receiving device 5 is within the predetermined range of the predetermined default value, the data is retransmitted at the coding rate of the coded data transmitted on the broadcast transmission line. When the delay obtained from the receiving device 5 is less than the predetermined range of the predetermined default value, the code of the maximum value that can be used by the transmitting device 2 (or the transmitting device 3) related to the coded data transmitted on the broadcast transmission line. When the delay obtained from the receiving device 5 exceeds the predetermined range of the predetermined default value by changing to the conversion rate to improve the transmission efficiency, the transmitting device 2 (or the transmitting device) related to the coded data transmitted on the broadcast transmission line. The coding rate is changed to the minimum value that can be used in 3) so that the tolerance against packet loss due to the delay is prevented in advance.
(8) Considering only the packet loss rate, when the packet loss rate obtained from the receiving device 5 is within a predetermined range of a predetermined default value, the coded data transmitted on the broadcast transmission line is retransmitted as the coding rate. When the packet loss rate obtained from the receiving device 5 is less than the predetermined range of the predetermined default value, it can be used by the transmitting device 2 (or the transmitting device 3) related to the coded data transmitted on the broadcast transmission line. When the packet loss rate obtained from the receiving device 5 exceeds the predetermined range of the predetermined default value, the coded data transmitted on the broadcast transmission line is used. The coding rate is changed to the minimum value that can be used by the transmitting device 2 (or the transmitting device 3) to increase the resistance to packet loss.
(9) Considering both the delay and the packet loss rate, the delay obtained from the receiving device 5 is within a predetermined range of a predetermined default value, or the packet loss rate obtained from the receiving device 5 is predetermined. When it is within the predetermined range of the default value, it shall be retransmitted with the coding rate of the coded data transmitted on the broadcast transmission line as it is, and the delay obtained from the receiving device 5 is less than the predetermined range of the preset value and the reception is received. When the packet loss rate obtained from the device 5 is less than the predetermined range of the predetermined default value, the maximum value that can be used by the transmission device 2 (or the transmission device 3) related to the coded data transmitted on the broadcast transmission line. The transmission efficiency is improved by changing to the coding rate, the delay obtained from the receiving device 5 exceeds the predetermined range of the predetermined default value, and the packet loss rate obtained from the receiving device 5 is the predetermined default value. When it exceeds a predetermined range, the coding rate is changed to the minimum value that can be used by the transmitting device 2 (or the transmitting device 3) related to the coded data transmitted on the broadcast transmission line to improve the resistance to packet loss. ..

(Method of generating coded data when changing the code rate: When changing to a higher code rate)
With reference to FIG. 4, when the coded data related to the retransmission request is changed to a higher code rate, the retransmission request processing unit 63 changes the code rate adaptation to the storage unit 61 and the code rate according to the coding rate change standard exemplified above. An example of controlling the unit 64 to generate the coded data when the code rate is changed will be described. 4 (a) to 4 (d) show a higher code for the coded data related to the retransmission request when the code rate is changed by the code rate adaptive change unit 64 in the transmission server 6 of the embodiment according to the present invention, respectively. It is a figure which shows the generation method of the coded data (at the time of changing to the conversion rate).

First, FIG. 4A is a diagram showing a configuration of an error correction code frame of a block code showing coded data transmitted on a broadcast transmission line. Usually, in digital broadcasting, a plurality of types of selectable coding rates are predetermined. For example, in ARIB STD-B44, among the LDPC codes which are block codes, 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 (≈) Eleven types of coding rates of 5/6), 105/120 (≈7 / 8), and 109/120 (≈9 / 10) are specified.

Information on the coding rate of the coded data transmitted on the broadcast transmission line is usually transmitted as a TMCC (Transmission and Multiplexing Configuration Control) signal, which is a transmission control signal in digital broadcasting, but is transmitted from the transmission server 6. It may be configured to notify in advance via the IP network 8. Further, as described above, regarding the information on the coding rate of the coded data to be retransmitted in response to the retransmission request, the transmission server 6 indicates that when the coding rate is changed by the IP packet generation unit 62. After generating and transmitting the code rate change notification packet as a notification, or including the code rate information, the coded data packet is transmitted to the receiving device 5. Here, 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 on the broadcasting transmission line, the receiving device 5 has information on the coding rate on the broadcasting transmission line. Since it is only necessary to know only the transmission server 6, the transmission server 6 may omit the advance notification of the code rate change notification packet.

_{As shown in FIG. 4A, where F b} is the coding rate of the coded data in the block code of the code length N bits transmitted on the broadcast transmission line, the information bit of the coded data (that is, in the block code). The main signal) is composed of N × F _b bits, and the parity is composed of N × (1-F _b ) bits. Normally, when a block code is used on a broadcast transmission line, the number of bits of the code length of the error correction code frame is often constant regardless of the coding rate so that it can be easily handled on the broadcast transmission line. 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, the coding rate of the coded data to be retransmitted via the IP network 8 When F _i, the encoded data transmitted by the broadcast transmission channel as coding rate F _i of the coded data to be retransmitted over IP rope 8 when changing higher than the coding rate, the information bits transmitted by the broadcast transmission path used as it is, into a coding rate F _i.

Therefore, the transmission server 6 that has received the retransmission request packet from the receiving device 5 extracts the communication quality information included in the retransmission request packet by the retransmission request processing unit 63, and based on the communication quality information, the communication quality management unit 65. It is determined whether or not to change the coding rate by referring to the coding rate change standard managed in.

Then, the retransmission request processing section 63, when it is determined to change the coding rate F _b of the transmission encoded data in a broadcast transmission path to the coding rate F _i is (F b _{<F i),} First, FIG. 4 ( Of the coded data of N bits of code length related to the retransmission request shown in a), _{only the information bit of N × F b} bits (that is, the main signal in the block code) is read out from the storage unit 61 (FIG. 4 (b). )reference).

Subsequently, the retransmission request processing unit 63 controls the coding rate adaptation change unit 64, and the N × F _b bit information bit (that is, in the block code) read from the storage unit 61 by the error correction coding unit 643. with respect to the main signal), it is added to a known value (e.g., insertion location to known between transmission and reception of N × (F i _{-F b)} bits with all zero bits) as padding bits between transmission and reception, this It applies error correction coding processing as a coding rate F _i to the information bits and padding bits, generates parity of N × (1-F _i) bits (see FIG. 4 (c)). For example, error correction coding unit 643, a coding rate F _i, N × F _b information bits (i.e., main signal in the block code) while using a transmission apparatus 2 (or transmitted from the coding rate F _b The code rate is changed to the maximum value that can be used in the device 3). In this example, the padding bit is added after the information bit, but the padding bit may be added before the information bit, that is, the insertion position of the padding bit is the code after the change. it is sufficient to set in advance as known between transmission and reception by the value of the ratio F _i.

Then, the error correction coding unit 643 removes the padding bit and reconstructs the coded data for retransmission in which the parity of the N × (1- _{Fi ) bit is added to the information bit of the N × F b bit.} , Is output to the IP packet generation unit 62 (see FIG. 4D). Since the frame length of the reconstructed coded data for retransmission is shorter than the original code length N bits, the transmission efficiency is higher than when the coded data for the code length N bits is retransmitted to the receiving device 5. It gets higher.

(Method of generating coded data when changing the code rate: When changing to a lower code rate)
Next, referring to FIG. 5, when the coded data related to the retransmission request is changed to a lower coding rate, the retransmission request processing unit 63 encodes the storage unit 61 and the code according to the coding rate change standard exemplified above. An example of controlling the rate adaptation changing unit 64 to generate the coded data at the time of changing the coding rate will be described. 5 (a) to 5 (e) show a lower code for the coded data related to the retransmission request when the code rate is changed by the code rate adaptive change unit 64 in the transmission server 6 of the embodiment according to the present invention, respectively. It is a figure which shows the generation method of the coded data (at the time of changing to the conversion rate).

As shown in FIG. 5 (a), when the coding rate of the coded data in the block code having a code length N bits transmitted by the broadcast transmission path to F _b, the information bits of the encoded data (i.e., the block code The main signal) is composed of N × F _b bits, and the parity is composed of N × (1-F _b ) bits. Normally, when a block code is used on a broadcast transmission line, the number of bits of the code length of the error correction code frame is often constant regardless of the coding rate so that it can be easily handled on the broadcast transmission line. 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 to F _i, the information bits of the coding rate F _i Ordinarily N × F _i, parity, N × (1-F _i) becomes a bit, to become excessive relative to the coding length of the error correction code standards broadcasting standards, broadcast code rate F _i of the coded data to be retransmitted over IP rope 8 in this embodiment When changing the coding rate of the coded data transmitted on the transmission line to _{less than F b} , the original information bit is divided into two equal parts so that the code is stored in the code length of the error correction code standardized by the broadcasting standard. Reconfigure and reconstruct the encoded data.

More specifically, first, the transmission server 6 that has received the retransmission request packet from the receiving device 5 extracts the communication quality information included in the retransmission request packet by the retransmission request processing unit 63, and based on the communication quality information. , It is determined whether or not to change the coding rate with reference to the coding rate change standard managed by the communication quality control unit 65.

For example, assuming that the code rate change criterion of (9) above is followed, the retransmission request processing unit 63 has a delay obtained from the receiving device 5 that is less than a predetermined default value, or a packet loss rate obtained from the receiving device 5. If is less than the predetermined default value, it is determined that there is no change in the coding rate of the coded data transmitted on the broadcast transmission line (F _b = _Fi ), and the retransmission request shown in FIG. 5 (a) is concerned. The coding rate adaptation changing unit 64 is controlled so that the coded data having a code length of N bits is read from the storage unit 61 and output to the IP packet generation unit 62 as it is.

On the other hand, when the delay obtained from the receiving device 5 is equal to or more than a predetermined default value and the packet loss rate obtained from the receiving device 5 is equal to or more than a predetermined default value, the retransmission request processing unit 63 performs a broadcast transmission line. in determining the coding rate F _b of the transmission encoded data to change the coding rate _{F i (F b> F i} ), first, the code length N-bit code according to the retransmission request shown in FIG. 5 (a) Of the converted data, only the N × F _b bit information bit (that is, the main signal in the block code) is read from the storage unit 61 (see FIG. 5B).

Subsequently, the retransmission request processing unit 63 controls the coding rate adaptation change unit 64, and the N × F _b bit information bit (that is, in the block code) read from the storage unit 61 by the error correction coding unit 643. The main signal) is divided into two between transmission and reception by a predetermined division method ((N × F _b ) / 2). Here, an example is made in which the first half and the second half of the information bit position are divided into two equal parts (see FIG. 5C), but even if other division methods are used, such as dividing into two by odd-numbered bits and even-numbered bits. good.

Subsequently, the retransmission request processing unit 63 controls the coding rate adaptation change unit 64, and for each of the information bits ((N × F _b ) / 2) divided into two, a value known between transmission and reception ( For example, N × F _i − ((N × F _b ) / 2) bits (all 0 bits) are added as padding bits to the insertion positions known between transmission and reception, and the information bits and padding bits are used. applies error correction coding processing as a coding rate _{F i,} to generate the parity of N × _{(1-F i)} bits (see FIG. 5 (d)). For example, error correction coding unit 643, a coding rate F _i, N × F _b information bits (i.e., main signal in the block code) while using a transmission apparatus 2 (or transmitted from the coding rate F _b Change to the minimum code rate that can be used in device 3). In this example, the padding bit is added after the information bit, but the padding bit may be added before the information bit, that is, the insertion position of the padding bit is the code after the change. it is sufficient to set in advance as known between transmission and reception by the value of the ratio F _i.

Then, the error correction coding unit 643 removes the padding bit and adds the parity of N × (1- _{Fi ) bit to the information bit of (N × F b} ) / 2 bit to encode the coded data for retransmission. Is reconfigured and output to the IP packet generation unit 62 (see FIG. 5E). The frame length of the reconstructed coded data for retransmission is shorter than the original code length N bits, does not exceed the code length of the error correction code standardized by the broadcasting standard, and the retransmission request. The coded data according to the above can be changed to a lower coding rate, and the correction capability is higher than in the case of retransmitting without changing the coding rate.

In this way, when the transmission server 6 receives the retransmission request packet, it is encoded by adaptively changing the coding rate of the encoded data related to the retransmission request based on the communication quality information included in the retransmission request packet. A data packet is generated and transmitted to the receiving device 5.

(How to generate a coded data packet)
The transmission server 6 is an IP packet generation unit in order to achieve high correction performance even for burst packet loss caused by the IP line 8 when transmitting the encoded data requested to be retransmitted to the receiving device 5 through the IP network 8. According to 62, an n × m interleave frame described later is constructed with reference to FIG. 6, an IP packet sequence with an identification header, a sequence number, and an IP header is generated, and the transmission order of IP packets is interleaved according to the sequence number. Then, it is preferable to transmit the encoded data packet to the receiving device 5.

More specifically, with reference to FIG. 6, a method of generating an IP packet of the IP packet generation unit 62 in the transmission server 6 will be described. 6 (a) to 6 (d) are explanatory views of an IP packet generation method of the IP packet generation unit 62 in the transmission server 6 of the embodiment according to the present invention, respectively.

First, IP packet generating unit 62, a coding rate adaptively changing unit 64, respectively constituted by code length n bits of the same code rate F _i, the synchronization signal related to the retransmission request (frame number or time information) An error correction code frame for m frames having a continuous synchronization signal (frame number or time information) is input starting from the error correction code frame that constitutes the coded data to form an n × m interleaved frame. Although m is a fixed value, it can be variably set from the outside and is a value shared between transmission and reception. Further, an n = N when code length n bits of code rate F _i has not changed since the code length N bits of encoded rate F _b used in the broadcast transmission path, the code length of the code rate F _b When changed from N bits, n <N.

Therefore, the IP packet generation unit 62 temporarily stores the error correction code frames of m frames including the error correction code frames as the coded data related to the retransmission request in the storage unit (not shown) so as to be arranged in the vertical direction (not shown). See FIG. 6 (a)).

Subsequently, the IP packet generation unit 62 reads each bit from the beginning into the error correction code frame of the m frame by the interleaving unit 621, and n packets the m-bit IP payload as the packet length excluding the header of the generated IP packet. Minutes are generated (see FIG. 6B). That is, of the 1 to n bits of each error correction code frame, the same bit of each bit is collected one by one and used as m bits, which is used as an IP payload.

Subsequently, the IP packet generation unit 62 includes an identification header for making each interleave frame related to the interleave processing identifiable on the receiving device 5 side in the IP payload for n packets generated by the interleave unit 621, and each error. An IP packet for n packets is generated by adding a sequence number for specifying which bit is represented in the correction code frame and an IP header as a header of the coded data packet (see FIG. 6C). In this example, the sequence numbers are represented as 1 to n in an easy-to-understand manner, but the expression form can be used to identify which bit of the error correction code frame each IP packet represents for the receiving device 5. Is optional.

Further, as shown in FIG. 6B, one interleaved frame is composed of IP payloads for n packets generated from a plurality of error correction code frames. Therefore, if the IP packet generation unit 62 assigns, for example, ID = "1" to the identification header added to a certain interleaved frame, ID = "2" is assigned to the identification header added to the next interleaved frame. The identification header to be added to the next interleaved frame is assigned while incrementing ID = "3" so that the interleaved frame to which the ID = "3" belongs can be identified by the value of the identification header. Therefore, as shown in FIG. 6 (c), the identification headers are added so as to have the same value in one interleaved frame. Therefore, on the receiving device 5 side, by referring to the identification header, it becomes possible to identify which interleaved frame the IP payload of the received encoded data packet belongs to.

Subsequently, the IP packet generation unit 62 interleaves the generated n packets of IP packets by the interleaving unit 621 in the order of transmission to the IP network 8 according to the sequence number based on a predetermined rule (for example, ascending order of the sequence number). It may be transmitted in, or it may be a transmission order of another sequence number determined between transmission and reception), and it is transmitted to the receiving device 5 as a coded data packet.

The IP packet generation unit 62 in the present embodiment needs m (m is an integer of 1 or more) error correction code frames including the error correction code frames as the coded data related to the retransmission request, in other words. For example, the interleaving unit 621 cannot execute the interleaving process until the error correction code frames for m frames are aligned. Therefore, when time loss becomes a problem, only n1 (<n) as the sequence number of the n-bit error correction code frame related to the retransmission request is used as the sequence number, and m (m is an integer of 1 or more). The total number of IP packets holding the corresponding sequence number may be reduced by extracting from the error correction code frame. Then, m and n are fixed values but can be variably set from the outside, so that the packet length of each IP packet can be adjusted.

Further, although the IP packet is generated by collecting one bit from each error correction code frame, it is also possible to collect a plurality of bits from each error correction code frame. Conversely, it is possible to treat two frames of error correction code frames as one frame, or to generate 2n m-bit packets. The IP payload for n packets generated in this way is regarded as one interleaved frame, and an identification header for making each interleaved frame identifiable on the receiving device 5 side and a sequence number for identifying each IP payload are assigned. That is, other interleaving techniques should be applied if the transmission order of each bit of the error correction code frame is rearranged so that the packet loss in the IP network 8 can be assumed in advance and alleviated. Is possible. Generally, the longer the period (signal length) targeted for interleaving processing, the more resistant to burst packet loss. Therefore, the optimum interleaving processing should be executed within an acceptable period for the entire transmission system 1. The interleave unit 621 is configured.

[Receiver]
FIG. 7 is a block diagram showing a schematic configuration of the receiving device 5 according to the embodiment of the present invention. The receiving device 5 includes a demodulation unit 51, an error correction decoding unit 52, a retransmission request packet generation unit 53, an IP packet reception unit 54, a switching unit 55, and a communication quality measurement unit 56.

The demodulation unit 51 receives the modulated wave signal radiated from the transmission device 2 (or the transmission device 3) via the broadcast transmission line (satellite broadcast transmission line or terrestrial broadcast transmission line), demodulates the signal, and obtains the demodulation process. The coded data is output to the error correction decoding unit 52 via the switching unit 55.

The error correction decoding unit 52 calculates the log-likelihood ratio (LLR) of each bit of the coded data obtained from the demodulation unit 51 in advance of the decoding process of the error correction code, and this prior log-likelihood ratio. Using the degree ratio (pre-LLR), the error correction code frame constituting the code length of the error correction code is reconstructed, and the decoding process corresponding to the error correction coding process in the transmission device 2 (or the transmission device 3) is performed. It is a decoder that generates received data and outputs it to the outside for reproducibility.

Here, the error correction decoding unit 52 includes a decoding possibility determination unit 521, a coded data complementing unit 522, and a data combining unit 523.

The decoding passability determination unit 521 determines whether or not the coded data constituting the error correction code frame can be error-corrected and decoded, and when it is determined that the coded data can be decoded, the coded data is decoded as it is to generate the received data, and the bit error of the coded data is generated. If it is determined that the data cannot be corrected and cannot be decoded, the retransmission request information for the coded data constituting the error correction code frame is output to the retransmission request packet generation unit 53. In the data transmission method using the broadcast transmission line, the coded data of the error correction code frame unit obtained by the receiving device 5 sequentially receiving via the demodulator 51 is included in the TMCC signal or the main signal transmitted together. Since it can be identified based on the time information to be transmitted and can be managed by a synchronization signal (frame number or time information) like the transmission server 6, this retransmission request information is an error correction code for retransmitting as a synchronization signal. It may include time information that makes the frame identifiable, or it may include the frame number.

The coded data complementing unit 522 extracts the coded data related to the retransmission request from the coded data packet received from the transmission server 6 in response to the transmission of the retransmission request packet by the retransmission request packet generation unit 53, and performs the error. This is a functional unit that complements the coded data in the correction code frame so that it can be used for decoding.

Then, the error correction / decoding unit 52 complements the coded data acquired via the IP network 8 with respect to the coded data in the error correction code frame by the function of the coded data complementing unit 522, and corrects the error within a predetermined time. It is configured to repeat the request for retransmission of the selected coded data in the error correction code frame until it can be decoded by the code decoding process.

When the coded data related to the retransmission request is changed to a lower coding rate and the information bits are divided, the data combining unit 523 previously transmits the divided decoded information bits to and from the transmission server 6. It is a functional unit that generates received data by recombining according to the specified division method.

If the error correction decoding unit 52 cannot decode the data within a predetermined time by the decoding process, the error correction decoding unit 52 generates the received data in a state including a bit error.

Further, in this example, when the transmission server 6 changes the coding rate of the coded data to be retransmitted, a coding rate change notification packet is generated as a notification to that effect, and after transmission, the coded data packet is received. It transmits to the device 5. Therefore, the error correction decoding unit 52 uses the function of the coded data complementing unit 522 to determine the coding rate of the coded data obtained via the IP network 8 based on the presence or absence of the code rate change notification when the broadcast is received. It is determined whether or not the data is different from the above, padding bits are added as appropriate according to the coding rate, and complementary processing for replacement of the likelihood ratio required for decoding is performed.

When the retransmission request packet generation unit 53 determines that the decoding is not possible by the decoding passability determination unit 521, the retransmission request packet generation unit 53 requests the transmission server 6 to retransmit the encoded data in the error correction code frame, so that the encoded data is transmitted. A retransmission request packet in the form of an IP packet including the retransmission request information indicating that the retransmission is requested and the communication quality information obtained from the communication quality measurement unit 56 is generated and transmitted to the transmission server 6 via the IP network 8. It is a functional part.

The IP packet receiving unit 54 receives the encoded data packet of the IP packet string storing the encoded data retransmitted in response to the retransmission request packet from the transmission server 6, and receives the encoded data related to the retransmission request. This is a functional unit that acquires and outputs the data to the error correction / decoding unit 52 via the switching unit 55. The IP packet receiving unit 54 uses the identification header and the sequence number to perform reverse processing of the interleaving unit 621 on the transmitting server 6 side to reconstruct the encoded data retransmitted in response to the retransmission request. It has a part 541.

The switching unit 55 switches and controls the reception path of the coded data by the reception path switching signal by the error correction decoding unit 52. That is, the switching unit 55 operates so as to input the coded data, which is mainly transmitted via the broadcast transmission line and demodulated by the demodulation unit 51, to the error correction / decoding unit 52. However, when the error correction / decoding unit 52 determines that the coded data obtained via the broadcast transmission line cannot be decoded by the decoding passability determination unit 521, the switching unit 55 is controlled by the reception path switching signal by the error correction / decoding unit 52. Then, the coded data retransmitted via the IP network 8 and obtained from the IP packet receiving unit 54 is input to the error correction decoding unit 52 until it can be decoded by the error correction code decoding process within a predetermined time. Further, the error correction decoding unit 52 encodes the code obtained via the broadcast transmission line when the error correction code can be decoded by the error correction code decoding process within the predetermined time by the reception path switching signal, or after the predetermined time has elapsed. The switching unit 55 is switched and controlled so that the data is input to the error correction decoding unit 52.

The communication quality measurement unit 56 measures either one or both of the delay related to communication with the transmission server 6 and the packet loss rate based on the amount of packet loss generated related to communication with the transmission server 6 in units of predetermined periods. This is a functional unit that sequentially outputs communication quality information including one or both of the delay information and the packet loss rate information of the communication line to the retransmission request packet generation unit 53 while holding the update.

As described above, the delay information of the communication line includes the transmission time of the retransmission request packet transmitted from the receiving device 5 to the transmitting server 6 and the reception of the encoded data packet retransmitted from the transmitting server 6 correspondingly. This is information indicating the transmission delay estimated by the time difference from the time.

Further, the packet loss rate information is regarded as a packet loss when the corresponding encoded data packet cannot be received from the transmission server 6 even after a predetermined time has elapsed from the transmission time of the retransmission request packet, and the packet loss rate information is in units of a predetermined period. This is information indicating the packet loss rate measured based on the communication record.

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

First, the receiving device 5 receives and demodulates the modulated wave signal radiated from the transmitting device 2 (or the transmitting device 3) via the broadcasting transmission line (satellite broadcasting transmission line or terrestrial broadcasting transmission line) by the demodulation unit 51. Then, the coded data obtained by this demodulation process is output to the error correction decoding unit 52 via the switching unit 55 (step S1). As described above, the switching unit 55 is controlled by the error correction / decoding unit 52.

Subsequently, the receiving device 5 reconstructs the error correction code frame by calculating the pre-LLR of each bit of the coded data obtained by the demodulation process by the error correction decoding unit 52, and the transmitting device 2 (or the transmitting device 5). The decoding process corresponding to the error correction coding process in 3) is executed (step S2).

Here, the error correction decoding unit 52 determines whether or not the coded data obtained from the transmission device 2 (or the transmission device 3) can be error-corrected and decoded by the decoding possibility determination unit 521 (step S3), and can decode the coded data. When it is determined, it is decoded as it is and the received data is reproducibly generated (step S3: No), and since the current reception route is not via the IP network 8 (step S9: No), the switching unit is used as the reception route for broadcasting and receiving as it is. The setting of 55 is maintained, and the process shifts to the demodulation / decoding process for the next coded data in chronological order. That is, the error correction decoding unit 52 attempts to decode the coded data obtained from the transmission device 2 (or the transmission device 3), and when there is no bit error or the bit error is within the correctable range. , Decrypt as it is and generate the received data reproducibly.

On the other hand, when the error correction decoding unit 52 determines that the decoding passability determination unit 521 cannot decode the coded data constituting the error correction code frame, the error correction decoding unit 52 retransmits the coded data constituting the error correction code frame. The request information is generated, output to the retransmission request packet generation unit 53, and instructed to generate a retransmission request packet indicating the retransmission request of the encoded data (step S3: Yes). Further, the decoding possibility determination unit 521 controls the switching unit 55 to switch to the reception path for inputting the coded data to the error correction decoding unit 52 via the IP network 8.

When the retransmission request packet generation unit 53 determines that the decoding is not possible by the decoding possibility determination unit 521, the retransmission request information and the retransmission request information are used to request the transmission server 6 to retransmit the coded data in the error correction code frame. , A retransmission request packet in the form of an IP packet including the communication quality information obtained from the communication quality measurement unit 56 is generated, and is transmitted to the transmission server 6 via the IP network 8 (step S4). Here, the communication quality information includes one or both of the delay information of the communication line and the packet loss rate information.

Therefore, when the transmission server 6 receives the retransmission request packet from the receiving device 5, the transmission server 6 extracts the retransmission request information and the communication quality information from the retransmission request packet, and changes the coding rate predetermined based on the communication quality information. According to the standard, it is decided whether or not to change the coding rate, and if so, which coding rate to change. As described above, the coding rate change standard is based on the same coding method as the error correction coding method used by the error correction coding unit 21 on the transmitting side, and is predetermined to be usable in the transmitting device 2 related to broadcasting. Among the code rates of the number of types, it is stipulated that the code rate is changed by distinguishing whether the code rate is higher or lower than the code rate of the coded data transmitted on the broadcast transmission line. Further, the transmission server 6 has a continuous synchronization signal (frame number or time information) starting from the error correction code frame constituting the coded data having the synchronization signal (frame number or time information) related to the retransmission request. Frame error correction A code frame is formed with 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, and the interleaved frame is m-frame error. An interleaving process is performed in a direction orthogonal to the correction code frame to generate a coded data packet of an IP packet string, which is transmitted to the receiving device 5 via the IP network 8. Further, when the coding rate is changed, the transmission server 6 generates a coding rate change notification packet as a notification indicating that fact, transmits the coded data packet, and then transmits the coded data packet. Therefore, the receiving device 5 determines whether or not the coding rate of the coded data obtained via the IP network 8 is different from that at the time of broadcasting reception by the IP packet receiving unit 54 and the error correction decoding unit 52. can.

Therefore, the receiving device 5 transmits the retransmission request packet to the transmitting server 6, and then the error correction code for m frames including the coded data of the decoding target retransmitted from the transmitting server 6 in response to the retransmission request packet. Upon receiving the coded data packet (IP packet string) of the frame, the deinterleave unit 541 performs reverse processing of the interleave unit 621 on the transmission server 6 side by using the identification header and the sequence number given to the IP packet. Then, the encoded data resent in response to the retransmission request is reconstructed and output to the error correction decoding unit 52 (step S5).

Subsequently, the receiving device 5 determines whether or not the coding rate of the coded data obtained via the IP network 8 is different from that at the time of broadcasting reception by the coded data complementing unit 522 in the error correction decoding unit 52 ( In step S6), when the coding rate of the coded data obtained via the IP network 8 is different from that at the time of receiving the broadcast (step S6: Yes), the code rate shown in FIG. 4 (d) or FIG. 5 (e) is In order to restore the changed error correction code frame, a padding bit known between transmission and reception according to the coding rate is added to an insertion position known between transmission and reception (step S7).

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

Subsequently, the coded data complementing unit 522 complements the coded data acquired via the IP network 8 so as to be used for the decoding process of the coded data in the error correction code frame (step S8). More specifically, the error correction / decoding unit 52 is configured as an error correction / decoding device for the block code, and in order to perform decoding using the log-likelihood ratio, the coded data complementing unit 522 acquires the data via the IP network 8. For the coded data, the log-likelihood ratio when the bit value is 0 is + ∞ (maximum value as the certainty of "0"), and the log-likelihood ratio when the bit value is 1 is-. ∞ (maximum value as the certainty of "1"), If packet loss occurs and a non-reachable bit occurs, it is complemented by replacing the log-likelihood ratio with 0.

Then, the error correction decoding unit 52 repeats the request for retransmission of the coded data (steps S2 to S8) until it can be decoded by the decoding process of the error correction code within a predetermined time, and based on the coded data that can be decoded. After the reception data is generated, when the current reception path is via the IP network 8 (step S9: Yes), the switching unit 55 is switched and controlled so as to switch the reception path to reception via the broadcast transmission line (step S10). ), In the time series, it shifts to the demodulation / decoding process for the next coded data. If the error correction decoding unit 52 cannot decode the data within a predetermined time by the decoding process, the error correction decoding unit 52 generates the received data in a state including the bit error, proceeds to step S9, controls the switching unit 55, and broadcasts. Switch the reception path to reception via the transmission line.

When the coded data related to the retransmission request is changed to a lower coding rate and the information bits are divided, the error correction decoding unit 52 obtains both of the coded data of the divided individual information bits. , The request for retransmitting the coded data transmitted on the broadcast transmission line is repeated until it can be decoded by the decoding process of the error correction code within a predetermined time. Then, when the error correction decoding unit 52 can decode both of the coded data of the divided individual information bits, the function of the data combining unit 523 transmits the divided decoded information bits. Received data is generated by recombining with the server 6 according to a predetermined division method.

By the way, as the retransmission request packet, a non-delivery notification packet generally used in the IP packet format can be used, and the encoded data packet is configured to perform retransmission in response to the non-delivery notification packet. Therefore, the error correction decoding unit 52 can replace the coded data obtained from the demodulation unit 51 with the coded data obtained by retransmission, and perform decoding again, and receive data within a predetermined time. It is possible to output reproducibly by repeatedly requesting retransmission until the data can be restored.

As described above, in the transmission system 1 shown in FIG. 1, when the transmission conditions deteriorate to the extent that data cannot be restored by the error correction code due to attenuation or fading due to rainfall, the receiving device 5 transmits the transmission server 6 through the IP network 8. Requests the retransmission of the coded data corresponding to. The transmission server 6 describes the coded data encoded by the same error correction code encoder (that is, the error correction coding unit 21) as when transmitted by the transmission device 2 (or the transmission device 3) via the broadcast transmission line. , The coding rate is adaptively changed according to the communication quality information, and transmitted to the receiving device 5 via the IP network 8.

The receiving device 5 complements the code bits acquired via the IP network 8 with respect to the coded data that could not be decoded by the decoder of the same error correction code as when it was received by radio waves (that is, the error correction decoding unit 52). Then try decoding again to restore the received data. Even when there is a lot of data lost via radio waves or when the IP network 8 is also considered to be a lost communication path and some data is lost, the receiving device 5 repeatedly requests retransmission until the received data can be restored within a predetermined time. By performing, it is possible to output reproducibly.

In particular, the data retransmitted by the transmission server 6 via the IP network 8 is used as the coded data in the block code of digital broadcasting, and the coded data is variably controlled to the coding rate according to the communication quality of the IP network 8. As a result, the number of retransmission requests can be reduced, and the transmission efficiency via the IP network 8 can be improved. Further, by using the same standardized code for the error correction code used for broadcasting and the error correction code used for transmission via the IP network 8, the receiving device 5 can be realized by preparing only one error correction decoder. The equipment scale can be reduced.

<Example>
Hereinafter, a more specific embodiment in which the transmission system 1 is configured for advanced wideband satellite digital broadcasting will be described.

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

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

Further, in the transmission system 1 illustrated in FIG. 9, an example in which the transmission device 2 and the transmission server 6 are separately connected by a local area network will be described, but the transmission device 2 is provided with the transmission server 6 and has a local area. Instead of connecting with a network, a simple signal cable may be used for connection.

The transmission device 2 illustrated in FIG. 9 is configured in the same manner as in FIG. 2 described above, and performs error correction coding processing on the transmission data related to digital broadcasting to impart error correction code parity (LDPC parity and BCH parity). This generates coded data, digitally modulates the coded data by a predetermined modulation method to generate a modulated wave signal, and a broadcast transmission line of an advanced broadband satellite digital broadcast including a broadcast satellite 4 via a transmission antenna 2a. It emits radio waves related to digital broadcasting via. In the advanced broadband satellite digital broadcasting, the number of bits for one frame of coded data is 44,880 bits, and the LDPC code is used as the internal code and the BCH code is used as the external code as the error correction coding process. Further, the transmission device 2 manages the sequentially generated coded data as an error correction code frame, adds a synchronization signal (frame number or time information), and transmits the coded data to the transmission server 6.

The receiving device 5 illustrated in FIG. 9 is configured in the same manner as in FIG. 7 described above, receives a modulated wave signal radiated from the transmitting device 2 via the receiving antenna 5a, demodulates the signal, and corrects an error in the transmitting device 2. Decoding processing corresponding to the coding processing is performed to generate received data so that it can be played back.

Further, the receiving device 5 determines whether or not the coded data obtained from the transmitting device 2 can be error-corrected and decoded, and when it is determined that the coded data can be decoded, the coded data is decoded as it is to generate the received data, and a bit error of the coded data is generated. If it is determined that the data cannot be corrected and cannot be decoded, a retransmission request packet in the form of an IP packet requesting retransmission of the corresponding encoded data is generated, and the retransmission request packet includes communication quality information and passes through the IP network 8. , Has a function of transmitting to the transmission server 6. Further, the receiving device 5 receives the encoded data retransmitted from the transmitting server 6 in response to the retransmission request in response to the retransmission request packet (encoding data transmitted on the broadcast transmission line according to the communication quality information on the transmitting server 6 side). (Reconstructed by changing the coding rate adaptively by distinguishing whether it is higher or lower than the coding rate of), the encoded data packet in the IP packet format is received, and the retransmission request is made. The coded data retransmitted according to the above is extracted and complemented according to the coding rate so as to be used for the decoding process, and the request for retransmitting the corresponding coded data is repeated until the decryption process can be performed within a predetermined time. When the coded data related to the retransmission request is changed to a lower coding rate and the information bits are divided, the divided decrypted information bits are transferred to and from the transmission server 6 according to a predetermined division method. It has a function of recombining to generate received data. If the receiving device 5 cannot decode the data within a predetermined time by the decoding process, the receiving device 5 generates the received data in a state including a bit error.

The transmission server 6 is configured in the same manner as in FIG. 2 described above, sequentially inputs the coded data generated by the transmission device 2, and manages the coded data in time series by the synchronization signal (frame number or time information) of the error correction code frame. Generates an IP packet format encoded data packet that stores the encoded data related to the retransmission request in response to the retransmission request packet received from the receiving device 5 via the IP network 8 with the function of saving while updating the predetermined time. Then, it has a function of transmitting data to the receiving device 5 via the IP network 8.

Therefore, in the present embodiment, the transmitting device 2 generates a modulated wave signal after performing error correction coding processing of the advanced broadband satellite digital broadcasting on the transmission data related to the digital broadcasting, and the broadcasting satellite 4 passes through the transmitting antenna 2a. Send via. The receiving device 5 first demodulates the modulated wave signal of the advanced broadband satellite digital broadcast received from the receiving antenna 5a, and attempts to restore the received data by error correction / decoding processing. The receiving device 5 restores the received data from the coded data and makes it playable as it is when the transmission environment is good and the data can be received without error, or when the influence of white noise or the like is within the range that can be decoded by the error correction code. .. When the transmission environment is poor such as rainfall attenuation and the coded data deteriorates to the extent that it cannot be decoded by the error correction code, the receiving device 5 operates in cooperation with the transmitting device 2 for the corresponding coded data through the IP network 8. Make a resend request to.

When a retransmission request is made from the receiving device 5 to the transmitting server 6 through the IP network 8, the transmitting server 6 variably controls the coding rate of the coded data after the error correction coding process according to the communication quality information, and the IP network. Retransmit to the receiving device 5 via 8. The receiving device 5 generates coded data that complements the coded data obtained from the IP network 8 and executes error correction / decoding processing to restore the received data and make it playable.

(Example: Reception control flow in a receiver of advanced wideband satellite digital broadcasting)
FIG. 10 is a flowchart showing a reception control flow in the receiving device 5 of the advanced wideband satellite digital broadcasting of one embodiment shown in FIG. The same step numbers as those in FIG. 8 are assigned the same numbers.

First, the receiving device 5 receives and demodulates the modulated wave signal radiated from the transmitting device 2 via the broadcast transmission line of the advanced broadband satellite digital broadcasting by the demodulation unit 51, and the coded data obtained by this demodulation processing. Is output to the error correction decoding unit 52 via the switching unit 55 (step S1). As described above, the switching unit 55 is controlled by the error correction / decoding unit 52.

Subsequently, in order for the receiving device 5 to execute the decoding process corresponding to the error correction coding process in the transmitting device 2 by the error correction decoding unit 52, first, the pre-LLR of each bit of the coded data is performed from the likelihood table. Calculate and reconstruct the error correction code frame (step S2A). In advanced broadband satellite digital broadcasting, the number of bits for one frame of coded data is 44,880 bits, and the LDPC code is used as the internal code and the BCH code is used as the external code for error correction coding processing. The degree table is used to calculate the probability that the bit is "0" and the prior log likelihood ratio that indicates the probability that the bit is "1".

Subsequently, the receiving device 5 performs LDPC decoding using the sum-product algorithm based on the log-likelihood ratio by the error correction decoding unit 52 (step S2B), and then performs power reverse diffusion processing and BCH code decoding processing. It is carried out (step S2C). In ARIB STD-B44, when the error of the bit error cannot be corrected completely in the decoding process of the BCH code of the external code and it is not error-free, the data is replaced with a null packet, a flag with an error is added, and so on. It stipulates.

Therefore, the error correction decoding unit 52 determines whether or not the coded data obtained from the transmission device 2 can be error-corrected and decoded by the decoding possibility determination unit 521, so that the bit error error is corrected by the BCH code decoding process. It is determined whether or not the error could not be completed or the error could be corrected by decoding but the predetermined number of BCH errors was reached (step S3'). That is, in this embodiment, paying attention to the fact that the correction ability of the LDPC code is uncertain and the correction ability of the BCH code is deterministic, the presence or absence of error-free of the BCH code connected to the LDPC code is used. Therefore, it is intended to realize an efficient retransmission request in Hybrid ARQ.

Here, the error correction / decoding unit 52 determines whether or not the coded data obtained from the transmission device 2 can be error-corrected / decoded by the decoding / rejection determination unit 521. Since the data is reproducibly generated (step S3': No) and the current reception path is not via the IP network 8 (step S9: No), the setting of the switching unit 55 is maintained as the reception path for receiving the broadcast as it is. In chronological order, the process shifts to the demodulation / decoding process for the next coded data.

On the other hand, when the error correction decoding unit 52 determines that the decoding passability determination unit 521 cannot decode the coded data constituting the error correction code frame, the error correction decoding unit 52 retransmits the coded data constituting the error correction code frame. The request information is generated, output to the retransmission request packet generation unit 53, and instructed to generate a retransmission request packet indicating the retransmission request of the encoded data (step S3': Yes). That is, when the error correction / decoding unit 52 cannot restore the received data from the encoded data due to deterioration of transmission conditions or the like, the error correction / decoding unit 52 requests the retransmission request packet generation unit 53 to make a retransmission request to the transmission server 6 by ARQ. Instruct. Further, the decoding possibility determination unit 521 controls the switching unit 55 to switch to the reception path for inputting the coded data to the error correction decoding unit 52 via the IP network 8.

In response to the instruction from the decoding possibility determination unit 521, the retransmission request packet generation unit 53 communicates with the retransmission request information indicating that the encoded data determined by the decoding possibility determination unit 521 that cannot be decoded is requested to be retransmitted. A retransmission request packet in the form of an IP packet including communication quality information obtained from the quality measurement unit 56 is generated and transmitted to the transmission server 6 via the IP network 8 (step S4). Here, the communication quality information includes one or both of the delay information of the communication line and the packet loss rate information.

Therefore, when the transmission server 6 receives the retransmission request packet from the receiving device 5, the transmission server 6 extracts the retransmission request information and the communication quality information from the retransmission request packet, and changes the coding rate predetermined based on the communication quality information. According to the standard, it is decided whether or not to change the coding rate, and if so, which coding rate to change. As described above, the coding rate change standard is based on the same coding method as the error correction coding method used by the error correction coding unit 21 on the transmitting side, and is predetermined to be usable in the transmitting device 2 related to broadcasting. Among the code rates of the number of types, it is stipulated that the code rate is changed by distinguishing whether the code rate is higher or lower than the code rate of the coded data transmitted on the broadcast transmission line.

Then, the transmission server 6 has a continuous synchronization signal (frame number or time information) starting from the error correction code frame constituting the coded data having the synchronization signal (frame number or time information) related to the retransmission request. Frame error correction A code frame is formed with 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, and the interleaved frame is m-frame error. An interleaving process is performed in a direction orthogonal to the correction code frame to generate a coded data packet of an IP packet string, which is transmitted to the receiving device 5 via the IP network 8. Further, when the coding rate is changed, the transmission server 6 generates a coding rate change notification packet as a notification indicating that fact, transmits the coded data packet, and then transmits the coded data packet. Therefore, the receiving device 5 determines whether or not the coding rate of the coded data obtained via the IP network 8 is different from that at the time of broadcasting reception by the IP packet receiving unit 54 and the error correction decoding unit 52. can. An example of changing the code rate by the transmission server 6 (typically described when the coded data related to the retransmission request is changed to a lower code rate) will be described later with reference to FIG. Further, for an example of the method of generating the retransmission request packet in the IP packet format by the transmission server 6 (when the encoded data related to the retransmission request is changed to a lower coding rate, which will be described as a representative), see FIG. Will be described later.

Therefore, the receiving device 5 transmits the retransmission request packet to the transmitting server 6, and then the error correction code for m frames including the coded data of the decoding target retransmitted from the transmitting server 6 in response to the retransmission request packet. Upon receiving the coded data packet (IP packet string) of the frame, the deinterleave unit 541 performs reverse processing of the interleave unit 621 on the transmission server 6 side by using the identification header and the sequence number given to the IP packet. Then, the encoded data resent in response to the retransmission request is reconstructed and output to the error correction decoding unit 52 (step S5).

Subsequently, the receiving device 5 determines whether or not the coding rate of the coded data obtained via the IP network 8 is different from that at the time of broadcasting reception by the coded data complementing unit 522 in the error correction decoding unit 52 ( In step S6), when the coding rate of the coded data obtained via the IP network 8 is different from that at the time of receiving the broadcast (step S6: Yes), the code rate shown in FIG. 4 (d) or FIG. 5 (e) is In order to restore the changed error correction code frame, a padding bit known between transmission and reception according to the coding rate is added to an insertion position known between transmission and reception (step S7).

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

Subsequently, the coded data complementing unit 522 complements the coded data acquired via the IP network 8 so as to be used for the decoding process of the coded data in the error correction code frame (step S8'). Assuming that the IP network 8 is a lost communication path, the error correction decoding unit 52 determines the correct bit value for the coded data received via the IP network 8, and packets in the communication path in the middle of the IP network 8. The correct bit value is unknown for packets lost due to loss or the like. More specifically, the error correction / decoding unit 52 is configured as an error correction / decoding device for the block code, and in order to perform decoding using the log-likelihood ratio, the coded data complementing unit 522 acquires the data via the IP network 8. For the coded data, the log-likelihood ratio when the bit value is 0 is + ∞ (maximum value as the certainty of "0"), and the log-likelihood ratio when the bit value is 1 is-. ∞ (maximum value as the certainty of "1"), If packet loss occurs and a non-reachable bit occurs, it is complemented by replacing the log-likelihood ratio with 0.

Then, the error correction decoding unit 52 repeats the request for retransmission of the coded data (steps S2 to S8') until it can be decoded by the decoding process of the error correction code within a predetermined time, and based on the coded data that can be decoded. After the reception data is generated in, when the current reception route is via the IP network 8 (step S9: Yes), the switching unit 55 is controlled to switch the reception route to the reception via the broadcast transmission line (step S9: Yes). S10), in chronological order, the process shifts to the demodulation / decoding process for the next coded data. Here, the error correction decoding unit 52 may be configured to completely restore the received data by repeatedly requesting retransmission until the error of the bit error in the decoding process of the BCH code disappears, but within a predetermined time It is preferable to avoid infinite loop processing by providing a limit.

When the coded data related to the retransmission request is changed to a lower coding rate and the information bits are divided, the error correction / decoding unit 52 obtains both of the coded data of the divided individual information bits. The request for retransmitting the coded data transmitted on the broadcast transmission line is repeated until the data can be decoded by the decoding process of the error correction code within a predetermined time, and the error correction decoding unit 52 uses the code of each divided information bit. When both of the converted data can be decoded, the divided data bit after decoding is recombined with the transmission server 6 according to a predetermined division method by the function of the data combination unit 523 to receive the received data. Generate.

By the way, as the retransmission request packet, a non-delivery notification packet generally used in the IP packet format can be used, and the encoded data packet is configured to perform retransmission in response to the non-delivery notification packet. Therefore, the error correction decoding unit 52 can replace the coded data obtained from the demodulation unit 51 with the coded data obtained by retransmission, and perform decoding again, and receive data within a predetermined time. It is possible to output reproducibly by repeatedly requesting retransmission until the data can be restored.

(Method of generating coded data when the code rate of one embodiment is changed: When changing to a lower code rate)
As described with reference to FIGS. 4 and 5, the transmission server 6 has a higher coding rate of the coded data related to the retransmission request than the coded data transmitted on the broadcast transmission line according to the communication quality information. The coding rate is adaptively changed and reconstructed by distinguishing between low and low.

That is, with respect to the coded data related to the retransmission request generated by the transmission server 6, only the difference is that the information bits are undivided when changing to a higher code rate and the information bits are divided when changing to a lower code rate. Therefore, here, with reference to FIG. 11 as an example of changing the coded data related to the retransmission request to a lower code rate as a representative, ARIB STD is performed by the retransmission request processing unit 63 in the transmission server 6. Within the range of the number of types of LDPC coding rate conforming to −B44, in this example, the storage unit 61 and the code rate adaptation changing unit 64 are controlled and encoded according to the coding rate changing standard of (9) above. An example of generating coded data when the rate is changed will be described.

In the example shown in FIGS. 11 (a) to 11 (e), the transmission server 6 has the highest LDPC code rate (109/120) within the range of the number of types of LDPC code rates conforming to ARIB STD-B44. The coded data (≈9 / 10) is received, stored in the storage unit 61, and the coded data requested to be retransmitted from the receiving device 5 via the IP network 8 when the radio wave reception condition deteriorates. This is an example in which the coding rate is changed to 61/120 (≈1/2) and the data is retransmitted.

As shown in FIG. 11A, here, the coding rate of the coded data in the LDPC code having a code length N = 44880 bits transmitted on the broadcast transmission line is set to F _b = 109/120 (≈9/10). do. In ARIB STD-B44, one error correction code frame has a constant code length of 44,880 bits regardless of the LDPC coding rate, and is composed of slot units based on the set division method. Therefore, the LDPC code is coded. As the information bits, the "slot header", "main signal (data to be transmitted)", "BCH code parity", and "stuff bit" are power-spread, and the parity of the LDPC code is It is added to form one error correction code frame. Then, in the storage unit 61 of the transmission server 6, the coded data of one error correction code frame unit shown in FIG. 11A is attached with a synchronization signal (frame number or time information) and managed in chronological order. It is saved while updating the specified time. The LDPC code parity at the LDPC coding rate 109/120 (≈9/10) is composed of 44880 × (1-109 / 120) = 4114 bits.

Therefore, the transmission server 6 that has received the retransmission request packet from the receiving device 5 extracts the communication quality information included in the retransmission request packet by the retransmission request processing unit 63, and determines the delay and the packet loss rate included in the communication quality information. Based on each information, it is determined whether or not to change the coding rate by referring to the coding rate change standard managed by the communication quality control unit 65.

Assuming that the code rate change criterion of (9) above is followed, the retransmission request processing unit 63 determines that the delay obtained from the receiving device 5 is less than the predetermined default value, or the packet loss rate obtained from the receiving device 5 is lower. If it is less than the predetermined default value, it is determined that there is no change in the LDPC coding rate of 109/120 (≈9/10) of the coded data transmitted on the broadcast transmission line, and the retransmission request shown in FIG. 11A is shown. The code rate adaptation change unit 64 is controlled so that the coded data having a code length of N bits according to the above is read from the storage unit 61 and output to the IP packet generation unit 62 as it is.

On the other hand, when the delay obtained from the receiving device 5 is equal to or more than a predetermined default value and the packet loss rate obtained from the receiving device 5 is equal to or more than a predetermined default value, the retransmission request processing unit 63 performs a broadcast transmission line. in the LDPC coding rate of the transmission encoded data _{F b = 109/120 (≒} 9/10), determines to change the LDPC coding rate _{F i = 61/120 (≒} 1/2) (F b> F _i), First, FIG. 11 (N × _F b = 40766 bits of the LDPC code encoded subject to information bits of the code length 44880 bits of the coded data according to the retransmission request indicated in a) (i.e., the power spreading Only the completed BCH coding bit) is read from the storage unit 61 (see FIG. 11B).

Subsequently, the error correction coding unit 643 controls the coding rate adaptation change unit 64, and the error correction coding unit 643 reads 40766 bits of information bits from the storage unit 61 (that is, the power-spread BCH). The coded bit) is divided into two between transmission and reception by a predetermined division method ((N × F _b ) / 2 = 20383 bits). Here, an example is made in which the first half and the second half of the information bit position are divided into two equal parts (see FIG. 11C), but even if other division methods are used, such as dividing into two by odd-numbered bits and even-numbered bits. good.

Subsequently, the retransmission request processing unit 63 controls the coding rate adaptation change unit 64, and for the first half and the second half of each of the information bits divided into two, known values between transmission and reception (for example, all 0s). Bit), N × F _i − ((N × F _b ) / 2) = 2431 bits are added as padding bits to the insertion position known between transmission and reception, and these information bits and padding bits are encoded. subjected to rate _{F i = 109/120 (≒} 9/10) to become LDPC encoding process to generate the parity of _{N × (1-F i)} = 4114 bits (see FIG. 11 (d)). In this example, the padding bit is added after the information bit, but the padding bit may be added before the information bit, that is, the insertion position of the padding bit is the code after the change. it is sufficient to set in advance as known between transmission and reception by the value of the ratio F _i.

Then, the error correction coding unit 643 removes the padding bit, reconstructs the encoded data (42449 bits) for retransmission in which 22066 bit parity is added to the 20383 bit information bit, and the IP packet generation unit 62. (See FIG. 11 (e)). The frame length of the reconstructed coded data for retransmission 42449 bits is shorter than the original code length 44880 bits, and is not excessive with respect to the code length of the error correction code standardized by the broadcasting standard. The coded data related to the retransmission request can be changed to a lower coding rate, and the correction capability is higher than in the case of resending without changing the coding rate.

In this way, when the transmission server 6 of the present embodiment receives the retransmission request packet, the LDPC coding rate of the encoded data related to the retransmission request is adaptively adjusted based on the communication quality information included in the retransmission request packet. It is modified to generate an encoded data packet and transmitted to the receiving device 5.

(Method of generating a coded data packet in IP packet format by the transmission server of one embodiment)
The coded data packet is configured by using one or more IP packets, and here, an example will be described in which the packet length excluding the IP header of the IP packet is set to 1000 bytes and has a fixed length. However, in reality, the packet length can be arbitrarily determined to be a variable length within a range that does not exceed the assumed MTU (Maximum Transmission Unit) of the IP network 8.

As described above, regarding the coded data related to the retransmission request generated by the transmission server 6, the information bit is undivided when changing to a higher coding rate, and the information bit is divided when changing to a lower coding rate. Since there is only a difference, here, FIG. 12 is referred to as an example when changing the coded data related to the retransmission request to a lower coding rate, and an n × m interleaved frame is used for the coded data. An example of generating a coded data packet (IP packet string) and transmitting the coded data packet (IP packet string) to the receiving device 5 will be described.

12 (a) to 12 (d) are explanatory views of an IP packet generation method of the IP packet generation unit 62 in the transmission server 6 of the embodiment according to the present invention, respectively.

First, IP packet generating unit 62, a coding rate adaptively changing unit 64, respectively constituted by code length n bits of the same code rate F _i, the synchronization signal related to the retransmission request (frame number or time information) An error correction code frame for m frames having a continuous synchronization signal (frame number or time information) is input starting from the error correction code frame that constitutes the coded data to form an n × m interleaved frame. Although m is a fixed value, it can be variably set from the outside and is a value shared between transmission and reception. Further, an n = N when code length n bits of code rate F _i has not changed since the code length N bits of encoded rate F _b used in the broadcast transmission path, the code length of the code rate F _b When changed from N bits, n <N.

Therefore, the IP packet generation unit 62 stores the m-frame error correction code frames (LDPC frames) including the error correction code frames as the coded data related to the retransmission request in the storage unit (not shown) so as to arrange them in the vertical direction. Temporarily store (see FIG. 12 (a)). In FIG. 12A, the IP packet generation unit 62 has 2 information bits when the coding data obtained from the coding rate adaptation changing unit 64 is an LDPC frame whose coding rate has been changed to a lower value. Since it is divided (in this example, the first half and the second half), LDPC frame # 1 (information bit first half), LDPC frame # 2 (information bit second half), LDPC frame # 3 (information bit first half), ..., Like the LDPC frame #m (second half of the information bit), the first half and the second half of the information bit are temporarily stored in the storage unit (not shown) so as to be arranged in the vertical direction.

Hereinafter, as described above with reference to FIG. 6, the IP packet generation unit 62 reads each bit from the beginning into the error correction code frame of the m frame by the interleaving unit 621, and removes the header of the generated IP packet. An IP payload of m bits as the length is generated for n packets (see FIG. 12B), and each interleave frame related to interleave processing can be identified on the receiving device 5 side in the generated IP payload for n packets. An identification header for this purpose, a sequence number for specifying which bit is represented in each error correction code frame, and an IP header are added as headers of encoded data packets to generate IP packets for n packets (). See FIG. 12 (c)). Then, the IP packet generation unit 62 interleaves the generated n packets of IP packets by the interleaving unit 621 in the order of transmission to the IP network 8 according to the sequence number based on a predetermined rule (for example, in ascending order of the sequence number). It may be transmitted, or it may be a transmission order of another sequence number determined between transmission and reception), and it is transmitted to the receiving device 5 as a coded data packet.

By transmitting the IP packet string of the encoded data subjected to the interleave processing as an encoded data packet from the transmitting server 6 to the receiving device 5, the resistance to burst packet loss in the IP network 8 becomes stronger. (That is, the packet loss correction capability is improved).

(Application example: Change of coding rate of LDPC code and change of correction ability of BCH code)
The error correction coding unit 643 in the coding rate adaptation changing unit 64 changes the coding rate of the coded data (coded data transmitted on the broadcast transmission line) related to the retransmission request and retransmits the LDPC code. In addition to changing the coding rate, the correction capability of the BCH code may be changed to be enhanced from 12 bits to 23 bits to reconstruct the coded data.

13 (a) to 13 (f), respectively, show lower coding of the coded data related to the retransmission request when the code rate is changed by the code rate adaptive change unit 64 in the transmission server 6 of the application example according to the present invention. It is a figure which shows the generation method of the coded data (at the time of changing to a rate). In comparison with the example shown in FIG. 11, FIG. 13 shows the LDPC code having the highest value within the range of the number of types of LDPC coding rate conforming to ARIB STD-B44 by the retransmission request processing unit 63 in the transmission server 6. The coded data having a conversion rate (109/120 (≈9 / 10)) is received and held in the storage unit 61, and when the radio wave reception condition deteriorates from the receiving device 5, a retransmission request is made via the IP network 8. An example is shown in which the coded data is generated by changing the code rate to 61/120 (≈1/2).

First, in FIG. 13A, similarly to FIG. 11A, the coding rate of the coded data in the LDPC code having a code length N = 44880 bits transmitted on the broadcast transmission line is set to F _b = 109/120 (≈). It is shown as 9/10). As described above, in ARIB STD-B44, one error correction code frame has a constant code length of 44,880 bits regardless of the LDPC coding rate, and is composed of slot units based on the set division method. The information bits to be encoded are the "slot header", "main signal (data to be transmitted)", "BCH code parity", and "stuff bit" that are power-spread, and are LDPC codes. Parity is added to form one error correction code frame. Then, in the storage unit 61 of the transmission server 6, the coded data of one error correction code frame unit shown in FIG. 13A is attached with a synchronization signal (frame number or time information) and managed in chronological order. It is saved while updating the specified time. The LDPC code parity at the LDPC coding rate 109/120 (≈9/10) is composed of 44880 × (1-109 / 120) = 4114 bits.

Therefore, the transmission server 6 that has received the retransmission request packet from the receiving device 5 uses the retransmission request processing unit 63 to obtain the communication quality information included in the retransmission request packet, as in the embodiment described with reference to FIG. 11 described above. Whether or not to change the coding rate by referring to the coding rate change standard managed by the communication quality management unit 65 based on each information of the delay and the packet loss rate extracted and included in the communication quality information. To judge.

Assuming that the code rate change criterion of (9) above is followed, the retransmission request processing unit 63 determines that the delay obtained from the receiving device 5 is less than the predetermined default value, or the packet loss rate obtained from the receiving device 5 is lower. If it is less than the predetermined default value, it is determined that there is no change in the LDPC coding rate of 109/120 (≈9/10) of the coded data transmitted on the broadcast transmission line, and the retransmission request shown in FIG. 13 (a). The code rate adaptation change unit 64 is controlled so that the coded data having a code length of N bits according to the above is read from the storage unit 61 and output to the IP packet generation unit 62 as it is.

On the other hand, when the delay obtained from the receiving device 5 is equal to or more than a predetermined default value and the packet loss rate obtained from the receiving device 5 is less than a predetermined default value, the retransmission request processing unit 63 performs a broadcast transmission line. in the LDPC coding rate of the transmission encoded data _{F b = 109/120 (≒} 9/10), determines to change the LDPC coding rate _{F i = 61/120 (≒} 1/2) (F b> F _i), First, FIG. 13 (N × _F b = 40766 bits of the LDPC code encoded subject to information bits of the code length 44880 bits of the coded data according to the retransmission request indicated in a) (i.e., the power spreading Only the completed BCH coding bit) is read from the storage unit 61 (see FIG. 13B).

Subsequently, in this application example, the retransmission request processing unit 63 controls the coding rate adaptation change unit 64, and the error correction coding unit 643 reads out 40766 bits of information bits (that is, power) from the storage unit 61. The spread BCH coded bit) is once subjected to power despreading processing, and then the "slot header", "main signal (data to be transmitted)", "12-bit correction capability BCH code parity", and "staff". It restores to the bit array of "bits", deletes the "slot header", and allocates the deleted bit area to BCH code parity (see FIG. 13 (c)). Therefore, the bit array of the "main signal (data to be transmitted)", "BCH code parity with 23-bit correction capability", and "stuff bit" is obtained without changing the total information bit length. As a result, the 12-bit correction BCH code described in ARIB STD-B44 is corrected to the 23-bit correction BCH code while maintaining the frame length of the error correction code frame after the change of the LDPC coding rate. For BCH code with 23-bit correction capability, for example, "Yoichi Suzuki, Specified Hashimoto, Takafumi Matsuzaki, Shoji Tanaka, Takeshi Kimura, Kenichi Tsuchida," LDPC code and BCH code Performance improvement of set division 8PSK coding modulation to which the concatenated code of is applied, "Journal of the Society of Electronics, Information and Communication Engineers B, V0l.97, no.8, PP.648-659, August 1, 2014").

Subsequently, the error correction coding unit 643 uses the information bits of the bit array of the “signal (data to be transmitted)”, “BCH code parity with 23-bit correction capability”, and “stuff bit” shown in FIG. 13 (c). After performing the power diffusion processing again, the information bit is divided into two by a predetermined division method between transmission and reception, as in the embodiment described with reference to FIG. 11 described above ((N × F _b). ) / 2 = 20383 bits). Here, an example is made in which the first half and the second half of the information bit position are divided into two equal parts (see FIG. 13D), but even if other division methods are used, such as dividing into two by odd-numbered bits and even-numbered bits. good.

Subsequently, the retransmission request processing unit 63 controls the coding rate adaptation change unit 64, and for the first half and the second half of each of the information bits divided into two, known values between transmission and reception (for example, all 0s). bit) at _{N × F i - (N ×} F b) = 2431 adds bits as padding bits and an encoding rate _F i = 61/120 with respect to the information bits and padding bits (≒ 1/2) by performing LDPC encoding process becomes, and generates the parity of _{N × (1-F i)} = 22066 bits (see FIG. 13 (e)). In this example, the padding bit is added after the information bit, but the padding bit may be added before the information bit, that is, the insertion position of the padding bit is the code after the change. it is sufficient to set in advance as known between transmission and reception by the value of the ratio F _i.

Then, the error correction coding unit 643 removes the padding bit, reconstructs the encoded data (42449 bits) for retransmission in which 22066 bit parity is added to the 20383 bit information bit, and the IP packet generation unit 62. Is output to (see FIG. 13 (f)). The frame length of the reconstructed coded data for retransmission 42449 bits is shorter than the original code length 44880 bits, and is not excessive with respect to the code length of the error correction code standardized by the broadcasting standard. The coded data related to the retransmission request can be changed to a lower coding rate, and the correction capability is higher than in the case of resending without changing the coding rate.

Further, by improving the correction capability of the BCH code, the packet loss tolerance in the IP network 8 can be improved. Regarding this change of BCH code, it is determined in advance between transmission and reception that the correction capability of BCH code is always changed when the LDPC code rate is changed, or depending on either one or both of the delay and the packet loss rate. In addition to the above-mentioned coding rate change criteria, the criteria for changing the correction capability of the BCH code, which is arbitrarily determined so as to switch the correction capability of the BCH code, is added to the above-mentioned coding rate change criteria, and at the same time as the notification of the coding rate change, before the transmission of the encoded data to be retransmitted. In addition, the receiving device 5 may be notified in advance.

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

As described above, according to the transmission system 1 of the present embodiment, the transmission request is executed from the receiving device 5 side to the transmitting server 6 side via the IP network 8 for the data loss that cannot be prevented only by the broadcast reception, and the transmitting server. By enabling data retransmission from the 6 side, the data can be complemented on the receiving device 5 side. In particular, the data retransmitted by the transmission server 6 via the IP network 8 is used as the coded data in the block code of digital broadcasting, and the coded data is variably controlled to the coding rate according to the communication quality of the IP network 8. This makes it possible to reduce the number of retransmission requests and further improve the transmission efficiency via the IP network. Further, by making both the error correction code for broadcast reception and the error correction code used for transmission via the IP network the same as the code format of the error correction code standardized by the broadcasting standard, the receiving device 5 has one error correction. This can be achieved simply by preparing a decoder, and the equipment scale can be reduced.

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

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

Further, once the reception path is switched and controlled via the IP network 8, the switching unit 55 in this modification receives the data via the IP network 8 unless it is controlled by the second reception path switching signal from the reception quality measurement unit 57. It operates so as to maintain the route and continue to receive the next coded data following the coded data requested to be retransmitted via the IP network 8 even after the retransmission request for the coded data.

The reception quality measurement unit 57 measures the reception quality (for example, MER (Modulation Error Ratio)) of the received modulated wave signal, determines whether or not the reception quality is equal to or higher than a predetermined value, and the switching unit 55 and The error correction decoding unit 52 is controlled.

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

Further, the reception quality measurement unit 57 receives the reception path of the switching unit 55 when the reception quality of the received modulated wave signal is less than a predetermined value and the reception path of the switching unit 55 is via the IP network 8. Is not performed by switching control of the switching unit 55 so as to remain via the IP network 8, and continues even after the error correction decoding unit 52 is requested to retransmit the coded data by the continuation instruction signal, and the IP network 8 continues. Instructs to retransmit and acquire the next encoded data via.

(Reception control flow in the receiving device of the modified example)
FIG. 15 is a flowchart showing a reception control flow in the receiving device 5 of the modified example according to the present invention. The same step numbers as those in FIG. 8 are assigned the same numbers.

Steps S1 to S8 shown in FIG. 15 are the same as steps S1 to S8 shown in FIG. 8, and further description thereof will be omitted.

That is, also in the receiving device 5 of this modification, the coded data transmitted via the broadcast transmission line and demolished by the demodulating unit 51 is input to the error correction decoding unit 52 via the switching unit 55 to correct the error. When the decoding unit 52 determines that the coded data obtained via the broadcast transmission line cannot be decoded by the decoding possibility determination unit 521, the switching unit 55 is switched and controlled to retransmit the coded data via the IP network 8. The request for retransmission of the coded data is repeated until the data can be acquired and decoded by the decoding process of the error correction code within a predetermined time (steps S1 to S8).

Then, in the receiving device 5 of the present modification, after the error correction decoding unit 52 generates the receiving data based on the encoded data that can be decoded, the current receiving path is not via the IP network 8 but is broadcast-received. If (step S9: No), the setting of the switching unit 55 is maintained as the reception path for receiving the broadcast as it is, and the process proceeds to the demodulation / decoding process for the next coded data in the time series.

On the other hand, when the receiving device 5 of the present modification generates the received data based on the encoded data that can be decoded by the error correction decoding unit 52, and then the current receiving path is via the IP network 8 (step S9). : Yes), the reception quality measurement unit 57 determines whether or not the reception quality of the received modulated wave signal is equal to or higher than a predetermined value (step S10A).

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

However, when the reception quality is less than a predetermined value and the reception path of the switching unit 55 is via the IP network 8 (step S10A: No), the reception quality measurement unit 57 sets the reception path of the switching unit 55. The switching unit 55 is not controlled to be switched via the IP network 8 so as to remain via the IP network 8, and the error correction decoding unit 52 is continuously requested to retransmit the coded data via the IP network 8 by the continuation instruction signal. The coded data is instructed to be retransmitted and acquired (step S10C), the process proceeds to step S4, and the same operation is performed thereafter. If the error correction decoding unit 52 cannot decode the data within a predetermined time by the decoding process, the error correction decoding unit 52 generates the received data in a state including the bit error, and proceeds to step S9.

Therefore, once the receiving device 5 of the present modification shown in FIGS. 14 and 15 is switched to the IP network 8, if the reception quality of the received modulated wave signal is less than a predetermined value, an error will occur in the future. It is predicted that the reception condition will continue to deteriorate to the extent that the bit error cannot be corrected by the correction / decoding process, and the IP network will be used for the coded data to be coded by the error correction / decoding unit 52 until the reception quality exceeds a predetermined value. The encoded data is retransmitted and acquired via 8.

Therefore, the transmission system 1 including the receiving device 5 of the present modification also includes all the advantages of the above-described embodiment, and in addition, the operation takes into consideration the reception quality of the received modulated wave signal. Stable digital data reception is possible.

[Outline of operation when the coded data related to the retransmission request is changed to a lower code rate and retransmitted]
In order to further enhance understanding, in reference to FIG. 16, in the transmission system 1 of the embodiment including one embodiment and one modification shown in FIGS. 1 to 15 described above, the coded data related to the retransmission request can be obtained. An outline of the operation when changing to a low coding rate and resending will be described.

FIG. 16 illustrates an outline of the operation when the transmission server 6 of the embodiment according to the present invention transmits to the receiving device 5 a coded data packet in which the coded data related to the retransmission request is changed to a lower code rate. It is a figure.

For example, as the coded data related to the retransmission request, the code rate (LDPC code rate) of the coded data transmitted on the broadcast transmission line conforms to ARIB STD-B44, and the code rate is 9/10 (109/120). (See FIG. 16 (a)).

First, the transmission server 6 discriminates whether to make the coding rate higher or lower than the coding rate of the coded data transmitted on the broadcast transmission line according to the communication quality information, and adaptively changes the coding rate to change the coding data. To reconstruct. Here, an example of changing the coding rate 9/10 of the coded data related to the retransmission request to a lower coding rate 1/2 will be described.

When the transmission server 6 changes the coding rate 9/10 of the coded data related to the retransmission request to a lower coding rate 1/2, the transmission server 6 shifts the information bit of the coded data related to the retransmission request between transmission and reception (transmission). The server 6 and the receiving device 5) are divided into two according to a predetermined division method (here, the first half and the second half are divided into two equal parts) (see FIG. 16B).

Subsequently, the transmission server 6 performs re-encoding to change the coding rate to 1/2 using the padding bit, and temporarily generates coded data to which a parity bit having a coding rate of 1/2 is added (FIG. 16). (C).

Then, the transmission server 6 generates an error correction code frame (LDPC frame) of the coded data in which the padding bit is deleted from the coded data to which the parity bit is added, and then forms an interleaved frame to form an interleaved coded data packet (interleaved coded data packet). An IP packet sequence) is formed and transmitted to the receiving device 5 via the IP network 8 (see FIG. 16D).

After receiving the coded data packet, the receiving device 5 performs deinterleaving as a reverse process on the transmitting server 6 side, adds a padding bit, and then decodes the coded data at a coding rate of 1/2 to obtain the packet. Erasure correction is performed (see FIG. 16E).

Then, the receiving device 5 relates to the coded data requested to be retransmitted by connecting the first half of the decoded information bit of the error correction code frame # 1 and the second half of the decoded information bit of the error correction code frame # 2. Received data with the information bits restored can be generated (see FIG. 16 (f)).

Therefore, according to the transmission system 1 according to the present invention, for data loss that cannot be prevented only by broadcast reception, a retransmission request is made from the receiving device 5 to the transmitting server 6 via the IP network 8, and the data resending is performed from the transmitting server 6. By making it possible, the data can be complemented on the receiving device 5 side. In particular, the data retransmitted by the transmission server 6 via the IP network 8 is used as the coded data in the block code of digital broadcasting, and the coded data is variably controlled to the coding rate according to the communication quality of the IP network 8. This makes it possible to reduce the number of retransmission requests, improve the transmission efficiency via the IP network 8, and enhance the resistance to packet loss. Further, by making both the error correction code for broadcast reception and the error correction code used for transmission via the IP network 8 the same as the code format of the error correction code standardized by the broadcasting standard, one on the receiving device 5 side. This can be achieved simply by preparing an error correction decoder, and the scale of the equipment can be reduced.

With respect to the above-described embodiment, a program for operating each means of the computer functioning as the transmission server 6 can be preferably used. Further, a program for operating each means of the computer functioning as the receiving device 5 can be preferably used. Specifically, at least a storage unit in which a control unit for controlling each means can be configured by a central processing unit (CPU) in a computer and a program necessary for operating each means is appropriately stored is at least. It can be configured with one memory. That is, by causing such a computer to execute the program by the CPU, the functions of the above-mentioned means can be realized. Further, a program for realizing the function of each means can be stored in a predetermined area of the above-mentioned storage unit (memory). Such a storage unit can be configured by a RAM or ROM inside the device, or can be configured by an external storage device (for example, a hard disk). Further, such a program can be configured as a part of software (stored in ROM or an external storage device) on an OS used in a computer. Further, the program for causing such a computer to function as each means can be recorded on a computer-readable recording medium. Further, each of the above-mentioned means may be configured as a part of hardware or software, and each of them may be combined and realized.

Examples, applications, and modifications of the above-described embodiment have been described as typical examples, but it is clear 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, the transmission server 6 has described an example in which encoded data is directly input from the transmission device 2 (or transmission device 3), but in relay broadcasting or the like, it is once received from the transmission device 2 (or transmission device 3). It may be in the form of receiving the modulated wave by the machine, demodulating it, and inputting the coded data obtained by this demodulation. Therefore, the present invention should not be construed as being limited by the examples described above, but only by the claims.

According to the present invention, since the error correction code used in digital broadcasting and the retransmission request can be efficiently combined, it is useful for data compensation related to digital broadcasting.

1 Transmission system 2 Transmission device for satellite broadcasting transmission line 2a Transmission antenna for satellite broadcasting transmission line 3 Transmission device for terrestrial broadcasting transmission line 3a Transmission antenna for terrestrial broadcasting transmission line 4 Broadcasting satellite 5 Receiver device 5a Satellite broadcasting transmission line Reception antenna for 5b Reception antenna for terrestrial broadcasting transmission line 6 Transmission server 7 Load distribution device 8 IP network 21 Error correction coding unit 22 Modulation unit 51 Demodition unit 52 Error correction decoding unit 53 Retransmission request packet generation unit 54 IP packet reception Section 55 Switching section 56 Communication quality measurement section 57 Reception quality measurement section 61 Storage section 62 IP packet generation section 63 Retransmission request processing section 64 Coding rate adaptation change section 521 Decoding / rejection judgment section 522 Coded data complement section 523 Data combination section 541 Deinterleaved part 621 Interleaved part 641,642 Switching part 643 Error correction coding part

Claims (13)

The coded data is digitally modulated using the error correction code related to digital broadcasting, and the coded data is transmitted to the receiving device via the broadcast transmission line. It is a transmission server that saves a predetermined amount of time and enables transmission to a receiving device via an IP (Internet Protocol) network.
The coded data generated by the transmission device is sequentially input, managed in time series by a synchronization signal based on the frame number or time information of the error correction code frame constituting the code length of the error correction code, and managed in time series. A storage unit that saves the coded data for a predetermined time while updating it,
The reception device receives a retransmission request packet generated when a bit error of encoded data cannot be corrected by using the error correction code via the IP network, and the reception is stored in the retransmission request packet. The communication quality information measured by the apparatus and the retransmission request information indicating the coded data of the error correction code frame related to the retransmission request are extracted, and the transmission is performed according to a predetermined coding rate change standard based on the communication quality information. It is determined whether or not to retransmit by changing the coding rate of the block code of the coded data generated by the apparatus, and according to the determination result, the retransmission request is related from the storage unit based on the retransmission request information. A retransmission request processing unit that reads out the encoded data, constructs encoded data in which the encoding rate is adaptively changed, and controls the retransmission of the encoded data toward the receiving device.
When the code rate of the block code of the coded data generated by the transmission device is changed or not changed by the control of the retransmission request processing unit, and the code rate is changed, the code rate is changed. Based on the same coding method as the error correction coding method used in the transmission device, and out of a predetermined number of coding rates that can be used by the transmission device, it was generated by the transmission device transmitted on the broadcast transmission line. A code rate adaptive change unit that performs error correction coding processing that changes the code rate by distinguishing whether it is higher or lower than the code rate of the coded data.
An IP packet generator that generates an IP packet format encoded data packet that stores the encoded data related to the retransmission request configured through control by the retransmission request processing unit and transmits it to the receiving device via the IP network. ,
A transmission server characterized by comprising. When the code rate adaptive change unit changes the code rate of the coded data generated by the transmission device under the control of the retransmission request processing unit,
When converting to a coding rate higher than the coding rate before the change, a padding bit known on the receiving device side is added to the information bit of the coded data according to the coded rate to be changed. The parity of the block code obtained by performing the error correction coding process and whose coding rate is changed is replaced with the parity added to the coded data generated by the transmission device and added, and the padding bit is removed. Generate the encoded data for retransmission
When converting to a coding rate lower than the coding rate before the change, the information bits of the coded data are divided between transmission and reception by a predetermined division method, and the divided according to the code rate to be changed. The parity of the block code obtained by adding the padding bit known on the receiving device side to the information bit of the above and changing the coding rate obtained by performing the error correction coding process is the code generated by the transmitting device. The transmission server according to claim 1, further comprising generating encoded data for retransmission in which the parity added to the converted data is replaced and added, and the padding bit is removed. The retransmission request processing unit has the predetermined coding rate based on one or both of the communication line delay information and the packet loss rate information measured by the receiving device as the communication quality information. The transmission server according to claim 1 or 2, wherein the coding rate of the coded data generated by the transmission device is changed according to a change criterion to determine whether or not to retransmit the coded data. When the code rate adaptive change unit changes the code rate of the coded data generated by the transmission device under the control of the retransmission request processing unit, in addition to changing the code rate of the block code. 1. The first aspect of the present invention is characterized in that the means for changing the correction ability of the error correction code connected to the block code is further provided while maintaining the frame length of the error correction code frame after the change of the coding rate. The transmission server according to any one of 3. The IP packet generation unit constitutes an interleaved frame using the plurality of error correction code frames, and can identify the interleaved frame in a payload obtained by interleaving each error correction code frame so as to traverse the frame. The coded data packet of the IP packet string by adding the identification header for specifying the number of bits in each error correction code frame, and the IP header which is the header of the coded data packet. The transmission server according to any one of claims 1 to 4, further comprising an interleaving unit for generating the above. A transmitter for digital broadcasting
A transmission device according to any one of claims 1 to 5, further comprising means for sequentially outputting encoded data encoded by using the error correction code related to the digital broadcasting. .. A transmitter for digital broadcasting
A transmission device comprising the transmission server according to any one of claims 1 to 5 inside the device. A receiving device that digitally modulates encoded data encoded by a transmitting device using an error correction code related to digital broadcasting and receives a modulated wave signal transmitted via a broadcasting transmission line.
A demodulator that receives and demodulates the modulated wave signal,
An error in which an error correction code frame constituting the code length of the error correction code is reconstructed from the coded data obtained by demodulation and a decoding process corresponding to the error correction code is performed to generate received data and make it playable. Correction and decoding section and
Retransmission request information indicating the encoded data of the error correction code frame related to the retransmission request for requesting the retransmission of the corresponding encoded data when the bit error of the encoded data cannot be corrected by using the error correction code. A retransmission request packet generation unit that generates a retransmission request packet in the IP packet format including the retransmission request packet and transmits the retransmission request packet to the transmission server according to any one of claims 1 to 5.
The encoded data packet in the IP packet format that stores the encoded data retransmitted in response to the retransmission request is received from the transmission server in response to the retransmission request packet, and the encoded data retransmitted in response to the retransmission request is received. IP packet receiver to extract and
One or both of the delay related to communication with the transmitting server and the packet loss rate based on the amount of packet loss generated related to communication with the transmitting server are measured and updated and held in predetermined period units. A communication quality measuring unit that sequentially outputs communication quality information including one or both of the delay information and the packet loss rate information of the communication line to the retransmission request packet generation unit so as to be included in the retransmission request packet. With
The error correction decoding unit
When it is determined whether or not the coded data obtained from the transmitting device can be error-corrected and decoded, and it is determined that the bit error of the coded data cannot be corrected and cannot be decoded, the retransmission request packet including the retransmission request bit position information is transmitted. Decoding possibility judgment unit to be generated and
Regarding the coded data retransmitted in response to the retransmission request, the coding rate of the coded data obtained by demodulating the coded data when the coding rate has not been changed, and the code when the coding rate has been changed. Coding that adds padding bits according to the conversion rate, attempts decoding processing through complementary processing related to replacement of the likelihood ratio required for decoding, and repeats the request for retransmission of the corresponding encoded data until decoding can be performed within a predetermined time. Data complement and
When the coded data related to the retransmission request is changed to a lower coding rate and the information bits are divided (divided into two equal parts in the example described in detail later), the divided information bits after decoding are referred to as described above. A data combination unit that generates received data by recombining with the transmission server according to a predetermined division method,
A receiving device characterized by having. The error correction code is composed of a concatenated code in which an LDPC code is concatenated as an internal code and a BCH code is concatenated as an external code. The receiving device according to claim 8, wherein it is determined that the bit error of the coded data cannot be corrected when the coded data is not error-free. A reception quality measuring unit for measuring the reception quality of the received modulated wave signal is further provided.
The reception quality measurement unit
When the reception path at the time of generating the reception data based on the coded data decrypted by the error correction decoding unit is the reception path for broadcasting reception instead of via the IP network, the reception path for broadcasting reception is maintained.
When the reception path at the time of generating the reception data based on the coded data decrypted by the error correction decoding unit is via the IP network, it is determined whether or not the reception quality is equal to or higher than a predetermined value, and the above. If the reception quality is equal to or higher than the predetermined value, the reception path is switched to receive the broadcast, and if the reception quality is less than the predetermined value, the reception path via the IP network is maintained, and the coded data is transmitted to the error correction / decoding unit. The receiving device according to claim 8 or 9, further comprising a means for instructing the next encoded data to be resently requested and acquired via the IP network even after the retransmission request. The IP packet receiving unit receives the encoded data packet of the IP packet string storing the encoded data retransmitted in response to the retransmission request from the transmitting server in response to the retransmission request packet, and interleaves by the transmitting server. 6. Receiver. A program for causing a computer to function as a transmission server according to any one of claims 1 to 5. A program for operating a computer as a receiving device according to any one of claims 8 to 11.

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