JP2007053466A - Communication system, communication terminal device and data requesting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve data transmission efficiency when communication error occurs. <P>SOLUTION: A receiving device 12 has a data request which solves simultaneous equations consisting of equations for received coded symbols to execute decoding for obtaining unknown information symbols, and selects undecoded information symbols to be requested to a distribution server 11 on the basis of results of this decoding. The data requesting section selects the information symbols required for solving the simultaneous equations on the basis of a degree of the unknown equation in the simultaneous equations in which the known information symbols are reflected as the results of decoding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a communication system, a communication terminal device, and a data request 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, a method that combines FEC (Forward Error Correction) with multicast or unicast communication using UDP (User Datagram Protocol) or IP (Internet Protocol) is proposed. Has been. Multicast in which reliability is improved by combining FEC or the like is called highly reliable multicast. As an error correction code used for the reliable multicast, for example, an LT code system described in Patent Document 1 is known.

  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. However, in a set composed of only one information symbol, an XOR operation value of one information symbol and “0” is used as an encoded 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, in an environment where the multicast distribution time is limited, ARQ (Automatic Repeat Request) or differential download is performed for those who have failed to distribute in order to achieve a distribution completion rate of 100%.

Also, a differential download method combining FEC and ARQ has been proposed, and it is possible to reduce the total number of retransmissions by retransmitting a packet in which an error is detected or a lost packet.
JP 2001-189665 A

  However, even if the differential download method is applied to the LT code, there is a problem that the number of retransmissions per user cannot be effectively reduced. In order to deal with this problem, the present inventors have already proposed a method of reducing the number of data transmissions required for completion of differential download using the characteristics of the LT code (Japanese Patent Application No. 2004-289243). And it has been a subject to further improve the data transmission efficiency at the time of a communication error.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a communication system, a communication terminal apparatus, and a data request method capable of improving the efficiency of data transmission at the time of a communication error. It is in.

  In order to solve the above problem, the communication system according to the present invention transmits an encoded symbol that is an exclusive OR operation value for each set of information symbols arbitrarily selected from a plurality of information symbols. A transmitting apparatus; a receiving apparatus that receives the encoded symbol and performs decoding to obtain an unknown information symbol by solving simultaneous equations composed of equations representing an exclusive OR operation relationship of the received encoded symbol; In the communication system, the receiving device includes data requesting means for selecting an unrestored information symbol to be requested to the transmitting device based on the decoding result, and the data requesting means As a result, based on the order of the undecoded equations in the simultaneous equations reflecting the known information symbols, the information symbol required to solve the simultaneous equations Selecting, characterized in that.

  In the communication system according to the present invention, the data request means selects an unknown information symbol included in an undecoded equation having a minimum degree.

  In the communication system according to the present invention, the data request means selects an unknown information symbol that is commonly included in a plurality of undecoded equations.

  In the communication system according to the present invention, the data request means calculates a score according to the order for each undecoded equation, and for each unknown information symbol, the data of the undecoded equation including the information symbol. A score is totaled, and an information symbol is selected based on the total value.

  In the communication system according to the present invention, when there is an unrestored information symbol that is not included in the undecoded equation, the data request unit requests the unrestored information symbol from the transmitting apparatus. To do.

  The communication terminal apparatus according to the present invention receives an encoded symbol that is an exclusive OR operation value for each set of information symbols arbitrarily selected from a plurality of information symbols, and receives the encoded symbol of the received encoded symbols. An unrestored information symbol requested to a communication partner based on a result of the decoding in a communication terminal device that performs decoding to obtain an unknown information symbol by solving simultaneous equations composed of equations representing an exclusive OR operation relationship The data requesting means for solving the simultaneous equations based on the order of the undecoded equations in the simultaneous equations reflecting the information symbols known as a result of the decoding. The information symbols necessary for the selection are selected.

  The data request method according to the present invention receives an encoded symbol that is an exclusive OR operation value for each set of information symbols arbitrarily selected from a plurality of information symbols, and receives the encoded symbol of the received encoded symbols. A data requesting method for performing decoding to obtain an unknown information symbol by solving simultaneous equations composed of equations representing an exclusive OR operation relationship, based on a result of the decoding, an unrequested request to a communication partner A data requesting process for selecting information symbols for restoration, wherein the data requesting process is based on the order of the undecoded equations in the simultaneous equations reflecting the information symbols known as a result of the decoding. An information symbol necessary for solving is selected.

  According to the present invention, since the information symbol to be requested is selected based on the order of the undecoded equation, the information symbol can be efficiently requested. As a result, the number of times of data transmission can be reduced, so that it is possible to improve the efficiency of data transmission at the time of a communication error.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a multicast distribution system will be described as an example of a communication system according to the present invention.
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, the distribution server (S) 11 encodes information symbols obtained by dividing the distribution data by the LT coding method, and multicasts the packet storing the obtained encoded symbols via the packet network 20. Send. The receiving terminals (R _{1 to} R ₅ ) 12 receive the multicast transmission packet from the distribution server 11 via the packet network 20.

  In the packet network 20, routers 21 that perform packet routing are arranged in a network. The router 21 supports multicast transfer.

FIG. 2 is a block diagram showing a configuration of the receiving terminal 12. In FIG. 2, the receiving terminal 12 includes a transmission / reception unit 31, a memory 32, a decoding unit 33, and a data request unit 34.
The transmission / reception unit 31 performs transmission and reception of multicast via the packet network 20. The memory 32 stores data multicast received by the transmission / reception unit 31. The decoding unit 33 performs decoding of a coded symbol (for example, decoding by the LT coding method) using the multicast reception data stored in the memory 32 to restore the information symbol. The data request unit 34 determines an unrestored information symbol requested to the distribution server 11 based on the decoding result in the decoding unit 33. The data request unit 34 transmits the determined request for unrestored information symbols to the distribution server 11 by the transmission / reception unit 31.

FIG. 3 is an explanatory diagram for explaining an encoding method of the LT code in the distribution server 11. FIG. 4 is an explanatory diagram for explaining a decoding method of the LT code in the decoding unit 33 of the receiving terminal 12.
First, an LT code encoding method in the distribution server 11 will be described with reference to FIG.
In FIG. 3, the distribution server 11 further divides the data block divided from the distribution data into a plurality of information symbols 101. Next, an exclusive OR (XOR) operation value for each set of information symbols arbitrarily selected from the plurality of information symbols 101 is calculated to obtain an encoded symbol 201. For example, the encoded symbol (X ₁ ) 201 is an XOR operation value of the information symbol (A) 101, the information symbol (B) 101, and the information symbol (D) 101. The encoded symbol (X ₈ ) 201 is an XOR operation value of one information symbol (F) 101 and “0”.

  In this way, a plurality of encoded symbols 201 are generated. Each encoded symbol 201 is expressed as an equation with a term composed only of an XOR operation of one or a plurality of information symbols 101. From the equations relating to each encoded symbol 201, an equation is obtained in which the encoded symbol 201 is known and the information symbol 101 is unknown. A simultaneous equation 301 composed of these plural equations is constructed. Each equation in the simultaneous equations 301 represents an exclusive OR operation relationship for obtaining a corresponding encoded symbol. The simultaneous equations 301 are shared between the distribution server 11 and each receiving terminal 12.

Next, an LT code decoding method in the decoding unit 33 of the receiving terminal 12 will be described with reference to FIG.
In FIG. 4, the decoding unit 33 of the receiving terminal 12 performs decoding to obtain an unknown information symbol 101 by solving simultaneous equations composed of equations related to the encoded symbol 201 received by multicast. The LT code decoding method in the decoding unit 33 of the receiving terminal 12 will be specifically described below based on the example of FIG.

The example of FIG. 4, seven coding _X 1 to X ₆ and _{X 8} of the eight encoded symbols 201 of FIG 3 corresponds to the example at the time of _encoding, X 1 to X ₈ symbol 201 but is multicast successfully received, one encoded symbols 201 X ₇ is not received by the packet loss.
First, the decoding unit 33 of the receiving terminal 12 among the equations relating to the seven encoded symbols 201 of X _{1 to} X ₆ and X ₈ received among the simultaneous equations 301 shared with the distribution server 11. Search for one that has only one unknown. As a result, an equation related to the encoded symbol (X ₈ ) 201 is found, and an information symbol (F) 101 that is an unknown number (solution) of the equation is obtained as the encoded symbol (X ₈ ) 201 (F = X ₈ ). .

Next, the encoded symbol (X ₈ ) 201 that is the information symbol (F) 101 includes the information symbol (F) 101 among the other undecoded equations (six equations related to X _{1 to} X ₆ ). Substitute for things. In the example of FIG. 4, only the equation related to X ₆ includes the information symbol (F) 101, and the encoded symbol (X ₈ ) 201 is substituted into the equation related to X ₆ . Thus, the unknowns equation according to X ₆ is reduced one, consisting only of two information symbols 101 C and D. By repeating this operation, the number of unknowns in each equation is sequentially reduced to only one to solve each equation, and the information symbol 101 that is the solution is obtained.

Here, when an equation having only one unknown cannot be obtained, the equation cannot be solved any more. For example, in the example of FIG. 4, the equation related to the encoded symbol (X ₈ ) 201 is solved, but even if the information symbol (F) 101 that is the solution is substituted into another equation, there is only one unknown. Is not obtained, and the six equations relating to X _{1 to} X ₆ cannot be solved. Therefore, the data request unit 34 requests the distribution server 11 for information symbols 101 necessary for solving the six equations relating to X _{1 to} X ₆ .

5-7 is explanatory drawing for demonstrating the 1st-3rd data request | requirement method by the data request | requirement part 34. FIG. The example of FIGS. 5 to 7 corresponds to the example at the time of decoding in FIG. 4 and the equation relating to the encoded symbol (X ₈ ) 201 has been solved, but the information symbol (F) 101 that is the solution thereof. Substituting into other equations does not result in an equation with only one unknown, and the six equations relating to X _{1 to} X ₆ cannot be solved.

[First data request method]
With reference to FIG. 5, the first data requesting method by the data requesting unit 34 will be described.
The data request unit 34 detects the orders of the six equations relating to X _{1 to} X ₆ that cannot be solved. The order of the equation refers to the number of unknowns in the equation. For example, since the unknown number of the equation relating to X ₁ is three information symbols 101 of A, B and D, the order of the equation relating to X ₁ is 3. Further, since the unknown number of the equation related to X ₆ is reduced to only two information symbols 101 of C and D, the order of the equation related to X ₆ is 2.

Next, the equation of the minimum order is searched from the orders of the six equations related to X _{1 to} X ₆ . As a result, three equations relating to X ₂ , X ₃ and X ₆ of order 2 are found.

Next, the unknown information symbol 101 included in the three equations relating to the found X ₂ , X ₃ and X ₆ is detected. As a result, five information symbols 101 of A to D are found.

  Next, one or a plurality of desired information symbols 101 of the found A to D are arbitrarily selected. For example, select at random. Then, the distribution server 11 is requested for the selected information symbol 101.

  According to the first data request method described above, since the request is made from an unknown number of equations (unknown information symbols) that can be solved with the smallest number of information symbols, compared to the case where information symbols are randomly requested. Thus, simultaneous equations can be solved efficiently. As a result, the number of times of data transmission can be reduced, so that it is possible to improve the efficiency of data transmission at the time of a communication error.

[Second data request method]
With reference to FIG. 6, the second data requesting method by the data requesting unit 34 will be described.
The data request unit 34 detects the orders of the six equations relating to X _{1 to} X ₆ that cannot be solved. Next, the equation of the minimum order is searched from the orders of the six equations related to X _{1 to} X ₆ . As a result, three equations relating to X ₂ , X ₃ and X ₆ of order 2 are found. Next, the unknown information symbol 101 included in the three equations relating to the found X ₂ , X ₃ and X ₆ is detected. As a result, five information symbols 101 of A to D are found.

  Next, with respect to the five discovered information symbols 101 of A to D, the number involved in the minimum order equation (the order 2 equation in the example of FIG. 4) is detected. As a result, the number of participation is detected as 1 for the information symbols 101 of A, B, D, and E, and 2 is detected for the information symbol 101 of C.

  Then, the information symbol 101 having a large number (for example, the maximum) participating in the minimum order equation is selected. As a result, the C information symbol 101 having the participation number “2” is selected. Then, the distribution server 11 is requested for the selected information symbol 101.

  In addition, you may make it select the information symbol 101 whose number involved in the minimum degree equation is more than a predetermined threshold value.

  According to the second data request method described above, an unknown number (unknown information symbol) of an equation that can be solved with the smallest number of information symbols, and an unknown number (unknown information symbol) involved in a larger number of equations. Since the request is made, the simultaneous equations can be solved more efficiently and quickly from the first data request method, and it is possible to further contribute to improving the efficiency of data transmission at the time of a communication error.

[Third data request method]
With reference to FIG. 7, the third data requesting method by the data requesting unit 34 will be described.
The data request unit 34 detects the orders of the six equations relating to X _{1 to} X ₆ that cannot be solved. Next, the score of each equation is calculated based on the orders of the six equations relating to the X _{1 to} X ₆ . In the example of FIG. 7, the reciprocal number “1 / order” of the order is used as the score.

Next, unknown information symbols 101 included in the six equations relating to X _{1 to} X ₆ are detected. As a result, five information symbols 101 of A to D are found. Next, for each of the five information symbols 101 of A to D, the scores of the equations involved are tabulated. As a result, for each of the five information symbols 101 from A to D, the total value of the scores of the equations involved is obtained. For example, since the information symbol 101 of A is involved in three equations relating to X ₁ , X ₃ and X ₅ , the total value “(1/3) + (1/2 ) + (1/4) = 13/12 ".

  Next, the information symbol 101 having the maximum score total value is selected. As a result, the B information symbol 101 having the score total value “17/12” is selected. Then, the distribution server 11 is requested for the selected information symbol 101.

  In addition, you may make it select the information symbol 101 whose score total value is more than a predetermined threshold value.

  According to the third data request method described above, since the request is made from unknown numbers (unknown information symbols) that are well evaluated by the total value of the score based on the order of the equations (number of unknowns), it is comprehensively comprehensive. The equation can be solved efficiently. As a result, the number of times of data transmission can be reduced, so that it is possible to improve the efficiency of data transmission at the time of a communication error.

  In the first to third data requesting methods described above, as a method of requesting data, the selected information symbols 101 may be sequentially requested, or the necessary information may be requested collectively. Good. For example, you may request | require collectively the part required in order to solve some (plural) undecoding equations. As a result, the number of data transmissions can be reduced.

[Fourth data request method]
A fourth data requesting method by the data requesting unit 34 will be described with reference to FIGS. The fourth data requesting method is a requesting method in a case where no encoded symbol related to an unrestored information symbol is normally received.
FIG. 8 shows an XOR operation relationship between six information symbols (A to F) 101 and seven encoded symbols (X _{1 to} X ₇ ) 201. In addition, a simultaneous equation 310 composed of equations of the respective encoded symbols (X _{1 to} X ₇ ) 201 is shown.

FIG. 9 shows a decoding process based on the encoded symbol 201 received by the receiving terminal 12. In FIG. 9, two encoded symbols 201 of X ₅ and X ₆ are not normally received due to packet loss. As a result, there is no undecoded equation including the E information symbol 101, and the E information symbol 101 cannot be obtained as it is. As described above, when there is an unrestored information symbol 101 that is not included in the undecoded equation, the data request unit 34 requests the unrestored information symbol 101 from the distribution server 11.

  According to the fourth data request method described above, when there is an unreconstructed information symbol that is not included in the undecoded equation related to the received encoded symbol, the unreconstructed information symbol is directly requested, Thereby, the information symbol can be obtained.

According to the embodiment described above, the following effects can be obtained.
(1) A person who has failed to receive multicast data can download the unrestored information symbol from the distribution server with a small number of downloads, and the communication fee can be reduced. In addition, since the download time can be reduced, it is possible to prevent slowing down of the operation of the computer due to an increase in load due to data download, and it is possible to reduce the stress on the user.
(2) The advantage of the sender is that the amount of communication (bandwidth) can be reduced and the load on the server related to data download can be reduced. In particular, when using a wireless communication network, wireless resources are valuable, and the reduction of the bandwidth used is an excellent effect. Also, in multicast, the number of delivery failures increases as the number of recipients increases, and the number of data downloads increases according to the number of delivery failures, so it is extremely difficult to reduce the number of downloads per delivery failure Effective.
(3) Even if the mobile terminal has only a small calculation capability, if the unrestored information symbol to be downloaded can be selected, the download can be completed in a small number of downloads and in a short time. The data can be recovered in the event of a communication error without impairing the convenience of the terminal. Further, even when the same content is distributed to a large number of mobile terminals, it is possible to contribute to maintaining good service quality due to the effect of reducing the load on the server related to bandwidth reduction and data download.

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 LT coding scheme has been described as an example of the coding scheme according to the present invention. However, an exclusive OR for each set of information symbols arbitrarily selected from a plurality of information symbols is described. Any coding method may be used as long as the arithmetic value is an encoded symbol, and the present invention is not limited to the LT coding method.

  Also, the decoding method of the coding method according to the present invention may be any method and is not particularly limited. For example, the present invention can be applied to the case where “Sum Product decoding method” or “Gaussian elimination method” is used.

  In the above-described embodiment, the multicast type is described as an example of the communication system according to the present invention. However, the present invention can be similarly applied to a unicast type.

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 block diagram which shows the structure of the receiving terminal 12 shown in FIG. It is explanatory drawing for demonstrating the encoding method of the LT code | symbol in the delivery server 11 shown in FIG. It is explanatory drawing for demonstrating the decoding method of the LT code | symbol in the decoding part 33 shown in FIG. It is explanatory drawing for demonstrating the 1st data request method by the data request | requirement part 34 shown in FIG. It is explanatory drawing for demonstrating the 2nd data request method by the data request | requirement part 34 shown in FIG. It is explanatory drawing for demonstrating the 3rd data request method by the data request | requirement part 34 shown in FIG. It is explanatory drawing for demonstrating the 4th data request method by the data request | requirement part 34 shown in FIG. It is explanatory drawing for demonstrating the 4th data request method by the data request | requirement part 34 shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Distribution server, 12 ... Receiving terminal (communication terminal device), 20 ... Packet network, 21 ... Router, 31 ... Transmission / reception part, 32 ... Memory, 33 ... Decoding part, 34 ... Data request part

Claims (7)

A transmitting apparatus that transmits an encoded symbol that is an exclusive OR operation value for each set of information symbols arbitrarily selected from a plurality of information symbols; and the received encoding symbol and the received encoding In a communication system comprising: a receiving device that performs decoding to obtain an unknown information symbol by solving simultaneous equations consisting of equations representing an exclusive OR operation relationship of symbols;
The receiving device is:
Based on the result of the decoding, comprising data request means for selecting unrestored information symbols to be requested to the transmitting device;
The data request means includes
Selecting information symbols necessary to solve the simultaneous equations based on the order of the undecoded equations in the simultaneous equations reflecting information symbols known as a result of the decoding;
A communication system characterized by the above. The data requesting means selects an unknown information symbol included in an undecoded equation having a minimum degree;
The communication system according to claim 1. The data requesting means selects an unknown information symbol that is commonly included in a plurality of undecoded equations;
The communication system according to claim 2. The data request means includes
For each undecoded equation, calculate a score according to the order,
For each unknown information symbol, the scores of undecoded equations containing the information symbol are aggregated,
Selecting an information symbol based on the aggregated value;
The communication system according to claim 1. The data request means, when there is an unrestored information symbol that is not included in the undecoded equation, requests the unrestored information symbol from the transmission device;
The communication system according to claim 1. An equation that represents an exclusive OR operation value for each set of information symbols arbitrarily selected from a plurality of information symbols, and represents an exclusive OR operation relationship of the received encoded symbols In a communication terminal device that performs decoding to obtain an unknown information symbol by solving simultaneous equations consisting of:
Based on the result of the decoding, comprising data request means for selecting unrestored information symbols to be requested to the communication partner,
The data request means includes
Selecting information symbols necessary to solve the simultaneous equations based on the order of the undecoded equations in the simultaneous equations reflecting information symbols known as a result of the decoding;
A communication terminal device. An equation that represents an exclusive OR operation value for each set of information symbols arbitrarily selected from a plurality of information symbols, and represents an exclusive OR operation relationship of the received encoded symbols A data request method when performing decoding to obtain an unknown information symbol by solving simultaneous equations consisting of:
A data requesting process for selecting an unrestored information symbol to be requested to a communication partner based on the decoding result;
The data request process includes:
Selecting information symbols necessary to solve the simultaneous equations based on the order of the undecoded equations in the simultaneous equations reflecting information symbols known as a result of the decoding;
A data request method characterized by the above.

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