Abstract:
Provided is a bit calculation method, which accurately and easily calculates how many bits are transmitted by codeword per PDSCH in advance before a modulator performs modulation by TTI unit on a PCH or a DL-SCH transferred by a TrCH encoder, in a base-station modulator applied to an LTE-advanced system. Accordingly, the bit calculation method enables smooth data transmission, and easily checks data transmission error.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2008-0129633, filed on Dec. 18, 2008 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The following disclosure relates to a bit calculation of transmission data, and in particular, to a bit calculation method and apparatus, which calculates beforehand how many bits are transmitted by codeword per Physical Downlink Shared Channel (PDSCH) before a modulator performs modulation by Transmission Time Interval (TTI) unit on a Physical Channel (PCH) or a Downlink Shared Channel (DL-SCH) transferred by a TrCH encoder, in a base-station modulator applied to an LTE-advanced system. 
       BACKGROUND 
       [0003]    A TrCH encoder of a base station encodes a PCH or a DL-SCH to transfer it to a modulator. The modulator performs transmission using a PDSCH on two channels from among a plurality of downlink transport channels. 
         [0004]    In reference to “3GPP TR 25.814 v7.1.0—Version September, 2006” for the implementation of an LTE-Advanced system, a resource allocation scheme between the PDSCH and other physical channels is not clearly defined. 
         [0005]    Accordingly, a node B scheduler allocating a resource to the PDSCH allocates the resource to the PDSCH as a localized type or a distributed type. If other transmitted physical channels are allocated to the allocated resource, the PDSCH uses an overwrite type through an occupied physical channel. 
         [0006]    Based on such a method, for the PCH or the DL-SCH transferred by the TrCH encoder, a method (where the modulator calculates beforehand how many bits are transmitted by codeword per PDSCH before performing modulation by TTI unit and enables safe transmission of the bits through the channel) is satisfied by multiplying a resource block (which is allocated by codeword per PDSCH) by an Orthogonal Frequency Division Multiplexing (OFDM) symbol which is transmitted during 1 TTI. 
         [0007]    In this way, the number of bits to transmit is easily obtained, but if a control channel occupies a resource to which the PCSCH is allocated, loss of a PDSCH signal is inevitable. 
         [0008]    In LTE standard “3GPP TS 36.211 v8.4.0—Version August, 2008”, which is one of the standards that are referred to as the basis for the development of a current LTE-Advanced system, a resource allocation scheme between the PDSCH and other transmitted physical channels has been clearly defined. 
         [0009]    For the PCH or the DL-SCH transferred by the TrCH encoder of the base station, calculation (on how many bits the modulator transmits by codeword per the PDSCH by TTI unit) is necessarily performed in an L1 controller or the node B scheduler that is the upper layer of the modulator, and thus, the PCH or the DL-SCH is not only used in the upper layer but is also transferred to the TrCH encoder and the modulator. Accordingly, downlink transmission is smoothly performed. 
         [0010]    However, while a Cell-Specific Reference Signal (CSRS), Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS) and Physical Broadcast Channel (PBCH) are allocated to a region to which a resource for the PDSCH is allocated, or PDSCH resource allocation is performed as the localized type or the distributed type due to factors such as a precoding type, because the number of layers, a modulation type, a transmitted antenna set and the number of codewords transmitted to a user terminal, the number of the bits of the PCH or DL-SCH which is actually transmitted by transmitted OFDM symbol varies. 
         [0011]    Accordingly, for the PCH or the DL-SCH transferred by the TrCH encoder, the modulator has difficulty in calculating in advance how many bits it transmits by codeword per PDSCH before performing modulation by TTI unit, and it is difficult to check the number of transmission bits beforehand in the L1 controller or the node B scheduler that is the upper layer of the modulator. 
       SUMMARY 
       [0012]    In one general aspect, a bit calculation apparatus includes: a resource allocation unit allocating a resource, on a downlink data channel; a channel analysis unit searching channel use circumstances to check a usable resource, on the resource required by the resource allocation unit; a subcarrier analysis unit checking a plurality of usable subcarriers, on the usable resource; and a bit calculation unit calculating the number of transmission bits per codeword transmitted through the downlink data channel according to the usable subcarriers and a modulation type of a modulator. 
         [0013]    The resource allocation unit may include: a resource allocation type analyzer searching a plurality of resource blocks required according to a resource allocation type; and a resource block compiler compiling the resource blocks searched by the resource allocation type analyzer. 
         [0014]    The resource allocation type analyzer may include: a first resource allocation type analyzer searching resource blocks by using a 25-bit bitmap; a second resource allocation type analyzer searching the resource blocks by using a 22-bit bitmap, a 2-bit subset indicator and a 1-bit span indicator; and a third resource allocation type analyzer searching the resource blocks by using a resource indication value. 
         [0015]    The channel analysis unit may include: a subframe transmission analyzer searching a plurality of OFDM symbols used for channel transmission to check a plurality of usable resource blocks by subframe; and a usable resource block compiler compiling the usable resource blocks by the subframe. 
         [0016]    The subframe transmission analyzer may search a first resource block which is always used to transmit a first sync signal, a second sync signal and a broadcasting channel, and a second resource block which is always used to transmit the first sync signal and the second sync signal, to calculate the usable resource block. 
         [0017]    The subcarrier analysis unit may include: a subcarrier calculator calculating the number of the usable subcarriers of a usable resource block per OFDM symbol by antenna set; and a subcarrier compiler compiling the number of the usable subcarriers of the resource block. 
         [0018]    The subcarrier calculator may include a transmission antenna set detector. When the transmission antenna set detected by the transmission antenna set detector is a first transmission path (Tx 1 paths), the subcarrier calculator may exclude the two subcarriers of the subcarriers of the each resource block from the usable subcarriers on three OFDM symbols. When the transmission antenna set detected by the transmission antenna set detector is a second transmission path (Tx 2 paths), the subcarrier calculator may exclude the four subcarriers of the subcarriers of the each resource block from the usable subcarriers on three OFDM symbols. When the transmission antenna set detected by the transmission antenna set detector is a fourth transmission path (Tx 4 paths), the subcarrier calculator may exclude the four subcarriers of the subcarriers of the each resource block from the usable subcarriers on five OFDM symbols. Accordingly, the subcarrier calculator may calculate the number of the usable subcarriers. 
         [0019]    The bit calculation unit may include: a multiplication offset calculator calculating a multiplication offset according to a precoding type, a modulation type and the number of codewords carried in the each subcarrier; and a bit operator calculating the number of the transmission bits per codeword with the multiplication offset, the total number of the usable subcarriers and the number of transmission bits based on a modulation type. 
         [0020]    In a case where the codeword is carried one by one, the multiplication offset calculator may calculate 1 as a multiplication offset value when the precoding type is an open-loop spatial multiplexing type or a closed-loop spatial multiplexing type, and may calculate 2 as the multiplication offset value when the precoding type is not the open-loop spatial multiplexing type or the closed-loop spatial multiplexing type. In a case where the codeword is carried two by two, the multiplication offset calculator may calculate 2 as the multiplication offset value when the precoding type is a spatial multiplexing type and the number of layers is four, and may calculate 1 as the multiplication offset value when the precoding type is not the spatial multiplexing type or the number of the layers is not four, on the first codeword. In the case where the codeword is carried two by two, the multiplication offset calculator may calculate 2 as the multiplication offset value when the precoding type is the spatial multiplexing type and the number of the layers is three or four, and may calculate 1 as the multiplication offset value when the precoding type is not the spatial multiplexing type or the number of the layers is not three or four, on the second codeword. 
         [0021]    In another general aspect, a bit calculation apparatus includes: a resource allocation unit allocating a resource, on a downlink data channel; a channel analysis unit searching channel use circumstances to check a usable resource, on the resource required by the resource allocation unit; a subcarrier analysis unit checking a plurality of usable subcarriers, on the usable resource; and a bit calculation unit calculating the number of transmission bits per codeword carried in the usable subcarrier through the downlink data channel. Herein, the resource allocation unit includes: a resource allocation type analyzer searching a plurality of resource blocks required according to a resource allocation type; and a resource block compiler compiling the resource blocks searched by the resource allocation type analyzer. The channel analysis unit includes: a subframe transmission analyzer searching a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols used for channel transmission to check a plurality of usable resource blocks by subframe; and a usable resource block compiler compiling the usable resource blocks by the subframe. The subcarrier analysis unit includes: a subcarrier calculator calculating the number of the usable subcarriers of the usable resource block per OFDM symbol by antenna set; and a subcarrier compiler compiling the number of the usable subcarriers of the resource block. The bit calculation unit includes: a multiplication offset calculator calculating a multiplication offset according to a precoding type, a modulation type and the number of codewords carried in the each subcarrier; and a bit operator calculating the number of transmission bits per codeword with the multiplication offset, the total number of the usable subcarriers and the number of transmission bits based on a modulation type. 
         [0022]    In another general aspect, a bit calculation method includes: allocating a resource, on a downlink data channel; searching channel use circumstances to check a usable resource, on the resource required by the resource allocation unit; checking a plurality of usable subcarriers, on the usable resource; and calculating the number of transmission bits per codeword transmitted through the downlink data channel according to the usable subcarriers and the modulation type of a modulator. 
         [0023]    The allocating of the resource may include searching a plurality of resource blocks required according to a resource allocation type; and compiling the searched resource blocks. 
         [0024]    The resource allocation type may include: a first resource allocation type for allocating the resource blocks by using a 25-bit bitmap; a second resource allocation type for allocating the resource blocks by using a 22-bit bitmap, a 2-bit subset indicator and a 1-bit span indicator; and a third resource allocation type for allocating the resource blocks by using a resource indication value. 
         [0025]    The checking of the usable resource may include: searching a plurality of OFDM symbols used for channel transmission to check a plurality of usable resource blocks by subframe; and compiling the usable resource blocks by the subframe. 
         [0026]    The checking of the usable resource blocks by subframe may include: searching a first resource block which is always used to transmit a first sync signal, a second sync signal and a broadcasting channel and a second resource block which is always used to transmit the first sync signal and the second sync signal, among the resource blocks of the OFDM symbols used for channel transmission; and determining the resource block except the first and second resource blocks as the usable resource block, among the resource blocks of the OFDM symbols. 
         [0027]    The checking of the usable resource may include: calculating the number of the usable subcarriers of a resource block per OFDM symbol by antenna set; and compiling the number of the calculated usable subcarriers. 
         [0028]    The calculating of the number of the usable subcarriers may include: detecting a transmission antenna set; excluding the two subcarriers of the subcarriers of the each resource block from the usable subcarrier on three OFDM symbols, when the transmission antenna set is a first transmission path (Tx 1 paths); excluding the four subcarriers of the subcarriers of the each resource block from the usable subcarrier on three OFDM symbols, when the transmission antenna set is a second transmission path (Tx 2 paths); excluding the four subcarriers of the subcarriers of the each resource block from the usable subcarrier on five OFDM symbols, when the transmission antenna set is a fourth transmission path (Tx 4 paths); and calculating the number of the usable subcarriers. 
         [0029]    The calculating of the number of the transmission bits per codeword may include: calculating a multiplication offset according to a precoding type, a modulation type and the number of codewords carried in the each subcarrier; and calculating the number of the transmission bits per codeword with the calculated multiplication offset, the total number of the usable subcarriers and the number of transmission bits based on a modulation type. 
         [0030]    The calculating of the multiplication offset may include: calculating 1 as a multiplication offset value when the precoding type is an open-loop spatial multiplexing type or a closed-loop spatial multiplexing type, and calculating 2 as the multiplication offset value when the precoding type is not the open-loop spatial multiplexing type or the closed-loop spatial multiplexing type, in a case where the codeword is carried one by one. The calculating of the multiplication offset may include: calculating 2 as the multiplication offset value when the precoding type is a spatial multiplexing type and the number of layers is four, and calculating 1 as the multiplication offset value when the precoding type is not the spatial multiplexing type or the number of the layers is not four, on the first codeword, in a case where the codeword is carried two by two. The calculating of the multiplication offset may include: calculating 2 as the multiplication offset value when the precoding type is the spatial multiplexing type and the number of the layers is three or four, and calculating 1 as the multiplication offset value when the precoding type is not the spatial multiplexing type or the number of the layers is not three or four, on the second codeword, in the case where the codeword is carried two by two. 
         [0031]    Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is a block diagram schematically illustrating a transmission bit calculation apparatus for calculating the total number of bits which a modulator transmits by codeword per PDSCH during 1 TTI in a normal CP type according to an exemplary embodiment. 
           [0033]      FIG. 2  is a flowchart schematically illustrating a method of compiling necessary resource blocks in a resource allocation unit according to an exemplary embodiment. 
           [0034]      FIG. 3  is a flowchart schematically illustrating a method of checking usable resources in a channel analysis unit according to an exemplary embodiment. 
           [0035]      FIG. 4  is a flowchart schematically illustrating a method of checking usable subcarriers in a subcarrier analysis unit according to an exemplary embodiment. 
           [0036]      FIG. 5  is a flowchart schematically illustrating a method of calculating the number of bits per codeword transmitted through the PDSCH in a bit calculation unit according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0037]    Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/of systems described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness. 
         [0038]    Exemplary embodiments relate to a method which calculates beforehand how many bits are transmitted by codeword per PDSCH by TTI before a modulator performs modulation, on a PCH or a DL-SCH through which a TrCH encoder transfers data. 
         [0039]    1 TTI is composed of OFDM symbol  0  to OFDM symbol  13 , and a section transmitted through the PDSCH is from the OFDM symbol  3  to the OFDM symbol  13 . The each OFDM symbol has the resource block of  0  to  99 , and the each resource block is composed of twelve subcarriers. 
         [0040]      FIG. 1  is a block diagram schematically illustrating a transmission bit calculation apparatus for calculating the total number of bits which a modulator transmits by codeword per PDSCH during 1 TTI in a normal CP type according to an exemplary embodiment. 
         [0041]    The transmission bit calculation apparatus according to an exemplary embodiment is divided into four devices. The transmission bit calculation apparatus according to an exemplary embodiment includes a resource allocation unit  101 , a channel analysis unit  113 , a subcarrier analysis unit  125 , and a bit calculation unit  131 . Herein, the resource allocation unit  101  is based on a resource allocation type for a PDSCH transmitted through a modulation process on a PCH or a DL-SCH. The channel analysis unit  113  determines whether a PSS, an SSS and a PBCH are used for a required resource allocation. The subcarrier analysis unit  125  analyzes whether to use subcarriers by OFDM symbol by a CSRS based on a transmitted antenna set. The bit calculation unit  131  calculates the total number of bits according to the number of transmitted codewords, a precoding type and a modulation type. 
         [0042]    The resource allocation unit  101 , which analyzes a resource block that is required for a resource by resource allocation type for the PDSCH transmitted through the modulation process on the PCH or the DL-SCH, includes a first resource allocation type analyzer  105 , a second resource allocation analyzer  107 , a third resource allocation type analyzer  109 , and a resource block compiler  111  compiling resource blocks required for resource allocation. 
         [0043]    The channel analysis unit  113 , which analyzes whether the PSS, the SSS and the PBCH are used for a required resource allocation, includes a subframe transmission analyzer  115 . The subframe transmission analyzer  115  analyzes whether to transmit the PSS, the SSS and the PBCH on the each resource block to which the resource allocation unit  101  requires analysis, and analyzes whether the resource block required by the channel analysis unit  101  is used according to a result of the analysis. 
         [0044]    The subframe transmission analyzer  115  includes a subframe # 0  transmission analyzer  117 , . . . , a subframe # 5  transmission analyzer  119 , . . . , and a subframe #P transmission analyzer  121 , with the point when a transmission is performed through the PDSCH on the P+1 number of subframes. 
         [0045]    The channel analysis unit  113  includes a usable resource block compiler  123  compiling resource blocks which are determined to be usable among required resource blocks. 
         [0046]    The subcarrier analysis unit  125 , which analyzes whether to use the subcarriers by OFDM symbol by the CSRS based on the transmitted antenna set, includes a subcarrier calculator  127  and a subcarrier compiler  129 . The subcarrier calculator  127  calculates the number of the usable subcarriers of a usable resource block per OFDM symbol by antenna set. The subcarrier compiler  129  compiles the number of the subcarriers which are determined to be usable. The subcarrier calculator  127  includes a transmission antenna set detector  128  detecting a transmission antenna set. 
         [0047]    The bit calculation unit  131  (which is based on the number of modulated codewords transmitted through the PDSCH, a precoding type and a modulation type) includes a multiplication offset calculator  133  and a bit operator  135 . The multiplication offset calculator  133  calculates a multiplication offset according to the number of the codewords transmitted to the respective subcarriers, the precoding type and the modulation type. The bit operator  135  calculates the number of transmission bits per codeword with the number of transmission bits based on the multiplication offset, the total number of usable subcarriers and the modulation type. 
         [0048]      FIG. 2  is a flowchart schematically illustrating a method of compiling necessary resource blocks in the resource allocation unit  101  according to an exemplary embodiment. 
         [0049]    The resource allocation unit  101  preferentially checks what the resource allocation type is in operation S 201 . 
         [0050]    When the resource allocation type is a resource allocation type  0  in operation S 202 , the first resource allocation type analyzer  105  finds a resource block corresponding to a resource block group represented in a 25-bit bitmap in operation S 203 . 
         [0051]    When the resource allocation type is a resource allocation type  1  in operation S 204 , the second resource allocation type analyzer  107  finds a resource block necessary for resource allocation by using a 22-bit bitmap, a 2-bit subset indicator and a 1-bit span indicator in operations S 205  to S 207 . 
         [0052]    When the resource allocation type is a resource allocation type  2  in operation S 208 , the third resource allocation type analyzer  109  calculates the length of a resource block which is continuously disposed with an initial resource block by using a Resource Indication Value (RIV) in operation S 209 . 
         [0053]    Resource allocation is performed in a localized type or a distributed type. In a case of the distributed type, the resource allocation unit  101  obtains a Virtual Resource Block (VRB) by a first gap or a second gap in operation S 210 , and thereafter maps the VRBs with Physical Resource Blocks (PRBs) to find a required resource block in operation S 211 . Even in a case of the localized type, the resource allocation unit  101  maps the VRBs and the PRBs into the same resource block to find a required resource block in operation S 211 . 
         [0054]    In this way, each operation has been performed according to the used resource allocation types, and thereafter the resource block compiler  111  compiles the resource blocks required for resource allocation in operation S 212 . 
         [0055]    The channel analysis unit  113  determines whether the required each resource block allocates the PDSCH or not, with time and frequency where the each resource block is disposed. 
         [0056]      FIG. 3  is a flowchart schematically illustrating a method of checking usable resources in the channel analysis unit  113  according to an exemplary embodiment. 
         [0057]    Referring to  FIG. 3 , the channel analysis unit  113  receives the compiled result of the resource requirements from the resource allocation unit  101 , and checks a subframe number through the subframe transmission analyzer  115  in operation S 301 . 
         [0058]    When the checked subframe number is 0 in operation S 302 , the subframe # 0  transmission analyzer  117  analyzes usable resource blocks. The subframe # 0  is the point when the PSS, the SSS and the PBCH are always transmitted, and thus, a resource block (corresponding to the positions of # 48  to # 52  among the resource blocks which is required in a section of the OFDM symbol # 5  to OFDM symbol # 10  of the OFDM symbols constituting the subframes) cannot be used for the transmission of the PDSCH because it is used for the transmission of the PSS, the SSS and the PBCH. Accordingly, the resource block is excluded from the usable resource blocks. 
         [0059]    When the checked subframe number is  5  in operation S 306 , the subframe # 5  transmission analyzer  119  analyzes the usable resource blocks. The subframe # 5  is the point when PSS and SSS channels are always transmitted and the PBCH is never transmitted, and thus, a resource block (corresponding to the positions of # 48  to # 52  among the resource blocks which is required in a section of the OFDM symbol # 5  and OFDM symbol # 6  of the OFDM symbols constituting the subframes) cannot be used for the transmission of the PDSCH because it is used for the transmission of the PSS and SSS channels. Accordingly, the resource block is excluded from the usable resource blocks. 
         [0060]    When subframes other than the subframes # 0  to # 5  in operation S 310 , because a point is the point when the PSS, the SSS and the PBCH are never transmitted in operation S 311 , all the required resource blocks are used for the transmission of the PDSCH. 
         [0061]    In this way, each operation has been performed with the point when the PDSCH is transmitted, and thereafter the usable resource block compiler  123  compiles the resource blocks which are checked as the usable resource block among the required resource blocks in operation S 312 . 
         [0062]    The subcarrier analysis unit  125  checks whether to enable the use of all the twelve subcarriers constituting the each resource block on each of the compiled usable resource blocks. 
         [0063]      FIG. 4  is a flowchart schematically illustrating a method of checking usable subcarriers in the subcarrier analysis unit  125  according to an exemplary embodiment. 
         [0064]    Referring to  FIG. 4 , the subcarrier analysis unit  125  first determines a transmission antenna set through the transmission antenna set detector  128  in operation S 401 . 
         [0065]    The subcarriers occupied by the CSRS are changed according to the transmission antenna set. Accordingly, the subcarrier analysis unit  125  preferentially analyzes the transmission antenna set for determining whether to enable the use of all the twelve subcarriers constituting the each resource block, on the compiled usable resource blocks for PDSCH resource allocation. 
         [0066]    When the transmission antenna set is a first transmission path (Tx 1 path) in operation S 402 , the subcarrier analysis unit  125  determines whether a point is the point for the OFDM symbol # 4 , the OFDM symbol # 7  and the OFDM symbol # 11  in operation S 403 . When the OFDM symbol # 4 , the OFDM symbol # 7  and the OFDM symbol # 11 , the two subcarriers of the twelve subcarriers constituting the each resource block on the each usable resource block cannot be used because of being used for CSRS transmission in operation S 404 . In this case, the subcarrier analysis unit  125  uses all the twelve subcarriers constituting the each resource block on the OFDM symbol where other PDSCH is transmitted. 
         [0067]    When the transmission antenna set is a second transmission path (Tx 2 paths) in operation S 405 , the subcarrier analysis unit  125  determines whether a point is the point for the OFDM symbol # 4 , the OFDM symbol # 7  and the OFDM symbol # 11  in operation S 406 . When the OFDM symbol # 4 , the OFDM symbol # 7  and the OFDM symbol # 11 , the four subcarriers of the twelve subcarriers constituting the each resource block on the each usable resource block cannot be used because of being used for CSRS transmission in operation S 407 . In this case, the subcarrier analysis unit  125  uses all the twelve subcarriers constituting the each resource block on the OFDM symbol where other PDSCH is transmitted. 
         [0068]    When the transmission antenna set is a third transmission path (Tx 3 paths) in operation S 408 , the subcarrier analysis unit  125  determines whether a point is the point for the OFDM symbol # 1 , the OFDM symbol # 4 , the OFDM symbol # 7 , the OFDM symbol # 8  and the OFDM symbol # 11  in operation S 409 . When the OFDM symbol # 1 , the OFDM symbol # 4 , the OFDM symbol # 7 , the OFDM symbol # 8  and the OFDM symbol # 11 , the four subcarriers of the twelve subcarriers constituting the each resource block on the each usable resource block cannot be used because of being used for CSRS transmission in operation S 410 . In this case, the subcarrier analysis unit  125  uses all the twelve subcarriers constituting the each resource block on the OFDM symbol where other PDSCH is transmitted. 
         [0069]    In this way, each operation has been performed according to the transmitted antenna set, and thereafter the subcarrier compiler  129  compiles the usable subcarriers on the usable resource blocks in operation S 411 . 
         [0070]    The bit calculation unit  131  calculates the number of bits which are transmitted though the usable subcarriers. 
         [0071]      FIG. 5  is a flowchart schematically illustrating a method of calculating the number of bits per codeword transmitted through the PDSCH in the bit calculation unit  131  according to an exemplary embodiment. 
         [0072]    The bit calculation unit  131  calculates the total number of bits which the modulator transmits by codeword per PDSCH by TTI unit according to whether one codeword or two codewords are carried in the compiled each subcarrier at a time and what the modulation type and the precoding type by PDSCH are. 
         [0073]    First, the bit calculation unit  131  determines whether one codeword or two codewords are carried in the compiled each subcarrier at a time in operation S 501 . 
         [0074]    When one codeword is carried through the PDSCH at a time in operation S 502 , i.e., when the PDSCH is considering carrying the codeword one by one, the multiplication offset calculator  133  calculates a Multiplication Offset (MO) according to the modulation type. When the bit calculation unit  135  calculates the total number of bits, the multiplication offset is necessary. 
         [0075]    The multiplication offset calculator  133  determines whether the precoding type is the large delay CDD of an open-loop spatial multiplexing type or a closed-loop spatial multiplexing type in operation S 503 . When the large delay CDD of an open-loop spatial multiplexing type or a closed-loop spatial multiplexing type, the multiplication offset calculator  133  calculates 2 as a multiplication offset value in operation S 504 . In cases other than this, the multiplication offset calculator  133  calculates 2 as a multiplication offset value in operation S 505 . 
         [0076]    When two codewords are carried through the PDSCH at a time in operation S 506 , i.e., when the PDSCH is considering carrying the codeword two by two, the multiplication offset calculator  133  calculates the multiplication offset value in different types on the codeword (which is carried two by two), i.e., codeword # 0  and codeword # 1 . 
         [0077]    When the first codeword (the codeword # 0 ) of the two codewords in operation S 507 , the multiplication offset calculator  133  determines whether the precoding type is a spatial multiplexing type and the number of layers is four in operation S 508 . 
         [0078]    When the determination result shows that the precoding type is the spatial multiplexing type and the number of the layers is four, the multiplication offset calculator  133  calculates 2 as the multiplication offset value in operation S 509 . In cases other than this, the multiplication offset calculator  133  calculates 1 as the multiplication offset value in operation S 510 . 
         [0079]    When the second codeword (the codeword # 1 ) of the two codewords in operation S 511 , the multiplication offset calculator  133  determines whether the precoding type is the spatial multiplexing type and the number of the layers is three or four in operation S 512 . 
         [0080]    When the determination result shows that the precoding type is the spatial multiplexing type and the number of the layers is three or four, the multiplication offset calculator  133  calculates 2 as the multiplication offset value in operation S 513 . In cases other than this, the multiplication offset calculator  133  calculates 1 as the multiplication offset value in operation S 514 . 
         [0081]    The bit calculation unit  135  multiplies the calculated multiplication offset value by the number of the usable subcarriers of the usable resource block of the resource blocks required for resource allocation and the number of transmission bits (2 in the case of QPSK, 4 in the case of 16QAM, and 6 in the case of 64QAM) based on the modulation type, to thereby calculate the total number of bits which the modulator transmits by codeword per PDSCH of TTI unit on the PCH or the DL-SCH in operation S 515 . 
         [0082]    A number of exemplary embodiments have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.