Patent Publication Number: US-2021167800-A1

Title: Method for selecting ldpc base code in multiple ldpc codes and apparatus therefor

Description:
TECHNICAL FIELD 
     The present invention relates to a wireless local area network (LAN) system and, more particularly, to a method of selecting a base code in a system supporting multiple low-density parity-check (LDPC) codes and an apparatus supporting the same. 
     BACKGROUND ART 
     A wireless access system has been widely deployed to provide a diverse range of communication services such as a voice communication service and a data communication service. Generally, the wireless access system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). For example, the multiple access system may include one of a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, a multi-carrier frequency division multiple access (MC-FDMA) system, and the like. 
     In a broadcast system as well as in the above-described communication system, a channel code is necessarily used. As an example of a general configuration method of the channel code, a transmitter may encode an input symbol using an encoder and transmit the encoded symbol. A receiver, for example, may receive the encoded symbol and decode the received symbol, thereby recovering the input symbol. In this case, the size of the input symbol and the size of the encoded symbol may be differently defined according to a communication system. For example, in a turbo code for data information used in a 3rd generation partnership project (3GPP) long term evolution (LTE) communication system, the size of the input symbol is a maximum of 6144 bits and the size of the encoded symbol is 18432 (6144*3) bits. For turbo coding of the LTE communication system, reference is made to 3GPP technical specification 36.212. 
     However, even when a signal-to-noise ratio (SNR) increases, the LTE turbo code is characterized in that performance improvement is not remarkable out of a predetermined region due to the structure of the code. Regarding this problem, although use of a code having a low error rate may be considered, complexity increases. 
     In a communication system, a high error rate may require unnecessary retransmission of data and cause failure in channel reception. In addition, a code having excessively high complexity may increase overhead of a base station (BS) and a user equipment (UE) and cause transmission and reception latency. Especially, in a future-generation communication system requiring faster data transmission and reception, the above-described problems need to be solved. Therefore, a coding method having low complexity while lowering an error rate is demanded. 
     Especially, with regard to 5th generation (5G) mobile communication technology, ultra-reliable and low-latency communication (URLLC) is under discussion. A URLLC scenario demands that error floor occur at a block error rate (BLER) of 10-5 or less. Herein, the error floor means a point at which reduction in error rate is slight although the size of information increases. In the LTE turbo code, the error floor occurs at a BLER of 10-4 or less as the size of information increases. Accordingly, an LDPC code may be used as an alternate of the turbo code. The LDPC code may achieve a low error rate with relatively low complexity. For efficient use of the LDPC code, a method of selecting a base code from multiple LDPC codes needs to be determined. 
     DISCLOSURE 
     Technical Problem 
     It is a technical object of the present invention to provide a method of selecting an LDPC code suitable for a given communication environment in a wireless LAN system using multiple LDPC codes. 
     Another technical object of the present invention is to provide a method of selecting a base code capable of being used in a wireless LAN system using multiple LDPC codes and selecting a lifting value considering the amount of shortening. 
     The present invention is not limited to what has been particularly described hereinabove and other technical objects can be derived from embodiments of the present invention. 
     Technical Solution 
     In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a method of encoding a quasi-cyclic low-density parity-check (QC LDPC) code supporting multiple base codes. The method comprises selecting a base code for generating a parity check matrix from among a first base code and a second base code; selecting a lifting value for generating the parity check matrix from among a plurality of lifting values; and generating the parity check matrix using the selected base code and the selected lifting value, wherein the base code is determined based on a code block size and a code rate, and the lifting value is determined based on parameters of the base code and the code block size. 
     If the code block size is larger than a preset code block size, the first base code may be selected as the base code, and if the code block size is smaller than the preset code block size, the second base code may be selected as the base code. 
     When a code block size supported by the first base code overlaps with a code block size supported by the second base code, if the code block size is larger than a preset code block size or the code rate is higher than a preset code rate, the first base code may be selected as the base code, and if the code block size is smaller than the preset code block size and the code rate is lower than the preset code rate, the second code block may be selected as the base code. 
     The preset code block size may be a maximum code block of the second base code. 
     The preset code block size may be a maximum code block size of the second base code, and the preset code rate may be a maximum code rate of the second base code. 
     The parameters of the base code and the plural lifting values may be determined in consideration of a maximum shortening value of the base code. 
     The maximum shortening value may be set not to exceed 8 times or 4 times the lifting value. 
     A minimum value of Z satisfying an equation of Z·K b , max≥K≤Z·K b , min may be selected as the lifting value, K may denote a code block size, Kb,max may denote the size of a maximum information bit sequence of the base code, and Kb,min may denote the size of a minimum information bit sequence of the base code. 
     The method of encoding the LDPC code may further include transmitting information about the selected base code from among the first base code and the second base code to a user equipment. 
     When the second base code supports a code rate higher than the preset code rate, if the code block size is smaller than the preset code block size and the code rate is lower than a code rate which is higher than the preset code rate, the second base code may be selected as the base code. 
     In accordance with another aspect of the present invention, there is provided an apparatus for encoding a quasi-cyclic low-density parity-check (QC LDPC) code supporting multiple base codes. The apparatus comprises a transceiver; and a processor. The processor selects a base code for generating a parity check matrix from among a first base code and a second base code, selects a lifting value for generating the parity check matrix from among a plurality of lifting values, and generates the parity check matrix using the selected base code and the selected lifting value, and wherein the base code is determined based on a code block size and a code rate, and the lifting value is determined based on parameters of the base code and the code block size. 
     Advantageous Effects 
     According to an embodiment of the present invention, an LDPC code can be generated using a proper base code suitable for various communication environments. 
     According to another embodiment of the present invention, an LDPC code can be generated by selecting a proper base code for an overlapping region when code blocks overlap in multiple LDPC codes. 
     Other technical effects in addition to the above-described technical effects can be derived from embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a flowchart illustrating an exemplary encoding procedure. 
         FIG. 2  is a diagram illustrating an exemplary transport block (TB) encoding procedure. 
         FIG. 3  is a diagram illustrating an exemplary recursive systematic convolutional (RSC) encoder. 
         FIG. 4  is a diagram illustrating an LTE turbo encoder. 
         FIG. 5  is a diagram illustrating an exemplary trellis according to an RSC encoder. 
         FIG. 6  is a diagram illustrating an exemplary trellis structure. 
         FIG. 7  is a diagram illustrating an exemplary structured parity check matrix. 
         FIG. 8  is a diagram illustrating an exemplary model matrix. 
         FIG. 9  is a diagram referenced to explain matrix transformation according to the number of shifts. 
         FIG. 10  is a flowchart illustrating an exemplary LDPC code decoding method. 
         FIG. 11  is a diagram illustrating an exemplary bipartite graph. 
         FIG. 12  is a diagram illustrating the structure of an LDPC code according to an embodiment of the present invention. 
         FIG. 13  is a diagram illustrating an exemplary rate matching procedure. 
         FIG. 14  is a diagram referenced to explain a base code selection method according to an embodiment of the present invention. 
         FIG. 15  is a diagram referenced to explain a device according to an embodiment of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary embodiments and is not intended to represent the only embodiments through which the concepts explained in these embodiments can be practiced. [41] The detailed description includes details for the purpose of providing an understanding of the present invention. However, it will be apparent to those skilled in the art that these teachings may be implemented and practiced without these specific details. In some instances, well-known structures and devices are omitted in order to avoid obscuring the concepts of the present invention and the important functions of the structures and devices are shown in block diagram form. 
     The following technology may be applied to a variety of wireless access systems using code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. CDMA may be embodied through radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA may be embodied through radio technology such as global system for mobile communications (GSM)/general packet radio service (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA may be embodied through radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and evolved UTRA (E-UTRA). UTRA is a part of a universal mobile telecommunications system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA in downlink and SC-FDMA in uplink. LTE-advanced (LTE-A) is an evolved version of 3GPP LTE. 
     For clarity of description, the following description focuses on the 3GPP LTE/LTE-A system. However, the technical features of the present invention are not limited thereto. Specific terms used in the following description are provided to aid in understanding the present invention. These specific terms may be replaced with other terms within the scope and spirit of the present invention. 
       FIG. 1  is a flowchart illustrating an exemplary encoding procedure. 
     The encoding procedure as illustrated in  FIG. 1  may be applied to numerous channel codes including a turbo code used in the LTE communication system. Hereinafter, for convenience of description, the encoding procedure will be described based on terms according to the standard specifications of the LTE communication system. 
     In the example of  FIG. 1 , a transmitter may generate a transport block (TB) (step S 101 ). The transmitter adds a cyclic redundancy check (CRC) bit for the TB to the TB (step S 102 ). The transmitter may generate code blocks from the TB to which the CRC bits are added (step S 103 ). For example, the transmitter may segment the TB into the code blocks based on an input size of an encoder. The transmitter may add the CRC bits to each of the segmented code blocks (step S 104 ). In this case, the size of the code block and the code block CRC bits may be 6144 bits. The transmitter may perform encoding and modulation with respect to each block which consists of a code block and code block CRC bits (step S 105 ). For example, turbo coding may be applied as described previously. 
     A decoding procedure may be performed in a reverse order of the encoding procedure of 
       FIG. 1 . For example, a receiver may decode each code block using a decoder corresponding to each encoder, configure one final TB, and perform CRC confirmation for the TB. 
     For example, the size of an input symbol may be different from the size of a TB from a media access control (MAC) layer. If the size of the TB is greater than a maximum size of the input symbol of the turbo code, the TB may be segmented into a plurality of code blocks (CBs). 
     According to standard of the LTE communication system, the size of the CB may be equal to a value obtained by subtracting the CRC bits from 6144 bits. The input symbol of the turbo code may be defined as data including a CB and a CRC or data including a TB (e.g., the size of the TB is less than 6144 bits) and a CRC. The CRC bits are significantly less than 6144 bits (e.g., the CRC bits are a maximum of 24 bits). Therefore, in the following description, a CB may refer to a CB itself or a CB and corresponding CRC bits and a TB may refer to a TB itself or a TB and corresponding CRC bits, unless defined otherwise). 
       FIG. 2  is a diagram illustrating an exemplary TB encoding procedure. 
       FIG. 2  illustrates an encoding procedure of a TB  201  corresponding to the above-described encoding procedure in relation to  FIG. 1 . First, a TB CRC  202  is added to the TB  201 . The TB CRC  202  may be used to confirm the TB  201  during a decoding procedure. Next, the TB  201  and the TB CRC  202  are divided into three CBs  203 . In this embodiment, while the TB  201  and the TB CRC  202  are divided into the three CBs  203 , the TB  201  may be divided into a plurality of CBs based on the input size of an encoder  205 . 
     CB CRCs  204  are added to the respective CBs  203 . The CB CRCs  204  may be used to confirm the CBs  203  by the receiver. The CBs  203  and the CB CRCs  204  may be encoded through respective encoders  205  and respective modulators  205 . 
       FIG. 3  is a diagram illustrating an exemplary recursive systematic convolutional (RSC) encoder. 
     An RSC encoder  300  of  FIG. 3  may be used for turbo coding. In  FIG. 3 , m denotes input data, C 1  denotes a systematic bit stream, and C 2  denotes a coded bit stream. Herein, the RSC encoder  300  has a code rate of 1/2. 
     The RSC encoder  300  may be configured by feeding back an encoded output to an input of a non-recursive, non-systematic convolutional encoder. In the embodiment of  FIG. 3 , the encoder  300  includes two delayers  301  and  302 . A value D of each of the delayers  301  and  302  may be determined according to a coding scheme. The delayers  301  and  302  may be configured by memories or shift registers. 
       FIG. 4  is a diagram illustrating an LTE turbo encoder. 
     A coding scheme of an LTE turbo encoder  400  uses a parallel concatenated convolutional code (PCCC) implemented through two 8-state constituent encoders  410  and  420  and one turbo code internal interleaver  430 . 
     In  FIG. 4 , the turbo encoder  400  includes the first constituent encoder  410 , the second constituent encoder  420 , and the turbo code internal interleaver  430 . The first constituent encoder  410  and the second constituent encoder  420  are 8-state constituent encoders. Each of the first constituent encoder  410  and the second constituent encoder  420  has a structure similar to the RSC encoder of  FIG. 3 . The first constituent encoder  410  and the second constituent encoder  420  include three delayers  411 ,  412 , and  413  and three delayers  421 ,  422 ,  423 , respectively. 
     In  FIG. 4 , D denotes a value determined based on a coding scheme. ck denotes an input to the turbo encoder  400 . Outputs from the first constituent encoder  410  and the second constituent encoder  420  are denoted as z k  and z′ k , respectively. An output from the turbo code internal interleaver  430  is denoted as c′ k . Generally, each of the delayers  411 ,  412 ,  413 ,  421 ,  422 , and  423  may delay an input value by one clock. However, each of the delayers  411 ,  412 ,  413 ,  421 ,  422 , and  423  may be configured to delay the input value by more than one clock according to internal configuration. Each of the delayers  411 ,  412 ,  413 ,  421 ,  422 , and  423  may be comprised of a shift register and may be configured so as to delay an input bit by a preset clock and then output the input bit therethrough. 
     The turbo code internal interleaver  430  may reduce an effect of a burst error which may be generated during signal transmission on a radio channel. For example, the turbo code internal interleaver  430  may be a quadratic polynomial permutation (QPP) interleaver. 
     A turbo code is a high-performance forward error correction (FEC) code used in the LTE communication system. For example, a data block coded by the turbo code may include three subblocks. One subblock may correspond to m-bit payload data. Another subblock may include n/2 parity bits for a payload, calculated using an RSC code. In addition, the other subblock may include n/2 parity bits for permutation of payload data, calculated using the RSC code. For example, the above permutation may be performed by the interleaver. Accordingly, the two different subblocks of parity bits may constitute one block together with the subblock for the payload. As an example, when m is equal to n/2, one block has a code rate of 1/3. 
     In the first constituent encoder  410 , a procedure in which the input c k  reaches the encoded bit z k  may be divided into two paths. The two paths include a first path connected to an output stage from an input stage without feedback and a second path fed back from the input stage back to the input stage. 
     On the first path, the input ck, the input ck passing through the delayer  411 , and the input ck passing through the delayers  411 ,  412 , and  413  are supplied to the output stage. A relationship between the input stage and the output stage for the first path may be expressed as a polynomial. The polynomial for the first path is referred to as a forward generator polynomial and may be expressed as gl of the following equation indicated below. 
         g 1( D )=1 +D+D   3    [Equation 1]
 
     Meanwhile, on the second path, the input c k , the input c k  passing through the delayers  411  and  142 , and the input c k  passing through the delayers  411 ,  412 , and  413  are fed back to the input stage. A polynomial for the second path is referred to as a recursive generator polynomial and may be expressed as g0 of the following equation indicated below. 
         g 0( D )=1 +D   2   +D   3    [Equation 2]
 
     In Equations 1 and 2, “+” denotes exclusive OR (XOR) and 1 represents that an input is subjected to delay zero times. In addition, D n  represents that an input is subjected to delay n times. 
       FIG. 5  is a diagram illustrating an exemplary trellis according to an RSC encoder. 
       FIG. 5  illustrates the structure of the trellis of the RSC encoder of  FIG. 3 . In  FIG. 5 , S i  denotes a state of i-th input data. In  FIG. 5 , each circle denotes a node. A line between nodes denotes a branch. A branch of a real line means a branch for an input value 1 and a branch of a dotted line means a branch for an input value 0. A value on the branch is expressed as m/C1C2 (input value/systematic bit, encoded bit). The trellis may have states exponentially proportional to the number of memories of the encoder. For example, if the encoder includes a memories, 2 a  states may be included in the trellis. 
     The trellis is a state machine illustrating state transition of an encoder allowable two states. A convolutional encoder such as the RSC encoder may perform encoding according to a trellis diagram. A codeword encoded by the RSC encoder may be decoded according to an algorithm based on a trellis structure. For example, a Viterbi or Bahl, Cocke, Jelinek and Raviv (BCJR) algorithm may be used. 
       FIG. 6  is a diagram illustrating an exemplary trellis structure. 
     In  FIG. 6 , n denotes the length of a codeword. Typically, additional bits are added to the end of an input sequence, thereby terminating a trellis. Generally, a sequence consisting of 0s is referred to as tail bits. The tail bits terminate the trellis by causing nodes of one state of the trellis to have a value of 0. 
     In  FIG. 6 , the length of the codeword may be determined in consideration of the length k of input data and the length t of tail bits. For example, when a code rate is R, the length n of the codeword may have a value of (k+t)/R. Generally, the length t of the tail bits may be determined as a length with which all delays (e.g., memories) of an encoder can be reset. As an example, the RSC encoder of  FIG. 3  may use a total of two tail bits. In addition, the turbo encoder of LTE communication as illustrated in  FIG. 4  may use three tail bits. 
     The tail bits have a relatively short length as compared with the length of input data. As described above, since the length of the codeword is associated with the length of the tail bits, if the length of the codeword is limited, code rate loss may occur due to the tail bits. However, although code rate loss is generated due to the tail bits, trellis termination using the tail bits is widely used because of low complexity of calculation and excellent error correction performance. 
     Puncturing is a scheme of puncturing a part of codewords. Through puncturing, since a part of codewords is punctured, partial codewords are not transmitted. For example, puncturing may be used to reduce code rate loss caused by addition of the tail bits. In this case, a receiver may perform decoding using a trellis corresponding to the sum of the length k of the input data and the length t of the tail bits. That is, the receiver may perform decoding under the assumption that the receiver has received codewords which are not punctured. In this case, the receiver may regard a branch from a node corresponding to a punctured bit (i.e., a bit which is not transmitted by a transmitter) as having no input value. That is, it is assumed that the input data for branches of a corresponding node is 0 or 1 with the same possibility. 
     As described above in relation to  FIG. 1 , a CRC for a CB is added to the CB. The CRC may be determined as a remainder derived after data to be transmitted is divided by a preset check value used as a divisor. Generally, the CRC may be added to the end of the transmission data. The receiver may compare the remainder after reception data is divided by the preset check value with the CRC or determine whether a remainder after entire reception data including the CRC is divided by the check value is 0. 
     If the size of a TB is 6144 bits, the size of the CRC may be a maximum of 24 bits. Accordingly, the other bits except for the CRC bits may be determined as the size of the CB. 
     The receiver may perform decoding with respect to each CB. Thereafter, the receiver may configure the TB from CBs and determine whether decoding has been successfully performed by checking the CRC for the TB. In a current LTE system, a CB CRC is used for early decoding termination. For example, if a CRC for one CB fails, the receiver may not decode the other CBs and transmit a negative acknowledgement (NACK) to the transmitter. 
     Upon receiving NACK, the transmitter may retransmit at least a part of transmission data. For example, the transmitter may retransmit a TB or one or more CBs. As an example, when the transmitter retransmits all of the TB, radio resources for retransmission may be excessively consumed. In addition, for example, when the receiver generates NACK due to failure of a CB CRC, the receiver may transmit information about a CB (e.g., an index of a CB) in which CRC failure has occurred to the transmitter. The transmitter may increase the efficiency of radio resources by transmitting only the CB in which CRC failure has occurred using the information about the CB. However, if the number of CBs increases, the amount of data for feeding back the information about the CBs (e.g., indexes of the CBs) increases. 
     In the LTE communication system, the receiver may inform the transmitter through an ACK/NACK signal whether data has been successfully received. In the case of frequency division duplex (FDD), ACK/NACK for data received in an i-th subframe is transmitted in an (i+4)-th subframe. If NACK is received in the (i+4)-th subframe, retransmission may be performed in an (i+8)-th subframe. This is to consider a time for processing the TB and a time for generating ACK/NACK because channel code processing for processing the TB consumes much time. In the case of time division duplex (TDD), ACK/NACK and retransmission subframes may be determined based on a time for processing the TB, a time for generating ACK/NACK, and uplink subframe allocation (e.g., TDD uplink/downlink configuration). In addition, ACK/NACK bundling and multiplexing may be used. 
     As described above, the turbo code shows restricted improvement in an error rate if an SNR exceeds a predetermined value. As an alternative to the turbo code, a low-density parity-check (LDPC) code has been proposed. The LDPC code is a linear block code and is used in IEEE 802.11n and 802.11ac and digital video broadcasting (DVB). The LDPC code may include a generation matrix and a parity check matrix. In the LDPC code, data may be encoded through a multiplication operation of message bits and the generation matrix. Generally, in communication specification using the LDPC code, the parity check matrix may be used instead of the generation matrix. For example, data may be encoded using the parity check matrix. 
     The linear block code may be generated based on a generation matrix G or a parity check matrix H. The linear block code is configured such that the product Hc t  of a transpose matrix of a codeword c and the parity check matrix has a value of 0 with respect to the whole codeword c. Decoding of the LDPC code may be performed, as identical to other linear block codes, by checking whether the product of the parity check matrix H and the codeword c is ‘0’. 
     For example, decoding of the LDPC code may be performed by checking whether the product (i.e., Hc t ) of a transpose matrix of the codeword c and the parity check matrix is 0. 
     In the LDPC code, most elements of the parity check matrix are 0 and there are a small number of elements having values other than 0 as compared with the length of the code. Therefore, the LDPC code may perform iterative decoding based on probability. In an initially proposed LDPC code, the parity check matrix has been defined in a non-systematic form and a small weight has been uniformly applied to rows and columns of the parity check matrix. A weight may mean the number of 1s included in a row or a column. 
     As described above, the density of elements having values other than 0 in a parity check matrix H of the LDPC code is low. Accordingly, the LDPC code has performance approximating to limits of Shannon&#39;s theorem while decoding complexity is kept low. Due to high error correction performance and low decoding complexity of this LDPC code, the LDPC code is suitable for high-speed wireless communication. 
     Structured LDPC code 
     As described previously, the parity check matrix H may be used to generate the LDPC code. The matrix H includes a large number of 0s and a small number of 1s. The size of the matrix H may be 10 5  bits or more. Many memories may be needed to express the H matrix. 
       FIG. 7  is a diagram illustrating an exemplary structured parity check matrix. 
     In the structured LDPC code, elements of the matrix H may be expressed as subblocks of a predetermined size as illustrated in  FIG. 7 . In  FIG. 7 , each of the elements of the matrix H represents one subblock. 
     In the IEEE 802.16e standard specification, a subblock is indicated by one integer index, so that the size of memories for expressing the matrix H may be reduced. Each subblock may be, for example, a permutation matrix of a predetermined size. 
       FIG. 8  is a diagram illustrating an exemplary model matrix. 
     For example, referring to the IEEE 802.16e standard specification, if the size of codewords is 2304 and a code rate 2/3, a model matrix used to encode/decode the LDPC code is as illustrated in  FIG. 8 . The model matrix may mean a parity check matrix including at least one subblock described below. The subblock may be referred to as the number of shifts in the following description. The model matrix may be extended to the parity check matrix based on a method which will be described later. Therefore, encoding and decoding based on a specific model matrix means encoding and decoding based on a parity check matrix generated by extending the model matrix. 
     In  FIG. 8 , index ‘−1’ indicates a zero matrix of a preset size. Index ‘0’ indicates an identity matrix of a preset size. A positive index except for ‘−1’ and ‘0’ indicates the number of shifts. For example, a subblock expressed as index ‘1’ may mean a matrix obtained by shifting an identity matrix once in a specific direction. 
       FIG. 9  is a diagram referenced to explain matrix transformation according to the number of shifts. 
     For example,  FIG. 9  illustrates the case in which the size of a subblock is 4 rows and 4 columns. In  FIG. 9 , the subblock is shifted from an identity matrix three times to the right. In this case, in a parity check matrix of a structured LDPC code, the subblock may be represented using an integer index of ‘3’. 
     Generally, encoding of the LDPC code may be performed by generating a generation matrix G from a parity check matrix H and encoding information bits using the generation matrix. To generate the generation matrix G, Gaussian reduction is performed with respect to the parity check matrix H to configure a matrix in the form of [P T : I]. If the number of the information bits is k and the size of encoded codewords is n, a matrix P is a matrix including k rows and n-k columns and a matrix I is an identity matrix having a size of k. [ 97 ] If the parity check matrix H has the form of [P T : I], the generation matrix G has a form of [I : P T ]. If k information bits are encoded, the encoded information bits may be expressed as a matrix x of one row and k columns. In this case, a codeword c is xG having a form of [x : xP]. Herein, x denotes an information part (or a systematic part) and xP denotes a parity part. 
     In addition, the information bits may be encoded directly from the matrix H without deriving the matrix G by designing the matrix H as a specific structure without using Gaussian reduction. For the structures of the above-described matrix H and matrix G, the product of the matrix G and a transpose matrix of the matrix H has a value of 0. Using such a characteristic and a relationship between the information bits and the codeword, the codeword may be obtained by adding parity bits to the end of the information bits. 
       FIG. 10  is a flowchart illustrating an exemplary LDPC code decoding method. 
     In a communication system, encoded data includes noise in a process of passing through a radio channel. Accordingly, a codeword c is expressed as a codeword c′ including noise in a receiver. The receiver performs demultiplexing and demodulation with respect to a received signal (step S 1000 ) and initializes decoding parameters (step S 1005 ). The receiver updates a check node and a variable node (steps S 1010  and S 1015 ) and performs syndrome check (step S 1020 ). That is, a decoding procedure may be ended by checking whether c′H T  is 0. If c′H T  is 0, the first k bits from c′ may be determined as the information bits x. If c′H T  is not 0, the information bit x may be recovered by searching for c′ satisfying the condition that c′H T  is 0 based on a decoding scheme such as a sum-product algorithm. 
       FIG. 11  is a diagram illustrating an exemplary bipartite graph. 
     In  FIG. 11 , left nodes v 0 , v 1 , . . . , v 11  represent variable nodes and right nodes c 1 , c 2 , . . . , c 6  represent check nodes. In the example of  FIG. 11 , a bipartite graph is illustrated focusing on the variable node v 0  and check node c 1  for convenience of description. Connection lines of the bipartite graph of  FIG. 11  may be referred to as edges. The bipartite graph of  FIG. 11  may be generated from Hc t . Therefore, in  FIG. 11 , edges from the variable node vo correspond to the first column of the parity check matrix H and edges from the check node c 1  correspond to the first row of the matrix H. 
     As described above, in order to successfully perform decoding, the product of the parity check matrix H and a transpose matrix of the codeword matrix c should have a value of ‘0’. Accordingly, values of variable nodes connected to one check node should be 0. Consequently, in  FIG. 11 , values of exclusive OR (XOR) of the variable nodes v 0 , v 1 , v 4 , v 6 , v 9 , vii connected to the check node c 1  should be ‘0’. Syndrome check means checking as to whether a value of XOR of variable nodes connected to each check node is 0. 
     Quasi-cyclic (QC) LDPC code 
     Hereinafter, a QC LDPC code will be described. 
     To acquire excellent performance of an LDPC code, a parity check matrix (or a generation matrix) may be randomly configured. The performance of the LDPC code may be improved as the length of a block increases. In decoding, the performance of the LDPC code may be improved through an optimal decoding method. However, due to complexity of optimal decoding, a belief propagation algorithm is used to decode the LDPC code. In addition, the randomly generated parity check matrix of the LDPC code has excellent performance but is very complicated in implementation and representation thereof. Hence, the above-described structured LDPC code is widely used. As the structured LDPC code, a QC LDPC code is widely used. 
     The QC LDPC code includes a zero matrix having a size of QxQ and a circulant permutation matrix (CPM) having a size of Q×Q. The CPM Pa has a form obtained by shifting an identity matrix having a size of Q×Q by a circular shift value a (refer to  FIG. 9 ). For example, as illustrated in  FIG. 7 , the parity check matrix H may include (mb+1)×(nb+1) CPMs. As described previously, a circular shift value of 0 represents an identity matrix and a circular shift value of −1 represents a zero matrix. In addition, the parity check matrix may be expressed as a matrix of circular shift values as illustrated in  FIG. 8 . Herein, a value of each circular shift may be configured to a value equal to or greater than −1 and equal to or less than Q−1. The matrix configured by circular shift values as illustrated in  FIG. 8  may be referred to as a circular shift matrix or a characteristic matrix. 
       FIG. 12  is a diagram illustrating the structure of an LDPC code according to an embodiment of the present invention. 
     In the following embodiment, a multi-edge QC LDPC code may be used. For example, as illustrated in  FIG. 12 , the multi-edge QC LDPC code may have a structure in which a high rate code similar to QC irregular repeat accumulation (IRA) (QC-IRA) and a single parity check code are concatenated. For example, a parity check matrix H of the multi-edge QC LDPC code may be defined as follows. 
     
       
         
           
             
               
                 
                   H 
                   = 
                   
                     [ 
                     
                       
                         
                           A 
                         
                         
                           0 
                         
                       
                       
                         
                           C 
                         
                         
                           I 
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     In the above equation, A denotes a high rate code having a structure similar to QC-IRA and 0 denotes a zero matrix. In addition, C and I denote an information part of the single parity check code and a parity part of the single parity check code, respectively. In  FIG. 12 , 0 denotes an identity matrix and −1 denotes a zero matrix. 
     In  FIG. 12 , K denotes the size of information to be encoded. In addition, M1 denotes a parity of a high rate code part and M2 denotes the size of a parity of a single parity check code part. P denotes a puncturing size applied to an LDPC code. 
     In this case, the size of P may be determined in consideration of a maximum number of iterations that an LDPC decoder can perform. In some embodiments of the present invention, the maximum number of iterations of the decoder may be 50 and then the size of P may be 2Z. However, the present invention is not limited to such a structure. In  FIG. 12 , a parity structure of the high rate code part A may be determined as a dual-diagonal structure in consideration of an encoding scheme. 
     For configuration of a QC LDPC code of a desired size, a lifting operation may be performed. Lifting is used to acquire a parity check matrix of a desired size from a preset parity check matrix. Various code lengths may be supported by changing a lifting size. For example, floor lifting or modulo lifting may be used. For example, a parity check matrix according to modulo lifting may be obtained as indicated by the following equation. 
     
       
         
           
             
               
                 
                   
                     H 
                     Q 
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               a 
                               ij 
                             
                              
                             MOD 
                              
                             
                                 
                             
                              
                             Q 
                           
                         
                         
                           
                             
                               if 
                                
                               
                                   
                               
                                
                               
                                 a 
                                 ij 
                               
                             
                             ≠ 
                             
                               - 
                               1 
                             
                           
                         
                       
                       
                         
                           
                             - 
                             1 
                           
                         
                         
                           
                             
                               if 
                                
                               
                                   
                               
                                
                               
                                 a 
                                 ij 
                               
                             
                             = 
                             
                               - 
                               1 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     In the above equation, Q denotes a lifting size and a ij  denotes a shift value of the i-th row and the j-th column of a preset parity check matrix (refer to  FIG. 8 ). In addition, MOD Q denotes a modulo operation based on the value Q. That is, in a circular shift matrix of the preset parity check matrix, values corresponding to the zero matrix are maintained and a modulo operation based on the lifting size Q is performed with respect to the other circular shift values. Therefore, shift values of the circular shift matrix are converted into values equal to or greater than −1 and equal to or less than Q−1. 
       FIG. 13  is a diagram illustrating an exemplary rate matching procedure. 
     The length of data bits capable of being substantially transmitted may be determined based on the size of available physical resources. Accordingly, a codeword having a code rate corresponding to the size of available physical resources may be generated through rate matching. For example, a shortening scheme or puncturing scheme may be used for rate matching. The shortening scheme may be performed, for example, by removing a part of an information part of the codeword. Since a part of information bits is reduced, a code rate may be reduced by the shortening scheme. The puncturing scheme may be performed, for example, by puncturing at least a part of a parity of the codeword. In puncturing, since the rate of the information bits increases, the code rate may increase. Therefore, theoretically, a codeword corresponding to an arbitrary code rate may be generated through a combination of the shortening scheme and the puncturing scheme. 
     Shortening and puncturing performance may be determined according to an order of shortened or punctured bits. However, in the QC LDPC code, an order of bit puncturing within a unit block of Q×Q does not affect performance. Therefore, after interleaving of the unit of the lifting size Q for a parity block is performed, puncturing may be performed from the last part of parity bits. In addition, shortening may be performed from the last part of the information bits. 
     Meanwhile, if the size of physical resources is greater than the length of an encoded LDPC code, rate matching may be performed through an iteration scheme. 
     Referring to  FIG. 13 , first, an information block including information bits to be transmitted is generated (step S 1301 ). If the size of a CB is less than the length of an LDPC information part, 0-bit information may be added to the end of the information block prior to encoding. In the example of  FIG. 13 , a 0-bit block is inserted into the end of the information block for later shortening (step S 1302 ). Next, encoding is performed based on the LDPC code with respect to the information block and the 0-bit block so that a codeword including a parity block may be generated (step S 1303 ). In step  51303 , the information block and the 0-bit block may correspond to an information part of the LDPC code and the parity block may correspond to a parity part of the LDPC code. 
     As described above, the shortening scheme may be applied for rate matching. In this case, the already inserted 0-bit block may be removed (step S 1304 ). In addition, for puncturing described later, interleaving (permutation) of a lifting size unit may be performed with respect to the parity block. In addition, for rate matching, the last part of the parity block may be punctured (step S 1305 ). 
     A 5G wireless LAN system supports a transmission rate from a maximum of 20 Gbps to a minimum of a few tens of bps (up to 40 bps in LTE). As such, a transmission environment supported by the 5G wireless LAN system is diverse. To efficiently encode information in such various environments, the LDPC code used for encoding should support various code rates. However, when information is encoded using one LDPC code as performed conventionally, a problem of inefficiency arises in terms of coping with the various communication environments. 
     The present invention proposes that the LDPC code use multiple base codes in order to provide effective encoding in various communication environments. 
     A few base codes proposed in the present invention may be base codes favorable for a large TB (large block) and a large amount of throughput or base codes favorable for small TB (small block) and short latency. 
     Unlike the turbo code, the LDPC code is disadvantageous in that rows of the matrix H to be processed increase as a code rate is lowered. For example, when the code rate of the LDPC code is 8/9, the number of rows to be processed by an encoder is 6, whereas, when the code rate is reduced to 2/3 under the same condition, the number of rows to be processed by the encoder increases by 18. As the number of rows to be processed increases threefold, latency also increases threefold. 
     In order to overcome these problems, the present invention proposes introducing an additional short code for encoding a small TB. As such multiple base codes are introduced, gain can be obtained in terms of decoding latency and power consumption. 
     A data packet transmitted between a BS and a UE has different characteristics depending upon whether the data packet is transmitted on uplink or downlink. When the data packet is transmitted on downlink, since the data packet transmitted on downlink has a relatively high code rate as compared with the data packet transmitted on uplink, large TB blocks occupy most of the traffic. Meanwhile, when the data packet is transmitted on uplink, relatively small TB blocks occupy most of the traffic. 
     In consideration of these characteristics, when an encoder of the transmitter encodes information using an LDPC base code suitable for each communication environment, latency can be effectively reduced. 
     Embodiment 1-1 
     A first base code proposed by the present invention may be used for a large CB and high throughput and a second base code may be used for a small CB and low latency. Table 1 shown below proposes several parameters of the first base code and the second base code. However, the features of the present invention are not limited to the parameters proposed by the table. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Base 
                 Size 
                 Code 
                   
                 Max 
                 Kb, max/ 
                 Lifting 
               
               
                 code 
                 M b  × N b   
                 Rate 
                 P b   
                 information 
                 Kb, min 
                 Values (Z) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 BC1 
                 6 × 38 
                 0.89 
                 2 
                 8192 
                 32/24 
                 256, 192, 144, 
               
               
                   
                   
                   
                   
                   
                   
                 108, 82 
               
               
                 BC2 
                 6 × 16 
                 0.71 
                 2 
                 2040 
                 10/6  
                 204, 128, 88, 
               
               
                   
                   
                   
                   
                   
                   
                 56, 36, 24, 
               
               
                   
                   
                   
                   
                   
                   
                 16, 10, 6 
               
               
                   
               
            
           
         
       
     
     In the above table, Mb denotes the size of a parity of each base code and Nb denotes the size of a codeword of each base code. In addition, Pb denotes the puncturing size of each base code. Kb,max denotes a maximum value of the number of columns of each base code and Kb,min denotes a minimum value of the number of columns of each base code. 
     A type of a lifting value may be determined in consideration of maximum information shortening. In this case, the amount of maximum shortening may be determined as (Kb,max−Kb, min) * Z. If there are a large number of types of a lifting value, a shortening size is reduced so that stable performance can be secured but implementation complexity increases. That is, there is a tradeoff between the types of the lifting value and the shortening size. 
     In some embodiments of the present invention, the lifting value may be set such that shortening in the case of the first base code does not exceed 8Z and shortening in the case of the second base code does not exceed 4Z. If the lifting value is configured as described above, performance deviations for various CB sizes can be minimized. 
     Table 2 shows some lifting values for the first base code according to an embodiment of the present invention. 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 number of column for base code 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 32 
                 30 
                 28 
                 27 
                 26 
                 25 
                 24 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Lifting 
                 256 
                 8192 
                 7680 
                 7168 
                 6912 
                 6656 
                 6400 
                 6144 
               
               
                 values 
                 192 
                 6144 
                 5760 
                 5376 
                 5184 
                 4992 
                 4800 
                 4608 
               
               
                   
                 144 
                 4608 
                 4320 
                 4032 
                 3888 
                 3744 
                 3600 
                 3456 
               
               
                   
                 108 
                 3456 
                 3240 
                 3024 
                 2916 
                 2808 
                 2700 
                 2592 
               
               
                   
                 82 
                 2624 
                 2460 
                 2296 
                 2214 
                 2132 
                 2050 
                 1968 
               
               
                   
               
            
           
         
       
     
     For example, if a CB size is given as 6140, it may be considered that 256 is selected as the lifting value and 2052=8192−6140 (a column value is 32) is set as a shortening value and 192 is selected as the lifting value and 4=6144−6140 (a column value is 32) is set as the shortening value. Although there are advantages and disadvantages of each case, when 2052 is set as the shortening value, performance degradation caused by shortening may occur. 
     Table 3 shows some lifting values of the second base code according to another embodiment of the present invention. However, the features of the present invention are not limited to the lifting values disclosed in Table 2 and Table 3. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 number of column for base code 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 10 
                 9 
                 8 
                 7 
                 6 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 Lifting 
                 204 
                 2040 
                 1836 
                 1632 
                 1428 
                 1224 
               
               
                   
                 values 
                 128 
                 1280 
                 1152 
                 1024 
                 896 
                 768 
               
               
                   
                   
                 88 
                 880 
                 792 
                 704 
                 616 
                 528 
               
               
                   
                   
                 56 
                 560 
                 504 
                 448 
                 392 
                 336 
               
               
                   
                   
                 36 
                 360 
                 324 
                 288 
                 252 
                 216 
               
               
                   
                   
                 24 
                 240 
                 216 
                 192 
                 168 
                 144 
               
               
                   
                   
                 16 
                 160 
                 144 
                 128 
                 112 
                 96 
               
               
                   
                   
                 10 
                 100 
                 90 
                 80 
                 70 
                 60 
               
               
                   
                   
                 6 
                 60 
                 54 
                 48 
                 42 
                 36 
               
               
                   
                   
               
            
           
         
       
     
     Embodiment 1-2 
     The first base code and the second base code according to another embodiment of the present invention may be proposed when CB sizes input to the LDPC code overlap. 
     Table 4 and Table 5 show several parameters of the first base code and the second base code according to another embodiment of the present invention. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Base 
                 Size 
                 Code 
                   
                 Max 
                 Kb, max/ 
                 Lifting 
               
               
                 Code 
                 M b  × N b   
                 Rate 
                 P b   
                 information 
                 Kb, min 
                 Values (Z) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 BC1 
                 6 × 38 
                 0.89 
                 2 
                 8192 
                 32/24 
                 256, 192, 144, 
               
               
                   
                   
                   
                   
                   
                   
                 108, 81, 61, 
               
               
                   
                   
                   
                   
                   
                   
                 46, 35, 27, 
               
               
                   
                   
                   
                   
                   
                   
                 21 
               
               
                 BC2 
                 6 × 16 
                 0.71 
                 2 
                 2560 
                 10/6  
                 256, 156, 96, 
               
               
                   
                   
                   
                   
                   
                   
                 64, 40, 25, 
               
               
                   
                   
                   
                   
                   
                   
                 16, 10, 6 
               
               
                   
               
            
           
         
       
     
     Table 6 and Table 7 show several lifting values of the first base code and the second base code, respectively, according to another embodiment of the present invention. 
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 number of column for code block 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 32 
                 30 
                 28 
                 27 
                 26 
                 25 
                 24 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Lifting 
                 256 
                 8192 
                 7680 
                 7168 
                 6912 
                 6656 
                 6400 
                 6144 
               
               
                 values 
                 192 
                 6144 
                 5760 
                 5376 
                 5184 
                 4992 
                 4800 
                 4608 
               
               
                   
                 144 
                 4608 
                 4320 
                 4032 
                 3888 
                 3744 
                 3600 
                 3456 
               
               
                   
                 108 
                 3456 
                 3240 
                 3024 
                 2916 
                 2808 
                 2700 
                 2592 
               
               
                   
                 81 
                 2592 
                 2430 
                 2268 
                 2187 
                 2106 
                 2025 
                 1944 
               
               
                   
                 61 
                 1952 
                 1830 
                 1708 
                 1647 
                 1586 
                 1525 
                 1464 
               
               
                   
                 46 
                 1472 
                 1380 
                 1288 
                 1242 
                 1196 
                 1150 
                 1104 
               
               
                   
                 35 
                 1120 
                 1050 
                 980 
                 945 
                 910 
                 875 
                 840 
               
               
                   
                 27 
                 864 
                 810 
                 756 
                 729 
                 702 
                 675 
                 648 
               
               
                   
                 21 
                 672 
                 630 
                 588 
                 567 
                 546 
                 525 
                 504 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 number of column for code block 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 10 
                 9 
                 8 
                 7 
                 6 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 Lifting 
                 256 
                 2560 
                 2304 
                 2048 
                 1792 
                 1536 
               
               
                   
                 values 
                 156 
                 1560 
                 1404 
                 1248 
                 1092 
                 936 
               
               
                   
                   
                 96 
                 960 
                 864 
                 768 
                 672 
                 576 
               
               
                   
                   
                 64 
                 640 
                 576 
                 512 
                 448 
                 384 
               
               
                   
                   
                 40 
                 400 
                 360 
                 320 
                 280 
                 240 
               
               
                   
                   
                 25 
                 250 
                 225 
                 200 
                 175 
                 150 
               
               
                   
                   
                 16 
                 160 
                 144 
                 128 
                 112 
                 96 
               
               
                   
                   
                 10 
                 100 
                 90 
                 80 
                 70 
                 60 
               
               
                   
                   
                 6 
                 60 
                 54 
                 48 
                 42 
                 36 
               
               
                   
                   
               
            
           
         
       
     
     When comparing Table 5 with Table 6, it may be appreciated that both the first base code and the second base code are applied when a CB size is 504 to 2560. Hereinafter, when base codes which can be selected according to CB sizes overlap (when CB sizes which can be supported by the respective base codes overlap), a method of selecting a base code for the LDPC code is proposed. The method of selecting the base code will be described below in detail. Separately from this method, the base code may be selectively selected according to a situation or accommodation capacity of the UE. 
     A method of selecting a plurality of lifting values which can be used in each base code will now be described in more detail. First, a maximum lifting value Zmax capable of being supported by a base code is selected and small lifting values may be sequentially selected. Next, Kb,min may be selected in consideration of a maximum shortening amount which can be supported by the base code. In the above example of the first base code, the case in which Zmax=256 and Kb,min=24 is shown. 
     Next, an i-th value of Z corresponding to the following equation may be selected as the lifting value of a corresponding base code. 
       ( Kb ,min+1)* Z ( i− 1)&gt;( Kb ,max)* Z ( i )&gt;=( Kb ,min)* Z ( i −1),   [Equation 5]
 
     In the above equation, n denotes a value i when the value increases up to a minimum lifting value desired to be supported. 
     Additionally, a plurality of lifting values supported by a base code may be determined according to the following equation. 
         Z ( i )=ceil( Z ( i −1)* Kb ,min/ Kb ,max)   [Equation 6]
 
     In the above equation, ceil(a) denotes a ceiling function of a. 
     Embodiment 1-3 
     Hereinafter, another embodiment for selecting a plurality of lifting values or a lifting set will be described. A plurality of lifting values capable of being used in a base code may be selected to be in the form of A*2{circumflex over ( )}B. 
     Table 7 shows a plurality of lifting value capable of being used by a base code of an LDPC code according to another embodiment of the present invention. 
     
       
         
           
               
               
             
               
                   
                 TABLE 7 
               
             
            
               
                   
                   
               
               
                   
                 B 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 A 
                 3 
                 6 
                 12 
                 24 
                 48 
                 96 
               
               
                   
                   
                 4 
                 8 
                 16 
                 32 
                 64 
                 128 
               
               
                   
                   
                 5 
                 10 
                 20 
                 40 
                 80 
                 160 
               
               
                   
                   
                 6 
                 12 
                 24 
                 48 
                 96 
                 192 
               
               
                   
                   
                 7 
                 14 
                 28 
                 56 
                 112 
                 224 
               
               
                   
                   
                 8 
                 16 
                 32 
                 64 
                 128 
                 256 
               
               
                   
                   
               
            
           
         
       
     
     Table 8 shows several parameters of the first base code and the second base code according to another embodiment of the present invention. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                 Base 
                 Size 
                 Code 
                   
                 Max 
                 Kb, max/ 
                 Lifting 
               
               
                 Code 
                 M b  × N b   
                 Rate 
                 P b   
                 information 
                 Kb, min 
                 Values (Z) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 BC1 
                 6 × 38 
                 0.89 
                 2 
                 8192 
                 32/25 
                 256, 224, 192, 
               
               
                   
                   
                   
                   
                   
                   
                 160, 128, 112, 
               
               
                   
                   
                   
                   
                   
                   
                 96, 80, 64, 
               
               
                   
                   
                   
                   
                   
                   
                 56, 48, 40, 
               
               
                   
                   
                   
                   
                   
                   
                 32, 28, 24, 
               
               
                   
                   
                   
                   
                   
                   
                 20, 16 
               
               
                 BC2 
                 6 × 16 
                 0.71 
                 2 
                 2560 
                 10/8  
                 256, 224, 192, 
               
               
                   
                   
                   
                   
                   
                   
                 160, 128, 112, 
               
               
                   
                   
                   
                   
                   
                   
                 96, 80, 64, 
               
               
                   
                   
                   
                   
                   
                   
                 56, 48, 40, 
               
               
                   
                   
                   
                   
                   
                   
                 32, 28, 24, 
               
               
                   
                   
                   
                   
                   
                   
                 20, 16, 14, 
               
               
                   
                   
                   
                   
                   
                   
                 12, 10, 8, 6 
               
               
                   
               
            
           
         
       
     
     Embodiment 2-1 
     Hereinafter, a method of selecting a base code and a lifting value from multiple LDPC codes according to an embodiment of the present invention will be described. 
     As described above, if a TB size (TBS) is given on channel coding, a transmitter may segment a TB into CBs based on an input size of an encoder. In this case, in order to perform encoding suitable for an obtained CB size (CBS), the above-described matrix H should be determined. To determine the matrix H, the transmitter should set the base code and the lifting value. 
     Hereinafter, a method for the transmitter to select the base code and the lifting value in the above-described situations of Embodiments 1-1 to 1-3 will be described. 
     As in Embodiment 1-1, if a CBS generated by the transmitter does not overlap with a CBS which is supportable by the first base code and a CBS supportable by the second base code, the transmitter may select the base code based on a preset CBS. Referring to Table 2 and Table 3, if a CBS exceeds  2040 , the transmitter may select the first base code and, otherwise (when the 
     CBS is less than  2040 ), the transmitter may select the second base code. However, the features of the present invention are not limited to these numbers. 
       FIG. 14  is a diagram referenced to explain a base code selection method according to an embodiment of the present invention. 
       FIG. 14  illustrates a method of selecting a base code according a given code rate and 
     CBS when the CBS generated by the transmitter overlaps with the CBS which is supportable by the first base code and the CBS supportable by the second base code as in Embodiment 1-2. 
     In  FIG. 14 , r1max and r1min denote a maximum code rate and a minimum code rate, respectively, that the first base code can provide and r2 max and r2 min denote a maximum code rate and a minimum code rate, respectively, that the second base code can provide. 
     In addition, in  FIG. 14 , L1 max and L1 min denote a maximum CBS and a minimum CBS, respectively, that the first base code can provide. Similarly, L2 max and L2 min denote a maximum CBS and a minimum CBS, respectively, that the second base code can provide. 
     In Embodiment 1-2 for example, L1 max=8192, L2 max=2560, L1 min=504, and L2 min=36. However, the technical sprit and scope of the present invention are not limited to these numbers. 
     According to a graph illustrated in  FIG. 14 , if a CB generated by the transmitter is located in a horizontal real line region, the transmitter may select the first base code and perform encoding. Similarly, if the CB generated by the transmitter is located in a horizontal dotted line region, the transmitter may select the second base code and perform encoding. 
     If a characteristic of the CB generated by the transmitter is located in a diagonal real line region, i.e., a CBS and a code rate overlap with those of the first base code and second base code, a method for the transmitter to select a base code may be problematic. The present invention proposes a method for the transmitter to select the second base code. 
     Specifically, the transmitter may determine a TBS based on a given modulation and coding scheme (MC S) and a resource block (RB) with respect to encoding target information. Next, the transmitter may obtain a CBS k and a code rate r through CB segmentation. Thereafter, the transmitter may select a final base code through a condition clause or code interpretation, given according to Table 9 below . 
     
       
         
           
               
               
             
               
                   
                 TABLE 9 
               
               
                   
                   
               
             
            
               
                   
                 If(r &gt; r2_max) 
               
            
           
           
               
               
            
               
                   
                 Select BC1 
               
            
           
           
               
               
            
               
                   
                 Elseif(K &gt; L2_max) 
               
            
           
           
               
               
            
               
                   
                 Select BC1 
               
            
           
           
               
               
            
               
                   
                 ELSE 
               
            
           
           
               
               
            
               
                   
                 Select BC2 
               
            
           
           
               
               
            
               
                   
                 END 
               
               
                   
                   
               
            
           
         
       
     
     That is, if the code rate r is greater than the preset code rate r2 max or the CBS k is greater than the preset CBS L2 max, the transmitter may select the first base code as a base code of the LDPC code and, otherwise, the transmitter may select the second base code. 
     In principle, if an MCS which is supportable by the second base code is determined, the transmitter may select the base code by prioritizing the second base code rather than the first base code. However, the features of the present invention are not limited to such a configuration. 
     The base code that the LDPC code uses may be configured through additional signaling for the UE or the base code may be selected according to accommodation capability of the UE. 
     If the base code is selected by the transmitter, the transmitter may select the lifting value Z according to the following equation. 
         Z·K   b , max≥ K&gt;Z·K   b , min   [Equation 7]
 
     In the right term of Equation 7, it is desirable not to include an equal sign. If the equal sign is included, two selectable lifting values occur. 
     Embodiment 2-2 
     According to still another embodiment of the present invention, in selecting the base code, the transmitter may be configured to select the second base code even with respect to a CB having a higher code rate than a reference code rate of the second base code. In this case, the second base code may support a higher code rate than the reference code rate (0.71 according to Embodiment 1-2) through parity puncturing. For example, when up to the fifth column of a parity can be used, a code rate may be about 10/15 (0.77). 
     According to this embodiment, if a CBS is less than L2 max and a code rate is lower than rp (where rp&gt;r2 max) which is higher than a conventional reference code rate, the transmitter may select the second base code to perform LDPC coding. 
     In Embodiment 1-2, if a CBS is less than 2560 and a code rate is lower than 0.77, the transmitter may select the second base code to perform LDPC coding. In this case, since the transmitter may use a larger lifting value relative to a conventional code rate, gain can be obtained in terms of latency. In this case, M1 parity permutation may be needed for performance improvement. 
     Embodiment 3 
       FIG. 15  is a diagram referenced to explain a device according to an embodiment of the present invention. 
     Referring to  FIG. 15 , a BS  10  according to the present invention may include a reception module  11 , a transmission module  12 , a processor  13 , a memory  14 , and a plurality of antennas  15 . The transmission module  12  may transmit a variety of signals, data, and information to an external device (e.g., UE). The reception module  11  may receive a variety of signals, data, and information from the external device (e.g., UE). The reception module  11  and the transmission module  12  may be referred to as a transceiver. The processor  13  may control overall operation of the BS  10 . The plural antennas  15  may be configured according to, for example, a  2 -dimensional antenna arrangement. 
     The processor  13  of the BS  10  according to an example of the present invention may be configured to receive channel state information according to the examples proposed in the present invention. The processor  13  of the BS  10  processes information received by the BS  10  and information to be transmitted to the outside of the BS  10 . The memory  14  may store the processed information for a predetermined time and may be replaced with a component such as a buffer (not shown). 
     Referring to  FIG. 15 , a UE  20  according to the present invention may include a reception module  21 , a transmission module  22 , a processor  23 , a memory  24 , and a plurality of antennas  25 . Use of the plurality of antennas  25  means that the UE  20  supports Multiple Input Multiple Output (MIMO) transmission and reception using the plurality of antennas  25 . The transmission module  22  may transmit a variety of signals, data, and information to an external device (e.g., BS). The reception module  21  may receive a variety of signals, data, and information from the external device (e.g., BS). The reception module  21  and the transmission module  22  may be referred to as a transceiver. The processor  23  may control overall operation of the BS  10 . 
     The processor  23  of the UE  10  according to an example of the present invention may be configured to transmit channel state information according to the examples proposed in the present invention. The processor  23  of the UE  20  processes information received by the UE  20  and information to be transmitted to the outside of the UE  10 . The memory  24  may store the processed information for a predetermined time and may be replaced with a component such as a buffer (not shown). 
     The detailed configurations of the UE  10  may be implemented such that the above-described various embodiments of the present invention are independently applied or two or more embodiments of the present invention are simultaneously applied. Redundant matters will not be described herein for clarity. 
     In described various embodiments of the present invention, while the BS has been mainly described as an example of a downlink transmission entity or an uplink reception entity and the UE has been mainly described as an example of a downlink reception entity or an uplink transmission entity, the scope of the present invention is not limited thereto. For example, a description of the BS may be identically applied when a cell, an antenna port, an antenna port group, a remote radio head (RRH), a transmission point, a reception point, an access point, or a relay is a downlink transmission entity to the UE or an uplink reception entity from the UE. In addition, the principle of the present invention described through various embodiments of the present invention may be identically applied to a relay acting as a downlink transmission entity to the UE or an uplink reception entity from the UE, or a relay acting as an uplink transmission entity to the BS or a downlink reception entity from the BS. 
     The embodiments of the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. 
     In a hardware configuration, the method according to the embodiments of the present invention may be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, or microprocessors. 
     In a firmware or software configuration, the method according to the embodiments of the present invention may be implemented in the form of modules, procedures, functions, etc. performing the above-described functions or operations. Software code may be stored in a memory unit and executed by a processor. The memory unit may be located at the interior or exterior of the processor and may transmit and receive data to and from the processor via various known means. 
     The embodiments described above are combinations of components and features of the present invention in a prescribed form. Each component or feature may be considered selective unless explicitly mentioned otherwise. Each component or feature may be executed in a form that is not combined with other components and features. Further, some components and/or features may be combined to configure an embodiment of the present invention. The order of operations described in the embodiments of the present invention may be changed. Some components or features of an embodiment may be included in another embodiment or may be substituted with a corresponding component or feature of the present invention. It is obvious to those skilled in the art that claims that are not explicitly cited in each other in the appended claims may be presented in combination as an embodiment of the present invention or included as a new claim by subsequent amendment after the application is filed. 
     It will be apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit and essential characteristics of the invention. Thus, the above embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the invention should be determined by reasonable interpretation of the appended claims and all changes which come within the equivalent scope of the invention are within the scope of the invention. 
     INDUSTRIAL APPLICABILITY 
     The embodiments of the present invention are applicable to various wireless access systems and broadcast communication systems. The wireless access systems include, for example, a 3GPP system, a 3GPP2 system, and/or an IEEE 802.xx system. The embodiments of the present invention may be applied not only to the wireless access systems but also to all technical fields employing the wireless access systems.