JP4476767B2 - Multicast distribution system, communication terminal device, and data retransmission method - Google Patents

Description

  The present invention relates to a multicast distribution system, a communication terminal device, and a data retransmission method.

  In recent years, multicast distribution techniques for efficiently distributing large volumes of data to a large number of recipients have been studied. For example, the receiver performs error correction based on the received data in order to increase resistance against communication errors such as noise added to the transmission data transmitted by the sender or loss of transmission data during transmission. A communication method using an encoding method for restoring distribution data has been proposed. For example, Patent Document 1 discloses a communication method using a Fountain encoding method, which is one of encoding methods configured only by exclusive OR (XOR) operations.

  In a communication method using a Fountain code, a sender divides distribution data into blocks of a predetermined size, and encodes each data block unit to generate transmission data. In the encoding process, one or a plurality of data blocks are selected based on a certain probability, and the result of XORing the selected data block is set as the code word of the set. Then, the code word generation operation is repeated until the simultaneous linear equations having all data blocks as solutions are established as redundant, and the generated code word is used as transmission data. Further, a redundant simultaneous linear equation for associating a code word as a result of the XOR operation for each set of data blocks is shared between the sender and the receiver.

  The receiver restores the distribution data by decoding the received codeword. At this time, the reception and decoding of the code word are repeated until the restoration of the distribution data is completed. In this decoding process, the simultaneous linear equations are solved using the received code word. One general solution of the simultaneous linear equations (hereinafter referred to as weight 1 decoding method) will be described. In the weight 1 decoding method, first, attention is paid to an equation that has a one-to-one relationship and a solution is obtained immediately. That is, a code word of an equation (equation of weight 1) corresponding to one code word and one data block is received. A search is performed from the data to obtain a code word that is a solution of the equation (that is, the data block). The found code word is XORed with the code word comprising the data block. Next, the codeword of the equation that newly becomes “weight 1” based on the found codeword is searched, and the codeword that becomes the solution of the equation (that is, the data block) is obtained. By repeating this operation, all solutions (data blocks) are obtained.

FIG. 14 and FIG. 15 are explanatory diagrams for explaining the above-described weight 1 decoding method.
In FIG. 14, in step 0, the sender divides the distribution data into four data blocks A, B, C, and D. Then, for each set of data blocks selected from the data blocks A to D, an XOR operation is performed on the value of each data block in the set to generate a code word that becomes transmission data. In the example of FIG. 14, five codewords X ₁ , X ₂ , X ₃ , X ₄ , and X ₅ are generated. The value of the code word X ₁ is the XOR operation result of each value of the data blocks A, B, and C, the value of the code word X ₂ is the XOR operation result of each value of the data blocks A and B, and the code word X ₃ Is equal to the value of the data block C, the value of the code word X ₄ is the XOR operation result of the values of the data blocks A, B, D, and the value of the code word X _{5 is} the value of each of the data blocks A, C This is the result of XOR operation.

In step 1, the recipient, from the received code word, to find the code word X ₃ of weight 1. The value of the codeword X ₃ is equal to the value of the data block C. Then, the found value of the code word X ₃ is XORed with each value of the code words X ₁ and X ₅ made up of the data block C. These XOR operation results are the values of codewords X ′ ₁ and X ′ ₅ .

In step 2, a new codeword X ′ ₅ with a weight of 1 is found. The value of the code word X ′ ₅ is equal to the value of the data block A. Then, the found value of the code word X ′ ₅ is XORed with each value of the code word X ′ ₁ , X ₂ , X ₄ consisting of the data block A. These XOR operation results are the values of code words X ″ ₁ , X ′ ₂ , and X ′ ₄ .

Similarly, in step 3 of FIG. 15, a new code word X ″ ₁ with a weight of ₁ is found. The value of this code word X ″ ₁ is equal to the value of the data block B. Then, the value of the found code word X ″ ₁ is XORed with each value of the code words X ′ ₂ and X ′ ₄ consisting of the data block B. These XOR operation results are the values of the code words X ″ ₂ and X ″ ₄ .

In step 4 of FIG. 15, a new codeword X ″ ₄ with a weight of 1 is found. The value of the code word X ″ ₄ is equal to the value of the data block D.
In step 5, since a new codeword with weight 1 is not found, decoding ends.
In the examples of FIGS. 14 and 15, all the solutions of the simultaneous linear equations are obtained, that is, all the data blocks A to D are restored.

  As conceptually shown in FIGS. 14 and 15, the weight 1 decoding method can be realized by matrix calculation in actual computer processing.

Since the simultaneous linear equations are configured as redundant as described above, even if a part of the codeword transmitted from the sender cannot be received normally due to a communication error, all the solutions (data Block). However, depending on the method and degree of codeword reception error, not all solutions (data blocks) can be obtained, and the distribution data cannot be completely restored. In this case, the receiver requests the sender to retransmit the data block that could not be restored. Alternatively, it is requested to retransmit a codeword that has a reception error.
JP 2001-189665 A

  However, the conventional method for dealing with a communication error described above has a problem that the amount of retransmission is large and the efficiency is low. For example, when a receiver requests a data block that could not be restored, in fact, if there is a small amount of codewords that resulted in a reception error, the unanswered equations can be solved all at once and a large amount of unrecovered data blocks can be obtained. Regardless, it requires a large amount of unrestored data blocks and is very inefficient. On the other hand, when requesting a codeword that has received a reception error, a large amount of codewords with a large number of reception errors are requested, even though the number of unrestored data blocks is smaller than that of a reception error codeword. Is bad.

  The present invention has been made in view of such circumstances, and its purpose is to divide distribution data into a predetermined number of data blocks and perform an exclusive OR operation for each arbitrarily selected set of data blocks. Another object of the present invention is to provide a multicast distribution system, a communication terminal apparatus, and a data retransmission method capable of improving the efficiency of data retransmission when a communication error occurs in a multicast distribution system that transmits the codeword generated in the multicast format.

  In order to solve the above problems, the multicast distribution system according to the present invention generates distribution data by dividing the distribution data into a predetermined number of data blocks and performing an exclusive OR operation for each arbitrarily selected data block set. In a multicast distribution system including a transmission device that transmits a codeword in a multicast format, the multicast distribution system includes a communication terminal device that receives the transmitted codeword via a network and decodes the received codeword by a weight 1 decoding method, The communication terminal apparatus includes first retransmission requesting means for requesting the transmission apparatus to retransmit a data block having a large weight according to the weight 1 decoding method from among data blocks that have failed to be restored as a result of the decoding. It is characterized by that.

  In the multicast distribution system according to the present invention, the second retransmission request means for requesting the transmitting apparatus to retransmit all data blocks that have failed to be restored, and the third requesting the transmitting apparatus to retransmit the lost codeword. A retransmission requesting means; and a retransmission method selecting means for selecting any one of the first to third retransmission requesting means based on the ratio of data blocks that have failed to be restored and the ratio of lost codewords. It is characterized by having.

  In the multicast distribution system according to the present invention, the retransmission method selection means defines a first upper limit of a ratio of data blocks that have failed to be restored as a condition to be satisfied in order to select the second retransmission request means. It has a threshold value.

  In the multicast distribution system according to the present invention, the retransmission method selection means includes a second threshold value that defines a high range of lost codeword ratios and a third range that defines a lower range of lost codeword ratios And when the second threshold is satisfied, the second retransmission requesting unit is changed to the second retransmission requesting unit when the selection condition related to the second retransmission requesting unit based on the first threshold is not satisfied. And when the third threshold is satisfied, the third retransmission request means is selected, and when both the second and third thresholds are not satisfied, the first retransmission request means is selected. It is characterized by selecting.

  In the multicast distribution system according to the present invention, the retransmission method selection means has a function or a table representing selection contents of the retransmission request means for all combinations of the number of data blocks that have failed to be restored and the number of lost codewords. It is characterized by that.

  The communication terminal device according to the present invention divides distribution data into a predetermined number of data blocks, and transmits a codeword generated by performing an exclusive OR operation for each set of arbitrarily selected data blocks in a multicast format. A receiving unit that receives the transmitted codeword from a device via a network; a decoding unit that decodes the received codeword using a weight 1 decoding method; and a data block that has failed to be restored as a result of the decoding. And a first retransmission request means for requesting the transmission apparatus to retransmit a data block having a large weight according to the weight 1 decoding method.

  In the communication terminal apparatus according to the present invention, a second retransmission request means for requesting the transmitting apparatus to retransmit all data blocks that have failed to be restored, and a third requesting the transmitting apparatus to retransmit the lost codeword A retransmission requesting means; and a retransmission method selecting means for selecting any one of the first to third retransmission requesting means based on the ratio of data blocks that have failed to be restored and the ratio of lost codewords. It is characterized by having.

  In the communication terminal apparatus according to the present invention, the retransmission method selection means defines a first upper limit of a ratio of data blocks that have failed to be restored as a condition to be satisfied in order to select the second retransmission request means. It has a threshold value.

  In the communication terminal apparatus according to the present invention, the retransmission method selection means includes a second threshold value that defines a high-order range of the lost codeword ratio and a third range that defines a lower-order range of the lost codeword ratio. And when the second threshold is satisfied, the second retransmission requesting unit is changed to the second retransmission requesting unit when the selection condition related to the second retransmission requesting unit based on the first threshold is not satisfied. And when the third threshold is satisfied, the third retransmission request means is selected, and when both the second and third thresholds are not satisfied, the first retransmission request means is selected. It is characterized by selecting.

  In the communication terminal apparatus according to the present invention, the retransmission scheme selection means has a function or a table representing selection contents of the retransmission request means for all combinations of the number of data blocks that have failed to be restored and the number of lost codewords. It is characterized by that.

  The data retransmission method according to the present invention divides distribution data into a predetermined number of data blocks and transmits a code word generated by performing an exclusive OR operation for each arbitrarily selected set of data blocks in a multicast format. A data retransmission method in a multicast distribution system comprising an apparatus, wherein a communication terminal device that receives the transmitted codeword via a network decodes the received codeword by a weight 1 decoding method, and the decoding As a result, it includes a first retransmission request process for requesting the transmitting apparatus to retransmit a data block having a large weight according to the weight 1 decoding method from among data blocks that have failed to be restored.

In the data retransmission method according to the present invention, the communication terminal apparatus requests the transmission apparatus to retransmit all data blocks that have failed to be restored, and transmits the lost codeword to the transmission apparatus. A retransmission requesting one of the first to third retransmission request processes based on the third retransmission request process requested by the user, the ratio of data blocks that failed to be restored, and the ratio of lost codewords And a method selection process.

In the data retransmission method according to the present invention, in the retransmission scheme selection process, as a condition to be satisfied in order to select the second retransmission request process , a first upper limit of a ratio of data blocks that have failed to be restored is defined. It has a threshold value.

In the data retransmission method according to the present invention, in the retransmission scheme selection process, a second threshold value that defines a higher range of the ratio of lost codewords and a third range that defines a lower range of the ratio of lost codewords And when the second threshold is satisfied when the selection condition related to the second retransmission request process based on the first threshold is not satisfied, the second retransmission request process is performed. And when the third threshold is satisfied, the third retransmission request process is selected, and when both the second and third thresholds are not satisfied, the first retransmission request process is selected. It is characterized by selecting.

In the data retransmission method according to the present invention, the retransmission method selection process includes a function or a table representing selection contents of the retransmission request process for all combinations of the number of data blocks that have failed to be restored and the number of lost codewords. It is characterized by that.

  According to the present invention, in a multicast distribution system that divides distribution data into a predetermined number of data blocks and transmits a codeword generated by performing an exclusive OR operation for each arbitrarily selected set of data blocks in a multicast format. Therefore, it is possible to improve the efficiency of data retransmission when a communication error occurs.

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 FIG. 1, a distribution server 11 encodes distribution data by a Fountain encoding method, which is one of encoding methods composed only of an exclusive OR (XOR) operation, and stores a packet in which the obtained code word is stored. Is multicast transmitted via the packet network 20. The receiving terminal 12 receives the multicast transmission packet from the distribution server 11 via the packet network 20.

  In the above encoding process, the distribution data is divided into a predetermined number of data blocks, one or a plurality of the divided data blocks are selected, and the result of XOR operation of the selected data block is obtained as It is a code word. Then, the code word generation operation is repeated until the simultaneous linear equations having all data blocks as solutions are established as redundant, and the generated code word is used as transmission data. Further, the redundant simultaneous linear equations for associating the code word that is the result of the XOR operation for each set of data blocks are shared between the distribution server 11 and the receiving terminal 12. The simultaneous linear equations are shared by storing in each memory a predetermined determinant (a table showing combinations of data blocks for performing an XOR operation) in each distribution server 11 and receiving terminal 12. . Alternatively, for each packet transmitted by the sender, information on the combination of data blocks subjected to the XOR operation is added in the header.

  The packet network 20 is provided with a router 21 that performs packet routing. The router 21 supports multicast transfer.

Next, the decoding operation of the receiving terminal 12 will be described.
FIG. 2 is a flowchart showing the flow of the decoding process performed by the receiving terminal 12 shown in FIG.
In FIG. 2, the receiving terminal 12 decodes the codeword stored in the multicast received packet by the weight 1 decoding method (steps S101 and S102). As a result of this decoding, when a data block that has failed to be restored is generated (NO in step S103), the receiving terminal 12 transmits a retransmission request to the distribution server 11.
In the present embodiment, one of the following three retransmission methods 1 to 3 is selected to make a retransmission request to the distribution server 11.

[Resending method 1]
The distribution server 11 is requested to retransmit all data blocks that have failed to be restored. The data block to be retransmitted is determined based on the sequence number added to the data block. The receiving terminal 12 requests the distribution server 11 one by one by designating the data block to be retransmitted with the corresponding sequence number. This request order may follow a sequence number or may be random. The distribution server 11 unicasts the data block to be retransmitted to the receiving terminal 12 in response to the received retransmission request.

[Retransmission method 2]
The distribution server 11 is requested to retransmit a codeword that has been lost due to a reception error. The code word to be retransmitted is determined based on the sequence number added to the code word. The receiving terminal 12 creates a retransmission request list of codewords to be retransmitted and transmits it to the distribution server 11. In the retransmission request list, a sequence number corresponding to the codeword to be retransmitted is described. The distribution server 11 unicasts the codeword to be retransmitted to the receiving terminal 12 based on the received retransmission request list.

[Resending method 3]
Of the data blocks that have failed to be restored, the distribution server 11 is requested to retransmit a data block having a large weight. A data block having a large weight refers to a data block having a large proportion of unsolved equations in a simultaneous linear equation that associates a code word that is an XOR operation result for each set of data blocks that are encoding units. The receiving terminal 12 requests the data block from the distribution server 11 in descending order of weight. It is efficient and preferable to request the number of data blocks that can be stored in one packet in one request. The distribution server 11 unicasts the data block to be retransmitted to the receiving terminal 12 in response to the received retransmission request.

  Returning to FIG. 2, when a data block that has failed to be restored is generated (NO in step S <b> 103), the receiving terminal 12 performs the above retransmission based on the percentage of data blocks that have failed to be restored and the percentage of codewords that have been lost due to reception errors One of the methods 1 to 3 is selected (steps S104 and S106). In this embodiment, the ratio of data blocks that have failed to be restored is expressed as a predetermined number of divisions when the distribution data is divided into data blocks, that is, the number of data blocks that have failed to be restored relative to the total number of data blocks. Similarly, the ratio of lost codewords is expressed as the number of lost codewords relative to the total number of data blocks.

Specifically, when the number of data blocks that have failed to be restored is less than the threshold value a (YES in step S104), the retransmission method 1 is selected and a retransmission request is made to the distribution server 11 (step S105).
When the number of data blocks that have failed to be restored is greater than or equal to the threshold value a (NO in step S104), if the number of lost codewords Loss_number is less than the threshold value b, the retransmission method 2 is selected and the distribution server 11 A retransmission request is made (step S107).

When the number of data blocks that have failed to be restored is greater than or equal to the threshold a (NO in step S104), if the number of lost codewords Loss_number is greater than or equal to the threshold c, the retransmission method 1 is selected, and the distribution server 11 A retransmission request is made (step S105).
In the case where the number of data blocks that have failed to be restored is greater than or equal to the threshold a (NO in step S104), if the number of lost codewords Loss_number is greater than or equal to the threshold b and less than or equal to the threshold c, the retransmission scheme 3 is selected. A retransmission request is made to the distribution server 11 (step S108).

  Next, when the receiving terminal 12 receives a response from the distribution server 11 in response to the retransmission request (step S109), the receiving terminal 12 returns to step S102, and again tries weight 1 decoding using the received retransmission data. The above retransmission request and re-decoding are repeated until the restoration of all data blocks is completed.

FIG. 3 is a conceptual diagram for explaining the decoding process according to the present embodiment.
In the example of FIG. 3, the distribution server 11 of the sender S divides the distribution data into three data blocks A, B, and C. Then, for each set of data blocks selected from the data blocks A to C, an XOR operation is performed on the values of each data block in the set, and five codewords X ₁ , X ₂ , X _{3 serving as} transmission data are obtained. , X ₄ and X ₅ are generated. The value of the code word X ₁ is the XOR operation result of each value of the data blocks A, B, and C, the value of the code word X ₂ is the XOR operation result of each value of the data blocks A and B, and the code word X ₃ Is equal to the value of the data block C, the value of the code word X ₄ is the XOR operation result of the values of the data blocks A and B, and the value of the code word X ₅ is the XOR of the values of the data blocks A and C. It is a calculation result.

Of the receivers R ₁ , R ₂ , R ₃ , R ₄ , and R ₅ , the receivers R ₄ and R ₅ successfully decode all of the data blocks A, B, and C from their normally received codewords. is doing.

Recipient R ₁ is unsuccessfully decoded, by selecting the retransmission scheme 3, the weight is requesting retransmission of the maximum data block A. This is because the ratio of data blocks that cannot be restored is large (in the example of FIG. 3, all data blocks A, B, and C cannot be restored), and the percentage of lost codewords is neither large nor small (see FIG. In the example 3, 2 out of 5 are lost), so an efficient retransmission is attempted by the retransmission method 3.

Receiver R ₂ is unsuccessfully decoded, by selecting the retransmission scheme 2, requesting retransmission of the codeword X ₃ was lost. This is because the ratio of data blocks that cannot be restored is large (in the example of FIG. 3, all data blocks A, B, and C cannot be restored) and the percentage of lost codewords is small (in the example of FIG. 3). Therefore, efficient retransmission is attempted by the retransmission method 2.

Recipient R ₃ is unsuccessfully decoded, by selecting the retransmission scheme 1, all data blocks A not be restored, requesting retransmission of the B. This is because the ratio of lost codewords is large (in the example of FIG. 3, 3 out of 5 are lost).

  According to the above-described embodiment, since any one of the retransmission schemes 1 to 3 is selected based on the ratio of data blocks that have failed to be restored and the ratio of codewords that have been lost due to reception errors, It is possible to perform retransmission according to the reception state, and it is possible to improve the efficiency of data retransmission when a communication error occurs.

  Of the retransmission methods 1 to 3, only the retransmission method 3 may be performed. By always performing retransmission method 3, it is possible to perform data retransmission more efficiently than the conventional retransmission method that performs only one of retransmission methods 1 and 2.

Next, a method for obtaining threshold values a, b, and c used for selection determination of the above-described retransmission methods 1 to 3 will be described.
In this embodiment, threshold values a, b, and c are obtained based on computer simulation.

First, parameters (given by the implementation environment) that are the premise of computer simulation will be described. The parameters used in the computer simulation are shown below.
・ Distributed data ・ Multicast encoding method (how to select the number of data blocks K and XOR operation (choose_XOR_func))
・ Multicast decoding method (weight 1 decoding method)
-Number of multicast delivery codewords (send_packet)
・ Disappearance probability (p)
-Number of recipients (receiver_number)
・ Number of simulations (trial_number)

  In this computer simulation, in multicast distribution to “receiver_number” recipients, the multicast encoding / decoding method (XOR operation base), distribution data, and multicast distribution time are preset. Further, it is assumed that the transmission rate of communication is substantially constant, and the number of codewords (packets) that can be distributed within the multicast distribution time is constant (send_packet). The assumed transmission rate may be an average of experimental values in an actual environment or may be an estimated value from experience.

  It is assumed that codewords (packets) at the time of multicast transmission are lost with an average loss probability (p) (random loss). The value of the probability of disappearance (p) may be an average of experimental values in an actual environment, or may be an estimated value from experience. Further, when the loss pattern of the communication path can be mathematically modeled, it is preferable to use that pattern without using the loss probability (p). A general encoding parameter is the number of data blocks K and how to select an XOR operation (choose_XOR_func). For the random number, a general pseudo random number generator is used. The number of computer simulations (trial_number) is arbitrarily set by the person who performs the simulation.

Next, a simple flow of computer simulation and its measurement items will be described.
The computer simulation is performed by repeating the following measurement for the number of simulations (trial_number).
When multicast distribution is performed using the above parameters (excluding the number of simulations), it is assumed that there is a receiver who has failed to restore data (if there is no such receiver, one simulation is completed). For each recipient who failed to restore the data, the above-described retransmission methods 1, 2, and 3 are used, and the following four measurement items 1 to 4 are measured as a set.
Measurement item 1: Number of data blocks that the receiver has not restored by multicast (number of data blocks that have not been restored)
Measurement item 2: Number of codewords lost in multicast delivery (number of lost codewords)
・ Measurement item 3; Retransmission method used ・ Measurement item 4; Number of retransmissions required for data restoration by the retransmission method When the above measurement is completed for all recipients that failed to restore data, the simulation is 1 The batch ends.
The threshold values a, b, and c are obtained using the measurement results obtained by the simulation. In all the simulations, only one retransmission method 3 is used when there is no single recipient who has failed to decode data.

Next, how to determine the threshold values a, b, and c will be described in detail.
First, the following parameters εa, εb, εc are determined for each of the threshold values a, b, c.
・ Near ε for parameter determination εa, εb, εc ≧ 0
The parameter ε is a parameter that defines a trade-off relationship between the amount of retransmission (number of times) of the sender and the amount of calculation of the receiver when the retransmission method is selected. For example, it is a parameter that provides a reference for making a determination such that “if the difference in retransmission amount is about ε, it is better to use the retransmission method with the smaller calculation amount”.
The parameter ε also functions as a parameter that determines an allowable range of error. For example, “Retransmission method 3 is used as much as possible, but even if a simulation error of about ε is taken into consideration, if it is judged that another retransmission method is better, one using the better retransmission method It is a parameter that provides a reference for making a judgment such as “good”.

  The values of the parameters εa, εb, and εc are determined by a simulation executor, a retransmission designer, or a sender. For example, the value of the parameter ε is obtained by comparing the amount of calculation that can be accepted by the receiver's terminal with the amount of retransmission that is allowed depending on the network. In this case, the amount of calculation and the amount of retransmission are converted into a reference value of the same cost and compared to obtain an optimum parameter. For example, the value of the parameter ε that minimizes “(cost of retransmission amount) + (cost of calculation amount)” is calculated.

  Next, using the measurement results obtained by the simulation, the threshold values are obtained in the order of threshold value a, threshold value b, and threshold value c. 4, 5, and 6 are table diagrams illustrating examples of totalization of measurement results obtained by simulation for obtaining the threshold value a, the threshold value b, and the threshold value c according to the present embodiment. FIG. 4 shows an example of counting the measurement results of the average number of retransmissions in retransmission method 1. FIG. 5 shows a tabulation example of the measurement result of the average number of retransmissions in retransmission scheme 2. FIG. 6 shows a totaling example of the measurement results of the average number of retransmissions in retransmission scheme 3. 4 to 6, the average is obtained for each row or column for each value. Each value shown in FIGS. 4 to 6 is a value for convenience of explanation.

[How to obtain the threshold value a]
For retransmission scheme 1, the average number of retransmissions is determined using the number of data blocks that have failed to be restored as a parameter. This average number of retransmissions corresponds to the average value shown in the bottom row of FIG.
Also, regarding retransmission scheme 2 and retransmission scheme 3, retransmission schemes 2 and 3 are based on their respective parameters (number of data blocks that have failed to be restored (number of unrestored data blocks) and number of lost codewords (number of lost codewords)). When the optimal retransmission method is selected by selecting a retransmission method that minimizes the number of retransmissions, an average number of retransmissions is obtained with the number of data blocks that have failed to be restored as parameters. For example, the table shown in FIG. 7 is created from the results of FIGS. Specifically, the results shown in FIGS. 5 and 6 are compared, the element having the minimum value is used as the element in the table shown in FIG. 7, and the average is recalculated.

  4 and 7 are compared, and the average number of retransmissions in retransmission method 1 in FIG. 4 is less than εa than the average number of retransmissions in the retransmission method in FIG. Among the “number of data blocks that failed to be restored” satisfying this, the maximum number of data blocks is selected as the threshold value a. For example, when “εa = 0.01”, the threshold value a is “1” as shown in FIG. However, “the number of data blocks is“ 1 ”or more and the average number of retransmissions of retransmission scheme 1 is less than εa than the average number of retransmissions of retransmission schemes 2 and 3 combined” It is assumed that “number” does not exist.

[How to find the threshold value b]
The method for obtaining the threshold value b is basically the same as the method for obtaining the threshold value a described above.
For retransmission schemes 2 and 3, the average number of retransmissions using the number of lost codewords as a parameter is obtained. These average retransmission times correspond to the average values shown in the rightmost columns of FIGS. 5 and 6, respectively. Next, these two average retransmission counts are compared, and the maximum code among the “number of lost codewords” satisfying that the average retransmission count of retransmission scheme 2 is less than εb than the average retransmission count of retransmission scheme 3 The number of words is selected as the threshold value b. For example, when “εb = 0.1”, as shown in FIG. 9 based on FIG. 5 and FIG. 6, the threshold value b is “6”. However, if there is no “number of lost codewords” that satisfies that “the number of lost codewords” is 7 or more and the average number of retransmissions in retransmission scheme 2 is less than εb than the average number of retransmissions in retransmission scheme 3 To do.

[How to find threshold c]
For retransmission schemes 1 and 3, the average number of retransmissions using the number of lost codewords as a parameter is obtained. These average retransmission times correspond to the average values shown in the rightmost columns of FIGS. 4 and 6, respectively. Next, these two average retransmission times are compared, and the maximum code number among the “lost codewords” satisfying that the average retransmission number of retransmission method 1 is equal to or smaller than εc than the average retransmission number of retransmission method 3 The number of words is selected as the threshold c. If the threshold value c that matches the condition is smaller than the threshold value b, the value of the threshold value b is used as the threshold value c. For example, as illustrated in FIG. 10 based on FIGS. 5 and 6, the threshold c is “send_packet −1”. However, there is a “number of lost codewords” that satisfies that “the number of lost codewords” is “send_packet −2” or less and the average number of retransmissions in retransmission method 1 is less than εc than the average number of retransmissions in retransmission method 3. If not.

The threshold values a, b, and c can be obtained by the method described above.
The threshold values a, b, and c can be optimized by sufficiently increasing the number of simulations (trial_number).
Further, the ε neighborhoods εa and εb are set to appropriate values according to the number of simulations. The ε neighborhood εc is set to an appropriate value based on whether the number of retransmissions or the amount of calculation on the receiving side is important. However, when it is difficult to determine appropriate values for the ε neighborhoods εa, εb, and εc, all values may be set to “0”.
Further, the number of multicast delivery codewords (send_packet) and the erasure probability (p) are selected with a small error relative to the actual environment.

  FIG. 11 is a diagram showing selection areas of retransmission schemes 1, 2, and 3 based on the above-described threshold values a, b, and c. In FIG. 11, the “region where no event occurs” is a region where at least k code words are necessary to restore the number of k blocks, and thus cannot occur.

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, in the above-described embodiment, the retransmission schemes 1, 2, and 3 are selected based on the threshold values a, b, and c. However, each of the combinations of the number of data blocks that have failed to be restored and the number of lost codewords is used. A retransmission method selection function or a retransmission method selection table in which the retransmission method to be defined is prepared in advance, and the receiving terminal 12 may select the retransmission methods 1, 2, and 3 based on the function or table. The flow of the decoding process performed by the receiving terminal 12 in this case is shown in FIG.

  The retransmission method selection function or the retransmission method selection table is created in advance using the measurement result of the computer simulation described above. FIG. 13 is a diagram illustrating a configuration example of the retransmission method selection table 101. Hereinafter, a method for creating a retransmission method selection function or a retransmission method selection table will be described.

  First, based on the measurement results of the computer simulation described above, the retransmission method is used for all the combinations of two parameters (the number of data blocks that have failed to be restored (the number of unrestored data blocks) and the number of lost codewords (number of lost codewords)). The average number of retransmissions when 1, 2 and 3 are used is obtained by computer simulation. That is, when a certain number of data blocks cannot be restored and a certain number of codewords are lost, if a certain retransmission scheme is used, the average number of retransmissions required for retransmission scheme 1, Calculate every second or third.

  Next, the retransmission method with the smallest number of retransmissions among the three retransmission methods 1 to 3 is selected as the retransmission method for the set related to the two parameters. If a retransmission method with the same average number of retransmissions occurs, the retransmission method with a smaller number is selected. That is, retransmission method 1 is given the highest priority, and then retransmission method 2 is given priority. When a certain set related to two parameters is not found in the simulation measurement results, retransmission method 3 is selected as the retransmission method for the set.

  According to the method of selecting a retransmission method described above, a retransmission method is performed for each set consisting of each value of the number of data blocks that failed to be restored (range 1 to K) and each value of the number of lost codewords (range 1 to send_packet). A retransmission method selection function or a retransmission method selection table representing these selection results is created.

  In the above-described embodiment, retransmission method 1 corresponds to the second retransmission request unit, retransmission method 2 corresponds to the third retransmission request unit, and retransmission method 3 corresponds to the first retransmission request unit. ing.

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 flowchart which shows the flow of the decoding process which the receiving terminal 12 shown in FIG. 1 performs. It is a conceptual diagram for demonstrating the decoding process which concerns on one Embodiment of this invention. It is a 1st table figure which shows the example of totalization of the measurement result obtained by the simulation for calculating | requiring the threshold value a which concerns on one Embodiment of this invention, the threshold value b, and the threshold value c. It is a 2nd table figure which shows the example of totalization of the measurement result obtained by the simulation for calculating | requiring the threshold value a, the threshold value b, and the threshold value c which concern on one Embodiment of this invention. It is a 3rd table figure which shows the example of totalization of the measurement result obtained by the simulation for calculating | requiring the threshold value a which concerns on one Embodiment of this invention, the threshold value b, and the threshold value c. It is the 1st explanatory view for explaining how to ask for threshold value a concerning one embodiment of the present invention. It is the 2nd explanatory view for explaining how to ask for threshold value a concerning one embodiment of the present invention. It is the 2nd explanatory view for explaining how to ask for threshold b concerning one embodiment of the present invention. It is the 2nd explanatory view for explaining how to ask for threshold c concerning one embodiment of the present invention. It is a figure which shows each selection area | region of the resending schemes 1, 2, and 3 based on threshold value a, b, c based on one Embodiment of this invention. It is a flowchart which shows the flow of the decoding process which concerns on other embodiment which the receiving terminal 12 shown in FIG. 1 performs. It is a figure which shows the structural example of the resending method selection table 101 which concerns on the same embodiment. It is a 1st conceptual diagram for demonstrating the weight 1 decoding method which concerns on this invention. It is the 2nd conceptual diagram for demonstrating the weight 1 decoding method which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Distribution server, 12 ... Receiving terminal (communication terminal device), 20 ... Packet network, 21 ... Router, 101 ... Retransmission method selection table.

Claims (15)

In a multicast distribution system including a transmission device that divides distribution data into a predetermined number of data blocks and transmits a codeword generated by exclusive OR operation for each set of arbitrarily selected data blocks in a multicast format,
A communication terminal device that receives the transmitted codeword via a network and decodes the received codeword by a weight 1 decoding method;
The communication terminal device
A first retransmission requesting unit that requests the transmitting apparatus to retransmit a data block having a large weight according to the weight 1 decoding method among data blocks that have failed to be restored as a result of the decoding. Multicast distribution system. Second retransmission requesting means for requesting the transmission apparatus to retransmit all data blocks that have failed to be restored;
Third retransmission request means for requesting the transmitter to retransmit a lost codeword;
A retransmission method selection means for selecting any one of the first to third retransmission request means based on the ratio of data blocks that have failed to be restored and the ratio of lost codewords;
The multicast distribution system according to claim 1, further comprising: The retransmission method selection means includes
3. The multicast distribution system according to claim 2, further comprising: a first threshold value that defines an upper limit of a ratio of data blocks that have failed to be restored as a condition to be satisfied in order to select the second retransmission request unit. . The retransmission method selection means includes
A second threshold that defines a high range of lost codeword percentages and a third threshold that defines a lower range of lost codeword percentages;
In the case where the selection condition related to the second retransmission request unit by the first threshold is not satisfied,
When the second threshold is satisfied, select the second retransmission request means,
When the third threshold is satisfied, select the third retransmission request means,
4. The multicast distribution system according to claim 3, wherein when both the second and third threshold values are not satisfied, the first retransmission request means is selected. The retransmission method selection means includes
3. The multicast distribution system according to claim 2, further comprising a function or a table representing the selection contents of the retransmission request means for all combinations of the number of data blocks that have failed to be restored and the number of lost codewords. The transmission data is divided into a predetermined number of data blocks and a code word generated by performing an exclusive OR operation for each set of arbitrarily selected data blocks is transmitted in a multicast format from the transmission device via the network. Receiving means for receiving the encoded codeword;
Decoding means for decoding the received codeword by a weight 1 decoding method;
First retransmission request means for requesting the transmission apparatus to retransmit a data block having a large weight according to the weight 1 decoding method from among data blocks that have failed to be restored as a result of the decoding;
A communication terminal device comprising: Second retransmission requesting means for requesting the transmission apparatus to retransmit all data blocks that have failed to be restored;
Third retransmission request means for requesting the transmitter to retransmit a lost codeword;
A retransmission method selection means for selecting any one of the first to third retransmission request means based on the ratio of data blocks that have failed to be restored and the ratio of lost codewords;
The communication terminal device according to claim 6, further comprising: The retransmission method selection means includes
8. The communication terminal apparatus according to claim 7, comprising a first threshold value that defines an upper limit of a ratio of data blocks that have failed to be restored as a condition to be satisfied in order to select the second retransmission request unit. . The retransmission method selection means includes
A second threshold that defines a high range of lost codeword percentages and a third threshold that defines a lower range of lost codeword percentages;
In the case where the selection condition related to the second retransmission request unit by the first threshold is not satisfied,
When the second threshold is satisfied, select the second retransmission request means,
When the third threshold is satisfied, select the third retransmission request means,
9. The communication terminal apparatus according to claim 8, wherein when both the second and third threshold values are not satisfied, the first retransmission request unit is selected. The retransmission method selection means includes
8. The communication terminal apparatus according to claim 7, further comprising a function or a table representing a selection content of the retransmission request unit for all combinations of the number of data blocks that have failed to be restored and the number of lost codewords. Data retransmission in a multicast distribution system including a transmission device that divides distribution data into a predetermined number of data blocks and transmits a codeword generated by exclusive OR operation for each set of arbitrarily selected data blocks in multicast format A method,
A communication terminal apparatus that receives the transmitted codeword via a network,
Decoding the received codeword by a weight 1 decoding method;
A first retransmission request process for requesting the transmission apparatus to retransmit a data block having a large weight according to the weight 1 decoding method among data blocks that have failed to be restored as a result of the decoding;
A data retransmitting method comprising: The communication terminal device
A second retransmission request process for requesting the transmitter to retransmit all data blocks that have failed to be restored;
A third retransmission request process for requesting the transmitter to retransmit a lost codeword;
A retransmission scheme selection process for selecting any one of the first to third retransmission request processes based on a ratio of data blocks that have failed to be restored and a ratio of lost codewords;
The data retransmission method according to claim 11, further comprising: In the retransmission scheme selection process,
13. The data retransmission method according to claim 12, further comprising: a first threshold value that defines an upper limit of a ratio of data blocks that have failed to be restored as a condition to be satisfied in order to select the second retransmission request process. . In the retransmission scheme selection process,
A second threshold that defines a high range of lost codeword percentages and a third threshold that defines a lower range of lost codeword percentages;
In a case where a selection condition related to the second retransmission request process according to the first threshold is not satisfied,
When the second threshold is satisfied, select the second retransmission request process ,
When the third threshold is satisfied, select the third retransmission request process ,
Data retransmission method of claim 13, wherein selecting said first retransmission request process when not met in both the second and third both thresholds. In the retransmission scheme selection process,
13. The data retransmission method according to claim 12, further comprising a function or a table representing selection contents of the retransmission request process for all combinations of the number of data blocks that have failed to be restored and the number of lost codewords.

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