JP4722693B2 - Communications system - Google Patents

Description

  The present invention relates to a communication system and a data distribution method.

  In recent years, multicast communication technology that efficiently distributes the same large-capacity data to a large number of recipients has attracted attention. Also, in order to protect data from noise and loss that occur during communication, packet level error correction code (FEC) is used for multicast or unicast communication using UDP (User Datagram Protocol) or IP (Internet Protocol). A method of combining correction) has been proposed. Multicast in which reliability is improved by combining FEC or the like is called highly reliable multicast. Known error correction codes used for reliable multicast include, for example, LT codes (see, for example, Patent Document 1), Raptor codes, and low-density parity-check codes (LDPC codes).

Here, general FEC will be described.
The sender divides the data into data blocks, and further divides the data blocks into minimum input units of encoding called information symbols. Next, encoding is performed for each data block and converted into a code word. The code word is composed of a minimum output unit of encoding called an encoded symbol. Each coded word is divided into packets with the coded symbol as a minimum unit and transmitted. The receiver performs decoding from a plurality of received encoded symbols to restore the data block. Data reception is completed when all the data blocks divided by the sender can be restored.

  In the LT coding method, an exclusive OR (XOR) operation value for each set of information symbols arbitrarily selected from a plurality of information symbols is used as a coded symbol. The set of information symbols may be composed of a plurality of information symbols or may be composed of only one information symbol. That is, one encoded symbol is expressed as an equation with a term composed only of an XOR operation of one or a plurality of information symbols. From the equation for the encoded symbol, an equation is obtained in which the encoded symbol is known and the information symbol is unknown. A simultaneous equation comprising the equations of the plurality of encoded symbols is constructed. At the time of decoding, an unknown information symbol is obtained by solving the simultaneous equations.

  In communication using the LT coding method, it is possible to obtain high reliability efficiently by adjusting the distribution time, and basically there is no need for retransmission. However, a distribution completion rate of 100% is achieved in an environment where the multicast distribution time is limited or the multicast distribution time must be reduced as much as possible for reasons such as increasing the distribution schedule and the number of distribution data. Therefore, differential download (ARQ: Automatic Repeat Request) is performed for those who have failed to deliver.

Also, a differential download method combining FEC and ARQ is known. For example, even if the simple differential download method (resending a lost packet) is used for communication using the LT code method, the lost packet There is a problem that it is difficult to select a packet effective for data recovery from among them, or that the number of retransmissions per user cannot be effectively reduced even if it is selected at random. On the other hand, in the retransmission technique described in Non-Patent Document 1, the number of differential downloads is reduced using the characteristics of FEC based on the XOR operation.
JP 2001-189665 A Tsutomu Sasaki, 4 others, “Proposal of a retransmission method in reliable multicast using forward error correction code based on XOR operation”, IEICE Tech. Bulletin, NS2004-288, March 2005.

However, the above-described conventional technology has the following problems.
(1) In the retransmission technique described in Non-Patent Document 1, since processing for selecting information symbols and packets to be retransmitted by the receiving terminal is performed, the load on the receiving terminal is increased and the battery life is shortened due to an increase in power consumption. There is a concern about increase in processing delay of communication and communication applications. In addition, since the amount of data when notifying the packet delivery apparatus of information symbols and packets to be retransmitted increases according to the number of differential downloads, there is a problem of reduced data transfer efficiency. Also, it is necessary to know the algorithm and data structure of the error correction code used for the XOR-based FEC, and when applied to an existing system, the data (in the FEC decoding operation stored in the memory of the receiving terminal) ( Since it is necessary to newly provide a function for accessing an undecoded information symbol, information symbol XOR information, and the like, problems such as an increase in terminal cost arise.

(2) In a simple differential download method in which a lost packet is retransmitted, the receiving terminal performs a process of detecting a lost packet, and thus there is a concern about the influence of the load as in (1) above. Further, since the transfer amount when notifying the packet distribution device of the detected packet increases according to the amount of lost packets and the total number of packets, the efficiency is poor in a wireless environment where the packet loss rate is large. Further, in order to detect a lost packet, regular identification data such as a sequence number is required for the packet.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to improve the efficiency of data transmission at the time of a communication error and to prevent an increase in load on the receiving apparatus.

  In order to solve the above-described problem, the communication system according to the present invention encodes a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data. A transmitting device that transmits a coded symbol, and a receiving device that receives the coded symbol and decodes the received coded symbol, and the receiving device represents a received amount of the coded symbol when decoding fails. The transmission apparatus has means for transmitting reception amount information to the transmission apparatus, and the transmission apparatus has means for determining an encoded symbol to be additionally distributed based on the reception amount information.

  In the communication system according to the present invention, the transmission device includes additional distribution number calculating means for calculating an additional distribution number of encoded symbols from the reception amount information, and is generated so as to be different from the first encoded symbol set. The encoded symbols are transmitted by unicast to the receiving device by the calculated number of additional distributions from the second encoded symbol set.

  In the communication system according to the present invention, the transmission device includes additional distribution number calculation means for calculating an additional distribution number of encoded symbols based on the set of reception amount information obtained from a plurality of reception devices, The encoded symbols are transmitted by multicast to the plurality of receiving apparatuses by the calculated number of additional distributions from the second encoded symbol set generated differently from the first encoded symbol set.

  A communication system according to the present invention includes: a transmission apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data; A receiving device that receives the encoded symbol and decodes the received encoded symbol, and the receiving device has means for transmitting the requested number of encoded symbols to the transmitting device when decoding fails. The transmission apparatus has means for determining an encoded symbol to be additionally distributed based on the number of requests.

  In the communication system according to the present invention, the transmission apparatus unicasts the required number of encoded symbols from the second encoded symbol set generated differently from the first encoded symbol set. It is characterized by transmitting to.

  In the communication system according to the present invention, the transmission device includes additional distribution number calculation means for calculating an additional distribution number of encoded symbols based on the set of request numbers obtained from a plurality of reception devices. The encoded symbols are transmitted by multicast to the plurality of receiving apparatuses by the calculated number of additional distributions from the second encoded symbol set generated differently from the one encoded symbol set.

  In the communication system according to the present invention, a code using a random number is used as a code used to generate the first encoded symbol set and the second encoded symbol set, and the transmission apparatus transmits encoded symbols. The random number sequence information used to generate the encoded symbol is sometimes included in the same packet and transmitted.

  In the communication system according to the present invention, a code using an exclusive OR operation is used as a code used to generate the first coded symbol set and the second coded symbol set, and the transmitting device When transmitting an encoded symbol, information on an exclusive OR operation relationship between the encoded symbol and the information symbol related to the generation of the encoded symbol is included in the same packet and transmitted.

  The communication system according to the present invention is characterized in that the first coding symbol set and the second coding symbol set are generated using the same coding parameter and different random number sequences.

  In the communication system according to the present invention, the second coded symbol set has a property different from the first coded symbol set among the third coded symbol sets generated redundantly by the method. The coding symbol is selected and generated so as to satisfy the condition of

  In the communication system according to the present invention, the condition is a distribution regulation of the number of information symbols used to generate each encoded symbol included in the second encoded symbol set.

  In the communication system according to the present invention, the condition is a definition of an exclusive OR operation number of information symbols used for generating each encoded symbol included in the second encoded symbol set. And

  In the communication system according to the present invention, the code is an LT code, a raptor code, or an LDPC code.

  In the communication system according to the present invention, a third encoded symbol set generated by a unique code having the same encoding parameter is divided into the first encoded symbol set and the second encoded symbol set. It is characterized by using.

  In the data distribution method according to the present invention, a transmission apparatus transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data. A first step of receiving the coded symbol, a second step of decoding the received coded symbol, and a receiving device when the decoding failure in the receiving step, A third step of transmitting reception amount information representing a reception amount to the transmission device; and a fourth step in which the transmission device determines an encoded symbol to be additionally distributed based on the reception amount information. It is characterized by.

  In the data distribution method according to the present invention, a transmission apparatus transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data. A first step of receiving the coded symbol, a second step of decoding the received coded symbol, and a receiving device when the decoding failure in the receiving step, The method includes a third process of transmitting a request number to the transmission apparatus, and a fourth process in which the transmission apparatus determines an encoded symbol to be additionally distributed based on the request number.

  ADVANTAGE OF THE INVENTION According to this invention, while improving the efficiency of the data transmission at the time of a communication error, the increase in the load concerning a receiver can be prevented.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a multicast distribution system according to an embodiment of the present invention. In the present embodiment, multicast distribution is described as an example, but the present invention is not limited to multicast distribution, and can be similarly applied to unicast distribution.
In FIG. 1, the sender has a distribution server 1 and an additional distribution server 2. The recipient has a communication terminal 3. Distribution server 1, additional distribution server 2, and communication terminal 3 are each connected to network 4. In the network 4, routers 5 that perform packet routing are arranged in a network. The router 5 supports multicast transfer.

  The distribution server 1 encodes information symbols obtained by dividing the distribution data, and performs multicast transmission 101 via the network 4 on the packet storing the obtained encoded symbols. The communication terminal 3 receives a multicast transmission packet from the distribution server 1 via the network 4. The communication terminal 3 decodes the received encoded symbol and, when the decoding fails, transmits reception amount information 110 indicating the reception amount of the encoded symbol to the additional distribution server 2. The additional distribution server 2 receives the reception amount information 110 from the communication terminal 3 via the network 4. Then, the additional distribution server 2 performs additional distribution 120 of encoded symbols based on the reception amount information 110. The encoded symbol additional distribution 120 may be multicast distribution or unicast distribution.

Next, a data distribution process according to the present embodiment will be described with reference to FIG.
FIG. 2 is a sequence chart showing a procedure of data distribution processing according to the present embodiment. As shown in FIG. 2, the data distribution process according to the present embodiment includes three phases 1, 2, and 3.

[Phase 1]
Phase 1 is a stage in which basic encoded symbols are distributed.
In phase 1, first, in step S11, the sender's distribution server 1 divides the distribution data into a plurality of data blocks, and encodes each data block using an error correction code (FEC). The data block refers to a division unit when data is divided into several parts and transmitted. A set of encoded symbols obtained by the encoding is defined as an encoded symbol set A. Next, the distribution server 1 multicast-distributes the encoded symbols of the encoded symbol set A by a specified amount. The prescribed amount may be a predetermined number (a prescribed number), or may be a time limit (a prescribed time) when distribution is performed.

In step S12, the communication terminal 3 of the receiver receives the encoded symbol by multicast, and starts decoding when a predetermined decoding start condition such as the number of receptions is satisfied. The decoding may be performed every time the encoded symbol is received, or may be performed every time the received encoded symbol reaches a certain amount.
In step S13, it is determined whether or not the decoding is successful before the end of the multicast distribution. If the decryption is successful, the data distribution ends. On the other hand, if the decoding fails, the process proceeds to phase 2. Note that decoding fails even when the above decoding start condition is not satisfied.

[Phase 2]
Phase 2 is a stage in which additional encoded symbols are distributed.
In phase 2, first, in step S21, the communication terminal 3 of the receiver transmits the reception amount information in phase 1 to the additional delivery server 2 of the sender. The reception amount information is information representing the reception amount of the encoded symbol, and for example, the reception number or loss number of the encoded symbol, the reception number or loss number of the packet, etc. can be used.
In step S <b> 22, the sender's additional distribution server 2 receives the received amount information from the communication terminal 3. Then, the additional distribution server 2 obtains the number of encoded symbols (the number of additional distributions) necessary for successful decoding of the distribution failure recipient based on the reception amount information. The number of additional distributions may be calculated from a predetermined arithmetic expression, or may be obtained by holding in advance a predetermined table having a correspondence relationship between reception amount information and the number of encoded symbols and referring to the table. Good.
In step S23, the additional distribution server 2 uses the encoded symbol set B different from the encoded symbol set A used for distribution in the phase 1, and distributes the encoded symbols of the encoded symbol set B by the number of additional distributions. . This additional distribution may be multicast distribution or unicast distribution. The encoded symbol set B may be prepared in advance, or may be created at the time of reception amount information reception or additional distribution. In addition, when additional distribution is performed by multicast distribution, the number of additional distributions for successful decoding of all the distribution failure recipients is obtained from reception amount information from a plurality of distribution failure recipients.

In step S24, when the communication terminal 3 of the receiver receives the encoded symbol that has been additionally distributed, the encoded symbol that has been additionally distributed, the encoded symbol received in phase 1, and the information decoded in phase 1 are also received. Decoding is started using a symbol and an encoded symbol that holds information of an undecoded information symbol after decoding.
In step S25, it is determined whether or not the decoding is successful. If the decryption is successful, the data distribution ends. On the other hand, if the decoding fails, the process proceeds to phase 3.

[Phase 3]
Phase 3 is a stage of distributing information symbols before encoding in order to complete the data distribution.
In phase 3, first, in step S <b> 31, the communication terminal 3 of the recipient transmits a message notifying the failure of decoding in phase 2 to the delivery server 1 of the sender.
In step S32, the distribution server 1 distributes all information symbols of the distribution data by a reliable communication method such as TCP (Transmission Control Protocol). Phase 3 is basically aimed at making data distribution to all recipients successful, so it is usually preferable to use unicast distribution. However, when using multicast distribution, the distribution time should be sufficient. Increase the reliability by making it longer.

  In phase 3, an undecoded information symbol may be requested from the receiver, and only the requested information symbol may be unicasted from the transmitter.

  Further, in the embodiment of FIG. 2, when the decoding of the phase 2 fails, the phase 3 is immediately shifted to. However, the phase 2 may be performed again. However, the encoded symbol sets used for distribution in each phase 2 are different from each other, and different from the encoded symbol set A in phase 1 are prepared.

  Next, a method for calculating the number of additional distributions in Phase 2 will be described.

  In general, in FEC, the reliability can be estimated from the relationship between the encoding rate and the number of encoded symbols received. It is also possible to estimate the reliability by computer simulation. In the present embodiment, the number of additional distributions is calculated based on the reliability. Hereinafter, the case where additional distribution is performed by unicast distribution and the case where multicast distribution is performed will be described separately. Here, the reception number r of encoded symbols is used as reception amount information obtained from a receiver that failed to decode.

[When performing additional delivery by unicast delivery]
In calculating the number of additional distributions when performing additional distribution by unicast distribution, a simulation (or analysis) using the reception number r and the encoding rate is performed, and the target reliability is determined from the reliability obtained from the result. Calculate the number of additional deliveries to achieve. As a method of calculating the number of additional distributions, for example, a predefined function may be used, or a reliability table illustrated in FIG. 3 may be prepared in advance and calculated from the reliability table.

  In the reliability table of FIG. 3, the vertical axis indicates the error rate as the reliability, and the horizontal axis indicates the number of received encoded symbols. From the reliability table, the number of receptions for achieving the target error rate is obtained. The difference between the number of receptions for achieving the target error rate and the number of receptions r obtained from the recipients who failed to decode is calculated as the number of additional distributions.

Further, as the function F used for calculating the number of additional distributions, for example, a function F (for example, a code C related to the encoding symbol set A, a code C ′ related to the encoding symbol set B, and the reception number r) is used. C, C ′, r), and a function F_e (C, C ′, E, r) in which reliability E is further added as an argument. For example, the reliability E may be defined as a redundant delivery amount from the basic delivery amount F of Phase 1 as in the following equation.
F_e (C, C ′, E, r) = F (C, C ′, r) + E
Normally, the reliability is determined by the number of recipients, but the number of recipients is not included in the input value (argument) of the above function, assuming that the sender knows to some extent.

  In addition, according to this unicast distribution, since a highly reliable communication method such as TCP is used, it is rare that the encoded symbol to be additionally distributed does not reach the receiver.

[When performing additional distribution by multicast distribution]
In the calculation of the number of additional distributions in the case of performing additional distribution by multicast distribution, a set of received numbers r (received number set B) obtained from a plurality of recipients that failed to decode and codes C and C ′ are used as arguments. A function G (C, C ′, B) to be defined is defined in advance, and the number of additional distributions is calculated using the function G (C, C ′, B). Here, the code C is a code related to the coding symbol set A, and the code C ′ is a code related to the coding symbol set B. Note that the reception number set B has a one-to-one correspondence with a set of loss rates associated with a plurality of recipients whose decoding has failed. Further, in the combination of the loss rate and the number of receptions, the “set” may be a set or a vector.

The function G (C, C ′, B) can be defined as follows, for example.
Suppose that N packets are multicast transmitted in phase 1 and that K packets need to be received in order for decoding to succeed with a predetermined high probability. Here, the relationship between the number of packets N and K is defined by the symbol C. For example, in the case of a Raptor code, K is 105% of N. The relationship between N and K can be calculated using simulation or the like. In addition, it is assumed that a similar loss pattern also occurs during multicast transmission during additional distribution in phase 2.

  When attention is paid to the smallest reception number a in the reception number set B, the loss rate of the receiver is “(N−a) / N”, and the receiver remains at the loss rate “K−”. The number of packets necessary to receive “a” packets in phase 2 is “N (K−a) / a”.

  In addition, in order to improve reliability, when α packets for redundancy (for example, a certain number (such as 5), the number corresponding to the square root of N (K−a) / a) are transmitted in phase 2, {[N (K−a) / a] + α} are additional distributions in phase 2. Instead of the redundant packet number α, the number of packets to be transmitted may be β times (for example, a fixed number times (eg, 1.1 times)). In that case, the additional delivery in Phase 2 is “β × N (K−a) / a”.

  Further, a function G_e (C, C ′, E, B) with the target reliability as an argument may be defined and used.

  Next, a method for generating the encoded symbol sets A and B used in the above phases 1 and 2 will be described.

The encoding symbol set A used in phase 1 and the encoding symbol set B used in phase 2 are generated differently. Provide a function to change the encoding parameter for each delivery or during delivery by understanding the algorithm and data format of error correction code (FEC) in advance or by inserting the encoding parameter into each packet. By changing the parameters, encoded symbol sets A and B having different properties can be generated. The error correction code is a code (encoding rate <1) that enables redundancy of input data (encoded data), and for example, an LT code, a Raptor code, or the like can be used. In the LT code and the Raptor code, examples of the encoding parameter to be changed include a distribution of the number of XOR operations at the time of encoding symbol generation. In the following description, in the FEC based on the XOR operation using the LT code, the Raptor code, or the like, the number of information symbols (the number of XOR operations) forming the encoded symbol is referred to as “order”, and the distribution is referred to as “order”. Referred to as "distribution".
Hereinafter, the order distribution changing method in each case will be described.

(1) Degree distribution changing method when FEC algorithm and data format are known First, an encoding symbol set T is generated using the same encoding parameters as the encoding symbol set A. However, the encoding parameter does not include a random number sequence. That is, a random number sequence used when generating the encoded symbol set B is different from the encoded symbol set A. Also, the encoded symbol set T is generated so as to have a more redundant size than the encoded symbol set B.

  Next, a coding symbol set S is generated by selecting a coding symbol of the corresponding order from the coding symbol set T so that the degree distribution is different from that of the coding symbol set A. Since the FEC algorithm is known, it is possible to know the order of the encoded symbol.

  More specifically, first, the number of elements (coding symbols) of the coding symbol set S is determined, and then the coding symbol set is set so as to have a desired degree distribution different from the coding symbol set A. The number of encoded symbols of each order included in S is determined. Also, the encoding symbol set S as the initial set is set as an empty set. Next, an arbitrary encoding symbol is sequentially selected from the encoding symbol set T and included in the encoding symbol set S. At this time, the order of the encoded symbols included in the encoded symbol set S is confirmed, and it is determined whether the number of encoded symbols of each order included in the encoded symbol set S is satisfied. Then, an arbitrary encoded symbol is selected from the encoded symbol set T and included in the encoded symbol set S until the number of encoded symbols of each order is satisfied. Thereby, the encoded symbol set S is completed. Note that a coding symbol selected from the coding symbol set T is deleted from the coding symbol set T. Further, when the coding symbol set T becomes an empty set before the coding symbol set S is completed, the number of elements of the coding symbol set T as the initial set is increased from the previous time, and the coding symbol is again set. Attempt to generate the set S.

  By using the generated encoded symbol set S as the encoded symbol set B in phase 2, the degree distribution can be changed in a pseudo manner, and the number of additional distributions in phase 2 can be reduced.

(2) Order distribution changing method in the case where a function for changing the encoding parameter is provided for each delivery or during delivery by inserting the encoding parameter into each packet, etc. In this case, encoding is performed so as to obtain a desired order distribution. Encoding for generating the encoding symbol set B is performed using the parameters. In accordance with the encoding, the encoding parameter to be inserted into the packet is changed.

  Note that the different properties of the encoded symbol sets A and B are not limited to the above-described degree distribution. When the format and parameters of the data structure corresponding to the desired change feature can be changed by the same method as in the above (1) and (2), different encoded symbol sets A and B can be generated.

  As a method of generating encoded symbol sets A and B having different properties by using features other than the order distribution, for example, the weight distribution composed of the weights of the encoded symbols is different between the encoded symbol sets A and B. It is possible to create a method. As the weight of the encoded symbol, for example, the number of XOR operations of information symbols at the time of encoding in the LT code can be used.

  More specifically, first, based on the weight distribution to be satisfied of the encoding symbol set B different from the weight distribution of the encoding symbol set A and the number of elements of the encoding symbol set B, it is included in the encoding symbol set B. Determine the weight of the encoded symbols and the number of encoded symbols for each weight. Also, the encoding symbol set T is generated using the same encoding parameters as the encoding symbol set A. However, the encoding parameter does not include a random number sequence. That is, a random number sequence used when generating the encoded symbol set B is different from the encoded symbol set A. Also, the encoded symbol set T is generated so as to have a more redundant size than the encoded symbol set B. Also, the encoding symbol set S as the initial set is set as an empty set.

  Next, an arbitrary encoding symbol is sequentially selected from the encoding symbol set T and included in the encoding symbol set S. At this time, the weights of the encoded symbols included in the encoded symbol set S are confirmed, and it is determined whether the number of encoded symbols of each weight included in the encoded symbol set S is satisfied. Then, an arbitrary encoded symbol is selected from the encoded symbol set T and included in the encoded symbol set S until the number of encoded symbols for each weight is satisfied. Thereby, the encoded symbol set S is completed. Note that a coding symbol selected from the coding symbol set T is deleted from the coding symbol set T. Further, when the coding symbol set T becomes an empty set before the coding symbol set S is completed, the number of elements of the coding symbol set T as the initial set is increased from the previous time, and the coding symbol is again set. Attempt to generate the set S. It should be noted that the generation of the encoded symbol set S can be simplified by providing a certain range for the target weight distribution.

  Next, an embodiment of the data distribution apparatus of the sender and the communication terminal of the receiver will be described.

FIG. 4 shows an embodiment of the sender data distribution apparatus 10.
4, the phase 1 distribution unit 20 corresponds to the distribution server 1 in FIG. 1, and the phase 2 distribution unit 30 corresponds to the additional distribution server 2 in FIG.
In the phase 1 distribution unit 20, the encoding unit 21 encodes the distribution data to generate an encoded symbol set A. The memory 22 stores the generated encoded symbol set A. The transmission unit 23 transmits the encoded symbols of the encoded symbol set A stored in the memory 22 via the network. In addition, the encoding unit 21 generates a coding symbol set B different from the coding symbol set A. The memory 24 stores the generated encoded symbol set B. In addition, the encoding unit 21 notifies the transmission unit 23 and the phase 2 distribution unit 30 of information related to encoding.

  In the phase 2 distribution unit 30, the transmission / reception unit 31 transmits the encoded symbol of the additional distribution in phase 2 via the network, and receives the reception amount information from the communication terminal of the recipient via the network. The memory 32 stores reception amount information received by the transmission / reception unit 31. The transmission encoded symbol number calculation unit 33 calculates the number of encoded symbols to be additionally distributed based on the reception amount information stored in the memory 32. The transmission encoding symbol selection unit 34 reads out the encoding symbols of the encoding symbol set B from the memory 24 of the phase 1 distribution unit 20 by the number of encoding symbols calculated by the transmission encoding symbol number calculation unit 33. The read encoded symbols of the encoded symbol set B are transmitted by the transmission / reception unit 31 via the network.

FIG. 5 shows an embodiment of the communication terminal 3 of the recipient.
In FIG. 5, the transmission / reception unit 41 receives the encoded symbols of phase 1 and the encoded symbols of additional distribution in phase 2 via the network. The memory 42 stores the encoded symbols of the phases 1 and 2 received by the transmission / reception unit 41, respectively. The decoding unit 43 performs decoding in phases 1 and 2 using the encoded symbols stored in the memory 42. The reception encoded symbol number calculation unit 44 calculates the reception amount from the decoding result of the decoding unit 43 and creates the reception amount information. The transmission / reception unit 41 transmits the generated reception amount information to the data distribution apparatus 10 of the sender via the network.

  According to the above-described embodiment, when reliable multicast data distribution using forward error correction is performed, a receiver and a sender that failed to decode due to loss of encoded symbols during communication or insufficient number of received encoded symbols. The amount of communication can be reduced. In addition, an increase in load on the receiving terminal can be prevented.

Further, according to the present embodiment, the following effects can be obtained.
(1) Since the receiver side that has failed in distribution does not select the differential download request data, the amount of calculation performed at the communication terminal on the receiver side can be greatly reduced. Thereby, for example, in a portable terminal, it is possible to suppress battery consumption and prevent processing delays in communication applications and the like.
(2) Since only the received amount information is required from the recipient who failed to deliver to the sender, the amount of data transmitted from the recipient to the sender can be reduced (specifically, the number of packets, the packet size, etc. can be reduced). it can).

(3) If you know what the encoding parameters mean (especially those related to the encoding rate), the internal implementation of encoding / decoding, the transmission packet data structure, the internal data structure at the time of decoding failure, etc. There is no need to know in particular, there are few changes to the existing system, and the implementation is simple. In the case of using a set of encoded symbols having the same characteristics in phase 1 for distributing basic encoded symbols and phase 2 for distributing additional encoded symbols, You don't have to know anything about what it means.
(4) When the LT code or the Raptor code is used, it is not necessary to specify a lost packet, so that the mounting is simplified, such as the need for the packet sequence number.

(5) The same packet format can be delivered in phase 1 and phase 2.
(6) In phase 2, by performing additional distribution of encoded symbols by multicast, the total transfer amount of additional distribution can be reduced when there are many unsuccessful distribution persons and the packet loss rate is high.
(7) Unlike the method of appropriately repeating the retransmission request and decoding described in Non-Patent Document 1, since the encoded symbols to be added can be delivered together in one communication session, decoding is performed with the communication session established. In such a case, it is not necessary to re-establish the communication session over and over every time decryption is performed, and a communication band for re-establishing the communication session is unnecessary, which is efficient.

(8) In the case of multicast distribution in which stochastic encoding is performed, such as an LT code or a Raptor code, the generation rule of an encoded symbol set at the time of additional distribution in phase 2 is changed decisively (for example, the above-mentioned The degree distribution of the LT code and the XOR operation relationship are changed using the method of changing the order distribution and weight distribution, or only those satisfying the selection are transmitted), and the number of times of delivery is smaller than when the generation rule is not changed. Additional distribution can be terminated. In this case, knowing the FEC algorithm and data format, or providing a function for changing the encoding parameters (related to the degree distribution) between the sender and the receiver in each device of the sender and the receiver. Good. However, it is necessary to match the implementation of each device of the sender and the receiver so that encoding and decoding operate normally even if the encoding parameter is changed. For example, a function for changing the encoding parameter for each distribution by inserting the encoding parameter into each packet, or a function for changing the encoding parameter during the distribution may be provided.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like within a scope not departing from the gist of the present invention.
For example, instead of receiving amount information from the receiver, the requested number of encoded symbols (the number of additional distributions in phase 2) may be notified. In this case, in the above-described embodiment, the receiver performs calculation of the number of additional distributions performed in the phase 2 performed by the sender, but it is not necessary to specify the encoded symbols to be additionally distributed. There is little burden on it. When the number of requested encoding symbols from the receiver is larger than the number of elements of the encoded symbol set B, all the encoded symbols in the encoded symbol set B are additionally distributed.

  Further, when the additional distribution is performed by multicast distribution, for example, the code C related to the encoding symbol set A, the code C ′ related to the encoding symbol set B, and the reception amount set D of each receiver are used as arguments. The function H (C, C ′, D) may be defined. As the function H (C, C ′, D), for example, it is necessary to multicast N packets in phase 1 and to receive K packets in order for decoding to succeed with a predetermined high probability. Is defined as follows. Focusing on the largest request number a ′ in the set D, the loss rate of the recipient is “(N−K + a ′) / N”. As a result, the number of additional distributions in phase 2 required for the receiver to receive the remaining a ′ encoded symbols with this loss rate is “N × a ′ / (K−a ′)”. . In order to improve the reliability, the redundantly encoded symbols are additionally distributed, and “N × a ′ / (K−a ′) + α” or “β × N × a ′ / (K−a). ')' Additional delivery.

  It is also possible to use the same error correction code (the same encoding parameter) in phase 1 and phase 2. In that case, adjustment is made so that the encoding rate corresponds to the sum of the transmission rates of phase 1 and phase 2.

  Further, if the encoded symbol set B for additional distribution in phase 2 can be generated at the time of execution of phase 2, it is not necessary to generate the encoded symbol set B in advance. Therefore, it is preferable that the encoded symbol set B is dynamically generated when the phase 2 is executed in consideration of the case where it is difficult to estimate the required minimum amount or the case where it is difficult to hold it.

  Note that a rateless code such as an LT code or a Raptor code is suitable for dynamic generation of a coded symbol set because a coded symbol set of any size can be generated semi-permanently in principle.

  In addition, the LT code and the Raptor code can generate a set of encoded symbols having different properties by changing the degree distribution and the XOR operation relationship. In addition, an LDPC code can be used as a code according to the present invention. Similarly, in an LDPC code, a parameter indicating an XOR operation relationship of parity is changed, or some parity generation methods are received from a sender. By sharing them with each other, it is possible to generate encoded symbol sets having different properties. Accordingly, by using the LT code, the Raptor code, or the LDPC code, it becomes easy to change the coded symbol set B used in the phase 2 in order to reduce the number of additional distributions.

  Further, as an error correction code according to the present invention, in addition to the above-described rateless codes such as LT codes and Raptor codes, codes applicable to coding rates such as Reed-Solomon codes can be applied. In the case of a code in which the coding rate is defined, if 100% of the coding symbols for the specified rate are received, the reliability is sufficiently achieved. Therefore, the number of additional distributions in phase 2 is the specified rate. An insufficient number of encoded symbols per minute is sufficient.

Moreover, the following variations (cases 1 and 2) are possible for the first encoded symbol set used in phase 1 and the second encoded symbol set used in phase 2 in the above-described embodiment.
(Case 1)
The same encoded symbol set having a larger number of elements than the number transmitted in phase 1 and the number transmitted in phase 2 is used for the first encoded symbol set and the second encoded symbol set. Then, after determining the number of transmissions in phases 1 and 2, a coding symbol to be transmitted is selected stochastically from the coding symbol set of each phase. In this case, the first encoded symbol set and the second encoded symbol set are the same, but the probability that the encoded symbol sets actually transmitted in each phase are different is very high. Similar effects can be obtained.

(Case 2)
As in the case 1, the same encoded symbol set is used for the first encoded symbol set and the second encoded symbol set. A determination function for selecting a coding symbol to be transmitted so that a set of coding symbols actually transmitted in phase 1 and phase 2 is different when selecting a transmission coding symbol after determining the number of transmissions in each phase. Provide. As a result, the first encoded symbol set and the second encoded symbol set are the same, but the encoded symbol sets that are actually transmitted in each phase can be made different. It is possible to obtain the effect.

It is a block diagram which shows the structure of the multicast delivery system which concerns on one Embodiment of this invention. It is a sequence chart which shows the procedure of the data delivery process which concerns on the same embodiment. It is a graph which shows the structural example of the reliability table which concerns on the same embodiment. It is a block diagram which shows the structure of the data delivery apparatus 10 which concerns on the Example of this invention. It is a block diagram which shows the structure of the communication terminal 3 which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Delivery server, 2 ... Additional delivery server, 3 ... Communication terminal, 4 ... Network, 5 ... Router, 20 ... Phase 1 delivery part, 21 ... Encoding part, 22, 24, 32, 42 ... Memory, 23 ... Transmission , 30 ... phase 2 distribution unit, 31, 41 ... transmission / reception unit, 33 ... transmission encoded symbol number calculation unit, 34 ... transmission encoded symbol selection unit, 43 ... decoding unit, 44 ... reception encoded symbol number calculation unit

Claims (16)

A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting reception amount information indicating the reception amount of encoded symbols to the transmission apparatus when decoding fails,
The transmission apparatus includes means for determining an encoded symbol to be additionally distributed based on the received amount information,
The transmission apparatus includes additional distribution number calculation means for calculating an additional distribution number of encoded symbols from the received amount information, and from a second encoded symbol set generated differently from the first encoded symbol set Transmit the encoded symbols by the calculated number of additional distributions to the receiving device by unicast,
A code using a random number is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmission device includes information on a random number sequence used for generation of the encoded symbol at the time of transmission of the encoded symbol, and transmits the same packet,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a distribution rule for the number of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting reception amount information indicating the reception amount of encoded symbols to the transmission apparatus when decoding fails,
The transmission apparatus includes means for determining an encoded symbol to be additionally distributed based on the received amount information,
The transmission apparatus includes additional distribution number calculation means for calculating an additional distribution number of encoded symbols from the received amount information, and from a second encoded symbol set generated differently from the first encoded symbol set Transmit the encoded symbols by the calculated number of additional distributions to the receiving device by unicast,
A code using a random number is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmission device includes information on a random number sequence used for generation of the encoded symbol at the time of transmission of the encoded symbol, and transmits the same packet,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a definition of the number of exclusive OR operations of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting reception amount information indicating the reception amount of encoded symbols to the transmission apparatus when decoding fails,
The transmission apparatus includes means for determining an encoded symbol to be additionally distributed based on the received amount information,
The transmission apparatus includes additional distribution number calculation means for calculating an additional distribution number of encoded symbols from the received amount information, and from a second encoded symbol set generated differently from the first encoded symbol set Transmit the encoded symbols by the calculated number of additional distributions to the receiving device by unicast,
A code using an exclusive OR operation is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmitter transmits information including the exclusive OR operation relationship between the encoded symbol and the information symbol related to the generation of the encoded symbol in the same packet when transmitting the encoded symbol,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a distribution rule for the number of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting reception amount information indicating the reception amount of encoded symbols to the transmission apparatus when decoding fails,
The transmission apparatus includes means for determining an encoded symbol to be additionally distributed based on the received amount information,
The transmission apparatus includes additional distribution number calculation means for calculating an additional distribution number of encoded symbols from the received amount information, and from a second encoded symbol set generated differently from the first encoded symbol set Transmit the encoded symbols by the calculated number of additional distributions to the receiving device by unicast,
A code using an exclusive OR operation is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmitter transmits information including the exclusive OR operation relationship between the encoded symbol and the information symbol related to the generation of the encoded symbol in the same packet when transmitting the encoded symbol,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a definition of the number of exclusive OR operations of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting reception amount information indicating the reception amount of encoded symbols to the transmission apparatus when decoding fails,
The transmission apparatus includes means for determining an encoded symbol to be additionally distributed based on the received amount information,
The transmitting apparatus includes additional distribution number calculating means for calculating the number of additional distributions of encoded symbols based on the set of reception amount information obtained from a plurality of receiving apparatuses, and is different from the first encoded symbol set. The number of additional distributions calculated from the second set of encoded symbols generated as described above is transmitted to the plurality of receiving devices by multicast,
A code using a random number is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmission device includes information on a random number sequence used for generation of the encoded symbol at the time of transmission of the encoded symbol, and transmits the same packet,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a distribution rule for the number of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting reception amount information indicating the reception amount of encoded symbols to the transmission apparatus when decoding fails,
The transmission apparatus includes means for determining an encoded symbol to be additionally distributed based on the received amount information,
The transmitting apparatus includes additional distribution number calculating means for calculating the number of additional distributions of encoded symbols based on the set of reception amount information obtained from a plurality of receiving apparatuses, and is different from the first encoded symbol set. The number of additional distributions calculated from the second set of encoded symbols generated as described above is transmitted to the plurality of receiving devices by multicast,
A code using a random number is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmission device includes information on a random number sequence used for generation of the encoded symbol at the time of transmission of the encoded symbol, and transmits the same packet,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a definition of the number of exclusive OR operations of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting reception amount information indicating the reception amount of encoded symbols to the transmission apparatus when decoding fails,
The transmission apparatus includes means for determining an encoded symbol to be additionally distributed based on the received amount information,
The transmitting apparatus includes additional distribution number calculating means for calculating the number of additional distributions of encoded symbols based on the set of reception amount information obtained from a plurality of receiving apparatuses, and is different from the first encoded symbol set. The number of additional distributions calculated from the second set of encoded symbols generated as described above is transmitted to the plurality of receiving devices by multicast,
A code using an exclusive OR operation is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmitter transmits information including the exclusive OR operation relationship between the encoded symbol and the information symbol related to the generation of the encoded symbol in the same packet when transmitting the encoded symbol,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a distribution rule for the number of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting reception amount information indicating the reception amount of encoded symbols to the transmission apparatus when decoding fails,
The transmission apparatus includes means for determining an encoded symbol to be additionally distributed based on the received amount information,
The transmitting apparatus includes additional distribution number calculating means for calculating the number of additional distributions of encoded symbols based on the set of reception amount information obtained from a plurality of receiving apparatuses, and is different from the first encoded symbol set. The number of additional distributions calculated from the second set of encoded symbols generated as described above is transmitted to the plurality of receiving devices by multicast,
A code using an exclusive OR operation is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmitter transmits information including the exclusive OR operation relationship between the encoded symbol and the information symbol related to the generation of the encoded symbol in the same packet when transmitting the encoded symbol,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a definition of the number of exclusive OR operations of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting the requested number of encoded symbols to the transmitting apparatus when decoding fails,
The transmission device includes means for determining an encoded symbol to be additionally distributed based on the number of requests,
The transmitting apparatus transmits the requested number of encoded symbols from the second encoded symbol set generated differently from the first encoded symbol set to the receiving apparatus by unicast;
A code using a random number is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmission device includes information on a random number sequence used for generation of the encoded symbol at the time of transmission of the encoded symbol, and transmits the same packet,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a distribution rule for the number of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting the requested number of encoded symbols to the transmitting apparatus when decoding fails,
The transmission device includes means for determining an encoded symbol to be additionally distributed based on the number of requests,
The transmitting apparatus transmits the requested number of encoded symbols from the second encoded symbol set generated differently from the first encoded symbol set to the receiving apparatus by unicast;
A code using a random number is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmission device includes information on a random number sequence used for generation of the encoded symbol at the time of transmission of the encoded symbol, and transmits the same packet,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a definition of the number of exclusive OR operations of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting the requested number of encoded symbols to the transmitting apparatus when decoding fails,
The transmission device includes means for determining an encoded symbol to be additionally distributed based on the number of requests,
The transmitting apparatus transmits the requested number of encoded symbols from the second encoded symbol set generated differently from the first encoded symbol set to the receiving apparatus by unicast;
A code using an exclusive OR operation is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmitter transmits information including the exclusive OR operation relationship between the encoded symbol and the information symbol related to the generation of the encoded symbol in the same packet when transmitting the encoded symbol,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a distribution rule for the number of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting the requested number of encoded symbols to the transmitting apparatus when decoding fails,
The transmission device includes means for determining an encoded symbol to be additionally distributed based on the number of requests,
The transmitting apparatus transmits the requested number of encoded symbols from the second encoded symbol set generated differently from the first encoded symbol set to the receiving apparatus by unicast;
A code using an exclusive OR operation is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmitter transmits information including the exclusive OR operation relationship between the encoded symbol and the information symbol related to the generation of the encoded symbol in the same packet when transmitting the encoded symbol,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a definition of the number of exclusive OR operations of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting the requested number of encoded symbols to the transmitting apparatus when decoding fails,
The transmission device includes means for determining an encoded symbol to be additionally distributed based on the number of requests,
The transmitting apparatus includes additional distribution number calculating means for calculating an additional distribution number of encoded symbols based on the set of request numbers obtained from a plurality of receiving apparatuses, and is different from the first encoded symbol set. The number of additional distributions calculated from the second set of encoded symbols generated in (b) is transmitted to the plurality of receiving devices by multicast,
A code using a random number is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmission device includes information on a random number sequence used for generation of the encoded symbol at the time of transmission of the encoded symbol, and transmits the same packet,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a distribution rule for the number of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting the requested number of encoded symbols to the transmitting apparatus when decoding fails,
The transmission device includes means for determining an encoded symbol to be additionally distributed based on the number of requests,
The transmitting apparatus includes additional distribution number calculating means for calculating an additional distribution number of encoded symbols based on the set of request numbers obtained from a plurality of receiving apparatuses, and is different from the first encoded symbol set. The number of additional distributions calculated from the second set of encoded symbols generated in (b) is transmitted to the plurality of receiving devices by multicast,
A code using a random number is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmission device includes information on a random number sequence used for generation of the encoded symbol at the time of transmission of the encoded symbol, and transmits the same packet,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a definition of the number of exclusive OR operations of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting the requested number of encoded symbols to the transmitting apparatus when decoding fails,
The transmission device includes means for determining an encoded symbol to be additionally distributed based on the number of requests,
The transmitting apparatus includes additional distribution number calculating means for calculating an additional distribution number of encoded symbols based on the set of request numbers obtained from a plurality of receiving apparatuses, and is different from the first encoded symbol set. The number of additional distributions calculated from the second set of encoded symbols generated in (b) is transmitted to the plurality of receiving devices by multicast,
A code using an exclusive OR operation is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmitter transmits information including the exclusive OR operation relationship between the encoded symbol and the information symbol related to the generation of the encoded symbol in the same packet when transmitting the encoded symbol,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a distribution rule for the number of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above. A transmitting apparatus that transmits encoded symbols from a first encoded symbol set of encoded symbols obtained by encoding distribution data using a code that enables redundancy of encoded data;
A receiving device that receives the encoded symbol and decodes the received encoded symbol;
The receiving apparatus has means for transmitting the requested number of encoded symbols to the transmitting apparatus when decoding fails,
The transmission device includes means for determining an encoded symbol to be additionally distributed based on the number of requests,
The transmitting apparatus includes additional distribution number calculating means for calculating an additional distribution number of encoded symbols based on the set of request numbers obtained from a plurality of receiving apparatuses, and is different from the first encoded symbol set. The number of additional distributions calculated from the second set of encoded symbols generated in (b) is transmitted to the plurality of receiving devices by multicast,
A code using an exclusive OR operation is used as a code used to generate the first encoded symbol set and the second encoded symbol set,
The transmitter transmits information including the exclusive OR operation relationship between the encoded symbol and the information symbol related to the generation of the encoded symbol in the same packet when transmitting the encoded symbol,
For generating the first encoded symbol set and the second encoded symbol set, the same encoding parameter is used and different random number sequences are used,
The second encoded symbol set is encoded so as to satisfy a condition of having a property different from that of the first encoded symbol set from among the third encoded symbol sets generated redundantly by the method. Generated by selecting a symbol,
The condition is a definition of the number of exclusive OR operations of information symbols used to generate each encoded symbol included in the second encoded symbol set.
A communication system characterized by the above.

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