Patent Publication Number: US-2021194537-A1

Title: Spreading a response signal using a first set of orthogonal sequences and a reference signal using a second set of shorter orthogonal sequences

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 16/243,417, filed Jan. 9, 2019, which is a continuation of application Ser. No. 15/286,817, filed Oct. 6, 2016, granted as U.S. Pat. No. 10,200,083, which is a continuation of application Ser. No. 14/616,844, filed Feb. 9, 2015, granted as U.S. Pat. No. 9,484,982, which is a continuation of application Ser. No. 13/648,976, filed Oct. 10, 2012, granted as U.S. Pat. No. 8,953,544, which is a continuation of application Ser. No. 13/301,643 filed Nov. 21, 2011, granted as U.S. Pat. No. 8,311,079, which is a continuation of Ser. No. 13/280,190 filed Oct. 24, 2011, granted as U.S. Pat. No. 8,199,792, which is a continuation of application Ser. No. 13/165,538 filed Jun. 21, 2011, granted as U.S. Pat. No. 8,179,947, which is a continuation of application Ser. No. 12/593,904 filed Sep. 29, 2009, granted as U.S. Pat. No. 8,009,721, which is a national stage entry of PCT/JP2008/001526 filed Jun. 13, 2008 and claims priority to JP 2007-159580 filed Jun. 15, 2007 and JP 2007-161966 filed Jun. 19, 2007, the entire contents of each of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a radio communication apparatus and a reference signal generating method. 
     BACKGROUND 
     In mobile communication, ARQ (Automatic Repeat Request) is applied to downlink data from a radio communication base station apparatus (hereinafter abbreviated to “base station”) to radio communication mobile station apparatuses (hereinafter abbreviated to “mobile stations”). That is, mobile stations feedback response signals representing error detection results of downlink data, to the base station. Mobile stations perform a CRC (Cyclic Redundancy Check) of downlink data, and, if CRC=OK is found (i.e. if no error is found), feedback an ACK (ACKnowledgement), and, if CRC=NG is found (i.e. if error is found), feedback a NACK (Negative ACKnowledgement), as a response signal to the base station. These response signals are transmitted to the base station using uplink control channels such as a PUCCH (Physical Uplink Control CHannel). 
     Also, the base station transmits control information for reporting resource allocation results of downlink data, to mobile stations. This control information is transmitted to the mobile stations using downlink control channels such as L1/L2 CCHs (L1/L2 Control CHannels). Each L1/L2 CCH occupies one or a plurality of CCEs (Control Channel Elements). If one L1/L2 CCH occupies a plurality of CCEs, the plurality of CCEs occupied by the L1/L2 CCH are consecutive. Based on the number of CCEs required to carry control information, the base station allocates an arbitrary L1/L2 CCH among the plurality of L1/L2 CCHs to each mobile station, maps the control information on the physical resources corresponding to the CCEs occupied by the L1/L2 CCH, and performs transmission. 
     Also, to efficiently use downlink communication resources, studies are underway to associate CCEs with PUCCHs. According to this association, each mobile station can decide the PUCCH to use to transmit response signals from the mobile station, from the CCEs corresponding to physical resources on which control information for the mobile station is mapped. 
     Also, as shown in  FIG. 1 , studies are underway to perform code-multiplexing by spreading a plurality of response signals from a plurality of mobile stations using ZC (Zadoff-Chu) sequences and Walsh sequences (see Non-Patent Document 1). In  FIG. 1 , (W 0 , W 1 , W 2 , W 3 ) represents a Walsh sequence with a sequence length of 4. As shown in  FIG. 1 , in a mobile station, first, a response signal of ACK or NACK is subject to first spreading to one symbol by a ZC sequence (with a sequence length of 12) in the frequency domain. Next, the response signal subjected to first spreading is subject to an IFFT (Inverse Fast Fourier Transform) in association with W 0  to W 3 . The response signal spread in the frequency domain by a ZC sequence with a sequence length of 12 is transformed to a ZC sequence with a sequence length of 12 by this IFFT in the time domain. Then, the signal subjected to the IFFT is subject to second spreading using a Walsh sequence (with a sequence length of 4). That is, one response signal is allocated to each of four symbols S 0  to S 3 . Similarly, response signals of other mobile stations are spread using ZC sequences and Walsh sequences. Here, different mobile stations use ZC sequences with different cyclic shift values in the time domain, or different Walsh sequences. Here, the sequence length of ZC sequences in the time domain is 12, so that it is possible to use twelve ZC sequences with cyclic shift values “0” to “11”, generated by cyclically shifting the same ZC sequence using the cyclic shift values “0” to “11”. Also, the sequence length of Walsh sequences is 4, so that it is possible to use four different Walsh sequences. Therefore, in an ideal communication environment, it is possible to code-multiplex maximum forty-eight (12×4) response signals from mobile stations. 
     Here, there is no cross-correlation between ZC sequences with different cyclic shift values generated from the same ZC sequence. Therefore, in an ideal communication environment, as shown in  FIG. 2 , a plurality of response signals subjected to spreading and code-multiplexing by ZC sequences with different cyclic shift values (0 to 11), can be separated in the time domain without inter-code interference, by correlation processing in the base station. 
     However, due to an influence of, for example, transmission timing difference in mobile stations, multipath delayed waves and frequency offsets, a plurality of response signals from a plurality of mobile stations do not always arrive at a base station at the same time. For example, as shown in  FIG. 3 , if the transmission timing of a response signal spread by the ZC sequence with cyclic shift value “0” is delayed from the correct transmission timing, the correlation peak of the ZC sequence with cyclic shift value “0” may appear in the detection window for the ZC sequence with cyclic shift value “1.” Further, as shown in  FIG. 4 , if a response signal spread by the ZC sequence with cyclic shift value “0” has a delay wave, an interference leakage due to the delayed wave may appear in the detection window for the ZC sequence with cyclic shift value “1.” Therefore, in these cases, the separation performance degrades between a response signal spread by the ZC sequence with cyclic shift value “0” and a response signal spread by the ZC sequence with cyclic shift value “1.” That is, if ZC sequences, cyclic shift values of which are adjacent, are used, the separation performance of response signals may degrade. 
     Therefore, up till now, if a plurality of response signals are code-multiplexed by spreading using ZC sequences, a sufficient cyclic shift value difference (i.e. cyclic shift interval) is provided between the ZC sequences, to an extent that does not cause inter-code interference between the ZC sequences. For example, when the difference between the cyclic shift values of ZC sequences is 4, only three ZC sequences with cyclic shift values “0,” “4,” and “8” amongst twelve ZC sequences with cyclic shift values “0” to “11,” are used for the first spreading of response signals. Therefore, if Walsh sequences with a sequence length of 4 are used for second spreading of response signals, it is possible to code-multiplex maximum twelve (3×4) response signals from mobile stations. 
     Non-Patent Document 1: Multiplexing capability of CQIs and ACK/NACKs form different UEs (ftp://ftp.3gpp.org/TSG_RAN/WG1_RL1/TSGR1.sub.--49/Docs/R1-072315.zip) 
     Example Problems to be Solved 
     As described above, if a Walsh sequence with a sequence length of 4, (W 0 , W 1 , W 2 , W 3 ), is used for second spreading, one response signal is allocated to each of four symbols (S 0  to S 3 ). Therefore, a base station that receives response signals from mobile stations needs to despread the response signals over a time period of four-symbols. On the other hand, if a mobile station moves fast, there is a high possibility that the channel conditions between the mobile station and the base station change during the above four-symbol time period. Therefore, when there is a mobile station moving fast, orthogonality between Walsh sequences that are used for second spreading may collapse. That is, when there are mobile stations moving fast, inter-code interference is more likely to occur between Walsh sequences than between ZC sequences, and, as a result, the separation performance of response signals degrades. 
     By the way, when some of a plurality of mobile stations moves fast and the rest of mobile stations are in a stationary state, the mobile stations in a stationary state, which are multiplexed with the mobile stations moving fast on the Walsh axis, are also influenced by inter-code interference. 
     SUMMARY 
     It is therefore an object of the present invention to provide a radio communication apparatus and reference signal generating method that can minimize degradation of the separation performance of response signals that are code-multiplexed. 
     The radio communication apparatus of the present invention employs a configuration having: a first spreading section that performs first spreading of a response signal using one of a plurality of first sequences that can be separated from each other because of different cyclic shift values; and a second spreading section that performs second spreading of the response signal subjected to the first spreading, using one of a plurality of second sequences, and in which a difference between cyclic shift values of first sequences associated with different, adjacent second sequences, is less than a difference between cyclic shift values of first sequences associated with the same second sequence. 
     According to the present invention, it is possible to minimize degradation of the separation performance of response signals that are code-multiplexed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a spreading method of response signals (prior art); 
         FIG. 2  is a diagram showing correlation processing of response signals spread by ZC sequences (in the case of an ideal communication environment); 
         FIG. 3  is a diagram showing correlation processing of response signals spread by ZC sequences (when there is a transmission timing difference); 
         FIG. 4  is a diagram showing correlation processing of response signals spread by ZC sequences (when there is a delay wave); 
         FIG. 5  is a block diagram showing the configuration of a base station according to Embodiment 1 of the present invention; 
         FIG. 6  is a block diagram showing the configuration of a mobile station according to Embodiment 1 of the present invention; 
         FIG. 7  is a diagram showing association between ZC sequences, Walsh sequences and PUCCHs according to Embodiment 1 of the present invention (variation 1); 
         FIG. 8  is a diagram showing association between the first sequences, second sequences and PUCCHs according to Embodiment 1 of the present invention; 
         FIG. 9  is a diagram showing association between ZC sequences, Walsh sequences and PUCCHs according to Embodiment 1 of the present invention (variation 2); 
         FIG. 10  is a diagram showing association between ZC sequences, Walsh sequences and PUCCHs according to Embodiment 1 of the present invention (variation 3); 
         FIG. 11  illustrates Walsh sequences according to Embodiment 2 of the present invention; 
         FIG. 12  is a diagram showing association between ZC sequences, Walsh sequences and PUCCHs according to Embodiment 2 of the present invention; 
         FIG. 13  is a diagram showing association between ZC sequences, Walsh sequences and PUCCHs according to Embodiment 3 of the present invention (variation 1); 
         FIG. 14  is a diagram showing association between ZC sequences, Walsh sequences and PUCCHs according to Embodiment 3 of the present invention (variation 2); and 
         FIG. 15  is a diagram showing a spreading method of a reference signal. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. 
     Embodiment 1 
       FIG. 5  illustrates the configuration of base station  100  according to the present embodiment, and  FIG. 6  illustrates the configuration of mobile station  200  according to the present embodiment. 
     Here, to avoid complicated explanation,  FIG. 5  illustrates components associated with transmission of downlink data and components associated with reception of uplink response signals to downlink data, which are closely related to the present invention, and illustration and explanation of the components associated with reception of uplink data will be omitted. Similarly,  FIG. 6  illustrates components associated with reception of downlink data and components associated with transmission of uplink response signals to downlink data, which are closely related to the present invention, and illustration and explanation of the components associated with transmission of uplink data will be omitted. 
     Also, in the following explanation, a case will be described where ZC sequences are used for first spreading and Walsh sequences are used for second spreading. Here, for first spreading, it is equally possible to use sequences, which can be separated from each other because of different cyclic shift values, other than ZC sequences. Similarly, for second spreading, it is equally possible to use orthogonal sequences other than Walsh sequences. 
     Further, in the following explanation, a case will be described where ZC sequences with a sequence length of 12 and Walsh sequences with a sequence length of 4, (W 0 , W 1 , W 2 , W 3 ), are used. However, the present invention is not limited to these sequence lengths. 
     Further, in the following explanation, twelve ZC sequences with cyclic shift values “0” to “11” will be referred to as “ZC #0” to “ZC #11,” and four Walsh sequences of sequence numbers “0” to “3” will be referred to as “W #0” to “W #3.” 
     Further, a case will be assumed in the following explanation where L1/L2 CCH #1 occupies CCE #1, L1/L2 CCH #2 occupies CCE #2, L1/L2 CCH #3 occupies CCE #3, L1/L2 CCH #4 occupies CCE #4 and CCE #5, L1/L2 CCH #5 occupies CCE #6 and CCE #7, L1/L2 CCH #6 occupies CCEs #8 to #11, and so on. 
     Further, in the following explanation, the CCE numbers and the PUCCH numbers, which are defined by the cyclic shift values of ZC sequences and Walsh sequence numbers, are associated therebetween on a one to one basis. That is, CCE #1 is associated with PUCCH #1, CCE #2 is associated with PUCCH #2, CCE #3 is associated with PUCCH #3, and so on. 
     In base station  100  shown in  FIG. 5 , control information generating section  101  and mapping section  104  receive as input a resource allocation result of downlink data. 
     Control information generating section  101  generates control information to carry the resource allocation result, on a per mobile station basis, and outputs the control information to encoding section  102 . Control information, which is provided per mobile station, includes mobile station ID information to indicate to which mobile station the control information is directed. For example, control information includes, as mobile station ID information, a CRC masked by the ID number of the mobile station, to which control information is reported. Control information is encoded in encoding section  102 , modulated in modulating section  103  and received as input in mapping section  104 , on a per mobile station basis. Further, control information generating section  101  allocates an arbitrary L1/L2 CCH in a plurality of L1/L2 CCHs to each mobile station, based on the number of CCE(s) required to report the control information, and outputs the CCE number corresponding to the allocated L1/L2 CCH to mapping section  104 . For example, when the number of CCE(s) required to report control information to mobile station #1 is one and therefore L1/L2 CCH #1 is allocated to mobile station #1, control information generating section  101  outputs CCE number #1 to mapping section  104 . Also, when the number of CCE(s) required to report control information to mobile station #1 is four and therefore L1/L2 CCH #6 is allocated to mobile station #1, control information generating section  101  outputs CCE numbers #8 to #11, to mapping section  104 . 
     On the other hand, encoding section  105  encodes transmission data for each mobile station (i.e. downlink data) and outputs the encoded transmission data to retransmission control section  106 . 
     Upon initial transmission, retransmission control section  106  holds the encoded transmission data on a per mobile station basis and outputs the data to modulating section  107 . Retransmission control section  106  holds transmission data until retransmission control section  106  receives as input an ACK of each mobile station from deciding section  116 . Further, upon receiving as input a NACK of each mobile station from deciding section  116 , that is, for retransmission, retransmission control section  106  outputs the transmission data associated with that NACK to modulating section  107 . 
     Modulating section  107  modulates the encoded transmission data received as input from retransmission control section  106 , and outputs the result to mapping section  104 . 
     For transmission of control information, mapping section  104  maps the control information received as input from modulating section  103  on a physical resource based on the CCE number received as input from control information generating section  101 , and outputs the result to IFFT section  108 . That is, mapping section  104  maps control information on the subcarrier corresponding to the CCE number in a plurality of subcarriers comprised of an OFDM symbol, on a per mobile station basis. 
     On the other hand, for transmission of downlink data, mapping section  104  maps the transmission data, which is provided on a per mobile station basis, on a physical resource based on the resource allocation result, and outputs the result to IFFT section  108 . That is, based on the resource allocation result, mapping section  104  maps transmission data on a subcarrier in a plurality of subcarriers comprised of an OFDM symbol, on a per mobile station basis. 
     IFFT section  108  generates an OFDM symbol by performing an IFFT of a plurality of subcarriers on which control information or transmission data is mapped, and outputs the OFDM symbol to CP (Cyclic Prefix) attaching section  109 . 
     CP attaching section  109  attaches the same signal as the signal at the tail end part of the OFDM symbol, to the head of the OFDM symbol as a CP. 
     Radio transmitting section  110  performs transmission processing such as D/A conversion, amplification and up-conversion on the OFDM symbol with a CP, and transmits the result from antenna  111  to mobile station  200  (in  FIG. 6 ). 
     On the other hand, radio receiving section  112  receives a response signal transmitted from mobile station  200 , via antenna  111 , and performs receiving processing such as down-conversion and ND conversion on the response signal. 
     CP removing section  113  removes the CP attached to the response signal subjected to receiving processing. 
     Despreading section  114  despreads the response signal by a Walsh sequence that is used for second spreading in mobile station  200 , and outputs the despread response signal to correlation processing section  115 . 
     Correlation processing section  115  finds the correlation value between the response signal received as input from dispreading section  114 , that is, the response signal spread by a ZC sequence, and the ZC sequence that is used for first spreading in mobile station  200 , and outputs the correlation value to deciding section  116 . 
     Deciding section  116  detects a correlation peak on a per mobile station basis, using a detection window set per mobile station in the time domain, thereby detecting a response signal on a per mobile station basis. For example, upon detecting a correlation peak in detection window #1 for mobile station #1, deciding section  116  detects the response signal from mobile station #1. Then, deciding section  116  decides whether the detected response signal is an ACK or NACK, and outputs the ACK or NACK to retransmission control section  106  on a per mobile station basis. 
     On the other hand, in mobile station  200  shown in  FIG. 6 , radio receiving section  202  receives the OFDM symbol transmitted from base station  100 , via antenna  201 , and performs receiving processing such as down-conversion and ND conversion on the OFDM symbol. 
     CP removing section  203  removes the CP attached to the OFDM symbol subjected to receiving processing. 
     FFT (Fast Fourier Transform) section  204  acquires control information or downlink data mapped on a plurality of subcarriers by performing a FFT of the OFDM symbol, and outputs the control information or downlink data to extracting section  205 . 
     For receiving the control information, extracting section  205  extracts the control information from the plurality of subcarriers and outputs it to demodulating section  206 . This control information is demodulated in demodulating section  206 , decoded in decoding section  207  and received as input in deciding section  208 . 
     On the other hand, for receiving downlink data, extracting section  205  extracts the downlink data directed to the mobile station from the plurality of subcarriers, based on the resource allocation result received as input from deciding section  208 , and outputs the downlink data to demodulating section  210 . This downlink data is demodulated in demodulating section  210 , decoded in decoding section  211  and received as input in CRC section  212 . 
     CRC section  212  performs an error detection of the decoded downlink data using a CRC, generates an ACK in the case of CRC=OK (i.e. when no error is found) and a NACK in the case of CRC=NG (i.e. when error is found), as a response signal, and outputs the generated response signal to modulating section  213 . Further, in the case of CRC=OK (i.e. when no error is found), CRC section  212  outputs the decoded downlink data as received data. Deciding section  208  performs a blind detection of whether or not the control information received as input from decoding section  207  is directed to the mobile station. For example, deciding section  208  decides that, if CRC=OK is found (i.e. if no error is found) as a result of demasking by the ID number of the mobile station, the control information is directed to the mobile station. Further, deciding section  208  outputs the control information directed to the mobile station, that is, the resource allocation result of downlink data for the mobile station, to extracting section  205 . Further, deciding section  208  decides a PUCCH to use to transmit a response signal from the mobile station, from the CCE number corresponding to subcarriers on which the control information directed to the mobile station is mapped, and outputs the decision result (i.e. PUCCH number) to control section  209 . For example, if control information is mapped on a subcarrier corresponding to CCE #1, deciding section  208  of mobile station  200  allocated with above L1/L2 CCH #1 decides that PUCCH #1 associated with CCE #1 is the PUCCH for the mobile station. For example, if control information is mapped on subcarriers corresponding to CCE #8 to CCE #11, deciding section  208  of mobile station  200  allocated with above L1/L2 CCH #6 decides that PUCCH #8 associated with CCE #8, which is the minimum number among CCE #8 to CCE #11, is the PUCCH directed to the mobile station. 
     Based on the PUCCH number received as input from deciding section  208 , control section  209  controls the cyclic shift value of the ZC sequence that is used for first spreading in spreading section  214  and the Walsh sequence that is used for second spreading in spreading section  217 . That is, control section  209  sets a ZC sequence, the cyclic shift value of which is associated with the PUCCH number received as input from deciding section  208 , in spreading section  214 , and sets the Walsh sequence associated with the PUCCH number received as input from deciding section  208 , in spreading section  217 . The sequence control in control section  209  will be described later in detail. 
     Modulating section  213  modulates the response signal received as input from CRC section  212  and outputs the result to spreading section  214 . 
     As shown in  FIG. 1 , spreading section  214  performs first spreading of the response signal by the ZC sequence set in control section  209 , and outputs the response signal subjected to first spreading to IFFT section  215 . 
     As shown in  FIG. 1 , IFFT section  215  performs an IFFT of the response signal subjected to first spreading, and outputs the response signal subjected to an IFFT to CP attaching section  216 . 
     CP attaching section  216  attaches the same signal as the tail end part of the response signal subjected to an IFFT, to the head of the response signal as a CP. 
     As shown in  FIG. 1 , spreading section  217  performs second spreading of the response signal with a CP by the Walsh sequence set in control section  209 , and outputs the response signal subjected to second spreading to radio transmitting section  218 . 
     Radio transmitting section  218  performs transmission processing such as D/A conversion, amplification and up-conversion on the response signal subjected to second spreading, and transmits the resulting signal from antenna  201  to base station  100  (in  FIG. 5 ). 
     According to the present embodiment, a response signal is subjected to two-dimensional spreading, by first spreading using a ZC sequence and second spreading using a Walsh sequence. That is to say, the present embodiment spreads a response signal on the cyclic shift axis and on the Walsh axis. 
     Next, sequence control in control section  209  (in  FIG. 6 ) will be explained in detail. 
     If ZC sequences are used for first spreading of a response signal, as described above, a sufficient cyclic shift value difference (e.g. cyclic shift value difference of 4) is provided between the ZC sequences, to an extent that does not cause inter-code interference between the ZC sequences. Therefore, orthogonality between response signals subjected to first spreading using ZC sequences, cyclic shift values of which are different, is little likely to collapse. By contrast, as described above, when there is a mobile station moving fast, orthogonality between Walsh sequences used for second spreading is likely to collapse. 
     Therefore, the present embodiment controls ZC sequences and Walsh sequences according to the association shown in  FIG. 7 , such that interference components remained in response signals subjected to despreading in despreading section  114  (in  FIG. 5 ) are absorbed by a slight difference between the cyclic shift values of ZC sequences. That is, control section  209  controls the cyclic shift values of ZC sequences that are used for first spreading in spreading section  214  and Walsh sequences that are used for second spreading in spreading section  217 , according to the association shown in  FIG. 7 . 
       FIG. 7  associates PUCCH #1 with ZC #0 and W #0, PUCCH #2 with ZC #4 and W #0, PUCCH #3 with ZC #8 and W #0, PUCCH #4 with ZC #1 and W #1, PUCCH #5 with ZC #5 and W #1, PUCCH #6 with ZC #9 and W #1, PUCCH #7 with ZC #2 and W #2, PUCCH #8 with ZC #6 and W #2, PUCCH #9 with ZC #10 and W #2, PUCCH #10 with ZC #3 and W #3, PUCCH #11 with ZC #7 and W #3, and PUCCH #12 with ZC #11 and W #3. 
     Therefore, for example, upon receiving as input PUCCH number #1 from deciding section  208 , control section  209  sets ZC #0 in spreading section  214  and W #0 in spreading section  217 . Also, for example, upon receiving as input PUCCH number #2 from deciding section  208 , control section  209  sets ZC #4 in spreading section  214  and W #0 in spreading section  217 . Also, for example, upon receiving as input PUCCH number #4 from deciding section  208 , control section  209  sets ZC #1 in spreading section  214  and W #1 in spreading section  217 . 
     Here, in  FIG. 7 , ZC sequences for first spreading when using W #1 in second spreading (i.e. ZC #1, ZC #5 and ZC #9) are acquired by cyclically shifting the ZC sequences for first spreading when using W #0 in second spreading (i.e. ZC #0, ZC #4 and ZC #8) by one. Also, ZC sequences for first spreading when using W #2 in second spreading (i.e. ZC #2, ZC #6 and ZC #10) are acquired by cyclically shifting the ZC sequences for first spreading when using W #1 in second spreading (i.e. ZC #1, ZC #5 and ZC #9) by one. Also, ZC sequences for first spreading when using W #3 in second spreading (i.e. ZC #3, ZC #7 and ZC #11) are acquired by cyclically shifting the ZC sequences for first spreading when using W #2 in second spreading (i.e. ZC #2, ZC #6 and ZC #10) by one. 
     Also, in  FIG. 7 , the difference between the cyclic shift values of ZC sequences associated with different, adjacent Walsh sequences, is less than the difference between the cyclic shift values of ZC sequences associated with the same Walsh sequence. For example, while the cyclic shift value difference is 1 between ZC #0 associated with W #0 and ZC #1 associated with W #1, the cyclic shift value difference is 4 between ZC #0 and ZC #4 associated with W #0. 
     Thus, in  FIG. 7 , ZC sequences are cyclically shifted by one every time the Walsh sequence number increases by one. That is, in the present embodiment, the minimum difference is 1 between the cyclic shift values of ZC sequences associated with adjacent Walsh sequences. In other words, in  FIG. 7 , adjacent Walsh sequences are associated with ZC sequences, cyclic shift values of which are different, and used for two-dimensional spreading for response signals. Therefore, even when inter-code interference between Walsh sequences occurs due to the collapse of orthogonality between the Walsh sequences, it is possible to suppress inter-code interference by spreading using ZC sequences. For example, referring to  FIG. 7 , a response signal that is transmitted using PUCCH #4 is subjected to two-dimensional spreading using ZC #1 and W #1, and a response signal that is transmitted using PUCCH #7 is subjected to two-dimensional spreading using ZC #2 and W #2. Therefore, even when inter-code interference between W #1 and W #2 occurs due to the collapse of orthogonality between W #1 and W #2, it is possible to suppress the inter-code interference by a slight difference between the cyclic shift values of ZC #1 and ZC #2. 
     On the other hand, in  FIG. 7 , like ZC #1 and ZC #2, ZC sequences, cyclic shift values of which are adjacent, that is, ZC sequences, between which the cyclic shift value difference is “1,” are used. By this means, orthogonality between ZC sequences may collapse, which causes inter-code interference between the ZC sequences. However, in  FIG. 7 , ZC sequences, between which a cyclic shift value difference is “1,” are associated with different Walsh sequences and used for two-dimensional spreading of response signals. Therefore, even when inter-code interference between ZC sequences occurs due to the collapse of orthogonality between the ZC sequences, it is possible to suppress inter-code interference by spreading using Walsh sequences. For example, referring to  FIG. 7 , a response signal that is transmitted using PUCCH #4 is subjected to two-dimensional spreading using ZC #1 and W #1, and a response signal that is transmitted using PUCCH #7 is subjected to two-dimensional spreading using ZC #2 and W #2. Therefore, even when inter-code interference between ZC #1 and ZC #2 occurs, it is possible to suppress inter-code interference by the difference between the sequences of W #1 and W #2. 
     Thus, the present embodiment absorbs the collapse of orthogonality on the Walsh axis (i.e. inter-code interference between Walsh sequences), on the cyclic shift axis, and absorbs the collapse of orthogonality on the cyclic shift axis (i.e. inter-code interference between ZC sequences), on the Walsh axis. In other words, the present embodiment compensates inter-code interference between Walsh sequences caused by the collapse of orthogonality between the Walsh sequences, by the spreading gain of ZC sequence, and compensates inter-code interference between ZC sequences caused by the collapse of orthogonality between the ZC sequences, by the spreading gain of Walsh sequence. Therefore, according to the present embodiment, it is possible to minimize degradation of the separation performance of code-multiplexed response signals. 
       FIG. 8  generalizes the association shown in  FIG. 7 . That is,  FIG. 8  illustrates a case where signals are spread using a plurality of first sequences that can be separated from each other because of different cyclic shift values and a plurality of orthogonal second sequences. That is, according to  FIG. 8 , when the difference between the cyclic shift values of a plurality of first sequences associated with the same second sequence is “k,” the difference between the cyclic shift values of a plurality of first sequences associated with a plurality of adjacent second sequences is “Δ” (Δ&lt;k). That is, in  FIG. 8 , the first sequences are shifted by Δ every time the second sequence number increases by one. 
     Also, as described above, the present embodiment can compensate inter-code interference between Walsh sequences by the spreading gain of ZC sequence, and compensate inter-code interference between ZC sequences by the spreading gain of Walsh sequence. Therefore, it is possible to make the difference between the cyclic shift values of ZC sequences associated with the same Walsh sequence less than “4” in  FIG. 7 .  FIG. 9  illustrates a case where this difference is “2.” While twelve PUCCHs of PUCCH #1 to PUCCH #12 are available in  FIG. 7 , twenty-four PUCCHs of PUCCH #1 to PUCCH #24 are available in  FIG. 9 . In other words, while twelve code resources amongst forty-eight code resources are used in  FIG. 7 , twenty-four code resources amongst forty-eight coded resources are used in  FIG. 9 . That is, the present embodiment can increase the efficiency of use of limited code resources and maximize the efficiency of use of code resources. 
     Also, if the association shown in  FIG. 10  are used, it is equally possible to produce the same effect as in the case of using the association shown in  FIG. 9 . 
     Embodiment 2 
     As shown in  FIG. 11 , when W #0 is (1, 1, 1, 1) and W #1 is (1, −1, 1, −1), the first two-chip units in W #0 and W #1 are orthogonal to each other, and the second two-chip units are orthogonal to each other. Similarly, when W #2 is (1, 1, −1, −1) and W #3 is (1, −1, −1, 1), the first two-chip units in W #2 and W #3 are orthogonal to each other, and the second two-chip units are orthogonal to each other. Therefore, if the change of channel condition is sufficiently small during two symbol time periods, inter-code interference do not occur between W #0 and W #1 and inter-code interference do not occur between W #2 and W #3. Therefore, it is possible to separate a plurality of response signals subjected to code-multiplexing by second spreading using W #0 and W #1, into the first two-chip units and the second two-chip units. Similarly, it is possible to separate a plurality of response signals subjected to code multiplexing by second spreading using W #2 and W #3, into the first two-chip units and the second two-chip units. 
     Therefore, with the present embodiment, control section  209  controls the cyclic shift value of a ZC sequence that is used for first spreading in spreading section  214  and a Walsh sequence that is used for second spreading in spreading section  217  according to the association shown in  FIG. 12 . In  FIG. 12 , the cyclic shift values of ZC sequences associated with W #0 and the cyclic shift values of ZC sequences associated with W #1 are the same in 0, 2, 4, 6, 8 and 10, and the cyclic shift values of ZC sequences associated with W #2 and the cyclic shift values of ZC sequences associated with W #3 are the same in 1, 3, 5, 7, 9 and 11. 
     Here, for example, to separate the response signal subjected to second spreading by W #0 when W #0, W #1 and W #2 are used for second spreading at the same time, the sum of S 0 , S 1 , S 2  and S 3  in  FIG. 1  is calculated. By this means, it is possible to remove the response signal components spread by W #1 and W #2, from a received signal. However, if a mobile station that uses W #1 and a mobile station that uses W #2 move fast, the difference by channel variation is remained in a separated response signal as inter-code interference. 
     That is, referring to W #1, S 0  and S 1  have different signs, and therefore the response signal component spread by W #1 is removed by adding S 0  and S 1 . But, inter-code interference of Δ#1 by channel variation is remained in the separated response signal. If the channel variation is linear, similarly, inter-code interference of Δ#1 is remained in the separated response signal between S 2  and S 3 . Therefore, inter-code interference of 2×Δ#1 in total is remained in the separated response signal. 
     On the other hand, referring to W #2, S 0  and S 1  have the same sign, and therefore response signal components spread by W #2 are removed by the difference between the signs of S 2  and S 3 . In this case, inter-code interference of ΔxΔ#2 in total is remained in the separated response signal. 
     That is, inter-code interference is reduced between a plurality of response signals subjected to code-multiplexing using a plurality of Walsh sequences between which the first two-chip units are orthogonal to each other and the second two-chip units are orthogonal to each other. Therefore, the present embodiment uses different Walsh sequences with little inter-code interference (e.g. W #0 and W #1) in combination with ZC sequences, cyclic shift values of which are the same, and uses different Walsh sequences with significant inter-code interference (e.g. W #0 and W #2) in combination with ZC sequences, cyclic shift values of which are different. 
     As described above, according to the present embodiment, by performing second spreading of response signals using Walsh sequences in which parts of the sequences shorter than the sequence length are orthogonal to each other, it is possible to improve the robustness to fast movement of mobile stations. 
     Embodiment 3 
     In code multiplexing by first spreading using ZC sequences, that is, in code multiplexing on the cyclic shift axis, as described above, a sufficient difference is provided between the cyclic shift values of ZC sequences, to an extent that does not cause inter-code interference between the ZC sequences. Therefore, orthogonality between ZC sequences is little likely to collapse. Also, even if there is a mobile station that moves fast, orthogonality between ZC sequences does not collapse. On the other hand, in code-multiplexing by second spreading using Walsh sequences, that is, in code-multiplexing on the Walsh axis, as described above, orthogonality between Walsh sequences is likely to collapse when there is a mobile station that moves fast. Therefore, upon code-multiplexing response signals by second spreading, it may be preferable to increase the average multiplexing level on the cyclic shift axis where orthogonality is little likely to collapse, and decrease the average multiplexing level on the Walsh axis where orthogonality is likely to collapse. Also, it may be preferable to equalize (unify) the multiplexing level on the Walsh axis between ZC sequences, such that the multiplexing level on the Walsh axis is not extremely high only in the response signal subjected to first spreading by a certain ZC sequence. That is, when a response signal is subject to two-dimensional spreading on both the cyclic shift axis and the Walsh axis, it may be preferable to reduce the average multiplexing level on the Walsh axis and equalize (unify) the multiplexing levels on the Walsh axis between ZC sequences. 
     That is, the present embodiment controls ZC sequences and Walsh sequences based on the association shown in  FIG. 13 . That is, control section  209  controls the cyclic shift value of a ZC sequence that is used for first spreading in spreading section  214  and a Walsh sequence that is used for second spreading in spreading section  217  based on the association shown in  FIG. 13 . 
     Here, in CCE #1 to CCE #12 associated with PUCCH #1 to PUCCH #12 shown in  FIG. 13 , probability P to use physical resources for response signals (i.e. physical resources for PUCCH) corresponding to the CCE numbers or the priority level of CCEs decreases in order from CCE #1, CCE #2, . . . , CCE #11 and CCE #12. That is, when the CCE number increases, the above probability P monotonically decreases. Therefore, the present embodiment associates PUCCHs with ZC sequences and Walsh sequences, as shown in  FIG. 13 . 
     That is, referring to the first and second rows along the Walsh axis (i.e. W #0 and W #1) in  FIG. 13 , PUCCH #1 and PUCCH #6 are multiplexed, and PUCCH #2 and PUCCH #5 are multiplexed. Therefore, the sum of the PUCCH numbers of PUCCH #1 and PUCCH #6, “7,” is equal to the sum of the PUCCH numbers of PUCCH #2 and PUCCH #5, “7.” That is, on the Walsh axis, PUCCHs of low numbers and PUCCHs of high numbers are associated and allocated. The same applies to PUCCH #3, PUCCH #4, and PUCCH #7 to PUCCH #12. Further, the same applies to the third row (W #2) and fourth row (W #3) on the Walsh axis. That is, in  FIG. 13 , between adjacent ZC sequences, the sum of the PUCCH numbers (i.e. the sum of the CCE numbers) of adjacent Walsh sequences is equal. Therefore, in  FIG. 13 , the average multiplexing levels on the Walsh axis are substantially equal (substantially uniform). 
     Also, to equalize (unify) the multiplexing level on the Walsh axis between ZC sequences when the difference between the cyclic shift values of ZC sequences associated with the same Walsh sequence is “2” (in  FIG. 9 ), it is preferable to control ZC sequences and Walsh sequences based on the association shown in  FIG. 14 . 
     In CCE #1 to CCE #24 associated with PUCCH #1 to PUCCH #24 shown in  FIG. 14 , probability P to use physical resources for response signals corresponding to the CCE numbers or the priority level of CCEs decreases in order from CCE #1, CCE #2, . . . , CCE #23 and CCE #24. That is, as described above, when the CCE number increases, the above probability P monotonically decreases. 
     Referring to the first and third rows on the Walsh axis (i.e. W #0 and W #2) in  FIG. 14 , PUCCH #1 and PUCCH #18 are multiplexed, and PUCCH #2 and PUCCH #17 are multiplexed. Therefore, the sum of the PUCCH numbers of PUCCH #1 and PUCCH #18, “19,” is equal to the sum of the PUCCH numbers of PUCCH #2 and PUCCH #17, “19.” Also, referring to the second and fourth rows along the Walsh axis (i.e. W #1 and W #3) in  FIG. 14 , PUCCH #12 and PUCCH #19 are multiplexed, and PUCCH #11 and PUCCH #20 are multiplexed. Therefore, the sum of the PUCCH numbers of PUCCH #12 and PUCCH #19, “31,” is equal to the sum of the PUCCH numbers of PUCCH #11 and PUCCH #20, “31”. That is, on the Walsh axis, PUCCHs of low numbers and PUCCHs of the high numbers are associated and allocated. The same applies to PUCCH #3 to PUCCH #10, PUCCH #13 to PUCCH #16 and PUCCH #21 to PUCCH #24. That is, in  FIG. 14 , similar to  FIG. 13 , between adjacent ZC sequences, the sum of the PUCCH numbers (i.e. the sum of the CCE numbers) of adjacent Walsh sequences is equal. Therefore, in  FIG. 14 , similar to  FIG. 13 , the average multiplexing levels on the Walsh axis are substantially equal (substantially uniform). 
     Thus, the present embodiment associates PUCCHs (i.e., CCEs) with sequences that are used for two-dimensional spreading, based on probability P to use physical resources for response signals corresponding to the CCE numbers or the priority level of CCEs. By this means, the average multiplexing level on the Walsh axis, that is, the expected values of the number of multiplexed PUCCHs on the Walsh axis are substantially equal (or substantially uniform). Thus, according to the present embodiment, the multiplexing level on the Walsh axis is not extremely high only in a response signal subjected to first spreading by a certain ZC sequence, so that it is possible to minimize the influence when orthogonality between Walsh sequences collapses. Therefore, according to the present embodiment, it is possible to further suppress the degradation of the separation performance of response signals subjected to code-multiplexing by second spreading. 
     Embodiments of the present invention have been described above. 
     Also,  FIG. 7 ,  FIG. 9 ,  FIG. 10 ,  FIG. 12 ,  FIG. 13  and  FIG. 14  illustrate a case of using four Walsh sequences of W #0 to W #3. But, in case of using two, three, five or more Walsh sequences, it is equally possible to implement the present invention in the same way as above. 
     Also, the above embodiment shows a configuration to compensate inter-code interference between Walsh sequences by the spreading gain of ZC sequence. But, the present invention is applicable not only to cases where complete orthogonal sequences such as Walsh sequences are used for second spreading, but is also to cases where, for example, incomplete orthogonal sequences such as PN sequences are used for second spreading. In this case, inter-code interference due to the incomplete orthogonality of PN sequences is compensated by a spreading gain of ZC sequence. That is, the present invention is applicable to any radio communication apparatuses that use sequences, which can be separated from each other because of different cyclic shift values, for first spreading and sequences, which can be separated because of differences of sequences, for second spreading. 
     Also, a case has been described above with the embodiments where a plurality of response signals from a plurality of mobile stations are code-multiplexed. But, it is equally possible to implement the present invention even when a plurality of reference signals (e.g. pilot signals) from a plurality of mobile stations are code-multiplexed. As shown in  FIG. 15 , when three symbols of reference signals R 0 , R 1  and R 2 , are generated from a ZC sequence (with a sequence length of 12), first, the ZC sequence is subjected to an IFFT in association with orthogonal sequences (F 0 , F 1 , F 2 ) with a sequence length of 3. By this IFFT, it is possible to acquire a ZC sequence with a sequence length of 12 in the time domain. Then, the signal subjected to an IFFT is spread using orthogonal sequences (F 0 , F 1 , F 2 ). That is, one reference signal (i.e. ZC sequence) is allocated to three symbols R 0 , R 1  and R 2 . Similarly, other mobile stations allocate one reference signal (i.e. ZC sequence) to three symbols R 0 , R 1  and R 2 . Here, individual mobile stations use ZC sequences, cyclic shift values of which are different in the time domain, or different orthogonal sequences. Here, the sequence length of ZC sequences in the time domain is 12, so that it is possible to use twelve ZC sequences with cyclic shift values “0” to “11,” generated from the same ZC sequence. Also, the sequence length of orthogonal sequences is 3, so that it is possible to use three different orthogonal sequences. Therefore, in an ideal communication environment, it is possible to code-multiplex maximum thirty-six (12×3) reference signals from mobile stations. 
     Also, a PUCCH used in the above-described embodiments is a channel to feed back an ACK or NACK, and therefore may be referred to as an “ACK/NACK channel.” 
     Also, a mobile station may be referred to as “UE,” a base station may be referred to as “Node B,” and a subcarrier may be referred to as a “tone.” Also, a CP may be referred to as a “GI (Guard Interval).” 
     Also, the method of detecting an error is not limited to a CRC. 
     Also, a method of performing transformation between the frequency domain and the time domain is not limited to IFFT and FFT. 
     Also, a case has been described with the above-described embodiments where the present invention is applied to mobile stations. But, the present invention is also applicable to a fixed radio communication terminal apparatus in a stationary state and a radio communication relay station apparatus that performs the same operations with a base station as a mobile station. That is, the present invention is applicable to all radio communication apparatuses. 
     Although a case has been described with the above embodiments as an example where the present invention is implemented with hardware, the present invention can be implemented with software. 
     Furthermore, each function block employed in the description of each of the aforementioned embodiments may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip. “LSI” is adopted here but this may also be referred to as “IC,” “system LSI,” “super LSI,” or “ultra LSI” depending on differing extents of integration. 
     Further, the method of circuit integration is not limited to LSI&#39;s, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of an FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells in an LSI can be reconfigured is also possible. 
     Further, if integrated circuit technology comes out to replace LSI&#39;s as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Application of biotechnology is also possible. 
     The disclosures of Japanese Patent Application No. 2007-159580, filed on Jun. 15, 2007, and Japanese Patent Application No. 2007-161966, filed on Jun. 19, 2007, including the specifications, drawings and abstracts, are incorporated herein by reference in their entireties. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to, for example, mobile communication systems.