Title of Invention  A METHOD AND A TRANSMITTER FOR GENERATING A BLOCK LOW DENSITY PARITY CHECK (LDPC) CODE HAVING A VARIABLE LENGTH 

Abstract  The invention relates to a method for generating a block low density parity check (LDPC) code having a variable length, the method comprising the steps of receiving an information word; and generating a block LDPC code by coding the information word using one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the block LDPC code, wherein the second parity check matrix is a parity check matrix defined by varying a size of the first parity check matrix, the first parity check matrix is a parity check matrix generated such that the block LDPC code has a predetermined length and is satisfied with a predetermined coding rate, the first parity check matrix comprises a predetermined number of partial blocks, and each of the partial blocks having a predetermined size, when the coding rate is 1/2, the first parity check matrix is expressed as one of the 5 tables shown in FIGS. 18, 22, 23, 26 and 27, wherein, in each of the 5 tables, blocks represent the partial blocks, numbers represent exponents of corresponding permutation matrixes, and blocks with no number represent partial blocks to which zero matrixes are mapped. 
Full Text  APPARATUS AND METHOD FOR CODING/DECODING BLOCK LOW DENSITY PARITY CHECK CODE WITH VARIABLE BLOCK LENGTH BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a mobile communication system, and in particular, to an apparatus and method for coding/decoding block low density parity check (LDPC) codes. 2. Description of the Related Art With the rapid development of mobile communication systems, it is necessary to develop technology capable of transmitting bulk data approximating the capacity of a wire network even in a wireless environment. To meet the increasing demand for a highspeed, highcapacity communication system capable of processing and transmitting various data such as image and radio data beyond the voiceoriented service, it is essential to increase the transmission efficiency of a system by using an appropriate channel coding scheme to thereby improve the overall system performance. However, the mobile communication system, because of its characteristics, inevitably generates errors during data transmission due to noise, interference and fading according to channel conditions. The generation of errors causes a loss of a great amount of information data. In order to prevent the loss of the information data due to the generation of errors, various error control schemes are currently in use and are based in part on channel characteristics to thereby improve the reliability of the mobile communication system. The most typical error control scheme uses error correction codes. With reference to FIG. 1, a description will now be made of a structure of a transmitter/receiver in a general mobile communication system. FIG. 1 is a diagram illustrating a structure of a transmitter/receiver in a general mobile communication system. Referring to FIG. 1, a transmitter 100 includes an encoder 111, a modulator 113 and a radio frequency (RF) processor 115, and a receiver 150 includes an RF processor 151, a demodulator 153 and a decoder 155. In the transmitter 100, transmission information data 'u', if generated, is delivered to the encoder 111. The encoder 111 generates a coded symbol 'c' by coding the information data 'u' with a predetermined coding scheme, and outputs the coded symbol 'c' to the modulator 113. The modulator 113 generates a modulation symbol V by modulating the coded symbol 'c' with a predetermined modulation scheme, and outputs the modulation symbol V to the RF processor 115. The RF processor 115 RFprocesses the modulation symbol V output from the modulator 113, and transmits the RFprocessed signal over the air via an antenna ANT. The signal transmitted over the air by the transmitter 100 in this way is received at the receiver 150 via its antenna ANT, and the signal received via the antenna is delivered to the RF processor 151. The RF processor 151 RFprocesses the received signal, and outputs the RFprocessed signal 'r' to the demodulator 153. The demodulator 153 demodulates the RFprocessed signal 'r' output from the RF processor 151 using a demodulation scheme corresponding to the modulation scheme applied in the modulator 113, and outputs the demodulated signal 'x' to the decoder 155. The decoder 155 decodes the demodulated signal 'x' output from the demodulator 153 using a decoding scheme corresponding to the coding scheme applied in the encoder 111, and outputs the decoded signal ' u' as finally decoded information data. In order for the receiver 150 to decode without errors the information data 'u' transmitted by the transmitter 100, there is a need for a highperformance encoder and decoder. Particularly, because a radio channel environment should be taken into consideration because of the characteristics of a mobile communication system, errors that can be generated due to the radio channel environment should be considered more seriously. The most typical error correction codes include turbo codes and low density parity check (LDPC) codes. It is well known that the turbo code is superior in performance gain to a convolutional code that is conventionally used for error correction, during high speed data transmission. The turbo code is advantageous in that it can efficiently correct an error caused by noise generated in a transmission channel, thereby increasing the reliability of the data transmission. The LDPC code can be decoded using an iterative decoding algorithm base on a sumproduct algorithm in a factor graph. Because a decoder for the LDPC code uses the sumproduct algorithm based iterative decoding algorithm, it is less complex than a decoder for the turbo code. In addition, the decoder for the LDPC code is easy to implement with a parallel processing decoder, compared with the decoder for the turbo code. Shannon's channel coding theorem illustrates that reliable communication is possible only at a data rate not exceeding a channel capacity. However, Shannon's channel coding theorem has proposed no detailed channel coding/decoding method for supporting a data rate up to the maximum channel capacity limit. Generally, although a random code having a very large block size exhibits a performance approximating a channel capacity limit of Shannon's channel coding theorem, when a MAP (Maximum A Posteriori) or ML (Maximum Likelihood) decoding method is used, it is actually impossible to implement the decoding method because of its heavy calculation load. The turbo code was proposed by Berrou, Glavieux and Thitimajshima in 1993, and exhibits a superior performance that approximates a channel capacity limit of Shannon's channel coding theorem. The proposal of the turbo code triggered active research on iterative decoding and graphical expression of codes, and LDPC codes proposed by Gallager in 1962 have been newly spotlighted in the research. Cycles exist in a factor graph of the turbo code and the LDPC code, and it is well known that iterative decoding in the factor graph of the LDPC code, where cycles exist, is suboptimal. Also, it has been experimentally proven that the LDPC code has excellent performance through iterative decoding. The LDPC code known to have the highest performance ever exhibits performances having a difference of only about 0.04 [dB] at a channel capacity limit of Shannon's channel coding theorem at a bit error rate (BER) 105, using a block size 107. In addition, although an LDPC code defined in Galois Field (GF) with q>2, i.e. GF(q), increases in complexity in its decoding process, it is much superior in performance to a binary code. However, there is no satisfactory theoretical description of successful decoding by an iterative decoding algorithm for the LDPC code defined in GF(q). The LDPC code, proposed by Gallager, is defined by a parity check matrix in which most of elements have a value of 0 and minor elements except the elements having the value of 0 have a nonzero value, e.g., a value of 1. In the following description, it will be assumed that a nonzero value is a value of 1. For example, an (N, j, k) LDPC code is a linear block code having a block length N, and is defined by a sparse parity check matrix in which each column has j elements having a value of 1, each row has k elements having a value of 1, and all of the elements except for the elements having the value of 1 have a value of 0. An LDPC code in which a weight of each column in the parity check matrix is fixed to 'j' and a weight of each row in the parity check matrix is fixed to 'k' as described above, is called a "regular LDPC code." Herein, the "weight" refers to the number of elements having a nonzero value among the elements constituting the parity check matrix. Unlike the regular LDPC code, an LDPC code in which the weight of each column in the parity check matrix and the weight of each row in the parity check matrix are not fixed is called an "irregular LDPC code." It is generally known that the irregular LDPC code is superior in performance to the regular LDPC code. However, in the case of the irregular LDPC code, because the weight of each column and the weight of each row in the parity check matrix are not fixed, i.e. are irregular, the weight of each column in the parity check matrix and the weight of each row in the parity check matrix must be properly adjusted in order to guarantee the superior performance. With reference to FIG. 2, a description will now be made of a parity check matrix of an (8, 2,4) LDPC code as an example of an (N, j, k) LDPC code. FIG. 2 is a diagram illustrating a parity check matrix of a general (8, 2, 4) LDPC code. Referring to FIG. 2, a parity check matrix H of the (8, 2, 4) LDPC code is comprised of 8 columns and 4 rows, wherein a weight of each column is fixed to 2 and a weight of each row is fixed to 4. Because the weight of each column and the weight of each row in the parity check matrix are regular as stated above, the (8, 2, 4) LDPC code illustrated in FIG. 2 becomes a regular LDPC code. The parity check matrix of the (8, 2, 4) LDPC code has been described so far with reference to FIG. 2. Next, a factor graph of the (8, 2, 4) LDPC code described in connection with FIG. 2 will be described herein below with reference to FIG. 3. FIG. 3 is a diagram illustrating a factor graph of the (8, 2, 4) LDPC code of FIG. 2. Referring to FIG. 3, a factor graph of the (8, 2, 4) LDPC code is comprised of 8 variable nodes of x1 300, x2 302, x3 304, X4 306, x5 308, X6 310, x7 312 and x8 314, and 4 check nodes 316, 318, 320 and 322. When an element having a value of 1, i.e. a nonzero value, exists at a point where an ith row and a j column of the parity check matrix of the (8, 2, 4) LDPC code cross each other, a branch is created between a variable node x; and a j check node. Because the parity check matrix of the LDPC code has a very small weight as described above, it is possible to perform decoding through iterative decoding even in a block code having a relatively long length, that exhibits performance approximating a channel capacity limit of Shannon's channel coding theorem, such as a turbo code, while continuously increasing a block length of the block code. MacKay and Neal have proven that an iterative decoding process of an LDPC code using a flow transfer scheme approximates an iterative decoding process of a turbo code in performance. In order to generate a highperformance LDPC code, the following conditions should be satisfied. (1) Cycles on a factor graph of an LDPC code should be considered. The term "cycle" refers to a loop formed by the edges connecting the variable nodesto the cheek nodes in a factor graph of an LDPC icode, and a fength of the cycle is defined as the number of edges constituting the loop. A long cycle means that the number of edges connecting the variable nodes to the check nodes constituting the loop in the factor graph of the LDPC code is large. In contrast, a short cycle means that the number of edges connecting the variable nodes to the check nodes constituting the loop in the factor graph of the LDPC code is small. As cycles in the factor graph of the LDPC code become longer, the performance efficiency of the LDPC code increases, for the following reasons. That is, when long cycles are generated in the factor graph of the LDPC code, it is possible to prevent performance degradation such as an error floor occurring when too many cycles with a short length exist on the factor graph of the LDPC code. (2) Efficient coding of an LDPC code should be considered. It is difficult for the LDPC code to undergo realtime coding compared with a convolutional code or a turbo code because of its high coding complexity. In order to reduce the coding complexity of the LDPC code, a Repeat Accumulate (RA) code has been proposed. However, the RA code also has a limitation in reducing the coding complexity of the LDPC code. Therefore, efficient coding of the LDPC code should be taken into consideration. (3) Degree distribution on a factor graph of an LDPC code should be considered. Generally, an irregular LDPC code is superior in performance to a regular LDPC code, because a factor graph of the irregular LDPC code has various degrees. The term "degree" refers to the number of edges connected to the variable nodes and the check nodes in the factor graph of the LDPC code. Further, the phrase "degree distribution" on a factor graph of an LDPC code refers to a ratio of the number of nodes having a particular degree to the total number of nodes. It has been proven by Richardson that an LDPC code having a particular degree distribution is superior in performance. With reference to FIG. 4, a description will now be made of a parity check matrix of a block LDPC code. FIG. 4 is a diagram illustrating a parity check matrix of a general block LDPC code. Before a description of FIG. 4 is given, it should be noted that the block LDPC code is a new LDPC code for which not only efficient coding but also efficient storage and performance improvement of a parity check matrix were considered, and the block LDPC code is an LDPC code extended by generalizing a structure of a regular LDPC code. Referring to FIG. 4, a parity check matrix of the block LDPC code is divided into a plurality of partial blocks, and a permutation matrix is mapped to each of the partial blocks. In FIG. 4, 'P' represents a permutation matrix having an NsxNs size, and a superscript (or exponent) apq of the permutation matrix P is either 0 located in the p row of the partial blocks of the parity check matrix, and 'q' indicates that a corresponding permutation matrix is located in the q* column of the partial blocks of the parity check matrix. That is, Papq represents a permutation matrix located in a partial block where the p row and the q column of the parity check matrix comprised of a plurality of partial blocks cross each other. That is, the 'p' and the 'q' represent the number of rows and the number of columns of partial blocks corresponding to an information part in the parity check matrix, respectively. The permutation matrix will now be described with reference to FIG. 5. FIG. 5 is a diagram illustrating the permutation matrix P of FIG. 4. As illustrated in FIG. 5, the permutation matrix P is a square matrix having an NsxNs size, and each of Ns columns constituting the permutation matrix P has a weight of 1 and each of Ns rows constituting the permutation matrix P also has a weight of 1. Herein, although a size of the permutation matrix P is expressed as NsxNs, it will also be expressed as Ns because the permutation matrix P is a square matrix. In FIG. 4, a permutation matrix P with a superscript apq=0, i.e. a , permutation matrix P°? represents an identity matrix INtXNs, and a permutation matrix P with a superscript apq=oo, i.e. a permutation matrix P00, represents a zero matrix. Herein, IN xNs represents an identity matrix with a size NsxNs. In the entire parity check matrix of the block LDPC code illustrated in FIG. 4, because the total number of rows is Nsxp and the total number of columns is Nsxq (for p rank, a coding rate can be expressed as Equation (1) regardless of a size of the partial blocks. If apq^oo for all p and q, the permutation matrixes corresponding to the partial blocks are not zero matrixes, and the partial blocks constitute a regular LDPC code in which the weight value of each column and the weight value of each row in each of the permutation matrixes corresponding to the partial blocks are p and q, respectively. Herein, each of permutation matrixes corresponding to the partial blocks will be referred to as a "partial matrix." Because (p1) dependent rows exist in the entire parity check matrix, a coding rate is greater than the coding rate calculated by Equation (1). In the case of the block LDPC code, if a weight position of a first row of each of the partial matrixes constituting the entire parity check matrix is determined, the weight positions of the remaining (Ns1) rows can be determined. Therefore, the required size of a memory is reduced to 1/NS as compared with the case where the weights are irregularly selected to store information on the entire parity check matrix. As described above, the term "cycle" refers to a loop formed by the edges connecting the variable nodes to the check nodes in a factor graph of an LDPC code, and a length of the cycle is defined as the number of edges constituting the loop. A long cycle means that the number of edges connecting the variable nodes to the check nodes constituting the loop in the factor graph of the LDPC code is large. As cycles in the factor graph of the LDPC code become longer, the performance efficiency of the LDPC code increases. In contrast, as cycles in the factor graph of the LDPC code become shorter, an error correction capability of the LDPC code decreases because performance degradation such as an error floor occurs. That is, when there are many cycles with a short length in a factor graph of the LDPC code, information on a particular node belonging to the cycle with a short length, starting therefrom, returns after a small number of iterations. As the number of iterations increases, the information returns to the corresponding node more frequently, so that the information cannot be correctly updated, thereby causing a deterioration in an error correction capability of the LDPC code. With reference to FIG. 6, a description will now be made of a cycle structure of a block LDPC code. FIG. 6 is a diagram illustrating a cycle structure of a block LDPC code of which a parity check matrix is comprised of 4 partial matrixes. Before a description of FIG. 6 is given, it should be noted that the block LDPC code is a new LDPC code for which not only efficient coding but also efficient storage and performance improvement of a parity check matrix were considered. The block LDPC code is also an LDPC code extended by generalizing a structure of a regular LDPC code. A parity check matrix of the block LDPC code illustrated in FIG. 6 is comprised of 4 partial blocks, a diagonal line represents a position where the elements having a value of 1 are located, and the portions other than the diagonallined portions represent positions where the elements having a value of 0 are located. In addition, 'P' represents the same permutation matrix as the permutation matrix described in conjunction with FIG. 5. In order to analyze a cycle structure of the block LDPC code illustrated in FIG. 6, an element having a value of 1 located in an i row of a partial matrix P is defined as a reference element, and an element having a value of 1 located in the ith row will be referred to as a "0point." Herein, "partial matrix" will refer to a matrix corresponding to the partial block. The 0point is located in an (i+af1 column of the partial matrix Pa. An element having a value of 1 in a partial matrix P , located in the same row as the Gpoint, will be referred to as a "1point." For the same reason as the 0 point, the 1point is located in an (i+b)& column of the partial matrix Pb. Next, an element having a value ofl in a partial matrix Pc, located in the same column as the 1point, will be referred to as a "2point." Because the partial matrix Pc is a matrix acquired by shifting respective columns of an identity matrix I to the right with respect to a modulo Ns by c, the 2point is located in an (i+b c)* row of the partial matrix Pc. In addition, an element having a value of 1 in a partial matrix Pd, located in the same row as the 2point, will be referred to as a "3point." The 3point is located in an (i+bc+d)th column of the partial matrix Pd. Finally, an element having a value of 1 in the partial matrix Pa, located in the same column as the 3point, will be referred to as a "4point." The 4point is located in an (i+bc+da)* row of the partial matrix Pa. In the cycle structure of the LDPC code illustrated in FIG. 6, if a cycle with a length of 4 exists, the 0point and the 4point are located in the same position. That is, a relation between the 0point and the 4point is defined by Equation (2) As a result, when the relationship of Equation (3) is satisfied, a cycle with a length 4 is generated. Generally, when a 0point and a 4ppoint are first identical to each other, a relation of i = i + p(bc + de)(modNs) is given, and the following relation shown in Equation (4) is satisfied. In other words, if a positive integer having a minimum value among the positive integers satisfying Equation (4) for a given a, b, c and d is defined as 'p', a cycle with a length of 4p becomes a cycle having a minimum length in the cycle structure of the block LDPC code illustrated in FIG. 6. In conclusion, as described above, for (ab+cd)*0, if gcd(Ns, ab+cd)=l is satisfied, then p = Ns. Herein, the gcd(Ns, ab+cd) is the function for calculating the "greatest common divisor" of the integers Ns and ab+cd. Therefore, a cycle with a length of 4NS becomes a cycle with a minimum length. A RichardsonUrbanke technique will be used as a coding technique for the block LDPC code. Because the RichardsonUrbanke technique is used as a coding technique, coding complexity can be minimized as the form of a parity check matrix becomes similar to the form of a full lower triangular matrix. With reference to FIG. 7, a description will now be made of a parity check matrix having a form similar to the form of the full lower triangular matrix. FIG. 7 is a diagram illustrating a parity check matrix having a form similar to the form of the full lower triangular matrix. The parity check matrix illustrated in FIG. 7 is different from the parity check matrix having a form of the full lower triangular matrix in the form of the parity part. In FIG. 7, a superscript (or exponent) apq of the permutation matrix P of an information part is either 0 an identity matrix INxN , and a permutation matrix P with a superscript apq=oo, i.e. a permutation matrix P00, represents a zero matrix. In. FIG.7, 'p' represents the number of rows of partial blocks mapped to the information part, and 'q' represents the number of columns of partial blocks mapped to the parity part. Also, superscripts ap, x and y of the permutation matrixes P mapped to the parity part represent exponents of the permutation matrix P. However, for the convenience of explanation, the different superscripts ap, x and y are used to distinguish the parity part from the information part. That is, in FIG. 7, Pa' and Pa" are also permutation matrixes, and the superscripts ai to ap are sequentially indexed to partial matrixes* located in a diagonal part of the parity part. In addftibn, Px and Py are also permutation matrixes, and for the convenience of explanation, they are indexed in a different way to distinguish the parity part from the inforaiatio'n part. If a block length of a block LDPC cod&na^m'g the parity check matrix illustrated in FIG. 7 is assumed to be N, the coding complexity of the block LDPC code linearly increases with respect to the block length N (0(N)). The biggest problem of the LDPC code having the parity check matrix of FIG. 7 is that if a length of a partial block is defined as Ns, Ns check nodes whose degrees are always 1 in a factor graph of the block LDPC code are generated. The check nodes with a degree of 1 cannot affect the performance improvement based on the iterative decoding. Therefore, a standard irregular LDPC code based on the RichardsonUrbanke technique does not include a check node with a degree of 1. Therefore, a parity check matrix of FIG. 7 will be assumed as a basic parity check matrix in order to design a parity check matrix such that it enables efficient coding while not including a check node with a degree of 1. In the parity check matrix of FIG. 7 comprised of the partial matrixes, the selection of a partial matrix is a very important factor for a performance improvement of the block LDPC code, so that finding an appropriate selection criterion for the partial matrix also becomes a very important factor. A description will now be made of a method for designing the parity check matrix of the block LDPC code based on the foregoing block LDPC code. In order to facilitate a method of designing a parity check matrix of the block LDPC code and a method for coding the block LDPC code, the parity check matrix illustrated in FIG. 7 is assumed to be formed with 6 partial matrixes as illustrated in FIG. 8. FIG. 8 is a diagram illustrating the parity check matrix of FIG. 7 which is divided into 6 partial blocks. Referring to FIG. 8, a parity check matrix of the block LDPC code illustrated in FIG. 7 is divided into an information part V, a first parity part pi, and a second parity part p2. The information part V represents a part of the parity check matrix, mapped to an actual information word during the process of coding a block LDPC code, like the information part described in conjunction with FIG 7, but for the convenience of explanation, the information part '&' is represented by different reference letters. The first parity part pi and the second parity part p2 represent a part of the parity check matrix, mapped to an actual parity during the process of coding the block LDPC code, like the parity pail described in conjunction with FIG.7, and the'parity part is divided into two parts. Partial matrixes A and C correspond to partial blocks A(802) and C (804)of the information part V, partial matrixes B and D correspond to partial blocks B(806) and D(808) of the first parity part pi, and partial matrixes T and E correspond to partial blocks T(810) and E (812)of the second parity part p2. Although the parity check matrix is divided into 7 partial blocks in FIG. 8, it should be noted that '0' is not a separate partial block and because the partial matrix T corresponding to the partial block T (810) have a full lower triangular form, a region where zero matrixes are arranged on the basis of a diagonal is represented by '0'. A process of simplifying a coding method using the partial matrixes of the information part 's', the first parity part pi and the second parity part p2 will be described later with reference to FIG. 10. The partial matrixes of FIG. 8 will now be described herein below with reference to FIG. 9. FIG. 9 is a diagram illustrating a transpose matrix of the partial matrix B shown in FIG. 8, the partial matrix E, the partial matrix T, and an inverse matrix of the partial matrix T, in the parity check matrix of FIG. 7. Referring to FIG. 9, a partial matrix B represents a transpose matrix of the partial matrix B, and a partial matrix T1 represents an inverse matrix of the partial matrix T. The p(K~ki) represents . The permutation matrixes illustrated in FIG. 9, for example, P°l, may be an identity matrix. As described above, if a superscript of the permutation matrix, i.e. ai is 0, the P"1 will be an identity matrix. Also, if a superscript of the permutation matrix, i.e. ai increases by a predetermined value, the permutation matrix is cyclic shifted by the predetermined value, so the permutation matrix P"1 will be an identity matrix. With reference to FIG. 10, a description will now be made of a'process of designing a parity check matrix of the block LDPC code. FIG. 10 is a flowchart illustrating a procedure for generating a parity check matrix of a general block LDPC code. Before a description of FIG. 10 is given, it should be noted that in order to generate a block LDPC code, a codeword size and a coding rate of a block LDPC code to be generated must be determined, and a size of a parity check matrix must be determined according to the determined codeword size and coding rate. If a codeword size of the block LDPC code is represented by N and a coding rate is represented by R, a size of a parity check matrix becomes N(lR)xN. Actually, the procedure for generating a parity check matrix of a block LDPC code illustrated in FIG. 10 is performed only once, because the parity check matrix is initially generated to be suitable for a situation of a communication system and thereafter, the generated parity check matrix is used. Referring to FIG. 10, in step 1011, a controller divides a parity check matrix with the size N(lR)xN into a total of pxq blocks, including p blocks in a horizontal axis and q blocks in a vertical axis, and then proceeds to step 1013. Because each of the blocks has a size of NsxNs, the parity check matrix is comprised of Nsxp columns and Nsxq rows. In step 1013, the controller classifies the pxq blocks divided from the parity check matrix into an information part's', a first parity part p1? and a second parity part p2, and then proceeds to steps 1015 and 1021. In step 1015, the controller separates the information part 's' into non zero blocks, or nonzero matrixes, and zero blocks, or zero matrixes according to the degree of distribution for guaranteeing a good performance of the block LDPC code, and then proceeds to step 1017. Because the degree of distribution for guaranteeing a good performance of the block LDPC code has been described above, a detailed description thereof will omitted herein. In step 1017, the controller determines the permutation matrixes Papq such that a minimum cycle length of a block cycle should be maximized as described above in the nonzero matrix portions in blocks having a low degree from among the blocks determined according to the degree distribution for guaranteeing a good performance of the ;,block LDPC code, and then proceeds to step K)19<. the permutation matrixes> P0pq should be determined taking into consideration the block cycles of not only the information part V but also the first parity partpi and the second parity part In step 1019, the controller randomly determines the permutation matrixes P"M in the nonzero matrix portions in the blocks having a high degree among the blocks determined according to the degree distribution for guaranteeing a good performance of the block LDPC code, and then ends the procedure. Even when the permutation matrixes Papq to be applied to the non zero matrix portions in the blocks having a high degree are determined, the permutation matrixes Papq must be determined by such that a minimum cycle length of a block cycle is maximized, and the permutation matrixes P"n are determined considering the block cycles of not only the information part V but also the first parity part px and the second parity part p2. An example of the permutation matrixes Papq arranged in the information part 's' of the parity check matrix is illustrated in FIG. 7. In step 1021, the controller divides the first part pi and the second parity part p2 into 4 partial matrixes B, T, D and E, and then proceeds to step 1023. In step 1023, the controller inputs the nonzero permutation matrixes Py and Pa> to 2 partial blocks among the partial blocks constituting the partial matrix B, and then proceeds to step 1025. The structure for inputting the nonzero permutation matrixes Py and P"1 to 2 partial blocks among the partial blocks constituting the partial matrix B has been described with reference to FIG. 9. In step 1025, the controller inputs the identity matrixes I to the diagonal partial blocks of the partial matrix T, inputs the particular permutation matrixes P"2,Pa\,Pa"1 to (i, i+1)* partial blocks under the diagonal components of the partial matrix T, and then proceeds to step 1027. The structure for inputting the identity matrixes I to the diagonal partial blocks of the partial matrix T and inputting the particular permutation matrixes P"2, Pa>, • ■ •, P""1 to (i, i+1 )* partial blocks under the diagonal components of the partial matrix T has been described with reference to FIG. 9. .. D,. and then proceeds to step 1029. In step 1029, the controller inputs a permutation matrix P"m to only the last partial block in the partial matrix E, and •then ends the procedure. The structure for inputting the 2 permutation matrixes P"m to only the last partial block among the partial blocks constituting the partial matrix E has been described with reference to FIG. 9. ELI SHASHA, SIMON LITSYN, ERAN SHARON ("MultiRate LDPC code for OFDMA PHY" INTERNET ARTICLE, 'Online! 27 June 2004 (20040627), XP002334837 Retrieved from the Internet: URL: http://www.ieee802.org/16/tge/contrib/C80216e04_185.pdf> 'retrieved on 20050705) describes a construction of a structured MultiRate LowDensity ParityCheck (MRLDPC) code for OFDMA PHY. A basic mother code is used for deriving various code rates by merging parity checks of the mother code. The mother code is constructed using a block paritycheck matrix with cyclic permutation blocks, similar to the codes suggested by Samsung. All codes derived from the mother code can be implemented on the same hardware of the mother code without additional cost. Since the basic code is structured, the implementation complexity is low. The codes' parity check matrices have a lower triangular paritybits section, enabling efficient linear encoding. Proposed flexible matrix's support rates, from Vi to 3A, for both large and small block size. This design of the matrixes improves the performance of both small and long blocks relative to the rigid matrixes proposed by Motorola and Intel, while using less hardware resources. 15B JONLARK KIM ("Explicit Construction of Families of LDPC Codes with Girth at Least Six" INTERNET ARTICLE, 'Online! October 2002 (200220), XP002333684 Retrieved from the Internet: URL: http://www.math.uic.edu/~pless/preprint/allerton.pdf> 'retrieved on 200506 28!) describes an explicit construction of LDPC codes whose Tanner graphs have known girth. For a prime power qand m _, 2, Lazebnik and Ustimenko construct a ^regular bipartite graph D(m; q) on 2qm vertices, which has girth at least 2dm=2e + 4. These graphs is regards as Tanner graphs of binary codes LU(/77; q). All the parameters of LU(2; q) are determined. We know that their girth is 6 and their diameter is 4. We know that LU(3; q) has girth 8 and diameter 6 and we conjecture its dimension. JOHN L. FAN ("Array Codes as LowDensity PartyCheck Codes" INTERNET ARTICLE, 'Online! September 2000 (200009), XP002333685 Retrieved from the Internet: URL: http://www.geocities.com/jfan_stanford/array_code5.pdf> 'retrieved on 20050628!) describes array codes. The array codes provide an example of a structured lowdensity paritycheck code whose algebraic structure also can used to decode large bursts of errors. SUMMARY OF THE INVENTION As described above, it is known that the LDPC code, together with the turbo code, has a high performance gain during highspeed data transmission and effectively corrects an error caused by noise generated in a transmission channel, contributing to an increase in the reliability of the data transmission. However, the LDPC code is disadvantageous in the coding rate, because the LDPC code has a relatively high coding rate, and it has a limitation in terms of the coding rate. Among the currently available LDPC codes, the major LDPC codes have a coding rate of 1/2 and only minor LDPC codes have a coding rate of 1/3. The limitation in the coding rate exerts a fatal influence on the highspeed, high capacity data transmission. Of course, although a degree of distribution representing the best performance can be calculated using a density evolution scheme in order to implement a relatively low coding rate for the LDPC code, it is difficult to implement an LDPC code having a degree distribution representing the best performance due to various restrictions, such as a cycle structure in a factor graph and hardware implementation. It is, therefore, an object of the present invention to provide an apparatus and method for coding/decoding an LDPC code having a variable block length in a mobile communication system. It is another object of the present invention to provide an apparatus and method for coding/decoding an LDPC code having a variable block length, coding complexity of which is minimized, in a mobile communication system. According to one aspect of the present invention, there is provided a method for coding a block Low Density Parity Check (LDPC) code having a variable length. The method includes receiving an information word; and coding the information word into a block LDPC code based on one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the information word into the block LDPC code. According to another aspect of the present invention, there is provided an apparatus for coding a block Low Density Parity Check (LDPC) code having a variable length. The apparatus includes an encoder for coding an information word into a block LDPC code according to one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the information word into the block LDPC code; and a modulator for modulating the block LDPC code into a modulation symbol using a predetermined modulation scheme. According to further another aspect of the present invention, there is provided a method for decoding a block Low Density Parity Check (LDPC) code having a variable length. The method includes receiving a signal; and selecting one of a first parity check matrix and a second parity check matrix according to a length of a block LDPC code to be decoded, and decoding the received signal according to the selected parity check matrix thereby detecting the block LDPC code. According to further another aspect of the present invention, there is provided an apparatus for decoding a block Low Density Parity Check (LDPC) code having a variable length. The apparatus includes a receiver for receiving a signal; and a decoder for selecting one of a first parity check matrix and a second parity check matrix according to a length of a block LDPC code to be decoded, and decoding the received signal according to the selected parity check matrix thereby detecting the block LDPC code. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: FIG. 1 is a diagram illustrating a structure of a transmitter/receiver in a general mobile communication system; FIG. 2 is a diagram illustrating a parity check matrix of a general (8, 2, 4) LDPC code; FIG; 3 is a diagram illustrating a factor graph Of the (8; 2, 4) LDPC code of FIG. 2; FIG. 4 is a diagram illustrating a parity check matrix of a general block LDPC code; FIG. 5 is a diagram illustrating the permutation matrix P of FIG. 4; FIG. 6 is a diagram illustrating a cycle structure of a block LDPC code of which a parity check matrix is comprised of 4 partial matrixes; FIG. 7 is a diagram illustrating a parity check matrix having a form similar to the form of a full lower triangular matrix; FIG. 8 is a diagram illustrating the parity check matrix of FIG. 7 which is divided into 6 partial blocks; FIG. 9 is a diagram illustrating a transpose matrix of a partial matrix B shown in FIG. 8, a partial matrix E, a partial matrix T, and an inverse matrix of the partial matrix T; FIG. 10 is a flowchart illustrating a procedure for generating a parity check matrix of a general block LDPC code; FIG. 11 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a first embodiment of the present invention; FIG. 12 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a second embodiment of the present invention; FIG. 13 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a third embodiment of the present invention; FIG. 14 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a fourth embodiment of the present invention; FIG. 15 is a flowchart illustrating a process of coding a variablelength block LDPC code according to the first to fourth embodiments of the present invention; FIG. 16 is a block diagram illustrating an internal structure of an apparatus for coding a variablelength block LDPC code according to embodiments of the present invention; FIG. 17 is a block diagram illustrating an internal structure of an apparatus for decoding a block LDPC code according to embodiments of the present invention; • •  FIG. 18 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a fifth embodiment of the present invention; ' FIG. 19 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a sixth embodiment of the present invention; FIG. 20 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a seventh embodiment of the present invention; FIG. 21 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a eighth embodiment of the present invention; FIG. 22 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a ninth embodiment of the present invention; FIG. 23 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a tenth embodiment of the present invention; FIG. 24 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a eleventh embodiment of the present invention; FIG. 25 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a twelfth embodiment of the present invention; FIG. 26 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a thirteenth embodiment of the present invention; FIG. 27 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a fourteenth embodiment of the present invention; and FIG. 28 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a fifteenth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Several preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness. The present invention proposes an apparatus and method for coding and decoding a block low density parity check (LDPC) code having a variable length (hereinafter referred to as a "variablelength block LDPC code"). That is, the present invention proposes an apparatus and method for coding and decoding a » variablelength block LDPC code in which a length of minimum cycle in a factor graph of a block LDPC code is maximized, the coding complexity of the block LDPC code isihimmized,* 2c degree distribution in the factor graph of the'block LDPC code has an optimal value of 1, and the variable block lengths are supported. Although not separately illustrated in the specification, the coding and decoding apparatus for a variablelength block LDPC code according to the present invention can be applied to the transmitter/receiver described with reference to FIG. 1. The next generation mobile communication system has evolved into a packet service communication system, and the packet service communication system, which is a system for transmitting burst packet data to a plurality of mobile stations, has been designed to be suitable for highcapacity data transmission. In order to increase the data throughput, a Hybrid Automatic Retransmission Request (HARQ) scheme and an Adaptive Modulation and Coding (AMC) scheme have been proposed. As the HARQ scheme and the AMC scheme support a variable coding rate, there is a need for block LDPC codes having various block lengths. The design of the variablelength block LDPC code, like the design of a general LDPC code, is implemented through the design of a parity check matrix. However, in a mobile communication system, in order to provide a variable length block LDPC code with one CODEC, i.e. in order to provide block LDPC codes having various block lengths, the parity check matrix should include parity check matrixes capable of representing block LDPC codes having different block lengths. A description will now be made of a parity check matrix of a block LDPC code providing a variable block length. First, a block LDPC code having a minimum length required in the system is designed for a desired coding rate. In the parity check matrix, if Ns indicating a size of its partial matrix is increased, a block LDPC code having a long block length is generated. The "partial matrix," as described above, refers to a permutation matrix corresponding to each of partial blocks obtained by dividing the parity check matrix into a plurality of partial blocks. Assuming that the block LDPC code is extended in such a manner that a block LDPC code with a short length is first designed and then a block LDPC code with a long length is • designed..because an increase in the size N'sof the'partial* matrix leads to a ■*• modification in the cycle structure, the exponents of the^drmutation matrixes of the parity check matrix are selected such that a cycle length should be maximized. Herein, a size of the partial matrix being Ns means that the partial matrix is a square matrix having a size of NsxNs, and for the convenience of description, the size of the partial matrix is represented by Ns. For example, assuming that a partial block size of a basic block LDPC code is Ns=2, when it is desired to extend the basic block LDPC code with Ns=2 to a block LDPC code with Ns=4 which is 2 times longer in length than the basic block LDPC code, a partial matrix, an exponent of which is 0, in a permutation matrix, can select a value of 0 or 2 if its length increases from Ns=2 to Ns=4. Among the two values, a value capable of maximizing the cycle should be selected. Likewise, in a block LDPC code with Ns=2, a partial matrix with an exponent of 1 can select a value of 1 or 3 if its length increases from Ns=2 to Ns=4. As described above, it is possible to design a block LDPC code having maximum performance for each block length by designing a block LDPC code using the basic block LDPC code while increasing a value Ns. In addition, one random block LDPC code among block LDPC codes having various lengths can be defined as a basic block LDPC code, contributing to an increase in memory efficiency. A description will now be made of a method for generating a parity check matrix of the variablelength block LDPC code. The present invention proposes 4 types of parity check matrixes for the variablelength block LDPC code according to coding rates, and the coding rates taken into consideration in the present invention include 1/2, 2/3, 3/4 and 5/6. Before a description of the parity check matrixes of the variablelength block LDPC code for the coding rates 1/2, 2/3, 3/4 and 5/6 is given, a process of coding a variablelength block LDPC code using a parity check matrix designed in the present invention will now be described with reference to FIG. 15. FIG. 15 is a flowchart illustrating a process of coding a variablelength block LDPC code according to first to fourth embodiments of the present invention. Before a description of FIG 15 is given, it is assumed that a parity ■■'. check matrix for the variablelength' block LDPC code is comprised of 6 partial ^ • matrixes as described with reference to FIG. 8. Referring to FIG. 15, in step 1511, a controller (not shown) receives an information word vector ' s' to be coded into the variablelength block LDPC code, and then proceeds to steps 1513 and 1515. It is assumed herein that a length of the information word vector ' s' received to be coded into the block LDPC code is k. In step 1513, the controller matrixmultiplies the received information word vector 's' by a partial matrix A of the parity check matrix (As), and then proceeds to step 1517. Herein, because the number of elements having a value of 1 located in the partial matrix A is much less than the number of elements having a value of 0, the matrix multiplication (As) of the information word vector s and the partial matrix A of the parity check matrix can be achieved with a relatively small number of sumproduct operations. In addition, in the partial matrix A, because the position where elements having a value of 1 are located can be expressed as exponential multiplication of a position of a nonzero block and a permutation matrix of the block, the matrix multiplication can be performed with a very simple operation as compared with a random parity check matrix. In step 1515, the controller performs matrix multiplication (Cs) on a partial matrix C of the parity check matrix and the information word vector ' s', and then proceeds to step 1519. In step 1517, the controller performs matrix multiplication (ET_1As) on the matrix multiplication result (As) of the information word vector 's' and the partial matrix A of the parity check matrix, and a matrix ET"1, and then proceeds to step 1519. Herein, because the number of elements having a value of 1 in the matrix ET"1 is very small as described above, if an exponent of a permutation matrix of the block is given, the matrix multiplication can be simply performed. In step 1519, the controller calculates a first parity vector P] by adding the ET" !As and the Cs (P^ET^As+Cs), and then proceeds to step 1521. Herein, the addition operation is an exclusive OR (XOR) operation, and its result becomes 0 for an operation between bits having the same value and 1 for an operation between bits having.different vaiues. That is, the process up to step 1519 is a ? process for calculating the fir,st parity vector Pj. Instep" 1521,"the controller multiplies a partial matrix*® ofihe1 parity check matrix by the first parity vector P^ (B Pt), adds the multiplication result (BP,) to the As (As + BP^), and then proceeds to step 1523. If the information word vector ' s ' and the first parity vector P, are given, they should be multiplied by an inverse matrix T'1 of a partial matrix T of the parity check matrix to calculate a second parity vector P2. Therefore, in step 1523, the controller multiplies the calculation result (As+ BPj) of step 1521 by the inverse matrix T"1 of the partial matrix T to calculate the second parity vector P2 (P2=T_1(As + BP^)), and then proceeds to step 1525. As described above, if the information word vector ' s' of a block LDPC code to be coded is given, the first parity vector P, and the second parity vector P2 can be calculated, and as a result, all codeword vectors can be obtained. In step 1525, the controller generates a codeword vector ' c' using the information word vector ' s', the first parity vector P_! and the second parity vector P2, and transmits the generated codeword vector 'cNext, with reference to FIG. 16, a description will be made of an internal structure of an apparatus for coding a variablelength block LDPC code according to the embodiments of the present invention. FIG. 16 is a block diagram illustrating an internal structure of an apparatus for coding a variablelength block LDPC code according to embodiments of the present invention. Referring to FIG. 16, the apparatus for coding a variablelength block LDPC code includes a matrixA multiplier 1611, matrixC multiplier 1613, a matrixET1 multiplier 1615, an adder 1617, a matrix B multiplier 1619, an adder 1621, a matrix T1 multiplier 1623, and switches 1625, 1627 and 1629. If an input signal, i.e. a lengthk information word vector ' s' to be coded into a variablelength block LDPC code, is received, the received lengthk information word vector 's' is input to the switch 1625, the matrixA multiplier 1611 and the matrixC multiplier 1613. The matrixA multiplier 1611 multiplies , the information word vector 's' by a partial matrix A of the full parity check matrix, and outputs the multiplication result to the matrixET"1 multiplier 1615 and the adder 1621. The matrixC multiplier 1613 multiplies the information *» wordtveetor' s' by a partial matrix C of th©*full"paritydieck matrix, and outputs the multiplication result to the adder 1617. The matrixET"1 multiplier 1615 multiplies the signal output from the matrixA multiplier 1611 by a partial matrix ET"1 of the full parity check matrix, and outputs the multiplication result to the adder 1617. The adder 1617 adds the signal output from the matrixET'1 calculator 1615 to the signal output from the matrixC multiplier 1613, and outputs the addition result to the matrixB multiplier 1619 and the switch 1627. Herein, the adder 1617 performs the XOR operation on a bitbybit basis. For example, if a length3 vector of x = (xl5 x2, x3) and a length3 vector of y = (yi, y2, y3) are input to the adder 1617, the adder 1617 outputs a length3 vector of z = (xi©y1? x2©y2, x3©y3) by XORing the length3 vector of x = (xi, x2, x3) and the length3 vector of y = (yi, y2, y3). Herein, the © operation represents the XOR operation, a result of which becomes 0 for an operation between bits having the same value, and 1 for an operation between bits having different values. The signal output from the adder 1617 becomes a first parity vector P,. The matrixB multiplier 1619 multiplies the signal output from the adder 1617, i.e. the first parity vector Pj, by a partial matrix B of the full parity check matrix, and outputs the multiplication result to the adder 1621. The adder 1621 adds the signal output from the matrixB multiplier 1619 to the signal output from the matrixA multiplier 1611, and outputs the addition result to the matrixT'1 multiplier 1623. The adder 1621, like the adder 1617, performs the XOR operation on the signal output from the matrixB multiplier 1619 and the signal output from the matrixA multiplier 1611, and outputs the XOR operation result to the matrixT"1 multiplier 1623. The matrixT"1 multiplier 1623 multiplies the signal output from the adder 1621 by an inverse matrix T"1 of a partial matrix T of the full parity check matrix, and outputs the multiplication result to the switch 1629. The output of the matrix T"1 multiplier 1623 becomes a second parity vector P2. Each of the switches 1625, 1627 and 1629? is switched on only at itstransmission time to transmit its associated signal. The switch 1625 is switched on at a transmission time of the information word vector, '§',,, the switch 1627 is switched on at a transmission ; time of the first parity vecter P,,i aad the switch 1629 is switched onat a* ■ * transmission time of the second parity vector P2. Because the embodiments of the present invention should be able to generate a variablelength block LDPC code, each of the matrixes used in the coding apparatus of FIG. 16 for a variablelength block LDPC code is changed each time a parity check matrix of the variablelength block LDPC code is changed, as will be described with reference to FIG. 17. Therefore, although not separately illustrated in FIG. 16, the controller modifies the matrixes used in the coding apparatus for the variablelength block LDPC code according as the parity check matrix of the variablelength block LDPC code changes. A description has been made of a method for generating a variablelength block LDPC code taking efficient coding into consideration. As described above, the variablelength block LDPC code, because of its structural characteristic, is superior in terms of the efficiency of a memory for storing the parity check matrixrelated information, and enables the efficient coding by properly selecting partial matrixes from the parity check matrix. However, as the parity check matrix is generated on a perblock basis, randomness decreases, and the decrease in randomness may cause performance degradation of the block LDPC code. That is, because an irregular block LDPC code is superior in performance to a regular block LDPC code as described above, it is very important to properly select partial matrixes from the full parity check matrix in a process of designing a block LDPC code. With reference to FIG. 11, a description will now be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 1/2. FIG. 11 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a first embodiment of the present invention. Before a description of FIG. 11 is given, it should be noted that the first embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 1/2. Referring to FIG. 11, if it is assumed that a possible size Ns of partial matrixes is 4, 8, 12, 16, 20, 24, 28, 32, 36 and 40; it ispossible to generate a block LDPC code having'»a length of 96, 192, 288^*3'Mr480,^576; 672, 768, 864 and 960 using the1 parity ehetk matrix illustrated in FIG. 11. A value written in each of partial blocks, i.e. partial matrixes, illustrated in FIG. 11 represents an exponent value of a corresponding permutation matrix. Herein, the parity check matrix of the variablelength block LDPC code is comprised of a plurality of partial blocks, arid partial matrixes individually corresponding to the partial blocks constitute the permutation matrix. For example, if the parity check matrix of the variablelength block LDPC code is comprised of pxq partial blocks, i.e. if the number of rows of partial blocks in the parity check matrix for the variablelength block LDPC code is 'p' and the number of columns of partial blocks in the parity check matrix for the variable length block LDPC code is 'q', permutation matrixes constituting the parity check matrix of the variablelength block LDPC code can be expressed as Papq, and a superscript apq of a permutation matrix P is either 0 block where a p* row and a q* column of the parity check matrix of the variable length block LDPC code comprised of a plurality of partial blocks cross each other. Therefore, an exponent value of a permutation matrix illustrated in FIG. 11 is given as apq, and by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix's exponent value of the parity check matrix for the variablelength block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. For a detailed description of the present invention, a definition of the following parameters will be given. A parity check matrix of a variablelength block LDPC code illustrated in FIG. 11 is referred to as a "mother matrix," the number of nonzero permutation matrixes among the partial matrixes, i.e. the permutation matrixes, constituting the mother matrix is defined as L, the exponents of the L nonzero permutation matrixes among the permutation matrixes constituting the mother matrix are represented by ai, a2, •••, &i, and a size of the' permutation matrixes constituting the' mother matrix is assumed to be Ns. Because' the number of nonzero • ^elrhutation matrixes among the permUtatiOWmStrMs '"constituting the mother matrix is L, an exponent of a first permutation matrix becomes a1? an exponent of a second permutation matrix becomes a2, and in this manner, an exponent of the last permutation matrix becomes aL. Unlike the mother matrix, a parity check matrix to be newly generated is referred to as a "child matrix," the number of nonzero permutation matrixes among the partial matrixes, i.e. the permutation matrixes, constituting the child matrix is defined as L, a size of the permutation matrixes constituting the child matrix is defined as Ns', and the exponents of the permutation matrixes constituting the child matrix are represented by af, a.2\ •", ai/ Because the number of nonzero permutation matrixes among the permutation matrixes constituting the child matrix is L, an exponent of a first permutation matrix becomes ai', an exponent of a second permutation matrix becomes a2', and in this manner, an exponent of the last permutation matrix becomes aL'. Using Equation (5) below, it is possible to generate a child matrix having a variable block length by selecting a size Ns' of the permutation matrixes constituting a child matrix to be generated from one mother matrix. Next, with reference to FIG. 12, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 2/3. FIG. 12 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a second embodiment of the present invention. Before a description of FIG. 12 is given, it should be noted that the second embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 2/3. Referring to FIG. 12, if it is assumed that a possible size Ns of partial matrixes is 8 and 16, it is possible to generate a block LDPC code having a length of 288 and 576 using the parity check matrix illustrated in FIG. 12. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG 12 represents an exponent value of a corresponding permutation 'matrix. Therefore, by performing a moduloNs operation (where Ns corresponds* tdia size of the partial matrix) on the exponent w ^ value of the permutation matrix, it is possible to calculate a permutation matrix's exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 13, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 3/4. FIG. 13 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a third embodiment of the present invention. Before a description of FIG. 13 is given, it should be noted that the third embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 3/4. Referring to FIG. 13, if it is assumed that a possible size Ns of partial matrixes is 3, 6, 9, 12, 15 and 18, it is possible to generate a block LDPC code having a variable length of 96, 192, 288, 384, 480 and 576 using the parity check matrix illustrated in FIG. 13. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 13 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix's exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 14, a description will be made of a detailed method for generating a variablelength block LDPC' code for a coding rate of 5/6. FIG. 14 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a fourth embodiment of the present invention. Before a description of BIG. 14 is given, it should.be noted that the fourth embodiment of the present invention proposes a parity check matrix of a variable lengthblock? LDPC code for a coding rate of 5/6. Referring, ^to FIG 14, if it is assumeoHhat a possible size Ns of partial matrixes isSand' 16/itis possible to generate a block LDPC code having a length of 288 and 576 using the parity check matrix illustrated in FIG. 14. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 14 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix's exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 18, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 1/2. FIG. 18 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a fifth embodiment of the present invention. Before a description of FIG. 18 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 1/2. Referring to FIG. 18, it is possible to generate a block LDPC code of length of 48NS according to a sixe of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 18. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 18 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 19, a description will be made of a detailed method for generating a variablelength block LDPC code fer a coding rate of 2/3. . FIG. 19 is a diagram illustrating a pai#y&heck matrix of a variablelength Tfblock LDPC code according to a sixth1 embodiment of the present invention. w Before a description of FIG. 19 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 2/3. Referring to FIG. 19, it is possible to generate a block LDPC code of length of 48NS according to a size of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 19. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 19 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 20, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 3/4. FIG. 20 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a seventh embodiment of the present invention. Before a description of FIG. 20 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 3/4. Referring to FIG. 20, it is possible to generate a block LDPC code of length of 48NS according to a sixe of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 20. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 20 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 21, a description will be made ■of a detailed method for generating a'rariatbltrlength block LDPC code for a coding■tate'of 3/4.1"" FIG. 21 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a eighth embodiment of the present invention. Before a description of FIG. 21 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 3/4. Referring to FIG. 21, it is possible to generate a block LDPC code of length of 48Ng according to a size of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 21. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 21 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 22, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 1/2. FIG. 22 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a ninth embodiment of the present invention. Before a description of FIG. 22 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 1/2. Referring to FIG. 22, it is possible to generate a block LDPC code of length of 24NS according to a size of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 22. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 22 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutationmatrix exponent value of the parity check matrix Tor the block LDPC code having the Ns value. If a result value obtained by performing a modulo*M§ operation on an exponent of a permutation* matrix is 0, the corresponding^permatation matrix becomes an identfty^matrix;^ **'v " Next, with reference to FIG. 23, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 1/2. FIG. 23 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a tenth embodiment of the present invention. Before a description of FIG. 23 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 1/2. Referring to FIG. 23, it is possible to generate a block LDPC code of length of 24NS according to a sixe of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 23. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 23 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 24, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 2/3. FIG. 24 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a eleventh embodiment of the present invention. Before a description of FIG. 24 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 2/3. Referring to FIG. 24, it is possible to generate a block LDPC code of length of 24NS according to a size of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 24. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 24 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent vatoe of ?the permutation matrix, it is possible to '"Calculate a permutation matrix exptmentvalue^fthe parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 25, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 2/3. FIG. 25 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a twelfth embodiment of the present invention. Before a description of FIG. 25 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 2/3. Referring to FIG. 25, it is possible to generate a block LDPC code of length of 24NS according to a size of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 25. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 25 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 26, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 1/2. FIG. 26 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a thirteenth embodiment of the present invention. Before a description of FIG. 26 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 1/2. Referring to FIG. 26, it is possible to generate a block LDPC code of length of 24NS according to a size of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 26. A value written in each^of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 26 represents an exponent vaiutr of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 27, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 1/2. FIG. 27 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a fourteenth embodiment of the present invention. Before a description of FIG. 27 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable length block LDPC code for a coding rate of 1/2. Referring to FIG. 27, it is possible to generate a block LDPC code of length of 24NS according to a size of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 27. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 27 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. Next, with reference to FIG. 28, a description will be made of a detailed method for generating a variablelength block LDPC code for a coding rate of 2/3. FIG. 28 is a diagram illustrating a parity check matrix of a variablelength block LDPC code according to a fifteenth embodiment of the present invention. Before a description of FIG. 28 is given, it should be noted that the fifth embodiment of the present invention proposes a parity check matrix of a variable ntengthiitolock LDPC code for a coding rate of"2/9.* Referring to FIG. 28, it is ^possible to geherate a block LDPC code of length'of 24Nj according to a size of Ns of a partial matrix, using the parity check matrix illustrated in FIG. 28. A value written in each of the partial blocks, i.e. the partial matrixes, illustrated in FIG. 28 represents an exponent value of a corresponding permutation matrix. Therefore, by performing a moduloNs operation (where Ns corresponds to a size of the partial matrix) on the exponent value of the permutation matrix, it is possible to calculate a permutation matrix exponent value of the parity check matrix for the block LDPC code having the Ns value. If a result value obtained by performing a moduloNs operation on an exponent of a permutation matrix is 0, the corresponding permutation matrix becomes an identity matrix. All of the LDPCfamily codes can be decoded in a factor graph using a subproduct algorithm. A decoding scheme of the LDPC code can be roughly divided into a bidirectional transfer scheme and a flow transfer scheme. When a decoding operation is performed using the bidirectional transfer scheme, each check node has a node processor, increasing decoding complexity in proportion to the number of the check nodes. However, because all of the check nodes are simultaneously updated, the decoding speed increases remarkably. Unlike this, the flow transfer scheme has a single node processor, and the node processor updates information, passing through all of the nodes in a factor graph. Therefore, the flow transfer scheme is lower in decoding complexity, but an increase in size of the parity check matrix, i.e. an increase in number of nodes, causes a decrease in the decoding speed. However, if a parity check matrix is generated per block like the variablelength block LDPC code having various block lengths according to coding rates, proposed in the present invention, then a number of node processors equal to the number of blocks constituting the parity check matrix are used. In this case, it is possible to implement a decoder which is lower than the bidirectional transfer scheme in the decoding complexity and higher than the flow transfer scheme in the decoding speed. Next, with reference to FIG. 17, a description will be made of an internal structure of a decoding apparatus for decoding a.variablelength block LDPC code using a parity check matrix according to an embodiment of the present invention.  . * * ■»■'• ■ ? FIG. 17 is a block diagram illustrating an internal structure of an apparatus for decoding a block LDPC code according to embodiments of the present invention. Referring to FIG. 17, the decoding apparatus for decoding a variablelength block LDPC code includes a block controller 1710, a variable node part 1700, an adder 1715, a deinterleaver 1717, an interleaver 1719, a controller 1721, a memory 1723, an adder 1725, a check node part 1750, and a hard decider 1729. The variable node part 1700 includes a variable node decoder 1711 and switches 1713 and 1714, and the check node part 1750 includes a check node decoder 1727. A signal received over a radio channel is input to the block controller 1710. The block controller 1710 determines a block size of the received signal. If there is an information word part punctured in a coding apparatus corresponding to the decoding apparatus, the block controller 1710 inserts '0' into the punctured information word part to adjust the full block size, and outputs the resultant signal to the variable node decoder 1711. The variable node decoder 1711 calculates probability values of the signal output from the block controller 1710, updates the calculated probability values, and outputs the updated probability values to the switches 1713 and 1714. The variable node decoder 1711 connects the variable nodes according to a parity check matrix previously set in the decoding apparatus for an irregular block LDPC code, and performs an update operation on as many input values and output values as the number of Is connected to the variable nodes. The number of Is connected to the variable nodes is equal to a weight of each of the columns constituting the parity check matrix. An internal operation of the variable node decoder 1711 differs according to a weight of each of the columns constituting the parity check matrix. Except when the switch 1713 is switched on, the switch 1714 is switched on to output the output signal of the variable node decoder 1711 to the adder 1715. The adder 1715 receives a signal output from the variable node decoder 1711 and an output signal of the interleaver 1719 in a previous iterative decoding process, subtracts the output signal of the interleaver 1719 in the previous iterative decoding process from the output signal of the variable node decoder 1711, and outputs the subtraction result to the deinterleaver 1717. If the decoding process is an initial decoding process, it should be regarded that the output signal of the interleaver 1719 is 0. The deinterleaver 1717 deinterleaves the signal output from the adder 1715 according to a predetermined interleaving scheme, and outputs the deinterleaved signal to the adder 1725 and the check node decoder 1727. The deinterleaver 1717 has an internal structure corresponding to the parity check matrix because an output value for an input value of the interleaver 1719 corresponding to the deinterleaver 1717 is different according to a position of elements having a value of 1 in the parity check matrix. The adder 1725 receives an output signal of the check node decoder 1727 in a previous iterative decoding process and an output signal of the deinterleaver 1717, subtracts the output signal of the deinterleaver 1717 from the output signal of the check node decoder 1727 in the previous iterative decoding process, and outputs the subtraction result to the interleaver 1719. The check node decoder 1727 connects the check nodes according to a parity check matrix previously set in the decoding apparatus for the block LDPC code, and performs an update operation on a number of input values and output values equal to the number of Is connected to the check nodes. The number of Is connected to the check nodes is equal to a weight of each of rows constituting the parity check matrix. Therefore, an internal operation of the check node decoder 1727 is different according to a weight of each of the rows constituting the parity check matrix. The interleaver 1719, under the control of the controller 1721, interleaves the signal output from the adder 1725 according to a predetermined interleaving scheme, and outputs the interleaved signal to the adder 1715 and the variable node decoder 1711. The controller 1721 reads the interleaving schemerelated information previously stored in the memory 1723, and controls an interleaving scheme of the interleaver 1719 and a deinterleaving scheme of the deinterleaver 1717 according to the read interleaving scheme information. Because the memory 1723 stores only a mother matrix with which the variablelength block LDPC code can be generated, the controller 1721 reads thea mother matrix stored in the memory 1723 and generates the exponentsof the petmutation matrixes constituting a corresponding child matrix using a size Ns' of a permutation matrix corresponding to a predetermined block size. In addition, the controller 1721 controls an interleaving scheme of the interleaver 1719 and a deinterleaving scheme of the deinterleaver 1717 using the generated child matrix. Likewise, if the decoding process is an initial decoding process, it should be regarded that the output signal of the deinterleaver 1717 is 0. By iteratively performing the foregoing processes, the decoding apparatus performs errorfree reliable decoding. After the iterative decoding is performed a predetermined number of times, the switch 1714 switches off a connection between the variable node decoder 1711 and the adder 1715, and the switches 1713 switches on a connection between the variable node decoder 1711 and the hard decider 1729 to provide the signal output from the variable node decoder 1711 to the hard decider 1729. The hard decider 1729 performs a hard decision on the signal output from the variable node decoder 1711, and outputs the hard decision result, and the output value of the hard decider 1729 becomes a finally decoded value. As can be appreciated from the foregoing description, the present invention proposes a variablelength block LDPC code of which a minimum cycle length is maximized in a mobile communication system, thereby maximizing an error correction capability and thus improving the system performance. In addition, the present invention generates an efficient parity check matrix, thereby minimizing decoding complexity of a variablelength block LDPC code. Moreover, the present invention designs a variablelength block LDPC code such that decoding complexity thereof should be in proportion to a block length thereof, thereby enabling efficient coding. In particular, the present invention generates a block LDPC code which is applicable to various coding rates and has various block lengths, thereby contributing to the minimization of hardware complexity. While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. We Claim: 1. A method for generating a block low density parity check (LDPC) code having a variable length, by a transmitter, the method comprising the steps of: receiving, by an encoder, an information word; generating, by the encoder, a block LDPC code by coding the information word using one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the block LDPC code; modulating, by a modulator, the block LDPC code; and transmitting, by a RF processor, the modulated block LDPC code, wherein the second parity check matrix is a parity check matrix defined by varying a size of the first parity check matrix, the first parity check matrix is a parity check matrix generated such that the block LDPC code has a predetermined length and is satisfied with a predetermined coding rate, the first parity check matrix includes a predetermined number of partial blocks, and each of the partial blocks having a predetermined size, when the coding rate is 1/2, the first parity check matrix is expressed as one of below 5 tables (FIGS. 18, 22, 23, 26 and 27). wherein, in each of the 5 tables, blocks represent the partial blocks, numbers represent exponents of corresponding permutation matrixes, and blocks with no number represent partial blocks to which zero matrixes are mapped. 2. A transmitter for generating a block low density parity check (LDPC) code having a variable length, the transmitter comprising: an encoder for receiving an information word and generating a block LDPC code by coding the information word using one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the block LDPC code, wherein the second parity check matrix is a parity check matrix defined by varying a size of the first parity check matrix, the first parity check matrix is a parity check matrix generated such that the block LDPC code has a predetermined length and is satisfied with a predetermined coding rate, the first parity check matrix includes a predetermined number of partial blocks, and each of the partial blocks having a predetermined size, when the coding rate is 1/2, the first parity check matrix is expressed as one of below 5 tables (FIGS. 18, 22, 23, 26 and 27), wherein, in each of the 5 tables, blocks represent the partial blocks, numbers represent exponents of corresponding permutation matrixes, and blocks with no number represent partial blocks to which zero matrixes are mapped. 3. A method for generating a block low density parity check (LDPC) code having a variable length by a transmitter, the method comprising the steps of: receiving, by an encoder, an information word; generating, by the encoder, a block LDPC code by coding the information word using one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the block LDPC code; modulating, by a modulator, the block LDPC code; and transmitting, by a RF processor, the modulated block LDPC code, wherein the second parity check matrix is a parity check matrix defined by varying a size of the first parity check matrix, the first parity check matrix is a parity check matrix generated such that the block LDPC code has a predetermined length and is satisfied with a predetermined coding rate, the first parity check matrix includes a predetermined number of partial blocks, and each of the partial blocks having a predetermined size, when the coding rate is 2/3, the first parity check matrix is expressed as one of below 5 tables (FIGS. 12, 19, 24, 25 and 28), wherein, in each of the 5 tables, blocks represent the partial blocks, numbers represent exponents of corresponding permutation matrixes, and blocks with no number represent partial blocks to which zero matrixes are mapped. 4. A method for generating a block low density parity check (LDPC) code having a variable length, by a transmitter, the method comprising the steps of: receiving, by an encoder, an information word; generating, by the encoder, a block LDPC code by coding the information word using one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the block LDPC code; modulating, by a modulator, the block LDPC code; and' transmitting, by a RF processor, the modulated block LDPC code, wherein the second parity check matrix is a parity check matrix defined by varying a size of the first parity check matrix, the first parity check matrix is a parity check matrix generated such that the block LDPC code has a predetermined length and is satisfied with a predetermined coding rate, the first parity check matrix includes a predetermined number of partial blocks, and each of the partial blocks having a predetermined size, when the coding rate is 3/4, the first parity check matrix is expressed as one of below 3 tables (FIGS. 13, 20 and 21), wherein, in each of the 3 tables, blocks represent the partial blocks, numbers represent exponents of corresponding permutation matrixes, and blocks with no number represent partial blocks to which zero matrixes are mapped. 5. A transmitter for generating a block low density parity check (LDPC) code having a variable length, the transmitter comprising: an encoder for receiving an information word, and generating a block LDPC code by coding the information word using one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the block LDPC code, wherein the second parity check matrix is a parity check matrix defined by varying a size of the first parity check matrix, the first parity check matrix is a parity check matrix generated such that the block LDPC code has a predetermined length and is satisfied with a predetermined coding rate, the first parity check matrix includes a predetermined number of partial blocks, and each of the partial blocks having a predetermined size, when the coding rate is 2/3, the first parity check matrix is expressed as one of below 5 tables (FIGS. 12, 19, 24, 25 and 28), wherein, in each of the 5 tables, blocks represent the partial blocks, numbers represent exponents of corresponding permutation matrixes, and blocks with no number represent partial blocks to which zero matrixes are mapped. 6. A transmitter for generating a block low density parity check (LDPC) code having a variable length, the transmitter comprising: an encoder for receiving an information word, and generating a block LDPC code by coding the information word using one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the block LDPC code, wherein the second parity check matrix is a parity check matrix defined by varying a size of the first parity check matrix, the first parity check matrix is a parity check matrix generated such that the block LDPC code has a predetermined length and is satisfied with a predetermined coding rate, the first parity check matrix includes a predetermined number of partial blocks, and each of the partial blocks having a predetermined size, when the coding rate is 3/4, the first parity check matrix is expressed as one of below 3 tables (FIGS. 13, 20 and 21), where, in each of the 3 tables, blocks represent the partial blocks, numbers represent exponents of corresponding permutation matrixes, and blocks with no number represent partial blocks to which zero matrixes are mapped. ABSTRACT TITLE: A method and a transmitter for generating a block low density parity check (LDPC) code having a variable length The invention relates to a method for generating a block low density parity check (LDPC) code having a variable length, the method comprising the steps of receiving an information word; and generating a block LDPC code by coding the information word using one of a first parity check matrix and a second parity check matrix depending on a length to be applied when generating the block LDPC code, wherein the second parity check matrix is a parity check matrix defined by varying a size of the first parity check matrix, the first parity check matrix is a parity check matrix generated such that the block LDPC code has a predetermined length and is satisfied with a predetermined coding rate, the first parity check matrix comprises a predetermined number of partial blocks, and each of the partial blocks having a predetermined size, when the coding rate is 1/2, the first parity check matrix is expressed as one of the 5 tables shown in FIGS. 18, 22, 23, 26 and 27, wherein, in each of the 5 tables, blocks represent the partial blocks, numbers represent exponents of corresponding permutation matrixes, and blocks with no number represent partial blocks to which zero matrixes are mapped. 

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Patent Number  257416  

Indian Patent Application Number  3537/KOLNP/2006  
PG Journal Number  40/2013  
Publication Date  04Oct2013  
Grant Date  30Sep2013  
Date of Filing  27Nov2006  
Name of Patentee  SAMSUNG ELECTRONICS CO. LTD.  
Applicant Address  416, Maetandong, Yeongtonggu, Suwonsi,Gyeonggido  
Inventors:


PCT International Classification Number  H04L 1/00  
PCT International Application Number  PCT/KR05/001239  
PCT International Filing date  20050428  
PCT Conventions:
