JP2013179617A - Channel decoding apparatus and method in digital broadcast communication system using low-density parity-check codes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a channel decoding apparatus and method in a digital broadcast communication system.SOLUTION: The apparatus and method in a digital broadcast communication system using a low-density parity-check (LDPC) code comprises: determining predetermined shortening and puncturing patterns on the basis of a received signal; inserting as many zeros as the number of shortened bits and setting as many erasures as the number of punctured bits, according to position information on the bits to be shortened and punctured; and decoding the LDPC code when bits subjected to the shortening or puncturing exist.

Description

  The present invention relates to a digital broadcast communication system using a low-density parity-check (hereinafter referred to as “LDPC”) code, and more particularly, to efficiently generate an LDPC code and decode a channel. The present invention relates to a channel decoding apparatus and a method thereof.

  In a wireless communication system, not only various channel noise and fading phenomenon, but also inter-symbol interference (hereinafter, referred to as “ISI”) significantly reduces link performance. Therefore, in order to realize a high-speed digital communication system that requires a large amount of data processing, high-speed data processing, and high-reliability data such as next-generation mobile communication, digital broadcast, and mobile Internet, noise, fading It is essential to develop technologies that overcome the ISI. In recent years, research on error correction codes has been actively conducted as a method for efficiently restoring distorted information to its original state and increasing the reliability of communication.

  The LDPC code, first introduced by Gallager in the 1960s, was not fully utilized due to its implementation complexity far exceeding the technology at that time. However, because the turbo codes discovered by 1993 Berrou, Glavieux, and Thiimajshima show performance close to Shannon's channel capacity, channel code based on iterative decoding and graphs, with much analysis on the performance and characteristics of turbo codes. A lot of research has been carried out on computerization.

  Due to such research, LDPC codes were re-researched in the late 1990s, applying iterative decoding based on sum-product algorithm on Tanner graph (a special case of factor graph) corresponding to LDPC codes Performing the decoding with, proved to have a performance close to Shannon's channel capacity.

  LDPC codes are usually shown using graph representation techniques, and many properties can be analyzed through methods based on graph theory, algebra, and probability theory. In general, a graph model of the channel code is useful for describing the code. When mapping information about encoded bits to vertices in the graph and mapping relationships between encoded bits to edges (ie, line segments) in the graph, the channel's graph model is It can be regarded as a communication network in which vertices exchange predetermined messages through each edge. Therefore, a natural decoding algorithm can be derived. For example, decoding algorithms derived from trellis considered as a kind of graph include the well-known Viterbi algorithm, and the Bahl, Cocke, Jelinek, and Raviv (BCJR) algorithms.

  The LDPC code is generally defined by a parity check matrix and can be expressed using a bipartite graph called a Tanner graph. In this bipartite graph, the vertices are divided into two different types. The LDPC code is represented by a bipartite graph made up of vertices called “variable nodes” and “check nodes”. This variable node is mapped one-to-one with the encoded bits.

  With reference to FIG.1 and FIG.2, the graph representation method of a LDPC code is demonstrated.

FIG. 1 shows an example of a parity check matrix H ₁ of an LDPC code configured with 4 rows and 8 columns. Referring to FIG. 1, 8 columns mean an LDPC code that generates a codeword of length 8, and each column is mapped to 8 encoded bits.

Figure 2 is a diagram illustrating a Tanner graph corresponding to H ₁ of FIG.

Referring to FIG. 2, a Tanner graph of an LDPC code includes eight variable nodes x ₁ (202), x ₂ (204), x ₃ (206), x ₄ (208), x ₅ (210), x ₆ (212), x ₇ (214), and x ₈ (216) and four check nodes (218, 220, 222, 224).

Here, the i th column and the j th row of the parity check matrix H ₁ of the LDPC code are mapped to the variable node x _i and the j th check node. Also, a value of 1 at the position where the i-th column and j-th row of the parity check matrix H ₁ of the LDPC code intersect each other, that is, a value other than 0, is the variable node x _i on the Tanner graph of FIG. Means that there is an edge between the j-th check node.

  In a Tanner graph of an LDPC code, the degree of a variable node and a check node means the number of edges connected to each node, which is a column corresponding to a related node in the parity check matrix of the LDPC code. Or the number of non-zero entries in the row.

For example, in FIG. 2, variable nodes x ₁ (202), x ₂ (204), x ₃ (206), x ₄ (208), x ₅ (210), x ₆ (212), x ₇ (214), And x ₈ (216) have orders of 4, 3, 3, 3, 2, 2, 2, and 2, respectively, and check nodes 218, 220, 222, and 224 have orders of 6, 5, 5, respectively. , And 5. Also, the number of non-zero entries in each column of the parity check matrix H ₁ of FIG. 1 corresponding to the variable node of FIG. 2 is the above-described orders 4, 3, 3, 3, 2, 2, 2, and 2. The number of entries that match and are not 0 in each row of the parity check matrix H ₁ of FIG. 1 corresponding to the check node of FIG. 2 matches the above-described orders 6, 5, 5, and 5.

To demonstrate the degree distribution (degree distribution) for a node of the LDPC code, defines the ratio of the total number of the number and variable nodes of the variable node degree is i as _{f i,} and the number of check nodes degree-j The ratio with the total number of check nodes is defined as g _j . For example, for the LDPC code corresponding to FIGS. 1 and _{2, f 2 = 4/8,} f 3 = 3/8, f 4 = 1/8, f i with respect to i ≠ 2, 3, 4 = 0, g ₅ = 3/4, g ₆ = 1/4, j ≠ 5, 6 for g _j = 0. When the length of the LDPC code is defined as N, that is, the number of columns is defined as N and the number of rows is defined as N / 2, the density of entries that are not 0 in the all parity check matrix having the above-described degree distribution is as follows. It is calculated like the following formula (1).

  In Equation (1), as N increases, the density of ‘1’ in the parity check matrix continuously decreases. In general, in an LDPC code, an LDPC code with a large N has a very low density of non-zero entries because the codeword length N is inversely proportional to the density of non-zero entries. For this reason, the LDPC code includes the meaning of “low-density” in its name.

  Next, characteristics of the parity check matrix of the structured LDPC code applied in the present invention will be described with reference to FIG.

Figure 3 is a diagram showing an LDPC code adopted as the standard technology in which is one DVB-S2 (Digital Video Broadcasting- Satellite Transmission 2 nd generation) in the European digital broadcast standard.

In FIG. 3, in the LDPC code, N ₁ indicates the length of the block, K ₁ indicates the length of the information word, and (N ₁ -K ₁ ) indicates the length of the parity. M ₁ and q are determined so as to satisfy q = (N ₁ −K ₁ ) / M ₁ . Preferably K ₁ / M ₁ should be an integer.

Referring to FIG. 3, the parity part of the parity check matrix, that is, the configuration from the K _1st column to the (N ₁ −1) th column has a dual diagonal configuration. Thus, for the distribution of the order of the columns corresponding to the parity part, all the columns have the order '2' except for the last column having the order '1'.

In the parity check matrix, the configuration from the information word part, that is, the 0th column to the (K ₁ −1) th column is made using the following rules.

By grouping [Rule 1] K ₁ piece corresponding to the information word in the parity-check matrix of the column into a plurality of groups composed of M ₁ single row, to generate a total K _{1 /} M ₁ column groups .

The method of forming columns belonging to each column group follows the rule 2 below.
[Rule 2] The position of “1” in each 0th column in the i (where i = 1,..., K ₁ / M ₁ ) th column group is determined.

When the order of the 0th column in each i-th column group is denoted by D _i , the position of the row having '1' is

Assuming that the position of the row with ‘1’

Is defined by the following equation (2) in the j-th column (where j = 1, 2,..., M ₁ −1) in the i-th column group.

According to Rule 2 described above, the order of the columns belonging to the i-th column group are all fixed to D _i. In order to easily understand the configuration of the DVB-S2 LDPC code that stores information related to the parity check matrix according to rule 2 described above, the following specific example is considered.

N ₁ = 30, K ₁ = 15, M ₁ = 5, and q = 3, and the three sequences of information about the position of the row with '1' for the 0th column in the three column groups are: It can be expressed as follows. Here, for convenience of explanation, these three sequences are defined as “weight value-1 position sequence”.

  This weight value-1 position sequence can be expressed only as position information corresponding to each column group as follows.

0 1 2
0 11 13
0 10 14

  That is, this i-th row sequence is obtained by sequentially showing information on the position of a row having 1 as such information in the i-th column group.

  If a parity check matrix is configured using information corresponding to the above-described example and rules 1 and 2, an LDPC code having the same concept as the DVB-S2 LDPC code of FIG. 4 can be generated.

  FIG. 4 is a diagram illustrating an example of a parity check matrix of an LDPC code.

  DVB-S2 LDPC codes designed according to rule 1 and rule 2 can be efficiently encoded using structural shapes. The process of performing LDPC encoding using a DVB-S2 parity check matrix will be described using the following example.

An encoding process using a DVB-S2 LDPC code when N ₁ = 16200, K ₁ = 10800, M ₁ = 360, and q = 15 will be described. An information word bit having a length K ₁ is

And the parity bits having length (N ₁ −K ₁ ) are

As shown.

  [Step 1] The encoder initializes the parity bits as follows.

  [Step 2] Information about a row having 1 as the information in the 0th column belonging to the 1st column group of the information word is read out from the position information of the stored parity check matrix.

  An example of only the position information related to the read information can be expressed as follows.

0 2084 1613 1548 1286 1460 3196 4297 24
81 3369 3451 4620 2622

  In addition, a plurality of position information related to the read information can be expressed as a weight value-1 position sequence as follows.

Updating the particular parity bits p _x as defined by the following equation (3) using the information and the information bits i ₀ read above. Where x is the respective

Means the value of

  In Equation (3) above,

Is

Can also be expressed as

Means binary addition.

[Step 3] 359 information word bits i _m after i ₀ (where m = 1, 2,...
359) is obtained by the following mathematical formula (4).

{X + (m mod M ₁ ) × q} mod (N ₁ −K ₁ )
M ₁ = 360, m = 1, 2,. . . 359 Formula (4)

  In the above equation (4), x is each

Means the value of Here, the above-described equation (4) has the same concept as the above-described equation (2).

Next, the operation approximated to Equation (3) is executed using the value obtained by Equation (4) described above. That is, the encoder for _{i m}

Update.

For example, when m = 1, that is, for i ₁ , the encoder performs the following equation (5):

をアップデートする。

Update.

The above formula (5) corresponds to the case where q = 15. The encoder is m =
1, 2,. . . 359, the above process is performed in the same manner.

[Step 4] Similar to step 2, the encoder performs the operation on the 361st information word bit i ₃₆₀ .

It reads the information, updates the particular parity bits p _x. Where x is

Means. The encoder is _responsible for the 359 information word bits i ₃₆₁ , i _362,. . . , I ₇₁₉ by applying Equation (4) in the same way,

Update.

  [Step 5] The encoder repeats the steps 2, 3, and 4 for each information word bit group having 360 information word bits.

  [Step 6] The encoder finally determines parity bits using the following equation (6).

In the above equation (6), the parity bit p _i is a parity bit obtained by completing the LDPC encoding.

  As described above, DVB-S2 performs LDPC encoding through the processes from Step 1 to Step 6.

  On the other hand, the LDPC coding as described above must be designed to be compatible to support the amount of data transmission required in an actual communication system. In particular, only an adaptive communication system that applies a hybrid automatic retransmission request (HARQ) method and an adaptive modulation and coding (AMC) method to support high-speed data transmission. In addition, a communication system that supports various broadcast services requires LDPC encoding having various block lengths to support various data transmission amounts according to system requirements.

  However, the conventional LDPC coding scheme has a limitation in performing channel coding and decoding by generating all LDPC codewords having the same length.

  Therefore, there is a problem that an LDPC encoding method for a high-speed digital communication system that requires a large amount of data processing, further high-speed data processing, and data with higher reliability is required. In addition, there is a problem that a channel coding and decoding scheme using a more efficient LDPC codeword is necessary.

  Therefore, the present invention has been made in view of the above-described conventional problems, and an object of the present invention is to change a variable length using a puncturing or shortening from an LDPC code having a fixed length in a digital broadcast communication system. An object of the present invention is to provide an apparatus and a method for generating an LDPC code and decoding a channel using the generated LDPC code.

ここで、

は、ｘよりも小さいか又は同一の最大整数であり、Ｎｐは、パンクチャーリングされるビット数であり、Ｋ_１は、短縮前のＬＤＰＣ符号の情報語の長さであり、Ｋ_２は、短縮後のＬＤＰＣ符号の情報語の長さであり、前記所定の短縮されたビット数は（Ｋ_１−Ｋ_２）である。 In order to achieve the above object, according to an aspect of the present invention, a channel decoding method in a digital broadcast communication system using a low density parity check (LDPC) code is provided. A shortening pattern and a puncturing pattern are determined based on the received signal. The value of the bit shortened according to the shortening pattern is set to zero. Erasure is set according to the puncturing pattern. If there is a bit that has been shortened or punctured, LDPC decoding is performed. The step of determining the shortening pattern and the puncturing pattern uses the following equation (7) to calculate a value of a coefficient A that represents a ratio between the number of punctured bits and the predetermined number of shortened bits. Including setting to 5/4 or 6/5.

here,

Is the largest integer less than or equal to x, Np is the number of bits to be punctured, K ₁ is the length of the information word of the LDPC code before shortening, and K ₂ is This is the length of the information word of the LDPC code after shortening, and the predetermined shortened number of bits is (K ₁ -K ₂ ).

ここで、

は、ｘよりも小さいか又は同一の最大整数であり、Ｎｐは、パンクチャーリングされるビット数であり、Ｋ_１は、短縮前のＬＤＰＣ符号の情報語の長さであり、Ｋ_２は、短縮後のＬＤＰＣ符号の情報語の長さであり、前記所定の短縮されたビット数は（Ｋ_１−Ｋ_２）である。 According to another aspect of the present invention, a channel decoding apparatus in a digital broadcast communication system using a low density parity check (LDPC) code is provided. The apparatus includes a demodulator that performs channel reception and demodulation. The apparatus determines a predetermined shortening and puncturing pattern based on the demodulated signal, and transmits position information regarding bits to be shortened and punctured to an LDPC decoder. It further includes a determination or estimation unit. The apparatus inserts zeros by the shortened number of bits according to the position information regarding the bits to be shortened and punctured, sets erasures by the number of punctured bits, and decodes the LDPC code. It further includes an LDPC decoder. In the shortening and puncturing pattern, the following equation (7) is used, and the value of the coefficient A representing the ratio between the number of punctured bits and the number of shortened bits is set to 5/4 or 6/5. Set.

here,

Is the largest integer less than or equal to x, Np is the number of bits to be punctured, K ₁ is the length of the information word of the LDPC code before shortening, and K ₂ is This is the length of the information word of the LDPC code after shortening, and the predetermined shortened number of bits is (K ₁ -K ₂ ).

  The apparatus and method of the present invention ensures scalability and flexibility of a digital broadcast communication system in a digital broadcast communication system using an LDPC code by using a variable length LDPC code using information on a given parity check matrix. be able to.

  In addition, the apparatus and method of the present invention can perform channel transmission by using an LDPC code that keeps a predetermined effective reception range using information on a given parity check matrix constant at a maximum in a digital broadcast communication system using an LDPC code. Can be guaranteed to the maximum.

  Furthermore, the apparatus and method of the present invention performs shortening or puncturing in applying shortening or puncturing to LDPC codewords generated to support various block lengths according to system requirements. It is guaranteed that the performance of the LDPC code is similar to the system performance of the LDPC code before performing shortening or puncturing. Therefore, a faster data processing speed can be guaranteed through shortening to the LDPC code and applying puncturing.

It is a figure which shows an example of the parity check matrix of LDPC code whose length is 8. It is a figure which shows the Tanner graph of the parity check matrix of LDPC code whose length is 8. It is a figure which shows the schematic structure of a DVB-S2 LDPC code. It is a figure which shows an example of the parity check matrix of the LDPC code of DVB-S2. It is a block diagram which shows the structure of the transmitter / receiver in the communication system which uses the LDPC code to which embodiment of this invention is applied. It is a graph which shows the performance curve obtained by applying shortening and puncturing to the DVB-S2 LDPC code to which the embodiment of the present invention is applied. It is a graph which shows the performance curve obtained by applying shortening and puncturing to the DVB-S2 LDPC code to which the embodiment of the present invention is applied. 4 is a graph illustrating a relational expression between a shortened number of bits and a number of punctured bits according to an exemplary embodiment of the present invention. 4 is a graph illustrating a relational expression between a shortened number of bits and a number of punctured bits according to an exemplary embodiment of the present invention. 4 is a graph illustrating a relational expression between a shortened number of bits and a number of punctured bits according to an exemplary embodiment of the present invention. 6 is a graph illustrating improved performance of a DVB-S2 LDPC code applying shortening and puncturing according to an embodiment of the present invention. 6 is a graph illustrating improved performance of a DVB-S2 LDPC code applying shortening and puncturing according to an embodiment of the present invention. 5 is a graph illustrating a change in code rate with respect to the length of an LDPC information word according to an embodiment of the present invention. 6 is a flowchart illustrating an LDPC decoding process in a receiver when a puncturing pattern according to an embodiment of the present invention is applied. It is a block diagram which shows the structure of the transmitter which uses the LDPC code by which the puncturing and the shortening which were proposed by embodiment of this invention were made. It is a block diagram which shows the structure of the receiver which uses the LDPC code by which the puncturing and the shortening which were proposed by embodiment of this invention were made.

  Next, a specific example of a mode for carrying out a channel coding and decoding apparatus and its method in a communication system using a low density parity check code according to the present invention will be described with reference to the drawings. Other objects, advantages and salient features of the present invention will become apparent to those skilled in the art from the accompanying drawings and the following detailed description made from the embodiments of the present invention.

  In the drawings, the same reference numerals and numbers are used in common as much as possible to the same components and parts. Moreover, in the following description, when it is judged that the concrete description regarding the well-known function or structure relevant to this invention makes the summary of this invention unknown, the detailed description is abbreviate | omitted.

  The present invention minimizes the variation in the effective reception range caused by the fixed ratio of shortened bits to punctured bits in a system that applies shortening and puncturing to LDPC codes. A method for changing a ratio of a shortened bit to a punctured bit according to a predetermined rule is provided. The present invention also provides an apparatus for generating LDPC-encoded blocks having various block lengths in a communication system using LDPC codes, and a control method thereof.

  FIG. 5 is a block diagram showing a configuration of a transceiver in a communication system using an LDPC code to which the present invention is applied.

  Referring to FIG. 5, an input signal u is encoded by an LDPC encoder 511 of a transmitter 510 that outputs a signal c. The output signal c is modulated by a modulator 513 that outputs a signal s for transmission over the wireless channel 520. Thereafter, the demodulator 531 of the receiver 530 demodulates the signal r from the reception (Rx) channel and outputs the signal x. The LDPC decoder 533 calculates an estimated value based on the demodulated Rx channel.

Is estimated. Here, the LDPC encoder 511 generates a parity check matrix according to a block length required by the communication system using a predetermined method.

  In particular, according to the present invention, the LDPC encoder 511 supports various block lengths using the LDPC code without the need for additional storage information. The method for supporting various block lengths according to the present invention uses puncturing or shortening techniques.

  The “puncturing method” used here is a technique that performs LDPC encoding of a given specific parity check matrix and generates an LDPC codeword, and then does not actually transmit a specific part of the LDPC codeword. means. Therefore, the receiver determines that the part not transmitted is lost.

  On the other hand, when comparing the puncturing method and the shortening method, these two technologies have the common feature of shortening the block length of the LDPC codeword, but the puncturing method is different from the shortening method. Does not limit the value of a particular bit. That is, this puncturing method does not simply transmit a specific part of a specific information word bit or generated parity bit, and treats a specific part not transmitted by the receiver as an erasure.

  Hereinafter, the puncturing method will be described using the parity check matrix of the DVB-S2 LDPC code shown in FIG.

In the parity check matrix shown in FIG. 3, the total length is N ₁ , the head part of this parity check matrix corresponds to the information word bit having length K ₁ , and the remaining rear part is length N ₁ -K. Corresponds to a parity bit having ₁ .

And the remaining rear part is a parity bit having length N ₁ -K ₁

Corresponding to

That is, when only bits in the N _P-number of predefined positions in the LDPC codeword that has already been generated with a length N ₁ is not transmitted, transmits the LDPC codeword with a length N ₁ -N _P The same effect can be obtained.

  In the parity check matrix described above, all the columns corresponding to the punctured bits are used as they are in the decoding process. Therefore, the puncturing method is different from the shortening method in this respect.

  When setting up the system, the transmitter and receiver can share or estimate location information regarding this punctured bit as well. Thus, the receiver treats the associated punctured bits as just erasures and performs decoding.

The puncturing a block length of _N 1 -N _P actually transmitted at the transmitter, since the length of an information word is changed without _{K 1,} the code rate _K 1 _{/ (N} 1 -N _P ), And is always larger than the code rate K ₁ / N ₁ given as the initial value.

  Hereinafter, characteristics when puncturing and shortening are simultaneously applied to a given LDPC encoding will be described.

For convenience of explanation, it is assumed that the length of the block of the first LDPC code and the length of the information word are N ₁ and K ₁ , respectively. Also, let the length of the block of the last LDPC code and the length of the information word be N ₂ and K ₂ , respectively. The final LDPC code is finally obtained by shortening and puncturing the first LDPC code.

When N ₁ −N ₂ = N _Δ and K ₁ −K ₂ = K _S are defined, the parity check matrix of the DVB-S2 LDPC code is shortened by K _S bits, and N _P (= N _Δ −K _S ) When puncturing with only bits is performed, an LDPC code having N ₂ and K ₂ as a block length and an information word length can be generated.

When N _Δ > 0 or K _S > 0 in the generated LDPC code, the code rate becomes and is generally different from the code rate K ₁ / N ₁ of the DVB-S2 LDPC code. Therefore, the algebraic characteristics change. Here, the case of N _Δ = K _{S corresponds to} the case where both shortening and puncturing are not applied or only shortening is performed.

In general, it is different from the code rate K ₁ / N ₁ of the DVB-S2 LDPC code. Therefore, the algebraic characteristics change. Here, the case of N _Δ = K _{S corresponds to} the case where both shortening and puncturing are not applied or only shortening is performed.

  As described above, the LDPC code can obtain a code rate and a block length required by the system when appropriately adjusting the number of shortened bits and the number of punctured bits.

  In this regard, embodiments of the present invention generate codes with different code rates by appropriately adjusting the ratio of shortening and puncturing using the characteristics of shortening and puncturing, We propose a method to keep the effective reception range constant at the maximum.

DVB-S2 code with code rate 1/5, N ₁ = 16200, K ₁ = 3240, M ₁ = 360, and q ₁ = 36 and code rate is 4/9, N ₁ = 16200, When applying certain pattern shortening and puncturing at a fixed ratio to both DVB-S2 LDPC codes where K ₁ = 7200, M ₁ = 360, and q ₁ = 25, the system performance is shown in FIG. As shown in FIG.

Referring to FIGS. 6 and 7, the performance difference when no shortening and puncturing is applied in the vicinity of the bit error rate (BER) = 10 ⁻⁵ and when K ₂ = 360 reaches approximately 2 dB. .

  In order to compensate for the loss of the effective reception range due to the performance difference as described above, the same code rate should not be applied to the LDPC code after the shortening and puncturing are applied to the LDPC code. That is, in order to obtain a larger coding gain, an LDPC code having a lower code rate must be transmitted through puncturing of fewer bits.

For example, in FIG. _6, in the case of K 2 = 360, in order to maintain the code rate 1/5, and set the _{N P} to 11520. However, as _{N P} is reduced gradually decreased code rate gradually, _{thereby, N 1 = 16200, K 1} = 3240, M 1 = 360, and most the DVB-S2 code, which is a _q 1 = 36 Cases with similar performance occur.

  Therefore, in order to make the performance of a given LDPC code and the performance of an LDPC code to which shortening and puncturing are applied have as high a predetermined value as possible, puncturing is performed less when many shortenings are applied. There must be.

  Therefore, the present invention proposes a shortening and puncturing method having the relationship graphs of FIGS. 8, 9, and 10 so that the effective reception range can be applied simply while keeping the effective reception range as large as possible. To do.

First, the relationship graph of FIG. 8 can be expressed as the following mathematical formula (7).

Where is the largest integer less than or equal to x.

  here,

Is the largest integer less than or equal to x.

In Equation (7), A to determine a slope value, the value of K ₂ in each case the smaller is set to a value for the performance of the LDPC code to determine the appropriate value of N _P so as not to decrease.

  The relationship graph of FIG. 9 can be expressed as the following mathematical formula (8).

In the above equation (8), when the value of K ₂ is less than or equal to a particular value, it retains the number of bits punctured constant. On the other hand, when the value of K ₂ is larger than the specific value, it applies a number of bits to be punctured by a particular ratio in proportion to (K 1 _{-K 2).}

On the other hand, in FIG. 9, the region of K ₂ may be divided into two or more intervals may be set to 2 or more intervals.

  The relationship graph of FIG. 10 can be expressed as the following mathematical formula (9).

Equation (9) defines the number of bits punctured by the region of K ₂ discontinuously. 10, the region of _{K 2} is set to three intervals. However, the region of K ₂ may be divided into more than three intervals may be set to three or more intervals.

Above formula (7), (8), FIG. 8 corresponding to and (9), the common point 9, and 10, the ratio of the shortening and puncturing when the length of K ₂ is short It is to be lowered. Accordingly, even when K ₂ decreases continuously, shortening and LDPC code performance of the puncturing is applied is not decreased continuously. In particular, in Equations (7), (8), and (9), Equation (7) improves performance by taking different ratios of punctured bits for all K ₂ . Can be obtained.

  However, the method defined by Equation (8) or Equation (9) may be more efficient when a slight performance improvement and low implementation complexity is desired by each system.

  11 and 12 illustrate a method corresponding to Equation (7) for the DVB-S2 LDPC code of FIGS. 6 and 7 in order to understand the performance of the shortening and puncturing method proposed in the embodiment of the present invention. It is a graph which shows the performance obtained by applying.

As shown in FIGS. 6 and 7, the value of the performance difference between the case of K ₂ having the smallest value and the case of K ₂ having the largest value is approximately 2 dB. However, referring to FIG. 11 and FIG. 12, it can be seen that the performance difference in the vicinity of BER = 10 ⁻⁵ has greatly decreased within 0.4 dB. In particular, FIGS. 11 and 12 show DVB-S2 LDPC codes having characteristics including N ₁ = 16200, K ₁ = 7200, M ₁ = 360, and q ₁ = 25, and a code rate R of 4/9. It is a figure which shows the performance curve with respect to.

  In FIG. 11, equation (10) is used to apply puncturing to the DVB-S2 LDPC code.

At this time, the number of bits is punctured N _P must be an integer

Perform the operation. When Expression (10) is used, the code rate has substantially the same value as 4/9.

  This can be confirmed using the following formula (11).

  As shown in FIG. 12, in order for the code after applying shortening and puncturing to the DVB-S2 LDPC code to keep the effective reception range constant at a maximum, the following equation (12) is used. Can be defined.

In the above formula (12), the integer 6/5 is a factor related to the slope.

It has the best value when limited in the form of (B is an integer).

When the above equation (12) is applied, the LDPC code rate R _eff effective for the information word length K ₂ can be expressed by the following equation (13).

FIG. 13 is a graph showing the change of the effective LDPC code rate R _eff with respect to the information word length K ₂ according to the embodiment of the present invention.

13, when the length _{K 2} information word shortened, code rate _{R eff} also decreases and the length _{K 2} information word becomes longer, indicating that also increases the code rate _{R eff.} That is, this effective LDPC code rate R _eff also changes according to the change in the information word length K ₂ . Also, in the range of K ₂ ≦ 7200, the value of R _eff is always less than or equal to 4/9.

For reference, the length of the block of the LDPC code according to the change of the effective LDPC code rate R _eff can be schematically expressed as the following formula (14).

  As described above, the effective reception range can be kept constant by changing the code rate according to the length of the information word.

  A mathematical expression that exhibits substantially the same performance as Expression (13) can be expressed by Expression (15) below.

As defined by Equation (15) above, in all different cases where similar _NP values are output, the calculation can be appropriately adjusted according to the implementation convenience to support similar performance.

If the value of the block length K ₂ + (N ₁ −K ₁ −N _P ) after applying shortening and puncturing to the DVB-S2 LDPC code must be a multiple of m, then K ₂ + (N An additional operation may be performed in each method for obtaining the values of Equations (7) to (15) such that ₁ −K ₁ −N _P ) = mC holds for an arbitrary integer C.

Here, (N ₁ −K ₁ −N _P ) is the number of parity bits actually transmitted after puncturing. That is, each step of calculating the values given by the mathematical formulas (7) to (14) can be changed little by little according to the additional conditions.

  FIG. 14 is a flowchart illustrating a reception process of a receiver according to an embodiment of the present invention.

  Referring to FIG. 14, the receiver performs puncturing and shortening pattern determination or estimation based on the signal received in step 1001.

  In step 1003, the receiver determines whether there are any punctured or shortened bits.

  If the result of the determination in step 1003 is that there are no punctured or shortened bits, the receiver proceeds to step 1009 and performs decoding.

  On the other hand, if the result of the determination in step 1003 is that there are punctured or shortened bits, the receiver proceeds to step 1005. The receiver provides the determined puncturing / shortening pattern to the LDPC decoder at step 1005.

  In step 1007, the LDPC decoder sets the determined punctured bit as a lost bit. Also, the LDPC decoder sets the probability that the shortened bit value is zero to 1.

  Thereafter, in step 1009, decoding of bits to which this puncturing and shortening is applied is executed.

  FIG. 15 is a block diagram illustrating a configuration of a transmitter using a punctured and shortened LDPC code according to an embodiment of the present invention.

  Referring to FIG. 15, the transmitter includes a controller 1110, a shortened pattern application unit 1120, an LDPC code parity check matrix extraction unit 1140, an LDPC encoder 1160, and a puncturing pattern application unit 1180.

  The LDPC code parity check matrix extraction unit 1140 extracts the parity check matrix of the shortened LDPC code. The LDPC code parity check matrix may be extracted using a check matrix preset in the memory, or the LDPC code parity check matrix may be directly generated at the transmitter.

  The control unit 1110 controls the shortening pattern application unit 1120 to determine a variable shortening pattern in consideration of the effective reception range based on each length of the information word. A shortening pattern application unit 1120 has a function of inserting a bit having a value of zero at a position corresponding to a shortened bit or removing a column corresponding to a shortened bit from a parity check matrix of a given LDPC code Fulfill.

  Here, the shortening pattern may be determined based on the shortening pattern stored in the memory, or may be generated using a sequence generator (not shown). Also, the shortening pattern may be determined by applying a density evolution analysis algorithm or the like to the parity check matrix and the length of a given information word.

  In addition, the control unit 1110 determines a puncturing pattern suitable for the modulation scheme and the length of bits to be punctured, and applies the determined puncturing pattern to the puncturing pattern application unit 1180. To control. Here, this puncturing pattern is determined so as to correct the effective reception range according to the length of the signaling information. Further, the puncturing pattern application unit 1180 may determine puncturing with a small number of bits in consideration of the shortening pattern.

  The control unit 1110 and the shortening pattern application unit 1120 perform encoding based on the LDPC code shortened through the LDPC encoder 1160. The LDPC codeword generated by the LDPC encoder 1160 performs puncturing so as to match the modulation scheme and the length of the punctured bit by the puncturing pattern application unit 1180.

  FIG. 16 is a block diagram showing a configuration of a receiver according to the embodiment of the present invention. In particular, FIG. 16 shows reception in a communication system using DVB-S2 LDPC code to which puncturing or shortening is applied, in which a transmitted signal is received and data desired by a user is restored from the received signal. An example of a vessel is shown.

  Referring to FIG. 16, the receiver includes a controller 1210, a shortening / puncturing pattern determination or estimation unit 1220, a demodulator 1230, and an LDPC decoder 1240.

  The demodulator 1230 receives and demodulates the shortened LDPC code. The shortening / puncturing pattern determination or estimation unit 1220 and the LDPC decoder 1240 receive the demodulated signal from the demodulator 1230.

  The control unit 1210 controls the shortening / puncturing pattern determination or estimation unit 1220 so as to estimate or determine information related to the puncturing or shortening pattern of the LDPC code from the demodulated signal. Thereafter, the shortening / puncturing pattern determination or estimation unit 1220 provides the LDPC decoder 1240 with position information regarding the determined puncturing and shortening bits.

  The shortening / puncturing pattern determination or estimation unit 1220 may generate the puncturing and shortening pattern using the puncturing and shortening pattern stored in the memory, or may use a generation method executed in advance. Can be used to generate puncturing / shortening patterns, or puncturing and shortening patterns can be determined or estimated by applying a density evolution analysis algorithm to the parity check matrix and the length of a given information word. You may go.

  Similar to the transmitter according to the embodiment of the present invention, when applying both shortening and puncturing, the shortening / puncturing pattern determination or estimation unit 1220 may first determine or estimate the shortening pattern, Alternatively, the determination or estimation of the puncturing pattern may be performed first. Further, the determination or estimation of the shortening pattern may be performed simultaneously with the determination or estimation of the puncturing pattern.

  The LDPC decoder 1240 assumes that the probability that this punctured bit is zero and the probability that this punctured bit is 1 are similar to ½, and decodes the data. Run. Also, the LDPC decoder 1240 processes the punctured bits as lost bits and performs decoding. Furthermore, the probability that the value of this shortened bit is zero is 1, that is, 100%. Therefore, the LDPC decoder 1240 prevents this shortened bit from participating in the decoding operation of the decoder. On the other hand, does the LDPC decoder 1240 allow the shortened bit to participate in the decoder's decoding operation based on the probability value 1 that the shortened bit is zero? Determine whether or not.

  When checking the length of the LDPC code shortened by the puncturing / pattern determination or estimation unit 1220, the LDPC decoder 1240 restores the data desired by the user from the received signal.

  As shown in FIG. 15, the transmitter according to the embodiment of the present invention performs shortening before the input of the LDPC encoder 1160 and performs puncturing at the output stage of the LDPC encoder 1160. On the other hand, in the receiver shown in FIG. 16, the LDPC decoder 1240 performs decoding while simultaneously recognizing information regarding puncturing and shortening.

  Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the scope and spirit of the invention. The scope of the present invention should not be limited to the above-described embodiments, but should be defined within the scope of the appended claims and their equivalents.

510 transmitter 511 LDPC encoder 513 modulator 520 channel 530 receiver 531 demodulator 533 LDPC decoder 1110 control unit 1120 shortened pattern application unit 1140 LDPC code parity check matrix extraction unit 1160 LDPC encoding unit 1180 puncturing pattern Application unit 1210 Control unit 1220 Shortening / puncturing pattern determination or estimation unit 1230 Demodulator 1240 LDPC decoder

Claims (6)

A channel decoding method in a digital broadcast communication system using a low density parity check (LDPC) code, comprising:
Determining a shortening pattern and a puncturing pattern based on the received signal;
If there are bits used to perform shortening or puncturing, then insert 0 for the number of bits shortened according to the determined shortening pattern and puncturing according to the determined puncturing pattern Setting erasures by the number of generated bits and performing LDPC decoding; and
The step of determining the shortening pattern and the puncturing pattern uses the following equation (7) to calculate a value of a coefficient A that represents a ratio between the number of punctured bits and the predetermined number of shortened bits. A channel decoding method in a digital broadcast communication system using a low density parity check code, comprising the step of setting to 5/4 or 6/5.

here,

Is the largest integer less than or equal to x, Np is the number of bits to be punctured, K ₁ is the length of the information word of the LDPC code before shortening, and K ₂ is This is the length of the information word of the LDPC code after shortening, and the predetermined shortened number of bits is (K ₁ -K ₂ ). The method of claim 1, wherein the number of punctured bits is determined by the following equation (12): a digital broadcast communication system using a low density parity check code according to claim 1.

  The length of the encoded block after the shortening and the puncturing has a value that is a multiple of a constant that is predetermined by an additional operation under a predetermined condition. A channel decoding method in a digital broadcast communication system using a low density parity check code. A channel decoding apparatus in a digital broadcast communication system using a low density parity check (LDPC) code, comprising:
A demodulator for receiving and demodulating the channel;
A shortening / puncturing pattern determination or estimation unit that determines a predetermined shortening and puncturing pattern based on the demodulated signal and transmits position information regarding the bits to be shortened and punctured to the LDPC decoder. When,
An LDPC decoder that decodes an LDPC code by inserting 0 as the number of shortened bits, setting erasures as many as the number of punctured bits, according to the positional information regarding the bits to be shortened and punctured And
In the shortening and puncturing pattern, the following equation (7) is used, and the value of the coefficient A representing the ratio between the number of punctured bits and the number of shortened bits is set to 5/4 or 6/5. A channel decoding apparatus in a digital broadcast communication system using a low density parity check code, characterized in that:

here,

Is the largest integer less than or equal to x, Np is the number of bits to be punctured, K ₁ is the length of the information word of the LDPC code before shortening, and K ₂ is This is the length of the information word of the LDPC code after shortening, and the predetermined shortened number of bits is (K ₁ -K ₂ ). The channel decoding apparatus in a digital broadcast communication system using a low density parity check code according to claim 4, wherein the number of punctured bits is determined according to the following equation (12).

  The length of the encoded block after the shortening and the puncturing has a value that is a multiple of a constant determined in advance by additional calculation under a predetermined condition. A channel decoding apparatus in a digital broadcast communication system using a low density parity check code.

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