JP2010041084A - Method and device for generating fec data - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for generating FEC data efficiently generating two-dimensional FEC data. <P>SOLUTION: This method for generating FEC data includes steps of: calculating a lowest common multiple L of a horizontal size of a matrix of two-dimensional FEC data requested by first to N-th terminal devices; and generating the two-dimensional FEC data respectively requested by the respective terminal devices by using a matrix for FEC data calculation where the number of media packets arranged in the horizontal direction is L. When p, k and T<SB>k</SB>denote an integer not smaller than 1 and not larger than N, an integer not smaller than 1 and not larger than L, and intermediate data for vertical FEC calculated by exclusive OR of data of media packets arranged in the vertical direction of the matrix for FEC data calculation, respectively, vertical FEC data of a q-th column of the two-dimensional FEC data requested by a p-th terminal device are calculated by expression of a step ST14 using T<SB>k</SB>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an FEC data generation method and an FEC data generation apparatus that efficiently generate two-dimensional FEC (Forward Error Correction) data.

  FIG. 1 is a diagram schematically showing a configuration of a conventional video distribution system. In FIG. 1, a video distribution server 300 divides digitally encoded audio and video data into packets and distributes them to a plurality of terminal devices (for example, terminal devices 1, 2, 3, 4) via a network 400. To do. When data is distributed from the video distribution server 300 via the network 400, packet loss may occur on the route from the video distribution server 300 to each terminal device. There is FEC as a technique for restoring the packet lost by this packet loss in each terminal device. In particular, parity FEC compliant with RFC 2733 is easy to implement and is widely used.

  FIG. 2 is a diagram illustrating a conventional method for generating FEC data. FIG. 2 shows a case where a media packet (indicated by a rectangle surrounding sequence numbers 01,..., 100 in the figure) is treated as a matrix having a row (horizontal) size of 10 packets and FEC data is generated. Yes. In this method, FEC data is generated for every 10 media packets in the horizontal direction. The generated FEC data is distributed from the video distribution server 300 to the terminal device together with the media packets (sequence numbers 01,..., 100) as FEC packets (indicated by H1,..., H10 in the figure). When the FEC is a parity FEC, the FEC data is calculated from the exclusive OR of the data of 10 media packets in the horizontal direction. For example, the first FEC data (FEC packet H1) is calculated from the exclusive OR of the data of the media packets (sequence numbers 01,..., 10), and the exclusion of the data of the media packets (sequence numbers 11,..., 20) is performed. The second FEC data (FEC packet H2) is calculated from the logical OR, and the FEC data (FEC packets H3, H4,...) Are calculated by the same method.

  FIG. 3 is a diagram illustrating a conventional method for generating two-dimensional FEC data. In FIG. 3, a media packet (indicated by a rectangle surrounding sequence numbers 01,..., 100 in the figure) is treated as a matrix of 10 packets in each row (horizontal) and column (vertical) size. The case of generating is shown. Two-dimensional FEC data is defined by the Pro-MPEG forum. In the two-dimensional FEC data generation method, the media packet is treated as a matrix with a predetermined vertical size and horizontal size, an exclusive OR of the media packet data is calculated for each row, and the media packet data for each column is calculated. An exclusive OR is calculated, and each of the calculation result of each row and the calculation result of each column is set as a horizontal FEC packet (for example, H1,..., H10) and a vertical FEC packet (for example, V1,..., V10), It is transmitted to the terminal device. By using the two-dimensional FEC data, the terminal device can restore the lost media packet from the vertical FEC even if two media packets in the same row are lost, and thus has high error correction capability.

  In general, even when the video distribution server simultaneously distributes the same media packet to a plurality of terminal devices, the appropriate matrix size of the media packets differs for each terminal device. Therefore, there is a proposal of a method for efficiently calculating FEC data for a plurality of terminal devices in the video distribution server (see, for example, Patent Document 1). In this FEC data calculation method, the exclusive OR of the transmission data is continuously calculated, and the calculated value of the exclusive OR at the previous FEC packet insertion time and the current FEC packet insertion scheduled time are calculated. The FEC data to be inserted this time is generated by calculating the exclusive OR with the calculated value of the exclusive OR.

JP 2006-67072 A (summary, FIG. 5)

  However, since the FEC data generation method disclosed in Patent Document 1 is a method for efficiently calculating one-dimensional FEC data, the two-dimensional FEC data of a plurality of terminal devices can be reduced with a small amount of calculation using this method. There is a problem that it cannot be calculated efficiently. In particular, when the matrix size of the media packet is different for each terminal device, or when the sequence number of the packet to be processed is not continuous when generating the vertical FEC data, it is possible to efficiently calculate the two-dimensional FEC data. There is a problem that you can not.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and an object thereof is to provide an FEC data generation apparatus and an FEC data generation method capable of efficiently generating two-dimensional FEC data. There is to do.

で計算される第２の縦方向ＦＥＣ用中間データとし、

を、前回同じ列で縦方向ＦＥＣデータを出力したときの前記第２の縦方向ＦＥＣ用中間データＣ′_ｐ，ｑに等しい第３の縦方向ＦＥＣ用中間データとしたときに、
前記２次元ＦＥＣデータを生成する前記ステップにおいて、第ｐの端末装置が要求する２次元ＦＥＣデータの第ｑ列の縦方向ＦＥＣデータＣ_ｐ，ｑを、次式

で計算することを特徴としている。 The FEC data generation method of the present invention includes:
Calculating a least common multiple of a horizontal size of a matrix of two-dimensional FEC data respectively requested by first to N-th terminal devices (N is an integer of 2 or more);
Each of the first to Nth terminal devices requests each of the first to Nth terminal devices using an FEC data calculation matrix having the least common multiple as the number of media packets arranged in the horizontal direction. Generating dimensional FEC data;
Let d _{i be} the data of the media packet with sequence number i (i = 1, 2,...)
p is an integer of 1 to N,
_Let L _{p be} the horizontal size of the matrix of two-dimensional FEC data required by the p-th terminal device,
L is the least common multiple,
k = 1, 2,..., L,
T _k is the first vertical FEC intermediate data calculated by exclusive OR of media packet data arranged in the vertical direction of the FEC data calculation matrix,
C ′ _{p, q} is _expressed as

The second vertical FEC intermediate data calculated in

Is the third vertical FEC intermediate data equal to the second vertical FEC intermediate data C′p _{, q} when the vertical FEC data was output in the same column last time,
In the step of generating the two-dimensional FEC data, the vertical FEC data C _{p, q} of the q-th column of the two-dimensional FEC data requested by the p-th terminal device is _expressed by the following equation:

It is characterized by calculating with.

  According to the present invention, even when a plurality of terminal devices request two-dimensional FEC data having different matrix sizes, the amount of calculation of the vertical FEC data of the two-dimensional FEC data requested by each of the plurality of terminal devices. Can be reduced, and the data processing load can be reduced.

  FIG. 4 shows a video distribution server 310 including an FEC data generation apparatus (that is, an apparatus that performs the FEC data generation method according to the embodiment) 311 according to the embodiment of the present invention, and a video distribution including the video distribution server. It is a figure which shows the structure of a system roughly. As shown in FIG. 4, the video distribution system includes a video distribution server 310 that can communicate via a network 400 such as the Internet, and a plurality of terminal devices that can communicate via the network 400 (in the figure, four units). Terminal devices 1, 2, 3, and 4 are shown, but the number of terminal devices may be other than four.). The video distribution server 310 includes an FEC data generation device 311, a media data storage unit 312 that stores digitally encoded audio and video data, and a data transmission / reception unit 313 that transmits and receives data via the network 400. . The video distribution server 310 divides the digitally encoded audio and video data into packets and distributes them to a plurality of terminal devices via the network 400. In addition, the video distribution server 310 receives from each terminal device a matrix size of two-dimensional FEC data suitable for the characteristics of the network 400 through which each terminal device and media packet pass.

FIG. 5 is a flowchart (part 1) illustrating an operation (FEC data generation method) of the FEC data generation device 311 according to the embodiment. FIG. 6 illustrates an operation (FEC data) of the FEC data generation device 311 according to the embodiment. It is a flowchart (the 2) which shows a data generation method. FIGS. 7A and 7B are diagrams for explaining a method of generating two-dimensional FEC data having a matrix size required by the first terminal device (hereinafter referred to as “terminal device 1”). FIGS. 8A and 8B are diagrams for explaining a method of generating matrix size two-dimensional FEC data required by the second terminal device (hereinafter referred to as “terminal device 2”). FIGS. 9A and 9B are diagrams for describing a method for generating two-dimensional FEC data having a matrix size required by a third terminal device (hereinafter referred to as “terminal device 3”). FIG. 10 is a diagram for explaining the FEC data generation method according to the embodiment of the present invention. FIGS. 7 (a) and 7 (b), FIG. 8 (a) and FIG. The vertical direction used to calculate the vertical FEC data (also referred to as “vertical FEC packet”) and horizontal FEC data (also referred to as “horizontal FEC packet”) shown in a) and (b). The FEC intermediate data T ₁ ,..., T ₂₀ and the horizontal FEC intermediate data S are shown.

The FEC data generation device 311 performs the following processing when generating two-dimensional FEC data. In the following description, N (N is a positive integer) terminal devices (clients) 1, 2,..., N exist as distribution destinations of media data (also referred to as “media packets”). , 2, ..., the horizontal (row) size each _L 1 of the matrix of two-dimensional FEC data N is _requested, L 2, ..., and _{L N,} the terminal apparatus 1, 2, 2-dimensional FEC that N requires _Let M ₁ , M ₂ ,..., _MN be vertical (column) sizes of the data matrix, respectively.

と、端末装置１，…，Ｎに供給する縦方向ＦＥＣデータ

とを用意する。 First, in step ST1 of FIG. 5, the FEC data generation device 311 sends the lateral FEC data to be supplied to the terminal devices 1,.

And longitudinal FEC data to be supplied to the terminal devices 1,.

And prepare.

Here, “R _p ” is two-dimensional FEC data requested by the terminal device p (p is an integer of 1 to N).

“C _{p, q} ” is the q-th column of the two-dimensional FEC data requested by the terminal device p (q is an integer of 1 to L _p ). L _p is the horizontal size of the matrix of the two-dimensional FEC data requested by the terminal device p.

Next, in step ST2 of FIG. 5, the FEC data generation device 311 performs the least common multiple L of the horizontal sizes L ₁ , L ₂ ,..., L _N of the matrix of the two-dimensional FEC data required by the terminal devices 1,. Calculate

を計算するために用いる横方向ＦＥＣ用中間データＳ，Ｓ′を初期化して０にする。この横方向ＦＥＣ用中間データＳは、図１０に示されている。 Next, in step ST3 of FIG. 5, the FEC data generation device 311 performs the lateral FEC data of the terminal devices 1,.

The horizontal FEC intermediate data S and S ′ used to calculate the value are initialized to zero. This intermediate FEC intermediate data S is shown in FIG.

を計算するために用いる第１の縦方向ＦＥＣ用中間データＴ_１，Ｔ_２，…，Ｔ_Ｌを初期化して０にする。この第１の縦方向ＦＥＣ用中間データ（Ｔ_１，Ｔ_２，…，Ｔ_２０）は、図１０に示されている。 In addition, the FEC data generation device 311 includes the vertical FEC data of the terminal devices 1,.

, _TL used for calculating the first vertical FEC intermediate data T ₁ , T ₂ ,. This first intermediate FEC intermediate data (T ₁ , T ₂ ,..., T ₂₀ ) is shown in FIG.

と、第３の縦方向ＦＥＣ用中間データ

とを用意し、第２の縦方向ＦＥＣ用中間データと第３の縦方向ＦＥＣ用中間データとを、初期化して０にする。 In addition, the FEC data generation device 311 includes the second vertical FEC intermediate data.

And intermediate data for the third vertical FEC

Are prepared, and the second vertical FEC intermediate data and the third vertical FEC intermediate data are initialized to zero.

Next, in step ST4 of FIG. 5, the FEC data generation device 311 determines that the variable i representing the sequence number being processed and the intermediate data being processed (that is, the first vertical FEC intermediate data T ₁ , T ₂ , .., T _k ,..., T _L ) are set to 1 for each variable k.

Next, in step ST5 of FIG. 5, FEC data generation apparatus 311, the media data storage unit 312, it determines whether or no media data _{d i} of the next 1 media packet of there. When the FEC data generation device 311 determines that there is no media data for the next one media packet, the processing ends. FEC data generation apparatus 311, when it is determined that the media data d _i of the next 1 media packet of there, the process advances to step ST6.

Next, in step ST <b> 6 of FIG. 5, the FEC data generation device 311 reads media data d _i for the next one media packet from the media data storage unit 312.

式（１）は、横方向ＦＥＣ用中間データＳとメディアデータｄ_ｉとの排他的論理和を、新たな横方向ＦＥＣ用中間データＳとすることを示している。また、式（２）は、第１の縦方向ＦＥＣ用中間データＴ_ｋとメディアデータｄ_ｉとの排他的論理和を、新たな第１の縦方向ＦＥＣ用中間データ用変数Ｔ_ｋとすることを示している。 Next, in step ST7 of FIG. 5, the FEC data generation device 311 uses the following equations (1) and (2) to calculate the horizontal FEC intermediate data S and the first vertical FEC intermediate data T _k (k is 1 is an integer that is greater than or equal to 1 and less than or equal to the least common multiple L).

Equation (1) is the exclusive OR of the lateral FEC intermediate data S and the media data d _i, indicates that the intermediate data S for the new lateral FEC. Further, the expression (2) sets the exclusive OR of the first vertical FEC intermediate data T _k and the media data d _i as a new first vertical FEC intermediate data variable T _k. Is shown.

  Next, in step ST8 of FIG. 5, the FEC data generation device 311 uses a variable p (p is an integer greater than or equal to 1 and less than or equal to N) representing the number of the terminal device being processed, and a matrix of two-dimensional FEC data. A variable q representing the column number is prepared, and 1 is set in the variable p.

Next, in step ST9 of FIG. 6, the FEC data generation device 311 determines whether or not the following equation (3) is satisfied.
i = 0 modL _p (3)
When the FEC data generation device 311 determines that Expression (3) is satisfied, that is, the sequence number i of the media packet is an integral multiple of the horizontal size L _p of the matrix of the two-dimensional FEC data requested by the terminal device p. When it is determined, the process proceeds to step ST10, and when it is determined that Expression (3) is not satisfied, that is, the sequence number i of the media packet is an integer of the horizontal size L _p of the matrix of the two-dimensional FEC data of the terminal device p. When it is determined that it is not doubled, the process proceeds to step ST12.

端末装置ｐの横方向ＦＥＣデータＲ_ｐは、横方向ＦＥＣ用中間データＳと横方向ＦＥＣ用中間データＳ′との排他的論理和から計算される。横方向ＦＥＣ用中間データＳ′は、ＦＥＣデータ生成装置３１１が前回横方向ＦＥＣデータを出力したときの横方向ＦＥＣ用中間データＳの値がセットされている。なお、１回目の式（４）の演算においては、横方向ＦＥＣ用中間データＳ′は０（図５のステップＳＴ３）である。 Next, in step ST10 of FIG. 6, the FEC data generation device 311 calculates the lateral FEC data R _p of the terminal device p using the following equation (4). Here, R _p indicates the lateral FEC data of the terminal device p.

Lateral FEC data R _p of the terminal device p is calculated from exclusive OR between the lateral FEC intermediate data S and lateral FEC intermediate data S '. In the horizontal direction FEC intermediate data S ′, the value of the horizontal direction FEC intermediate data S when the FEC data generation device 311 previously output the horizontal direction FEC data is set. In the first calculation of the equation (4), the horizontal FEC intermediate data S ′ is 0 (step ST3 in FIG. 5).

  Next, as shown in the equation (5), the value of the horizontal FEC intermediate data S calculated by the equation (4) is set in the horizontal FEC intermediate data S ′.

Next, in step ST11 of FIG. 6, the FEC data generation device 311 passes the lateral FEC data R _p to the data transmission / reception unit 313, and the data transmission / reception unit 313 transmits the lateral FEC data R _p to the terminal device p. .

In the present embodiment, the lateral FEC data R _p transmitted to the terminal device 1 (p = 1) is, for example, R ₁ shown in FIGS. 7A and 7B. In the present embodiment, the lateral FEC data R _p transmitted to the terminal device 2 (p = 2) is, for example, R ₂ shown in FIGS. 8A and 8B. Further, in this embodiment, lateral FEC data _{R p} to be transmitted to the terminal device 3 (p = 3) is, for example, _{R 3} shown in FIG. 9 (a) and (b).

Next, in step ST12 of FIG. 6, the FEC data generation device 311 calculates the variable q by the following equation (6).
q ← (i mod L _p M _p ) −L _p (M _p −1) (6)
Here, L _p represents the horizontal size of the matrix of the two-dimensional FEC data of the terminal device p, and M _p represents the vertical size of the matrix of the two-dimensional FEC data of the terminal device p.

Next, in step ST13 of FIG. 6, the FEC data generation device 311 determines whether or not the following equation (7) is satisfied.
1 ≦ q ≦ L _p (7)
The FEC data generation device 311 advances the process to step ST14 when it is determined that the expression (7) is satisfied, and advances the process to step ST16 when it is determined that the expression is not satisfied.

According to Expression (6) and Expression (7), L _p media packets in the last row in the matrix of L _p columns M _p rows of the two-dimensional FEC data requested by the terminal device p, that is, L _p columns M _p rows The process of step ST14 is performed from the {L _p (M _p −1) +1} th column media packet to the {L _p M _p } column media packet in the last row in the matrix. For example, in the case of the terminal device 1 (p = 1), when each media packet of sequence numbers 97,..., 100 shown in FIG. 7A is read and processed, and as shown in FIG. When the media packets having the sequence numbers 197,..., 200 are read and processed, the process of step ST14 is performed. For example, in the case of the terminal device 2 (p = 2), when reading and processing each media packet of the sequence numbers 96,..., 100 shown in FIG. 8A, and FIG. When the media packets having the sequence numbers 196,..., 200 shown in FIG. For example, in the case of the terminal device 3 (p = 3), when reading and processing each media packet of the sequence numbers 91,..., 100 shown in FIG. 9A, and FIG. When the media packets of sequence numbers 191,..., 200 shown in FIG.

Next, in step ST14 of FIG. 6, the FEC data generation device 311 calculates the second vertical FEC intermediate data C ′ _{p, q} in the q-th column of the terminal device p by the following equation (8).

式（９）では、端末装置ｐの第ｑ列の縦方向ＦＥＣデータＣ_ｐ，ｑを、端末装置ｐの第ｑ列の第２の縦方向ＦＥＣ用中間データ用変数Ｃ′_ｐ，ｑと端末装置ｐの第ｑ列の第３の縦方向ＦＥＣ用中間データ用変数Ｃ”_ｐ，ｑとの排他的論理和から計算している。 In addition, the FEC data generation device 311 calculates the vertical FEC data C _{p, q} in the q-th column of the terminal device p by the following equation (9).

In Expression (9), the vertical FEC data C _{p, q} in the q-th column of the terminal device p is replaced with the second vertical FEC intermediate data variable C ′ _{p, q} in the q-th column of the terminal device p and the terminal. It is calculated from the exclusive OR with the third longitudinal FEC intermediate data variable C ″ _{p, q} in the q-th column of the device p.

Next, as shown in Expression (10), the third longitudinal FEC intermediate data C ″ _{p, q} in the q-th column of the terminal apparatus p includes the terminal device p calculated in Expression (8). The value of the second vertical FEC intermediate data C ′ _{p, q in} the q column is set.

Next, in step ST15 in FIG. 6, FEC data generating device 311 passes the data transceiver 313 longitudinally FEC data _{C p} of the q rows of a two-dimensional FEC data matrix of the terminal device _p, the _q, data transmission and reception The unit 313 transmits the vertical direction FEC data variables C _{p, q} to the terminal device p.

  Next, in step ST16 of FIG. 6, the FEC data generation device 311 increments the value of p by 1. In step ST17 of FIG. 6, the FEC data generation device 311 performs the processing from step ST9 to ST16 N times ( When the process is repeated N times, the process proceeds to step ST18.

Next, in step ST18 of FIG. 6, the FEC data generation device 311 performs processing of the following equations (11) and (12), and then returns the processing to step ST5.
i ← i + 1 (11)
k ← (k + 1) modL (12)
Equation (11) represents a process of incrementing the sequence number i by 1. Expression (12) represents a process of incrementing k by 1 within a range of 1 ≦ k ≦ L (returns to 1 when the value of k becomes larger than L).

  Next, the operation when the video distribution server 310 distributes data to each of the terminal devices 1, 2, and 3 and the advantages of such operation will be described more specifically.

  As shown in FIGS. 7A and 7B, the terminal apparatus 1 (p = 1) requests two-dimensional FEC data having a matrix size (media packet matrix size) of Lp = 4 and Mp = 25. As shown in FIGS. 8A and 8B, the terminal device 2 (p = 2) has a two-dimensional matrix size (media packet matrix size) of Lp = 5 and Mp = 20. FEC data is requested, and as shown in FIGS. 9A and 9B, the terminal device 3 (p = 3) has a matrix size of Lp = 10 and Mp = 10 (the size of the media packet matrix). ) Two-dimensional FEC data. Further, in these drawings, a case where the media packet has a sequence number i from 1 (indicated as “01” in the figure) to 200 will be described.

At this time, in the conventional FEC data generation method, it is necessary to calculate FEC data for each terminal device. 7 (a) and 7 (b), 8 (a) and 8 (b), 9 (a) and 9 (b), the lateral FEC data (lateral FEC packet) for each terminal device 1, 2, 3 is obtained. Table 1 shows the number of exclusive OR calculations necessary for generating vertical FEC data (vertical FEC packet).

In the calculation of the lateral FEC data of the terminal device 1, for example, the sequence number 01 of the first row in FIG. 7 (a), ..., the 04 of the media data, each data _{d 01} of media packets and _{d 02} and _{d 03} And d ₀₄ are calculated, and the calculation of the exclusive OR three times per line is required. Therefore, as shown in Table 1, in the calculation of the lateral FEC data of the terminal device 1, 150 exclusive OR calculations are required. Based on the same concept, 160 times of exclusive OR calculation is required in the calculation of the lateral FEC data of the terminal device 2, and 180 times of exclusive calculation is required in the calculation of the lateral FEC data of the terminal device 3. Calculation of logical sum is required. In the calculation of the lateral FEC data, a total of 490 exclusive OR calculations are required.

In the calculation of the longitudinal FEC data of the terminal device 1, for example, FIGS. 7 (a) the first column of the sequence numbers in 01,05,09, ..., for 97 of the media data, each data _d 01 of media packets, d ₀₅ ,..., _D97 are exclusive ORed, and the calculation of 24 exclusive ORs per column is required. Therefore, as shown in Table 1, in the calculation of the longitudinal FEC data of the terminal device 1, 192 exclusive OR calculations are required. Based on the same concept, 190 times of exclusive OR calculation is required in the calculation of the vertical FEC data of the terminal device 2, and 180 times of exclusive OR is required in the calculation of the vertical FEC data of the terminal device 3. Calculation of logical sum is required. In the calculation of the vertical FEC data, a total of 562 exclusive OR calculations are required.

Next, the number of exclusive OR calculations in the case of the FEC data generation method according to the embodiment of the present invention is examined. In the present embodiment, the least common multiple L = 20, and as shown in FIG. 10 and step ST7 of FIG. 5, the horizontal FEC intermediate data S and the vertical FEC intermediate data T _k. (K = 1, 2,..., 20) is calculated. Then, from the calculated horizontal FEC intermediate data S and vertical FEC intermediate data T _k (k = 1, 2,..., 20), the horizontal FEC data R ₁ and the vertical FEC data C of the terminal device 1 are used. _{1, q} , horizontal FEC data R ₂ and vertical FEC data C _{2, q} of the terminal device _2, and horizontal FEC data R ₃ and vertical FEC data C _{3, q of} the terminal device 3 are calculated.

端末装置１が要求する２次元ＦＥＣデータの横方向ＦＥＣデータは、次式（１４）から計算される。

As can be understood from FIGS. 7A and 7B, step ST14 in FIGS. 10 and 6, and the above formulas (8) and (9), the vertical FEC data of the two-dimensional FEC data requested by the terminal device 1 is used. Is calculated from the following equation (13):

The lateral FEC data of the two-dimensional FEC data requested by the terminal device 1 is calculated from the following equation (14).

端末装置２が要求する２次元ＦＥＣデータの横方向ＦＥＣデータは、次式（１５）から計算される。

Further, as can be understood from FIGS. 8A and 8B, step ST14 of FIGS. 10 and 6, and the above formulas (8) and (9), the vertical direction of the two-dimensional FEC data required by the terminal device 2 FEC data is calculated from the following equation (14).

The lateral FEC data of the two-dimensional FEC data requested by the terminal device 2 is calculated from the following equation (15).

端末装置３が要求する２次元ＦＥＣデータの横方向ＦＥＣデータは、次式（１７）から計算される。

Further, as can be understood from FIGS. 9A and 9B, step ST14 in FIGS. 10 and 6, and the above formulas (8) and (9), the vertical direction of the two-dimensional FEC data required by the terminal device 3 is used. FEC data is calculated from the following equation (16).

The lateral FEC data of the two-dimensional FEC data requested by the terminal device 3 is calculated from the following equation (17).

As can be seen by comparing these equations, since the calculation results of T ₁ ,..., T ₂₀ are shared in generating the FEC data of the terminal devices 1, 2, and 3, each calculation is performed once. It can be seen that the amount of calculation can be reduced. In the FEC data generation method according to the present embodiment, the lateral FEC for each terminal device is obtained from FIGS. 7A and 7B, FIGS. 8A and 8B, and FIGS. 9A and 9B. Table 2 shows the number of exclusive OR calculations necessary for generating data and vertical FEC data.

  In the calculation of the lateral FEC data of the terminal device 1, the number of exclusive ORs required for the calculation of the lateral FEC data according to the equation (4) is 50, and the lateral FEC data of the terminal device 2 is calculated. , The number of exclusive OR calculations required for the calculation of the lateral FEC data by the equation (4) is 40, and the lateral FEC data of the terminal device 3 is calculated by the equation (4) in the lateral direction. The number of exclusive OR calculations required for calculating FEC data is 20 times. Further, as shown in Equation (1), the number of exclusive OR calculations necessary for calculating S is 199 times. Therefore, in the calculation of the lateral FEC data, a total of 309 exclusive OR calculations are required.

  Further, in the calculation of the vertical FEC data of the terminal device 1, the number of exclusive OR calculations required for calculating the vertical FEC data according to the equations (8) and (9) is 40 times. In the calculation of the vertical FEC data, the number of exclusive OR calculations required for calculating the vertical FEC data by the equations (8) and (9) is 40, and the vertical FEC data of the terminal device 3 is calculated. , The number of exclusive OR calculations required for calculating the vertical FEC data according to the equations (8) and (9) is 40. Further, as shown in Expression (2), the number of exclusive OR calculations necessary for calculating Tk is 180 times. Therefore, in the calculation of the longitudinal FEC data, a total of 300 exclusive OR calculations are required.

  As can be seen by comparing the total of Table 1 and the total of Table 2, the FEC data generation method according to the present embodiment can reduce the number of exclusive OR calculations.

  As described above, according to the FEC data generation device and the FEC data generation method of the present embodiment, even when a plurality of terminal devices request two-dimensional FEC data having different matrix sizes, By summing up these calculations, it is possible to reduce the overall calculation amount and to reduce the processing load on the video distribution server 310.

It is a figure which shows the structure of the conventional video delivery system roughly. It is a figure which shows the conventional one-dimensional FEC data generation method which produces | generates an FEC packet from the media packet of sequence numbers 01 to 100. FIG. It is a figure which shows the conventional 2D FEC data generation method which produces | generates a horizontal direction FEC packet and a vertical direction FEC packet from the media packets of sequence numbers 01-100. 1 schematically shows a configuration of a video distribution server including an FEC data generation apparatus according to an embodiment of the present invention (that is, an apparatus that performs an FEC data generation method according to an embodiment) and a video distribution system including the video distribution server. FIG. It is a flowchart (the 1) which shows operation | movement (namely, FEC data generation method) of the FEC data generation apparatus which concerns on embodiment of this invention. It is a flowchart (the 2) which shows operation | movement (namely, FEC data generation method) of the FEC data generation apparatus which concerns on embodiment of this invention. (A) And (b) is a figure for demonstrating the production | generation method of the two-dimensional FEC data whose matrix size which the terminal device 1 requests | requires is 25 rows 4 columns. (A) And (b) is a figure for demonstrating the production | generation method of the two-dimensional FEC data whose matrix size which the terminal device 2 requests | requires is 20 rows 5 columns. (A) And (b) is a figure for demonstrating the production | generation method of the two-dimensional FEC data whose matrix size which the terminal device 3 requests | requires is 10 rows 10 columns. It is a figure for demonstrating the FEC data generation method which concerns on embodiment of this invention, Fig.7 (a) and (b), Fig.8 (a) and (b), Fig.9 (a) and (b) The vertical FEC intermediate data and the horizontal FEC intermediate data used for calculating the horizontal FEC data and the vertical FEC data shown in FIG.

Explanation of symbols

1, 2, 3, 4 terminal devices,
310 video distribution server,
311 FEC data generator,
312 Media data storage unit,
313 data transmitter / receiver,
400 network.

Claims (4)

Calculating a least common multiple of a horizontal size of a matrix of two-dimensional FEC data respectively requested by first to N-th terminal devices (N is an integer of 2 or more);
Each of the first to Nth terminal devices requests each of the first to Nth terminal devices using an FEC data calculation matrix having the least common multiple as the number of media packets arranged in the horizontal direction. Generating dimensional FEC data; and
Let d _{i be} the data of the media packet with sequence number i (i = 1, 2,...)
p is an integer of 1 to N,
_Let L _{p be} the horizontal size of the matrix of two-dimensional FEC data required by the p-th terminal device,
L is the least common multiple,
k = 1, 2,..., L,
T _k is the first vertical FEC intermediate data calculated by exclusive OR of media packet data arranged in the vertical direction of the FEC data calculation matrix,
C ′ _{p, q} is _expressed as

The second vertical FEC intermediate data calculated in

Is the third vertical FEC intermediate data equal to the second vertical FEC intermediate data C′p _{, q} when the vertical FEC data was output in the same column last time,
In the step of generating the two-dimensional FEC data, the vertical FEC data C _{p, q} of the q-th column of the two-dimensional FEC data requested by the p-th terminal device is _expressed by the following equation:

A method for generating FEC data, characterized by: S is the first intermediate FEC intermediate data calculated by exclusive OR of media packet data up to sequence number i,
When S ′ is the second intermediate data for FEC in the horizontal direction calculated by exclusive OR of media packet data up to the sequence number (i−L _p ),
In the step of generating the 2 dimensional FEC data, the lateral FEC data R _p of the two-dimensional FEC data first p terminal device requests, when the sequence number i is J times the lateral size L _p, wherein 2. The FEC data generation method according to claim 1, wherein calculation is performed by an exclusive OR of the first horizontal FEC intermediate data S and the second horizontal FEC intermediate data S ′. Means for calculating a least common multiple of a lateral size of a matrix of two-dimensional FEC data respectively requested by first to N-th (N is an integer of 2 or more) terminal devices;
Each of the first to Nth terminal devices requests each of the first to Nth terminal devices using an FEC data calculation matrix having the least common multiple as the number of media packets arranged in the horizontal direction. Means for generating dimensional FEC data;
Let d _{i be} the data of the media packet with sequence number i (i = 1, 2,...)
p is an integer of 1 to N,
_Let L _{p be} the horizontal size of the matrix of two-dimensional FEC data required by the p-th terminal device,
L is the least common multiple,
k = 1, 2,..., L,
T _k is the first vertical FEC intermediate data calculated by exclusive OR of media packet data arranged in the vertical direction of the FEC data calculation matrix,
C ′ _{p, q} is _expressed as

The second vertical FEC intermediate data calculated in

Is the third vertical FEC intermediate data equal to the second vertical FEC intermediate data C′p _{, q} when the vertical FEC data was output in the same column last time,
The means for generating the two-dimensional FEC data uses the following formula to calculate the vertical FEC data C _{p, q} in the q-th column of the two-dimensional FEC data requested by the p-th terminal device:

The FEC data generation device characterized by the above calculation. S is the first intermediate FEC intermediate data calculated by exclusive OR of media packet data up to sequence number i,
When S ′ is the second intermediate data for FEC in the horizontal direction calculated by exclusive OR of media packet data up to the sequence number (i−L _p ),
Said means for generating said two-dimensional FEC data, the lateral FEC data R _p of the two-dimensional FEC data first p terminal device requests, when the sequence number i is J times the lateral size L _p, wherein 4. The FEC data generation apparatus according to claim 3, wherein calculation is performed by an exclusive OR of the first horizontal FEC intermediate data S and the second horizontal FEC intermediate data S ′. 5.

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