Patent Publication Number: US-2023144340-A1

Title: Base station device, and mobile station device

Description:
TECHNICAL FIELD 
     The present invention relates to a base station apparatus and a mobile station apparatus that performs a cell search based on a signal from that base station apparatus. 
     BACKGROUND ART 
     When powered on or during handover, a mobile station such as a mobile phone can communicate by appropriately selecting and using a cell (base station). Selection of a cell by a mobile station is called a cell search. In a cell search, a mobile station selects the optimal cell to be connected to when powered on. Specifically, each cell is identified by a unique scrambling code, and a cell search is performed by a mobile station detecting the scrambling code of the cell that transmits the signal with the greatest received power in a downlink. 
     A conventional technology related to this is a three-step initial cell search method in OFCDM (Orthogonal Frequency and Code Division Multiplexing) (see Patent Document 1, for example). 
     With the conventional technology described in Patent Document 1, scrambling codes can be fast detected by grouping scrambling codes into a number of groups. Specifically, in the first step, symbol timing is detected by means of guard interval correlation; in the second step, frame timing and a code group are simultaneously detected by calculating correlations between temporally adjacent OFDM symbols; and in the third step, a scrambling code is identified by means of correlation calculation from between pilot symbol and scrambling code candidates belonging to the code group detected in the second step. 
       FIG.  1    shows a conventional OFCDM frame configuration. As shown in  FIG.  1   , there are consecutive pilot symbols in the time domain at a frame boundary, and a code group sequence indicating a scrambling code group is multiplied by a frame-end pilot symbol. 
       FIG.  2    shows conventional second-step processing of a cell search performed by a mobile station. The mobile station performs frame timing and scrambling code group detection by calculating correlations between a sequence extracted by differential demodulation between adjacent symbols and a code group sequence of all code group candidates. A code group and frame timing are detected simultaneously by detecting the code group and timing for which the maximum correlation value between these adjacent pilot symbols is calculated. 
     Patent Document 1: Unexamined Japanese Patent Publication No. 2003-244763 
     BRIEF SUMMARY 
     Problems to be Solved by the Invention 
     However, a problem with the conventional technology is that, since a scrambling code group is identified using all code group candidates in the second step, and a scrambling code is identified in the third step by calculating correlations using all scrambling code candidates belonging to the identified scrambling code group, there is an increased amount of calculation until scrambling code identification. 
     According to one aspect, the present invention provides a base station apparatus and mobile station apparatus that enable cell search processing to be alleviated. 
     Means for Solving the Problems 
     A base station apparatus of the present invention employs a configuration that includes: a frame forming section that forms a frame by arranging a pilot symbol multiplied by a plurality of sequences contained in a sequence set corresponding to a code group to which a base station scrambling code assigned to that apparatus belongs at at least the start or end; and a transmitting section that transmits the formed frame. 
     A mobile station apparatus of the present invention employs a configuration that includes: a receiving section that receives a frame in which a pilot symbol multiplied by a plurality of sequences contained in a sequence set corresponding to a code group to which a base station scrambling code belongs is arranged at at least the start or end; a correspondence table in which the base station scrambling code and the sequence set are mutually associated; a correlation section that multiplies all the sequence candidates by the frame and calculates correlations; a sequence set detection section that detects frame timing and a plurality of sequences multiplied by the pilot symbol based on correlation values calculated by the correlation section; and a base station scrambling code detection section that identifies scrambling code candidates corresponding to the sequence set containing the detected sequences, and detects the base station scrambling code from among the scrambling code candidates. 
     Advantageous Effect of the Invention 
     According to the present invention, a base station apparatus and mobile station apparatus can be provided that enable cell search processing to be alleviated. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG.  1    is a drawing showing the transmission frame structure of a conventional base station apparatus; 
         FIG.  2    is a drawing showing a cell search operation of a conventional mobile station apparatus; 
         FIG.  3    is a block diagram showing the configuration of a base station apparatus according to Embodiment 1 of the present invention; 
         FIG.  4    is a drawing showing a sample configuration of a correspondence table of Embodiment 1; 
         FIG.  5    is a drawing explaining a frame configuration of Embodiment 1; 
         FIG.  6    is a block diagram showing the configuration of a mobile station apparatus according to Embodiment 1; 
         FIG.  7    is a drawing explaining the operation of the adjacent symbol correlation section and code group sequence correlation section in  FIG.  6   ; 
         FIG.  8    is a flowchart explaining the operation of the mobile station apparatus in  FIG.  6   ; 
         FIG.  9    is a block diagram showing the configuration of a mobile station apparatus according to Embodiment 2; 
         FIG.  10    is a flowchart explaining the operation of the mobile station apparatus in  FIG.  9   ; 
         FIG.  11    is a block diagram showing the configuration of a base station apparatus according to Embodiment 3; 
         FIG.  12    is a drawing explaining a frame configuration of Embodiment 3; 
         FIG.  13    is a block diagram showing the configuration of a mobile station apparatus according to Embodiment 3; 
         FIG.  14    is a flowchart explaining the operation of the mobile station apparatus in  FIG.  13   ; 
         FIG.  15    is a block diagram showing the configuration of a mobile station apparatus according to Embodiment 4; 
         FIG.  16    is a block diagram showing the configuration of a mobile station apparatus according to Embodiment 5; 
         FIG.  17    is a drawing showing a sample configuration of a correspondence table of Embodiment 5; 
         FIG.  18    is a flowchart explaining the operation of the mobile station apparatus in  FIG.  16   ; and 
         FIG.  19    is a block diagram showing the configuration of a mobile station apparatus according to Embodiment 6. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the embodiments, identical components are assigned the same reference numerals, and duplicate descriptions thereof are omitted. 
     Embodiment 1 
     As shown in  FIG.  3   , a base station apparatus  100  of Embodiment 1 has a coding section  105 , a modulation section  110 , a pilot signal generation section  115 , a code group sequence generation section  120 , a code group sequence multiplication section  125 , a frame configuration section  130 , a scrambling code generation section  135 , a scrambling section  140 , an IFFT section  145 , a GI insertion section  150 , a radio transmission section  155 , a radio reception section  160 , a GI removal section  165 , an FFT section  170 , a demodulation section  175 , and a decoding section  180 . 
     Coding section  105  has a transmit signal (DCH or the like) as input, performs predetermined coding, and outputs a coded signal to modulation section  110 . 
     Modulation section  110  has the coded signal from coding section  105  as input, performs predetermined primary modulation (generally, primary modulation according to the transmit signal QoS or radio channel state) in subcarrier units, and outputs a modulated signal to frame configuration section  130 . 
     Pilot signal generation section  115  generates a pilot signal (CPICH) common to all cells, and outputs the generated pilot signal to code group sequence multiplication section  125 . 
     Code group sequence generation section  120  has a scrambling code number as input from scrambling code generation section  135 . Then code group sequence generation section  120  references a scrambling code number/code group sequence set correspondence table (see  FIG.  4   ), and selects a code group sequence set to be multiplied by a frame-end pilot (CPICH). Code group sequence generation section  120  then outputs the selected scrambling code group sequence set to code group sequence multiplication section  125 . Here, the correspondence table shown in  FIG.  4    indicates the correspondence between a scrambling code unique to each base station apparatus  100  and a code group sequence set assigned to that scrambling code. This code group sequence set is composed of a plurality of code group sequences (which may be of one type). Code group sequences used in this embodiment are mutually-orthogonal orthogonal sequences. Here, code group sequences in a conventional system are used, but this is not a limitation, and any orthogonal sequences that are mutually orthogonal may be used. However, using orthogonal sequences already provided in a conventional system obviates the necessity of preparing orthogonal sequences for a system of this embodiment, enabling the system construction workload to be alleviated. 
     Code group sequence multiplication section  125  has a code group sequence set from code group sequence generation section  120  as input. Then code group sequence multiplication section  125  multiplies the pilot signal from pilot signal generation section  115  by all the code group sequences composing the code group sequence set. Code group sequence multiplication section  125  then outputs two sequences—the pilot signal itself, and a sequence in which the pilot signal has been multiplied by the code group sequences—to frame configuration section  130 . 
     Frame configuration section  130  has a modulated signal as input from modulation section  110 , and also has a pilot signal and a pilot signal multiplied by code group sequences as input from code group sequence multiplication section  125 . Then frame configuration section  130  forms a frame having a configuration in which a pilot signal is arranged at the start, and a pilot signal multiplied by code group sequences at the end, and a modulated signal (data) is arranged in the remainder (see  FIG.  5   ). Frame configuration section  130  then outputs an OFDM symbol with an OFDM symbol that is subcarrier number N symbols as a unit. 
     Scrambling code generation section  135  generates a scrambling code according to the scrambling code number unique to base station apparatus  100 . Then scrambling code generation section  135  outputs the scrambling code number to code group sequence generation section  120 , and also outputs the generated scrambling code to scrambling section  140 . 
     Scrambling section  140  has a scrambling code as input from scrambling code generation section  135  and also has transmit data as input from frame configuration section  130  in OFDM symbol units, and performs scrambling by multiplying each OFDM symbol by the scrambling code. The scrambled transmission data is output to IFFT section  145 . 
     IFFT section  145  has the scrambled transmission data as input from scrambling section  140 , generates a multicarrier signal by converting the frequency-domain signal to a time-domain signal, and outputs the multicarrier signal to GI (Guard Interval) insertion section  150 . 
     GI insertion section  150  inserts a guard interval for each OFDM symbol, and outputs a signal to which the guard interval is inserted, to radio transmission section  155 . 
     Radio transmission section  155  has the signal to which the guard interval is inserted, as input from GI insertion section  150 , performs RF processing such as up-conversion, and transmits the resulting signal via an antenna. 
     Radio reception section  160  receives a signal from a mobile station apparatus via the antenna, performs RF processing such as down-conversion, and outputs a signal that has undergone RF processing to GI removal section  165 . 
     GI removal section  165  has the signal that has undergone RF processing as input from radio reception section  160 , removes the guard interval, and outputs the resulting signal to FFT section  170 . 
     FFT section  170  has the received OFDM signal that has undergone guard interval removal as input from radio reception section  160 , converts the time-domain signal to a frequency-domain signal, and extracts subcarrier signals from the multicarrier signal. Then a signal that has undergone FFT processing is output to demodulation section  175 . 
     Demodulation section  175  has the signal that has undergone FFT processing as input from FFT section  170 , and performs demodulation on a subcarrier-by-subcarrier basis. After subcarrier demodulation, the signal is output to decoding section  180 . 
     Decoding section  180  has the demodulated signal as input from demodulation section  175 , performs appropriate error correction decoding, and extracts a received signal. 
     As shown in  FIG.  6   , a mobile station apparatus  200  of Embodiment 1 has a reception control section  205 , a radio reception section  210 , a symbol timing detection section  215 , a GI removal section  220 , an FFT processing section  225 , an adjacent symbol correlation section  230 , a code group sequence replica generation section  235 , a code group sequence correlation section  240 , a frame timing/code group detection section  245 , a scrambling code identification section  250 , a scrambling code replica generation section  255 , a descrambling section  260 , a decoding section  265 , a CRC check section  270 , a coding section  275 , a modulation section  280 , a GI insertion section  285 , and a radio transmission section  290 . 
     Reception control section  205  performs control relating to the output destination of an output signal from radio reception section  210  according to the state of mobile station apparatus  200 —that is, according to which step of the initial cell search mode is in effect, or whether normal receive mode is in effect—or the success or failure of code identification. Specifically, reception control section  205  controls the output destination of an output signal from radio reception section  210  by outputting an output destination directive signal to radio reception section  210 . This output destination directive signal indicates that symbol timing detection section  215  is the output destination when the state of mobile station apparatus  200  is the first step of the initial cell search mode, or indicates that GI removal section  220  is the output destination when the state of mobile station apparatus  200  is other than the first step. 
     Radio reception section  210  receives a signal from base station apparatus  100  via an antenna, and performs RF processing such as down-conversion. Then radio reception section  210  outputs a signal that has undergone RF processing to the output destination indicated by the above-described output destination directive signal from reception control section  205 . 
     Symbol timing detection section  215  has as input a signal that has undergone RF processing from radio reception section  210  when the mobile station apparatus is in the initial cell search mode. Symbol timing detection section  215  calculates guard interval correlation and detects OFDM symbol timing using the correlation characteristic of guard intervals in OFDM symbols. That is to say, this OFDM symbol timing is FFT window timing for implementing FFT. While guard interval correlation is executed in symbol units, the accuracy of symbol timing detection can be increased by averaging correlation values over one frame. Then symbol timing detection section  215  outputs the detected symbol timing result to GI removal section  220 , and also outputs to reception control section  205  a first step end report signal reporting that symbol timing has been detected—that is, the first step of the cell search has ended. 
     GI removal section  220  removes guard intervals from a received signal that has undergone RF processing in accordance with the OFDM symbol timing from symbol timing detection section  215 , and outputs the signal to FFT processing section  225 . 
     FFT processing section  225  has a received signal that has undergone guard interval removal from GI removal section  220  as input in OFDM symbol units, and executes FFT processing on this input signal. Then FFT processing section  225  outputs a signal that has undergone FFT processing to an output destination in accordance with the output destination directive signal from reception control section  205 . Specifically, when the current state of mobile station apparatus  200  is the second step of a cell search, FFT processing section  225  has as input an output destination directive signal indicating that adjacent symbol correlation section  230  is the output destination, and outputs a signal that has undergone FFT processing to adjacent symbol correlation section  230 . On the other hand, when the current state of mobile station apparatus  200  is the third step of a cell search, FFT processing section  225  has as input an output destination directive signal indicating that scrambling code identification section  250  is the output destination, and outputs an OFDM symbol containing a pilot signal that has undergone FFT processing and that is arranged at the start of a frame to scrambling code identification section  250 . Only a scrambling code is multiplied by this OFDM symbol containing a pilot signal arranged at the start of a frame, and any code group sequences is not multiplied. Alternatively, when an output destination directive signal other than an output destination directive signal indicating that adjacent symbol correlation section  230  is the output destination or an output destination directive signal indicating that scrambling code identification section  250  is the output destination is input from reception control section  205 , FFT processing section  225  outputs a signal that has undergone FFT processing to descrambling section  260 . 
     Adjacent symbol correlation section  230  has a signal that has undergone FFT processing as input from FFT processing section  225 , and calculates a correlation sequence with correlation calculated between two temporally consecutive OFDM symbols (see  FIG.  7   ). This correlation sequence calculation is performed over n frames in order to subsequently average correlation values between correlation sequence and code group sequence replica. A calculated correlation sequence is then output to code group sequence correlation section  240 . 
     Code group sequence replica generation section  235  generates all the code group sequences calculated beforehand in the system, and outputs these to code group sequence correlation section  240 . 
     As shown in  FIG.  7   , code group sequence correlation section  240  has a correlation sequence calculated by adjacent symbol correlation section  230  and code group sequences from code group sequence replica generation section  235  as input, and calculates correlations between the correlation sequence and all the code group sequences. This correlation computation is performed for n frames, and an average is calculated for n correlation values calculated from a correlation sequence and code group sequences calculated from OFDM symbols having the same temporal position in the frames. Then code group sequence correlation section  240  outputs all the averaged correlation values to frame timing/code group detection section  245 . 
     Frame timing/code group detection section  245  has averaged correlation values as input from code group sequence correlation section  240 , and detects the maximum correlation value giving the largest value among these. Then frame timing/code group detection section  245  stores the timing in the frame at which the maximum correlation value is calculated and the code group sequence used in multiplication when that maximum correlation value is calculated. 
     Then frame timing/code group detection section  245  calculates a threshold value used to detect other code group sequences of a code group sequence set by means of a predetermined method from the value of the maximum correlation value. Specifically, for example, a value calculated by subtracting a predetermined value X [dB] from the value of the maximum correlation value is used as the above-mentioned threshold value. Then, using the calculated threshold value, frame timing/code group detection section  245  detects the largest correlation value from among correlation values exceeding this threshold value among the remaining correlation values. Then the timing in the frame corresponding to the correlation value—excluding the above-mentioned stored maximum correlation value—having the largest value and having a value exceeding the threshold value, and the code group sequence used in multiplication when this correlation value is calculated, are stored. If there is no correlation value exceeding the threshold value other than the maximum correlation value, the code group sequence set multiplied in base station apparatus  100  that transmits a frame includes code group sequence of one type. In this case, frame timing/code group detection section  245  outputs the timing in the frame at which the previously stored maximum correlation value is calculated to reception control section  205 , and outputs the code group sequences corresponding to the maximum correlation value to scrambling code identification section  250 . 
     If there is a correlation value exceeding the threshold value other than the maximum correlation value, frame timing/code group detection section  245  determines whether or not the timing in the frame corresponding to the correlation value—excluding the above-mentioned stored maximum correlation value—having the largest value and having a value exceeding the threshold value, and the timing in the frame at which the maximum correlation value is calculated, coincide. That is to say, frame timing/code group detection section  245  determines whether or not timings corresponding to two large correlation values coincide. In this embodiment, a code group sequence set is assumed to be composed of two code group sequences, and therefore timing in a frame and code group sequences corresponding to these correlation values are detected as described above for two large correlation values. However, the number of code group sequences composing a code group sequence set is not limited to two, and may be greater than two. In this case, the number of correlation values detected should be increased according to the number of code group sequences. 
     If the result of the determination is that the timings corresponding to the above two correlation values do not coincide, frame timing/code group detection section  245  determines that the second step of the cell search has failed, and outputs a second step failure indicator that the second step has failed to reception control section  205 . The reason for determining that the second step of the cell search has failed if the timings corresponding to the above two correlation values do not coincide is that, since a pilot signal arranged in a frame-end OFDM symbol is multiplied by a code group-sequence set in base station apparatus  100 , it is necessary for the timings corresponding to the above two correlation values to coincide in order for the successful second step of the cell search. 
     On the other hand, if the result of the determination is that the timings corresponding to the above two correlation values coincide, frame timing/code group detection section  245  determines that second-step frame timing detection has succeeded, outputs the detected frame timing to reception control section  205 , and also outputs code group sequence identification information (for example, a code group sequences number) identifying the code group sequences corresponding to the detected two correlation values to scrambling code identification section  250 . In this embodiment, scrambling code candidates have already been narrowed down to two in the step leading to the third step, and the amount of processing is reduced compared with a conventional cell search method in which scrambling codes are only narrowed down to  16  corresponding to scrambling codes identified in the second step in the step leading to the third step. 
     Scrambling code identification section  250  identifies a scrambling code corresponding to the code group sequence identification information from frame timing/code group detection section  245 . 
     Specifically, if code group sequence identification information from frame timing/code group detection section  245  is of only one type, a scrambling code corresponding to this code group sequences identification information can be uniquely identified, and therefore identification information for the identified scrambling code is output to scrambling code replica generation section  255 , and a scrambling code replica generated accordingly is output to descrambling section  260 . 
     On the other hand, if code group sequence identification information from frame timing/code group detection section  245  is of two types, there are two scrambling code candidates identified from a combination of these code group sequences. Thus, identification information for these two scrambling code candidates is output to scrambling code replica generation section  255 , and scrambling code replicas generated accordingly are received. Then scrambling code identification section  250  calculates correlations by multiplying the respective scrambling code replicas received from scrambling code replica generation section  255  by an OFDM symbol containing a pilot signal located at the start of a frame received from FFT processing section  225 . Then the scrambling code replica for which the largest value is calculated among the calculated correlation values is identified as the scrambling code, and the identified scrambling code is output to descrambling section  260 . 
     There are various methods of performing scrambling code identification in scrambling code identification section  250 . For example, it is also possible to receive OFDM symbols containing a pilot signal located at the start of a frame, over n frames from FFT processing section  225 , calculate correlations by multiplying these n pilot signals by a scrambling code replica received from scrambling code replica generation section  255 , perform averaging for each correlation result, and identify the scrambling code replica for which the largest averaged correlation value is calculated as the scrambling code. 
     Scrambling code replica generation section  255  generates scrambling codes corresponding to scrambling code identification information from scrambling code identification section  250 , and outputs them to scrambling code identification section  250  as a scrambling code replicas. 
     Descrambling section  260  has a signal that has undergone FFT processing from FFT processing section  225  as input, performs descrambling by multiplying this signal by the scrambling code received from scrambling code identification section  250 , and outputs the descrambled signal to decoding section  265 . 
     Decoding section  265  has the descrambled signal as input, performs appropriate error correction decoding, and outputs the error correction decoding result to CRC check section  270 . 
     CRC check section  270  performs a CRC error check on the error correction decoding result from decoding section  265 , and if there is no error, determines that the initial cell search has been completed. On the other hand, if there is an error, CRC check section  270  outputs the CRC error check result to reception control section  205 , which should redo the initial cell search from the first step. On receiving this CRC error check result output when an error is present, reception control section  205  outputs an output destination directive signal to radio reception section  210  indicating that symbol timing detection section  215  is the output destination. 
     Coding section  275  has a transmit signal such as a DCH as input, executes predetermined coding, and outputs a coded signal to modulation section  280 . 
     Modulation section  280  has the coded signal as input, performs modulation according to the transmission signal QoS or radio channel state, and outputs a modulated signal to radio transmission section  290 . 
     Radio transmission section  290  has the modulated signal as input, performs RF processing such as up-conversion, and transmits the resulting signal via the antenna. 
     The operation of mobile station apparatus  200  having the above-described configuration will now be explained with reference to  FIG.  8   . 
     In step ST 1001 , symbol timing detection section  215  of mobile station apparatus  200  calculates the guard interval correlation, and detects the OFDM symbol timing using the correlation characteristics of OFDM guard interval in individual OFDM symbol. This is the first step of the initial cell search. 
     In step ST 1002  of the second step of the initial cell search, adjacent symbol correlation section  230  has a signal that has undergone FFT processing as input from FFT processing section  225 , and calculates a correlation sequence with correlation calculated between two temporally consecutive OFDM symbols. Correlation sequence calculation is performed at all symbol timings in a frame. 
     In step ST 1003 , code group sequence correlation section  240  has a correlation sequence calculated by adjacent symbol correlation section  230  and code group sequences from code group sequence replica generation section  235  as input, and calculates correlations between the correlation sequence and all the code group sequences. This correlation computation is performed for all symbol timings of n frames. 
     In step ST 1004 , code group sequence correlation section  240  performs averaging for n correlation values calculated between a correlation sequence calculated from OFDM symbols at the same temporal position in a frame and all code group sequences. That is to say, averaging is performed in frame units, and therefore an averaged correlation value for the number of OFDM symbols in one frame is calculated. 
     In step ST 1005 , frame timing/code group detection section  245  has averaged correlation values as input from code group sequence correlation section  240 , and detects the maximum correlation value among them. Then frame timing/code group detection section  245  stores the symbol timing at which the maximum correlation value is calculated and the code group sequence used in multiplication when that maximum correlation value is calculated. 
     The reason for storing the symbol timing at which the maximum correlation value is calculated and the code group sequence used in multiplication when that maximum correlation value is calculated is that this symbol timing position is a frame timing candidate, and this code group sequence is a key for identifying the scrambling code group. As there is no correlation between a pilot signal and transmit data, the correlation value between an OFDM symbol containing a pilot signal and an OFDM symbol containing transmit data is a small value. On the other hand, when the correlation is calculated between OFDM symbols containing ending and starting pilot symbols, and when the correlation is calculated between a code group sequence multiplied by an ending pilot signal and that code group sequence, a large peak appears. Therefore, OFDM symbol timing at which the correlation value between adjacent OFDM symbol correlation and a code group sequence is greatest has a high possibility of being frame timing. Also, a code group sequence giving the maximum correlation value has a high possibility of being a code group sequence multiplied by a pilot signal arranged at the end of a frame in base station apparatus  100  to be accessed. 
     In step ST 1006 , frame timing/code group detection section  245  calculates and sets a threshold value used to detect another code group sequence of a code group sequence set by means of a predetermined method from the value of the maximum correlation value. Specifically, for example, a value calculated by subtracting a predetermined value X [dB] from the maximum correlation value is used as the above-mentioned threshold value. 
     In step ST 1007 , frame timing/code group detection section  245  compares the threshold value calculated in step ST 1006  with above-described averaged correlation values other than the above-described maximum correlation value. 
     If the result of this comparison is that there is a correlation value exceeding the threshold value other than the maximum correlation value (step ST 1007 : YES), that correlation value is detected (step ST 1008 ). 
     In step ST 1009 , frame timing/code group detection section  245  stores the symbol timing of the correlation value detected in step ST 1008 , and the code group sequence used when calculating that correlation value. 
     In step ST 1010 , frame timing/code group detection section  245  compares the symbol timings (in other words, the symbol positions in a virtual frame) corresponding to the top two correlation values (the two correlation values in high-to-low value order) stored in step ST 1005  and step ST 1009 . 
     If the result of the comparison is that the two timings are not the same—that is, do not coincide—(step ST 1010 : NO), frame timing/code group detection section  245  determines that initial cell search second-step frame timing identification has failed, and returns to step ST 1001  by outputting a second step failure indicator that the second step has failed to reception control section  205 . 
     On the other hand, if the result of the comparison is that the two timings coincide (step ST 1010 : YES), frame timing/code group detection section  245  determines that second-step frame timing detection has succeeded, and the relevant frame timing and code group sequences are deemed to have been identified (step ST 1011 ). Then frame timing/code group detection section  245  outputs code group sequence identification information identifying the identified code group sequences to scrambling code identification section  250 . 
     Thus, the success or failure of frame timing identification can be determined based on a comparison of the symbol positions of two correlation values, and if frame timing is determined to have failed, subsequent calculation processing can be abandoned at that point, and initial cell search processing can be retried from the first step. As a result, a cell search can be redone without delay in the event of a failure, enabling fast cell search. 
     Also, if the result of the comparison is that there is no correlation value exceeding the threshold value other than the maximum correlation value (step ST 1007 : NO), the processing flow proceeds to step ST 1011 , and frame timing/code group detection section  245  identifies the items stored in step ST 1005  as the frame timing and code group sequence. Then frame timing/code group detection section  245  outputs code group sequence identification information identifying the identified code group sequence to scrambling code identification section  250 . 
     Next, the processing flow proceeds to the third step of the initial cell search, and in step ST 1012  scrambling code candidates corresponding to the code group sequence identification information from frame timing/code group detection section  245  are identified. Replicas of these candidate scrambling codes are generated sequentially, the correlation between a pilot signal and scrambling code replicas in a received signal of OFDM symbols in which a CPICH is multiplexed is calculated and a maximum correlation value is detected, and the scrambling code for which the maximum correlation value is calculated is identified. 
     Lastly, verification is performed as to whether the identified scrambling code is correct, and if it is incorrect, the processing flow returns to step ST 1001 . The above-described CRC error check or the like, for example, can be used for this error verification. 
     In the above description, it is assumed that a transmitted/received frame is configured with a pilot signal arranged at the start and a pilot signal multiplied by code group sequences arranged at the end, and a modulated signal (data) arranged in the rest of the frame, but frame structure is not limited to this configuration, and a configuration may also be used in which, conversely, a pilot signal multiplied by code group sequences is arranged at the start and a pilot signal is arranged at the end. Also, a pilot signal may occupy only one OFDM symbol in a frame, in which case a pilot symbol may be multiplexed in half of the subcarriers within that one OFDM symbol, and a symbol in which a pilot and code sequences are multiplied may be multiplexed in the other half of the subcarriers. It is only necessary to detect frame timing by arranging both pilot signals on either side of a frame boundary or by arranging a pilot symbol before or after the frame boundary. 
     Thus, according to Embodiment 1, a base station apparatus  100  is equipped with: a frame configuration section  130  that forms a frame by arranging a pilot symbol multiplied by a plurality of (code group) sequences contained in a (code group) sequence set corresponding to a code group to which a base station scrambling code assigned to that apparatus belongs at at least the start or end; and a radio transmission section  155  that transmits the formed frame. 
     By this means, a mobile station that receives an above-described frame can detect frame timing from the position of a pilot symbol contained in that frame, and furthermore candidates are narrowed down to sequences sets of the number of combinations of sequences contained in a sequence set at the most by detecting a sequence set multiplied by a pilot symbol due to the fact that a base station scrambling code and a (code group) sequence set containing a plurality of (code group) sequences are mutually associated, with the result that third-step scrambling code identification processing is alleviated, cell search processing can be alleviated, and a base station scrambling code corresponding to such sequence set candidates can be fast identified. 
     Also, according to Embodiment 1, a mobile station apparatus  200  is equipped with: a radio reception section  210  that receives a frame in which a pilot symbol multiplied by one or a plurality of (code group) sequences contained in a (code group) sequence set corresponding to a code group to which a base station scrambling code belongs is arranged at at least the start or end; a correspondence table in which the base station scrambling code and the sequence set are mutually associated; a code group sequence correlation section  240  (adjacent symbol correlation section  230 ) serving as a correlation section that multiplies all (code group) sequence candidates by the frame and calculates correlations; a frame timing/code group detection section  245  that detects frame timing and one or a plurality of (code group) sequences multiplied by the pilot symbol based on correlation values calculated by the correlation section; and a scrambling code identification section  250  that identifies scrambling code candidates corresponding to the sequence set containing the detected (code group) sequences, and detects the base station scrambling code from among the scrambling code candidates. 
     By this means, frame timing can be detected from the position of a pilot symbol contained in a received frame, and furthermore candidates are narrowed down to spreading code sets of the number of combinations of spreading codes contained in a spreading code set at the most by detecting a code group sequence set multiplied by a pilot symbol due to the fact that a base station scrambling code and a sequence set containing one or a plurality of (code group) sequences are mutually associated, with the result that cell search processing can be alleviated, and a base station scrambling code corresponding to such a spreading code set candidate can be fast identified. 
     Adjacent symbol correlation section  230  and code group sequence correlation section  240  serving as the above-described correlation section calculate correlations by sequentially multiplying all the (code group) sequence candidates by a correlation sequence between temporally adjacent symbols in a received frame, and frame timing/code group detection section  245  identifies only a number equal to the number of (code group) sequences contained in the (code group) sequence set in high-to-low value order from correlation values calculated by the correlation section, and detects symbol timing in the (virtual) frame at which that identified correlation value is calculated and the (code group) sequences used in multiplication when that identified correlation value is calculated as the frame timing and the (code group) sequences multiplied by the pilot symbol. 
     By thus calculating correlations by sequentially multiplying all the (code group) sequence candidates by a correlation sequence between temporally adjacent symbols in a received frame, and detecting frame timing and a sequence using this correlation value, the effect of phase noise added to a received frame in the propagation path or the like can be alleviated, and frame timing and a sequence can be detected more accurately. 
     Embodiment 2 
     In Embodiment 1, correlation values calculated by calculating correlations for a correlation sequence of adjacent OFDM symbols for each code group sequence are averaged for each code group sequence over n frames, after which the top one or two correlation values are detected by means of a threshold value comparison, and the code group sequences used by a base station is identified by detecting the code group sequences used in multiplication when the detected correlation value(s) is/are calculated. In contrast, in Embodiment 2, correlation values calculated by calculating correlations for a correlation sequence of adjacent OFDM symbols for each code group sequence are added for each code group sequence set, the sum of correlation values are averaged over n/2 frames, and then the code group sequence set by which multiplication is performed in order to calculate the largest correlation value among these averaged correlation values is identified. By this means, the scope of averaging processing is halved compared with the averaging processing performed over n frames in Embodiment 1, making a faster initial cell search possible. Also, the SN ratio of OFDM received symbols can be increased by performing adding processing, enabling values with the same high degree of reliability as in Embodiment 1 to be calculated even though the number of frames for which averaging processing is performed is halved, and making it possible to implement a highly reliable fast initial cell search. 
     As shown in  FIG.  9   , a mobile station apparatus  300  of Embodiment 2 has a code group sequence correlation section  310  and a frame timing/code group detection section  320 . 
     Code group sequence correlation section  310  has a correlation sequence calculated by adjacent symbol correlation section  230  and code group sequences from code group sequence replica generation section  235  as input, and calculates correlations between the correlation sequence and all the code group sequences. Then code group sequence correlation section  310  adds correlation values calculated by the above correlation calculation according to combinations corresponding to code group sequence sets. Code group sequence correlation section  310  then averages the sum of correlation values calculated by this addition for each code group sequence set over n/2 frames. Then code group sequence correlation section  310  outputs all the averaged sum of correlation values to frame timing/code group detection section  320 . 
     Frame timing/code group detection section  320  has averaged sum of correlation values as input from code group sequence correlation section  310 , and detects the maximum sum of correlation values giving the largest value among these. Then frame timing/code group detection section  320  identifies the symbol timing (position) at which the maximum sum of correlation values is calculated and the code group sequence set used in multiplication when the maximum sum of correlation values is calculated. 
     Frame timing/code group detection section  320  then outputs information identifying the identified code group sequence set to scrambling code identification section  250 . The information identifying the code group sequence set may be, for example, code group sequence identification information identifying code group sequences composing the code group sequence set, or a scrambling code number corresponding to the code group sequence set. 
     The operation of mobile station apparatus  300  having the above-described configuration will now be explained with reference to  FIG.  10   . 
     In step ST 1003 , code group sequence correlation section  310  has a correlation sequence calculated by adjacent symbol correlation section  230  and code group sequences from code group sequence replica generation section  235  as input, and calculates correlations between the correlation sequence and all the code group sequences. 
     In step ST 2001 , code group sequence correlation section  310  adds correlation values calculated by the above correlation calculation by means of combinations corresponding to code group sequence set on a symbol-by-symbol basis. 
     In step ST 2002 , code group sequence correlation section  310  averages the sum of correlation values calculated by this addition over n/ 2  frames on a symbol-by-symbol basis. Then code group sequence correlation section  310  outputs all the averaged sum of correlation values to frame timing/code group detection section  320 . 
     In step ST 2003 , frame timing/code group detection section  320  has averaged sum of correlation values as input from code group sequence correlation section  310 , and detects the maximum sum of correlation values giving the largest value among them. 
     In step ST 2004 , frame timing/code group detection section  320  identifies the symbol timing at which the maximum sum of correlation values is calculated and the code group sequence set used in multiplication when the maximum sum of correlation values is calculated. 
     Frame timing/code group detection section  320  then outputs information identifying the identified code group sequences set to scrambling code identification section  250 . 
     Thus, according to Embodiment 2, a mobile station apparatus  300  is equipped with: a radio reception section  210  that receives a frame in which a pilot symbol multiplied by a plurality of (code group) sequences contained in a (code group) sequence set corresponding to a base station scrambling code is arranged at at least the start or end; a correspondence table in which the base station scrambling code and the (code group) sequence set are mutually associated (see  FIG.  4   ); an adjacent symbol correlation section  230  and code group sequence correlation section  310  that calculate correlation values by successively multiplying all the (code group) sequence candidates by a correlation sequence between temporally adjacent symbols in the frame; a frame timing/code group detection section  320  that detects frame timing and (code group) sequences multiplied by the pilot symbol based on the correlation values; and a scrambling code identification section  250  that determines scrambling code candidates corresponding to the (code group) sequence set containing the detected (code group) sequences from the correspondence table, and detects the base station scrambling code from among the scrambling code candidates. 
     By this means, the SN ratio of a received symbol can be increased by performing correlation value adding processing within one symbol, enabling highly reliable values to be calculated even though the number of averaged frames is halved when averaging processing is performed over a plurality of frames, and making it possible to implement fast cell search. 
     Embodiment 3 
     In Embodiment 1, code group sequence multiplication of all code group sequences composing a code group sequence set is performed for all subcarriers in a frame-end OFDM symbol in base station apparatus  100 . In contrast, in Embodiment 3, subcarriers in a frame-end OFDM symbol are divided into a plurality of subcarrier blocks in a base station apparatus, and multiplication is performed for a plurality of code group sequences corresponding to a code group sequence set for each of these subcarrier blocks. 
     As shown in  FIG.  11   , a base station apparatus  400  of Embodiment 3 has a code group sequence multiplication section  410  and a frame configuration section  420 . 
     Code group sequence multiplication section  410  has a code group sequence set from code group sequences generation section  120  as input. Then code group sequence multiplication section  410  multiplies the pilot signal from pilot signal generation section  115  by the code group sequences composing the code group sequence set, as a result of which a pilot signal multiplied by each code group sequence is generated. Code group sequence multiplication section  410  then outputs a plurality of sequences including the pilot signal itself and a sequence in which the pilot signal has been multiplied by each code group sequence to frame configuration section  420 . 
     Frame configuration section  420  has a modulated signal as input from modulation section  110 , and also has a pilot signal and a pilot signal multiplied by code group sequences as input from code group sequence multiplication section  410 . Then frame configuration section  420  forms a frame having a configuration in which a pilot signal is arranged at the start, and a pilot signal multiplied by code group sequences at the end, and a modulated signal (data) is arranged in the remainder (see  FIG.  12   ). Furthermore, in a frame formed by this frame configuration section  420 , subcarriers in an OFDM symbol in which the end pilot signal is arranged are divided into several subcarrier blocks, and code group sequences including a code group sequence set are multiplied on a subcarrier-block by subcarrier-block basis. Specifically, in  FIG.  12   , subcarriers are divided into two subcarrier blocks comprising a low-frequency-side subcarrier block  1  and a high-frequency-side subcarrier block  2 , and, for example, code group sequence CG 1  that is a component of the code group sequence set corresponding to scrambling code number C 2  is multiplied by subcarrier block  1 , and CG 2  is multiplied by subcarrier block  2 . 
     To simplify the description, in  FIG.  12    subcarriers are divided into two subcarrier blocks corresponding to the number of code group sequences contained in a code group sequence set. However, this is not a limitation, and subcarriers may also be divided into two subcarrier groups. That is to say, subcarriers by which each code group sequence is multiplied need not be subcarrier blocks that are consecutive in the frequency domain, but may also be arranged in a skipping fashion. In this description, a subcarrier block is one form of subcarrier group. Also, if a code group sequence set corresponds to n code group sequences, the number of subcarrier groups in  FIG.  12    will be n. 
     Frame configuration section  420  then outputs an OFDM symbol with an OFDM symbol that is subcarrier number N symbols as a unit. 
     As shown in  FIG.  13   , a mobile station apparatus  500  of Embodiment 3 has an adjacent symbol correlation section  510 , a code group sequence correlation section  520 , and a frame timing/code group detection section  530 . 
     Adjacent symbol correlation section  510  has a signal that has undergone FFT processing as input from FFT processing section  225 , and calculates a correlation sequence with correlation calculated between two temporally consecutive OFDM symbols. This correlation sequence calculation is performed over n frames in order to perform subsequent averaging. A calculated correlation sequence is then output to code group sequence correlation section  520 . 
     Code group sequence correlation section  520  has a correlation sequence calculated by adjacent symbol correlation section  510  and code group sequences from code group sequence replica generation section  235  as input, and calculates correlations between the correlation sequence and all the code group sequences. Here, unlike in Embodiment 1, correlations are calculated on a subcarrier-block by subcarrier-block basis. That is to say, in Embodiment 3, the code group sequence length is half that in Embodiment 1. 
     This correlation calculation is performed for n frames, and code group sequence correlation section  520  calculates an average for n correlation values calculated from a correlation sequence and code group sequences calculated from OFDM symbols having the same temporal position in the frames. Then code group sequence correlation section  520  outputs all the correlation values averaged on a subcarrier-block by subcarrier-block basis to frame timing/code group detection section  530 . 
     Frame timing/code group detection section  530  has correlation values averaged on a subcarrier-block by subcarrier-block basis as input from code group sequence correlation section  520 , and detects the maximum correlation value giving the largest value for each subcarrier block. Then frame timing/code group detection section  530  stores the symbol timing (in a virtual frame) at which the maximum correlation value is calculated and the code group sequences used in multiplication when that maximum correlation value is calculated. 
     Also, frame timing/code group detection section  530  determines whether or not timings (in a frame) at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated coincide. 
     If the result of the determination is that timings in a frame at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated do not coincide, frame timing/code group detection section  530  determines that frame timing detection in the second step of the initial cell search has failed, and outputs a second step failure indicator that the second step has failed to reception control section  205 . 
     On the other hand, if the result of the determination is that timings (in a frame) at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated coincide, frame timing/code group detection section  530  determines that second-step frame timing detection has succeeded, outputs the detected frame timing to reception control section  205 , and also outputs code group sequence indicator identifying the detected code group sequences to scrambling code identification section  250 . 
     The operation of mobile station apparatus  500  having the above-described configuration will now be explained with reference to  FIG.  14   . 
     In step ST 3001 , code group sequence correlation section  520  has a correlation sequence calculated by adjacent symbol correlation section  510  and code group sequences from code group sequence replica generation section  235  as input, and calculates correlations between the correlation sequence and all the code group sequences. Here, this correlation calculation is performed on a subcarrier-block by subcarrier-block basis. 
     In step ST 3002 , code group sequence correlation section  520  performs averaging for each identical subcarrier block for n correlation values calculated between a correlation sequence calculated from OFDM symbols at the same temporal position in a frame and code group sequences. 
     In step ST 3003 , frame timing/code group detection section  530  has correlation values averaged on a subcarrier-block by subcarrier-block basis as input from code group sequence correlation section  520 , and detects the maximum correlation value for each subcarrier block. 
     In step ST 3004 , frame timing/code group detection section  530  determines whether or not timings at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated coincide. 
     If the result of the determination is that timings at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated do not coincide (step ST 3004 : NO), frame timing/code group detection section  530  determines that frame timing detection in the second step of the initial cell search has failed, and returns to step ST 1001  by outputting a second step failure indicator that the second step has failed to reception control section  205 . 
     On the other hand, if the result of the determination is that timings at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated coincide (step ST 3004 : YES), frame timing/code group detection section  530  determines that second-step frame timing detection has succeeded, and the relevant frame timing and code group sequences are deemed to have been identified (step ST 1011 ). Then frame timing/code group detection section  530  outputs the detected frame timing to reception control section  205 , and also outputs code group sequence indicator identifying the detected code group sequences to scrambling code identification section  250 . 
     In the above description, it has been assumed that there is orthogonality between a scrambling code and code group sequences that are component of a code group sequence set. However, in this embodiment, code group sequence used in multiplication differs for each subcarrier block, and therefore orthogonality between code group sequences is not necessarily essential. 
     Thus, according to Embodiment 3, a base station apparatus  400  is equipped with: a frame configuration section  420  that forms a frame in which a plurality of subcarriers are divided into a plurality of groups, and, for each group, a pilot symbol multiplied, one at a time, by (code group) sequences contained in a (code group) sequence set corresponding to a base station scrambling code assigned to that apparatus is arranged at at least the start or end; and a radio transmission section  155  that transmits the formed frame. 
     A mobile station that receives an above-described frame can detect frame timing from the position of a pilot symbol contained in that frame, and furthermore scrambling code candidates are narrowed down to the number of combinations of (code group) sequences contained in a (code group) sequence set at the most by detecting a (code group) sequence multiplied by each subcarrier block of a pilot symbol due to the fact that a base station scrambling code and a (code group) sequence set containing a plurality of (code group) sequences are mutually associated, with the result that cell search processing can be alleviated, and a base station scrambling code corresponding to such a spreading code set candidate can be fast identified. 
     Also, according to Embodiment 3, a mobile station apparatus  500  is equipped with: a radio reception section  210  that receives a frame in which a plurality of subcarriers are divided into a plurality of groups, and, for each subcarrier group, a pilot symbol multiplied, one at a time, by (code group) sequences contained in a (code group) sequence set corresponding to a base station scrambling code is arranged at at least the start or end; a correspondence table in which the base station scrambling code and the (code group) sequence set are mutually associated (see  FIG.  4   ); a code group sequence correlation section  520  (adjacent symbol correlation section  510 ) serving as a correlation section that calculates a correlation sequence by sequentially multiplying all (code group) sequence candidates by each subcarrier group; a frame timing/code group detection section  530  that detects, for each subcarrier group, frame timing and the (code group) sequences multiplied by the pilot symbol based on a correlation value calculated by the correlation section; and a scrambling code identification section  250  that identifies scrambling code candidates corresponding to a combination of detected (code group) sequences from the correspondence table, and detects the base station scrambling code from among the scrambling code candidates. 
     By this means, frame timing can be detected from the position of a pilot symbol contained in a received frame, and furthermore candidates are narrowed down to a (code group) sequence set of the number of combinations of (code group) sequences contained in a (code group) sequence set at the most by detecting a (code group) sequence multiplied by each subcarrier group of a pilot symbol due to the fact that a base station scrambling code is associated as a combination of a plurality of (code group) sequences, a base station scrambling code corresponding to such a (code group) sequence set candidate can be fast identified, and initial cell search processing can be alleviated. 
     Adjacent symbol correlation section  510  and code group sequence correlation section  520  serving as the above-described correlation section calculate correlations by sequentially multiplying all the (code group) sequence candidates by a correlation value between temporally adjacent symbols in a frame, and frame timing/code group detection section  530  detects the maximum correlation value in each subcarrier group from correlation values calculated by the correlation section, and detects the timing at which that detected maximum correlation value is calculated and the code group sequence used in multiplication when the detected maximum correlation value of each subcarrier group is calculated as the frame timing and the (code group) sequence multiplied by each subcarrier group of the pilot symbol. 
     Embodiment 4 
     In Embodiment 3, correlation is calculated for correlation values of adjacent OFDM symbols for each code group sequence and the calculated correlation values are averaged over n frames for each code group sequence and subcarrier block, after which identification is performed of the code group sequences used in multiplication when the largest correlation value is calculated on a subcarrier-block by subcarrier-block basis. In contrast, in Embodiment 4, correlation values calculated by calculating correlations for a correlation sequence of adjacent OFDM symbols for each code group sequence and subcarrier block are added for each code group sequence set, the sum of correlation values are averaged over n/2 frames, and then the code group sequence set by which multiplication is performed in order to calculate the largest correlation value among these averaged correlation values is identified. By this means, the SN ratio of correlation values within one OFDM symbol is improved, and therefore the scope of averaging processing performed over n frames is halved, making a faster cell search possible. Also, since the SN ratio of OFDM received symbols can be increased by performing adding processing, values with the same high degree of reliability as in Embodiment 3 can be calculated even though the number of frames for which averaging processing is performed is halved, and a faster cell search can be implemented. 
     As shown in  FIG.  15   , a mobile station apparatus  600  of Embodiment 4 has a code group sequence correlation section  610  and a frame timing/code group detection section  620 . 
     Code group sequence correlation section  610  has a correlation sequence calculated by adjacent symbol correlation section  510  and code group sequences from code group sequence replica generation section  235  as input, and calculates correlations between the correlation sequence and all the code group sequences. Here, correlation sequence calculation and correlation between the correlation sequence and all the code group sequences are performed on a subcarrier-block by subcarrier-block basis. 
     Then code group sequence correlation section  610  adds correlation values calculated by the above correlation calculation by means of combinations corresponding to code group sequence sets. Code group sequence correlation section  610  then averages the sum of correlation values calculated by this addition for each code group sequence set over n/2 frames. Then code group sequence correlation section  610  outputs all the averaged sum of correlation values to frame timing/code group detection section  620 . 
     Frame timing/code group detection section  620  has averaged sum of correlation values as input from code group sequence correlation section  610 , and detects the maximum sum of correlation values. Then frame timing/code group detection section  620  identifies the timing at which the maximum sum of correlation values is calculated and the code group sequence set used in multiplication when the maximum sum of correlation values is calculated. 
     Frame timing/code group detection section  620  then outputs information identifying the identified code group sequence set to scrambling code identification section  250 . The information identifying the code group sequence set may be, for example, code group sequence indicator identifying code group sequences composing the code group sequence set, or a scrambling code number corresponding to the code group sequence set. 
     In this embodiment, it is basically necessary to identify code group sequences from a sum of correlation values multiplied by a plurality of code group sequences, and it is therefore necessary to maintain orthogonality between code group sequences. 
     Thus, according to Embodiment 4, a mobile station apparatus  600  is equipped with: a radio reception section  210  that receives a frame in which a plurality of subcarriers are divided into a plurality of groups, and, for each subcarrier group, a pilot symbol multiplied, one at a time, by (code group) sequences contained in a (code group) sequence set corresponding to a base station scrambling code is arranged at at least the start or end; a correspondence table in which the base station scrambling code and the (code group) sequence set are mutually associated (see  FIG.  4   ); an adjacent symbol correlation section  510  and a code group sequence correlation section  610  serving as a correlation section that calculates correlations by multiplying all candidates of the (code group) sequences by a correlation sequence between temporally adjacent OFDM symbols in the frame for each subcarrier group and calculates a sum of correlation values by adding the calculated correlation values according to combinations corresponding to the (code group) sequence set; a frame timing/code group detection section  620  that specifies a maximum sum of correlation values from the sum of correlation values and detects a timing in the frame at which the specified maximum sum of correlation values is calculated and the (code group) sequences multiplied upon calculating the specified maximum sum of correlation values as the frame timing and the (code group) sequences multiplied by the pilot symbol; and a scrambling code identification section  250  that determines scrambling code candidates corresponding to the (code group) sequence set containing the detected (code group) sequences from the correspondence table, and detects the base station scrambling code from among the scrambling code candidates. 
     By this means, the SN ratio of received symbols can be increased by performing correlation value adding processing, enabling values with a high degree of reliability to be calculated even though the number of frames for which averaging is performed is halved when averaging processing is performed over a plurality of frames, and making it possible to implement a faster cell search. 
     Embodiment 5 
     In Embodiment 3, correlation is calculated for a correlation sequence of adjacent OFDM symbols for each code group sequence and the calculated correlation values are averaged over n frames for each code group sequence and subcarrier block, after which identification is performed of the code group sequences used in multiplication when the largest correlation value is calculated on a subcarrier-block by subcarrier-block basis. In contrast, in Embodiment 5, a scrambling code can also be identified at the point in time at which a per-subcarrier code group sequence is identified by further mutually associating subcarrier blocks and code group sequences. That is to say, the third step of a cell search can be omitted. 
     As shown in  FIG.  16   , a mobile station apparatus  700  of Embodiment 5 has a frame timing/code group detection section  710  and a scrambling code identification section  720 . 
     Frame timing/code group detection section  710  has correlation values averaged on a subcarrier-block by subcarrier-block basis as input from code group sequence correlation section  520 , and detects the maximum correlation value that gives the largest value for each subcarrier block. Then frame timing/code group detection section  710  stores the timing in a frame at which the maximum correlation value is calculated and the code group sequences used in multiplication when the maximum sum of correlation values is calculated. 
     Also, frame timing/code group detection section  710  determines whether or not timings in a frame at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated coincide. 
     If the result of the determination is that timings in a frame at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated do not coincide, frame timing/code group detection section  710  determines that frame timing detection in the second step of the initial cell search has failed, and outputs a second step failure indicator that the second step has failed to reception control section  205 . 
     On the other hand, if the result of the determination is that timings in a frame at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated coincide, frame timing/code group detection section  710  determines that second-step frame timing detection has succeeded, outputs the detected frame timing to reception control section  205 , and also outputs code group sequence indicator identifying the detected code group sequences, and indicator as to the subcarrier block in which that code group sequence is detected, to scrambling code identification section  720  in mutually associated form. 
     Scrambling code identification section  720  references the table shown in  FIG.  17    and identifies a scrambling code corresponding to the code group sequence indicator and subcarrier block indicator from frame timing/code group detection section  710 , causes scrambling code replica generation section  255  to generate the identified scrambling code, and outputs this to descrambling section  260 . In this embodiment, a base station apparatus multiplies a code group sequence set—that is, code group sequences stipulated for each subcarrier group—based on the base station&#39;s own scrambling code number in accordance with the table in  FIG.  17   . 
     The operation of mobile station apparatus  700  having the above-described configuration will now be explained with reference to  FIG.  18   . 
     If timings in a frame at which maximum correlation values detected on a subcarrier-block by subcarrier-block basis are calculated coincide (step ST 3004 : YES), in step ST 4001  frame timing/code group detection section  710  determines that second-step frame timing detection has succeeded and identifies the frame timing, and scrambling code identification section  720  references the table and identifies a scrambling code corresponding to the code group sequence indicator and subcarrier block indicator from frame timing/code group detection section  710 . 
     In the above description, it has been assumed that there is orthogonality between a scrambling code and code group sequences that are component of a code group sequence set. However, in this embodiment, subcarrier blocks are already orthogonal, and therefore orthogonality between code group sequences is not necessarily essential. 
     Thus, according to Embodiment 5, a mobile station apparatus  700  is equipped with: a radio reception section  210  that receives a frame in which a plurality of subcarriers are divided into a plurality of groups, and, for each subcarrier group, a pilot symbol multiplied, one at a time, by (code group) sequences contained in a (code group) sequence set corresponding to a base station scrambling code is arranged at at least the start or end; a correspondence table in which the base station scrambling code, the (code group) sequence set and indicator for the subcarrier group by which (code group) sequences contained in that (code group) sequence set is multiplied are mutually associated (see  FIG.  17   ); a code group sequence correlation section  520  serving as a correlation section that calculates correlations by sequentially multiplying all (code group) sequences by each subcarrier group; and a frame timing/code group detection section  710  and scrambling code identification section  720  that detect frame timing and (code group) sequences multiplied by the pilot symbol based on per-subcarrier-group correlation values calculated by the correlation section, and identify the base station scrambling code using the correspondence table based on the detected (code group) sequences and indicator for the group in which that (code group) sequences are detected. 
     By this means, subcarrier blocks and code group sequences are further mutually associated as compared with  FIG.  4   , enabling a scrambling code also to be identified at the point in time at which a code group sequence multiplied on a subcarrier-block by subcarrier-block basis is identified. As a result, the step corresponding to the third step of a conventional cell search can be omitted, enabling initial cell search processing to be alleviated, and a still faster cell search to be implemented. 
     Embodiment 6 
     In Embodiment 5, correlation is calculated for correlation values of adjacent OFDM symbols for each code group sequence and the calculated correlation values are averaged over n frames for each code group sequence and subcarrier block, after which identification is performed of the code group sequence used in multiplication when the largest correlation value is calculated on a subcarrier-block by subcarrier-block basis. In contrast, in Embodiment 6, correlation values calculated by calculating correlations for a correlation sequence of adjacent OFDM symbols for each code group sequence and subcarrier block are added for each code group sequence set, taking the correspondence between a subcarrier block and code group sequence into consideration, and the sum of correlation values are averaged over n/2 frames, and then the code group sequence set by which multiplication is performed in order to calculate the largest correlation value among these averaged correlation values is identified. By this means, the SN ratio of correlation values within one OFDM symbol is improved, and therefore the scope of averaging processing performed over n frames is halved, making a faster cell search possible. Also, since the SN ratio of OFDM received symbols can be increased by performing adding processing, values with the same high degree of reliability as in Embodiment 5 can be calculated even though the number of frames for which averaging processing is performed is halved, and a faster cell search can be implemented. “Adding for each code group sequence set, taking the correspondence between a subcarrier block and code group sequence into consideration” means that, even if the combination of code group sequences contained in code group sequence sets is the same, if the correspondence between code group sequences and subcarrier blocks is different, addition is performed with the code group sequence set treated as different code group sequence sets. 
     As shown in  FIG.  19   , a mobile station apparatus  800  of Embodiment 6 has a code group sequence correlation section  810  and a frame timing/code group detection section  820 . 
     Code group sequence correlation section  810  has a correlation sequence calculated by adjacent symbol correlation section  510  and code group sequences from code group sequence replica generation section  235  as input, and calculates correlations between the correlation sequence and all the code group sequences. Here, correlation sequence calculation and correlation calculation between the correlation sequence and all the code group sequences are performed on a subcarrier-block by subcarrier-block basis. 
     Then code group sequence correlation section  810  adds correlation values calculated by the above correlation calculation for each code group sequence set, taking the correspondence between a subcarrier block and code group sequence into consideration. Code group sequence correlation section  810  then averages the sum of correlation values calculated by this addition for each code group sequence set taking the correspondence between a subcarrier block and code group sequence into consideration over n/ 2  frames. Then code group sequence correlation section  810  outputs all the averaged sum of correlation values to frame timing/code group detection section  820 . 
     Frame timing/code group detection section  820  has averaged sum of correlation values as input from code group sequence correlation section  810 , and detects the maximum sum of correlation values. Then frame timing/code group detection section  820  identifies the timing at which the maximum sum of correlation values is calculated and the code group sequence set (taking the correspondence between a subcarrier block and code group sequences into consideration) used in multiplication when the maximum sum of correlation values is calculated. 
     Frame timing/code group detection section  820  then outputs code group sequence indicator identifying the detected code group sequences, and indicator as to the subcarrier block corresponding thereto, to scrambling code identification section  720  in mutually associated form. 
     In this embodiment, it is basically necessary to identify a code group sequence from a sum of correlation values multiplied by a plurality of code group sequences, and it is therefore necessary to maintain orthogonality between code group sequences. 
     Thus, according to Embodiment 6, a mobile station apparatus  800  is equipped with: a radio reception section  210  that receives a frame in which a plurality of subcarriers are divided into a plurality of groups, and, for each subcarrier group, a pilot symbol multiplied, one at a time, by (code group) sequences contained in a (code group) sequence set corresponding to a base station scrambling code is arranged at at least the start or end; a correspondence table in which the base station scrambling code, the (code group) sequence set and indicator for the subcarrier group by which (code group) sequences contained in that (code group) sequence set is multiplied are mutually associated (see  FIG.  17   ); an adjacent symbol correlation section  510  and a code group sequence correlation section  810  serving as a correlation section that calculates correlations by multiplying all candidates of the (code group) sequence by a correlation sequence between temporally adjacent OFDM symbols in the frame for each subcarrier group and calculates a sum of correlation values by adding the calculated correlation values for each (code group) sequence set specified by correspondence between the subcarrier groups and the (code group) sequences corresponding to the (code group) sequence set; a frame timing/code group detection section  820  that specifies a maximum sum of correlation values from the sum of correlation values, and identifies a timing in the frame at which the identified maximum sum of correlation values is calculated and the (code group) sequence set for which the identified maximum sum of correlation values is calculated; and a scrambling code identification section  720  that determines the base station scrambling code corresponding to the identified (code group) sequence set from the correspondence table. 
     By this means, the SN ratio of received symbols can be increased by performing correlation value adding processing, enabling values with a high degree of reliability to be calculated even though the number of frames for which averaging is performed is halved when averaging processing is performed over a plurality of frames, and making it possible to implement a faster cell search. 
     Other Embodiments 
     In Embodiments 1 through 4, when a base station scrambling code is identified in the third step of an initial cell search, a pilot symbol by which group code sequences have not been multiplied and only a base station scrambling code has been multiplied is described as being used. However, the present invention is not limited to this case, and a pilot symbol by which group code sequences have been multiplied (a pilot symbol arranged at the start of a frame in each embodiment) can be used. 
     As a concrete example, a case in which this is applied to Embodiment 1 will be described with reference to  FIG.  3   . 
     In this case, when the current state of mobile station apparatus  200  is the third step of a cell search, FFT processing section  225  has as input an output destination directive signal indicating that scrambling code identification section  250  is the output destination, and outputs an OFDM symbol containing a pilot signal that has undergone FFT processing and containing a pilot signal that is arranged at the end of a frame to scrambling code identification section  250 . 
     Scrambling code identification section  250  performs complex conjugate multiplication of code group sequences identified in the second step, and extracts a pilot signal by which only a scrambling code is multiplied. 
     The present application is based on Japanese Patent Application No. 2005-198608 filed on Jul. 7, 2005, the entire content of which is expressly incorporated herein by reference. 
     INDUSTRIAL APPLICABILITY 
     A base station apparatus and mobile station apparatus of the present invention are useful in enabling cell search processing to be alleviated.