Patent Publication Number: US-9413499-B2

Title: Code multiplexing transmission method, transmission apparatus and reception apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a code multiplexing transmission method, transmission apparatus and reception apparatus in an OFDM (Orthogonal Frequency Division Multiplexing)-based radio access scheme. 
     BACKGROUND ART 
     The communication system that is a successor to the Wideband Code Division Multiple Access (WCDMA) system, High-Speed Downlink Packet Access (HSDPA) system, High-Speed Uplink Packet Access (HSUPA) system and the like i.e. Long Term Evolution (LTE) has been determined by 3GPP that is the standardization group of WCDMA. As a radio access scheme in LTE, an Orthogonal Frequency Division Multiplexing Access (OFDMA) system is defined in downlink, while a Single-Carrier Frequency Division Multiple Access (SC-FDMA)) system is defined in uplink. 
     The OFDMA system is a multicarrier system for dividing a frequency band into a plurality of narrow frequency bands (subcarriers), and assigning data onto each subcarrier to perform transmission. The subcarriers are orthogonal to one another and arranged densely on the frequency axis, high-speed transmission is thereby achieved, and it is expected enhancing spectral efficiency. 
     The SC-FDMA system is a single-carrier transmission system for dividing the frequency band for each terminal, and performing transmission using frequency bands different from one another among a plurality of terminals. It is possible to reduce interference between terminals with ease and effectively, it is further possible to reduce variations in transmission power, and therefore, this system is preferable from the viewpoints of low power consumption in the terminal, wide coverage, etc. 
     In addition, various code multiplexing transmission (or spreading transmission using spreading sequences) are applied to LTE (for example, see Non-patent Document 1). For example, on the PHICH (Physical Hybrid-ARQ Indicator Channel) in downlink, code multiplexing is performed using the Walsh code to transmit ACK/NACK of hybrid ARQ in response to the PUSCH (Physical Uplink Shared Channel). Further, on the PUCCH (Physical Uplink Control Channel) in uplink, spreading transmission is performed using CAZAC sequences. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         Non-patent Document 1: 3GPP, TS36.211 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, when a code multiplexing transmission method is applied in the OFDM-based radio access scheme, it is required further improving characteristics. 
     The invention was made in view of such a respect, and it is an object of the invention to provide a code multiplexing transmission method, transmission apparatus and reception apparatus with characteristics improved capable of obtaining a high frequency diversity effect. 
     Solution to Problem 
     A first aspect of the invention includes the steps of receiving information symbols of a plurality of sequences input in parallel, generating different spreading codes based on orthogonal code sequences, giving different phase rotation to the information symbols or the spreading codes for each symbol sequence and then, spreading the information symbols with the spreading codes for each symbol sequence, and multiplexing spread information symbols corresponding to different symbol sequences, where the information symbols or the spreading codes are rotated by a phase rotation amount for enabling overlaps in a signal constellation in polar coordinates of the spread information symbols for transmitting different information symbols to be controlled to within a required range. 
     According to the first aspect of the invention, since the information symbols or the spread signals are rotated by the phase rotation amount such that overlaps in a signal constellation of the spread information symbols are controlled to within a required range, it is possible to increase the distance between spread symbols as possible, and to obtain the sufficient frequency diversity gain and coding gain. 
     Further, a second aspect of the invention includes the steps of receiving a transmission signal including code-multiplexed symbols obtained by multiplexing spread symbols corresponding to different symbol sequences, acquiring information of phase rotation given to information symbols or spreading codes in code-multiplexing, in a transmitter, the code-multiplexed symbols included in a reception signal, and detecting the code-multiplexed symbols from the reception signal based on the information of phase rotation. 
     Technical Advantage of Invention 
     According to the invention, in code multiplexing transmission in the OFDM-based radio access scheme, it is possible to suppress inter-code interference, obtain a high frequency diversity effect, and improve characteristics. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration of principal part of a radio transmitter; 
         FIG. 2  contains diagrams illustrating a constellation of spread symbols when a rotational Walsh code is used; 
         FIG. 3  is a diagram illustrating a constellation of spread symbols when the conventional Walsh code is used; 
         FIG. 4  is a diagram illustrating a configuration of a radio transmitter using a QAM code; 
         FIG. 5  contains conceptual diagrams of code multiplexing using an improved QAM code; 
         FIG. 6  contains conceptual diagrams of code multiplexing using the conventional QAM code; 
         FIG. 7( a )  is a functional block diagram of a transmission series in a baseband processing section in a base station apparatus, and  FIG. 7( b )  is a functional block diagram of a reception series in the baseband processing section in the base station apparatus; 
         FIG. 8  is a schematic diagram of a mobile communication system having mobile stations and base station apparatus; 
         FIG. 9  is a schematic configuration diagram of the base station apparatus as shown in  FIG. 8 ; 
         FIG. 10  is a schematic configuration diagram of the mobile station as shown in  FIG. 8 ; and 
         FIG. 11( a )  is a functional block diagram of a transmission series in a baseband processing section in the mobile station, and  FIG. 11( b )  is a functional block diagram of a reception series in the baseband processing section in the mobile station. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An Embodiment of the invention will specifically be described with reference to accompanying drawings. 
     Described first is a code multiplexing transmission method for providing known phase rotation for each symbol sequence. 
     In the code multiplexing transmission method, generally, data symbols of a plurality of sequences are multiplied by orthogonal spreading codes assigned for each symbol sequence for spreading modulation, spread symbols generated in spreading modulation are added to spread symbols of different symbol sequences for multiplexing, and the coded multiplexed symbols are placed on the frequency axis, subjected to Inverse Fast Fourier Transform (IFFT), and output as an OFDM signal. 
     It is possible to use orthogonal code sequences as spreading codes used in spreading data symbols. Among the orthogonal code sequences used as spreading codes in LTE are Walsh codes, CAZAC sequences, and phase rotation (DFT) sequences. Code multiplexing transmission using the Walsh code is adopted on the PHICH, and spreading transmission using the CAZAC sequence is adopted on the PUCCH. The PUSCH is regarded as code multiplexing transmission using the phase rotation (DFT) sequence. As the orthogonal code sequences, there are the Walsh code, CAZAC code, phase rotation (DFT) sequence, orthogonal M sequence, etc. and other orthogonal code sequences are also applicable. 
     Walsh code sequences with a length (spreading factor) L=2 n  are defined recursively by Equation (1). 
     
       
         
           
             
               
                 
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     In the Walsh code sequences as shown in Eq. 1, a vector of each row is a spreading code to some symbol. Since the Walsh code sequences are orthogonal sequences, it is possible to achieve sufficient transmission characteristics in mapping spread symbols to subcarriers with high fading correlation so as to maintain orthogonality among code-multiplexed symbols, and in performing channel equalization to recover orthogonality of codes in a receiver. 
     In addition, in MC-CDMA, so as to obtain the highest frequency diversity effect and improve transmission characteristics of MC-CDMA, it is effective assigning spread symbols corresponding to the spreading factor to subcarriers undergoing mutually independent fading variations, and performing maximum likelihood detection on the receiver side. In this case, assuming that the fading variation of each subcarrier follows the independent Rayleigh distribution, the upper limit based on Chernoff bound of pairwise error rate Pe is expressed by Equation (2). 
     
       
         
           
             
               
                 
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     Herein, SNR is a signal to noise power ratio, and di is the distance between spread symbols after performing ith code multiplexing with respect to combinations of information symbols corresponding to the number of multiplexes of two focused kinds of codes. In addition, QPSK modulation is assumed as data modulation. 
     In order to obtain sufficient frequency diversity gain and coding gain, it is desirable that the squared produce codeword distance between spread symbols is as large as possible without the distance di between spread symbols being all zero. However, in using spreading codes generated from the Walsh code sequences, when a combination of different information symbols is transmitted, the case of di=0 arises such that the same spread symbols are generated. 
       FIG. 3  is a diagram to explain the occurrence of inter-spread symbol distance di=0. Two information symbols subjected to QPSK modulation are respectively spread with the Walsh code with a length (spreading factor) L=2 and added. Seeing the signal constellation of multiplexed spread symbols of 16 spread symbols generated from two information symbols, maximum four spread symbols are placed in the same positions (di=0). Further, five positions exist where two spread symbols are placed in the same position (di=0). 
     To avoid the problem that the inter-symbol distance is zero in the Walsh code, the inventor of the invention conceived code sequences (hereinafter, referred to as a “rotational orthogonal code”) for giving fixed (known) phase rotation for each spreading code. In the following description, the Walsh code sequence given phase rotation is called a “rotational Walsh code”. The rotational Walsh code sequence R L  with a length (spreading factor)=L is generated by Equation (3) based on the Walsh code sequence W L .
 
[Formula 3]
 
 R   L   =W   L diag{ e   j0π/4(L-1)   , . . . ,e   j1π/4(L-1)   , . . . ,e   j(L-1)π/4(L-1) }  (3)
 
diag{ . . . } is a diagonal matrix having elements inside the parentheses as diagonal components. Unique phase rotation spaced uniformly in the range of 0 to π/4 is given for each spreading code. By this means, it is possible to prevent signal points of spread symbols in the constellation from overlapping.
 
     Different Phase rotation is given for each information symbol sequence, the Walsh code assigned to each sequence is then multiplied, and unique phase rotation is thereby given for each spreading code. By applying phase rotation to the spreading code (or information symbol) for each symbol sequence, it is possible to control the signal points of spread symbols on orthogonal coordinates not to overlap. 
     The fact that the signal points of spread symbols do not overlap is capable of including the case where a state in which part of spread symbols overlap exists, in addition to the state in which all the spread symbols do not overlap one another completely. It is important that it is possible to control the overlap state of the signal points of spread symbols to be desired state by giving fixed phase rotation for each information symbol sequence. This is not limited to the Walsh code, and corresponds to the case of performing spreading modulation using other orthogonal code sequences as spreading codes. 
     A radio transmitter to which is applied the code multiplexing transmission method for multiplexing codes using above-mentioned rotational orthogonal codes will specifically be described. 
       FIG. 1  is a diagram illustrating a configuration of principal part of the radio transmitter to which is applied the code multiplexing transmission method of the invention. The radio transmitter is provided with an orthogonal spreading code generating section  10 , phase rotation giving section  11 , spreading modulation section  12 , code multiplexing section  13 , subcarrier mapping section  14 , and Inverse Fast Fourier Transform section  15 . 
     The radio transmitter receives modulation symbols #1 to #L of a plurality of sequences that are obtained by modulating data symbols with a predetermined data modulation scheme. In the invention, the data content of the data symbol is not limited, and may be L sequences for performing serial-parallel transform on a single data symbol sequence on a predetermined symbol basis, or a data sequence of each user corresponding to the number (L) of users.  FIG. 1  shows the existence of a plurality of symbol sequences targeted for code multiplexing. The data modulation scheme of data symbols may be QPSK, 16QAM and other modulation schemes, and herein, it is assumed that modulation symbols #1 to #L are obtained by performing data modulation using QPSK. 
     In the radio transmitter as shown in  FIG. 1 , the orthogonal spreading code generating section  10  generates different spreading codes for each symbol sequence corresponding to a plurality of symbol sequences. Herein, the section  10  generates Walsh codes such that spreading codes have the length (spreading factor)=L. Meanwhile, the phase rotation giving section  11  gives fixed (known) phase rotation to L symbol sequences for each symbol sequence. Phase weight multiplying sections  11 - 1  to  11 -L constituting the phase rotation giving section  11  are rotated by a phase rotation amount calculated from (π/4)×(L−1) for L sequences in Eq. (3) as weights r 1  to rL. More specifically, the weights r 1  to rL for rotating the phase by (π/4)×(L−1) are beforehand calculated, and set on the phase weight multiplying sections  11 - 1  to  11 -L. In other words, L symbol sequences are given phase rotation with different weighting (phase rotation amount) by the weights r 1  to rL for each symbol sequence. 
     The spreading modulation section  12  is provided with spreading processing sections  12 - 1  to  12 -L corresponding to the number of symbol sequences, and different spreading codes generated in the orthogonal spreading code generating section  10  are given to respective spreading processing sections  12 - 1  to  12 -L. These spreading processing sections  12 - 1  to  12 -L receive information symbols given different phase rotation for each sequence output from corresponding phase weight calculating sections  11 - 1  to  11 -L of the phase rotation giving section  11 . Each of the spreading processing sections  12 - 1  to  12 -L multiplies a single information symbol given respective phase rotation by a respective spreading code to spread, and generates L spread symbols corresponding to the spreading factor for a single information symbol. 
     By thus performing phase rotation on the information symbol side targeted for spreading and then, multiplying by spreading codes, it is possible to obtain the effect equivalent to multiplying information symbols by rotational Walsh codes. In other words, there is the action of eliminating overlaps of signal points on the constellation among spread symbols of different symbol sequences. 
       FIG. 2( a )  shows a signal constellation on orthogonal coordinates of spread symbols spread by rotational Walsh codes of L=2. As shown in the figure, 16 signal points of spread symbols are arranged without any overlap. Further,  FIG. 2( b )  shows a signal constellation on orthogonal coordinates of spread symbols spread by rotational Walsh codes of L=4. As shown in the figure, 2 4  signal points of spread symbols are arranged without any overlap. In L=2, 4, QPSK is assumed as the modulation scheme of data symbols. 
     In the rotational Walsh code, by adding phase rotation equally spaced for each symbol sequence, it is understood that different spread symbols are certainly obtained in the case of transmitting a combination of different information symbols. 
     The code multiplexing section  13  is provided with spread symbol adding sections  13 - 1  to  13 -L corresponding to the number associated with the spreading factor of the spreading modulation section  12 . Each spread symbol adding section  13 - 1  receives spread symbols of different information symbols (#1 to #L) input from each of the spreading processing sections  12 - 1  to  12 -L. Each of the spread symbol adding sections  13 - 1  to  13 -L adds spread symbols of different symbol sequences (#1 to #L) output from the spreading modulation section  12  to generate a code multiplexed transmission symbol. 
     The code multiplexed transmission symbol output from each of the spread symbol adding sections  13 - 1  to  13 -L of the code multiplexing section  13  is provided to the subcarrier mapping section  14 . The subcarrier mapping section  14  divides the code multiplexed transmission symbol into a plurality of subcarriers to map onto the frequency axis, and performs subcarrier modulation corresponding to the code multiplexed transmission symbol. The multicarrier signal string is input to the Inverse Fast Fourier Transform section  15 , subjected to Inverse Fast Fourier Transform, and thus transformed into a waveform on the time axis, and the resultant is output to a radio transmission section. 
     According to such a radio transmitter, spread symbols of each symbol sequence (#1 to #L) added in the spread symbol adding sections  13 - 1  to  13 -L are spread symbols such that signal points on the constellation are absolutely different from one another. Accordingly, when each subcarrier undergoes independent Rayleigh fading in the propagation channel, it is possible to obtain the L-order diversity effect that is the highest when the receiver performs maximum likelihood detection. 
     In addition, since the rotational Walsh code sequences are of orthogonal codes, also in the case of performing signal detection such as MMSE (decorrelator) as a substitute for maximum likelihood detection, it is conceivable that good transmission characteristics are obtained. 
     In addition, as shown in  FIG. 2 , the signal point density of spread symbols is non-uniform in the rotational orthogonal codes including the above-mentioned rotational Walsh code sequences. 
     Therefore, proposed are spreading codes with a constellation of lattice-shaped arrangement of spread symbols subjected to code multiplexing so as to increase the inter-symbol distance di averagely. In right-angle phase amplitude modulation schemes (typified by QAM and 16QAM) of combination of amplitude modulation (AM) and phase modulation (PM), the signal constellation in which amplitude/phase assigned to the symbol is represented as a point in polar coordinates of two-dimensional plane is in the shape of an equally-spaced lattice. In the Description, the spreading code in which the signal constellation of code-multiplexed spread symbols is of lattice-shaped arrangement is called “QAM code”. 
     In the case of length (spreading factor) L=2, assuming QPSK modulation, when two information symbols are respectively mapped to the first layer and the second layer of 16QAM alternately between two spread symbols, the spreading code is of Equation (4). 
     
       
         
           
             
               
                 
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     In addition, to simplify the description, power is not normalized for representation. 
     However, as shown in  FIGS. 6( a ) and 6( b ) , the spreading code represented by Eq. 4 results in a combination of information symbols such that the inter-symbol distance is always short between two spread symbols. As information symbols of two sequences,  FIG. 6  shows symbols of one symbol sequence represented by marks (circle, triangle, square, pentagon), and symbols of the other symbol sequence represented by numbers (1, 2, 3, 4). Assuming that information symbols prior to spreading are modulated with QPSK, the symbol represented by the mark is placed in a signal point of any of the circle, triangle, square and pentagon, and the symbol represented by the number is placed in a signal point of any of 1, 2, 3 and 4. 
     By spreading QPSK-modulated symbols represented by the “marks” with the spreading code of Eq. (4), “mark” spread symbols  1  shown in  FIG. 6( a ) , and “mark” spread symbols  2  shown in  FIG. 6( b )  are generated. Further, by spreading QPSK-modulated symbols represented by the “numbers” with the spreading code of Eq. (4), “number” spread symbols  1  shown in  FIG. 6( a ) , and “number” spread symbols  2  shown in  FIG. 6( b )  are generated. Then, the first code multiplexed symbols shown in  FIG. 6( a )  are generated by adding the “mark” spread symbols  1  and “number” spread symbols  1 , and the second code multiplexed symbols shown in  FIG. 6( b )  are generated by adding the “mark” spread symbols  2  and “number” spread symbols  2 . 
     By comparing the first code-multiplexed symbols and second code-multiplexed symbols  2 , it is understood that the inter-symbol distances are always short between a spread symbol of combination of the information symbols “circle” and “2”, and a spread symbol of combination of the information symbols “triangle” and “1”. 
     Therefore, a spreading code represented by Equation (5) is generated so as to obtain a long inter-symbol distance averagely even in any combinations of information symbols. 
     
       
         
           
             
               
                 
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       FIGS. 5( a ) and 5( b )  show inter-symbol distances code-multiplexed symbols in the case of using the spreading code represented by Eq. (5). By comparing the first code-multiplexed symbols shown in  FIG. 5( a )  and second code-multiplexed symbols  2  shown in  FIG. 5( b ) , it is understood that the inter-symbol distance between a spread symbol of combination of the information symbols “circle” and “2”, and a spread symbol of combination of the information symbols “triangle” and “1” is increased in the second code-multiplexed symbols. 
     It is possible to recursively define QAM code sequences such that long inter-symbol distances are averagely obtained in any combinations of information symbols using Equation (6). 
     
       
         
           
             
               
                 
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     A radio transmitter to which is applied the code multiplexing transmission method using the QAM code as described above will specifically be described below. 
       FIG. 4  is a diagram illustrating a configuration of principal part of the radio transmitter using the QAM code. 
     The radio transmitter is provided with an orthogonal spreading code generating section  20 , spreading modulation section  21 , code multiplexing section  22 , subcarrier mapping section  23 , and Inverse Fast Fourier Transform section  24 . The code multiplexing section  22 , subcarrier mapping section  23 , and Inverse Fast Fourier Transform section  24  have the same functions as in the radio transmitter as shown in  FIG. 1  described previously. 
     The orthogonal code generating section  20  generates QAM code sequences defined by Eq. (6), and gives a different QAM code (spreading code) to each of spreading code processing sections  21 - 1  to  21 -L constituting the spreading modulation section  21 . The QAM codes given to the spreading modulation section  21  are designed so that the signal constellation of code-multiplexed spread symbols is a lattice-shaped arrangement so as to averagely increase the inter-symbol distance di. Accordingly, as shown in  FIGS. 5( a ) and 5( b ) , when “mark” symbols and “number” symbols which are QPSK-modulated and arranged on the IQ plane undergo spreading modulation with the QAM codes, the symbols are transformed into “mark” spread symbols  1 ,  2  and “number” spread symbols  1 ,  2  with the signal constellation of the lattice-shaped arrangement. In the case of L=2 as shown in  FIG. 5 , the “mark” spread symbols  1  and “number” spread symbols  1  are input to one spreading adding section  22 - 1  of the code multiplexing section  22  and added, and the “mark” spread symbols  2  and “number” spread symbols  2  are input to the other spreading adding section  22 - 2  of the code multiplexing section  22  and added. 
     Since spreading is performed using the QAM code defined by Eq. (5) or Eq. (6), with respect to the inter-symbol distances in the first code-multiplexed symbols and second code-multiplexed symbols, long inter-symbol distances are averagely obtained in any combinations of information symbols. 
     An Embodiment will be described below in which the code multiplexing transmission method using the above-mentioned rotational orthogonal code sequences is applied to a physical channel in LTE or LTE-Advanced. 
     A mobile communication system having mobile stations and base station apparatus will be described with reference to  FIG. 8 . 
     A mobile communication system  1000  is based on the LTE system, where the code multiplexing transmission method using the above-mentioned rotational orthogonal code sequences is applied to the PHICH that is a physical channel for transmitting ACK/NACK in downlink, and the PUSCH in uplink. The mobile communication system  1000  is provided with a base station apparatus  200  and a plurality of mobile stations  100  ( 100   1 ,  100   2 ,  100   3 , . . . ,  100   n , n is an integer where n&gt;0) that communicates with the base station apparatus  200 . The base station apparatus  200  is connected to an upper station, for example, access gateway apparatus  300 , and the access gateway apparatus  300  is connected to a core network  400 . Herein, the mobile station  100 , communicates with the base station apparatus  200  in a cell  50  by LTE. In addition, the access gateway apparatus  300  may be also referred to as MME/SGW (Mobility Management Entity/Serving Gateway). 
     In the following description, each mobile station ( 100   1 ,  100   2 ,  100   3 , . . . ,  100   n ) has the same configuration, function and state, and is descried as the mobile station  100 , below to give an explanation unless otherwise specified. For convenience in description, the mobile station performs radio communications with the radio base station, and more generally, may be user equipment (UE) including a mobile terminal and a fixed terminal. 
     In the mobile communication system  1000 , as a radio access scheme, OFDMA (Orthogonal Frequency Division Multiplexing Access) is applied in downlink, while SC-FDMA (Single-Carrier Frequency Division Multiple Access) is applied in uplink. As described above, OFDMA is a multicarrier transmission system for dividing a frequency band into a plurality of narrow frequency bands (subcarriers), and mapping data onto each subcarrier to perform communications. SC-FDMA is a single-carrier transmission system for dividing the system band into bands comprised of one or more consecutive resource blocks for each terminal so that a plurality of terminals uses mutually different bands, and thereby reducing interference among the terminals. 
     Described herein are communication channels in the LTE system. In downlink, used are the Physical Downlink Shared Channel (PDSCH) shared among the mobile stations  100   n , and the Physical Downlink Control Channel (Downlink L1/L2 control channel). On the Physical Downlink Shared Channel are transmitted signals of user data i.e. speech data and transmission data. Further, on the Physical Downlink Control Channel is notified scheduling information, spreading code information assigned to code multiplexing of transmission symbols on the PHICH and phase rotation information provided for each symbol sequence, spreading code information assigned to code multiplexing of transmission symbols on the PUSCH and phase rotation information provided for each symbol sequence, user IDs to perform communications using the Physical Downlink Shared Channel and information of the transport format of the user data i.e. Downlink Scheduling Information, user IDs to perform communications using the Physical Uplink Shared Channel and information of the transport format of the user data i.e. Uplink Scheduling Grant, etc. In addition, instead of signaling, the control information (spreading code information and phase rotation information) concerning code multiplexing of transmission symbols on the PHICH and PUSCH may be beforehand defined known information in the mobile station  100  to enable the mobile station  100  to code-multiplex transmission symbols without receiving signaling from the base station apparatus  200 . 
     Further, in downlink, broadcast channels are transmitted such as the Physical-Broadcast Channel (P-BCH) and Dynamic Broadcast Channel (D-BCH). The information transmitted on the P-BCH is Master Information Block (MIB), and the information transmitted on the D-BCH is System Information Block (SIB). The D-BCH is mapped to the PDSCH, and is transmitted to the mobile station  100   n  from the base station apparatus  200 . 
     In uplink, used are the Physical Uplink Shared Channel (PUSCH) shared among the mobile stations  100 , and the Physical Uplink Control Channel (PUCCH) that is a control channel in uplink. Symbol sequences of the user data i.e. speech data and transmission data transmitted on the Physical Uplink Shared Channel are code-multiplexed by the rotational orthogonal code and transmitted. Further, on the Physical Uplink Control Channel is transmitted precoding information for downlink MIMO transmission, acknowledgement information in response to the shared channel in downlink, radio quality information (CQI: Channel Quality Indicator) of downlink, etc. 
     In addition, in uplink, the Physical Random Access Channel (PRACH) for initial connection, etc. is defined. The mobile station  100  transmits a random access preamble on the PRACH. 
     The base station apparatus  200  according to the Embodiment of the invention will be described with reference to  FIG. 9 . The base station apparatus  200  according to this Embodiment is provided with a transmission/reception antenna  202 , amplifying section  204 , transmission/reception section  206 , baseband signal processing section  208 , call processing section  210  and transmission path interface  212 . The invention is applicable to MIMO transmission, but components concerning MIMO transmission are omitted in the Embodiment. 
     The user data (speech data for speech communications or transmission data for data communications) transmitted from the base station apparatus  200  to the mobile station  100  in downlink is input to the baseband signal processing section  208  via the transmission path interface  212  from an upper station positioned higher than the base station apparatus  200 , for example, access gateway apparatus  300 . 
     The baseband signal processing section  208  performs PDCP layer processing, segmentation and concatenation of user data, RLC (Radio Link Control) layer transmission processing such as transmission processing of RLC retransmission control, MAC (Medium Access Control) retransmission control e.g. transmission processing of HARQ (Hybrid Automatic Repeat request), scheduling, transmission format selection, channel coding, and Inverse Fast Fourier Transform (IFFT) processing on the data to transfer to the transmission/reception section  206 . Further, signals (downlink control information) of the Physical Downlink Control Channel also undergo the transmission processing such as channel coding and Inverse Fast Fourier Transform, and are transferred to the transmission/reception section  206 . 
     Further, the baseband signal processing section  208  notifies the mobile station  100  of control information for communications in the cell on the above-mentioned broadcast channel. The control information for communications in the cell is capable of including the system bandwidth in uplink or downlink, allocation information of radio resources allocated to the mobile station  100 , identification information (Root Sequence Index) for a route sequence to generate a signal of random access preamble on the PRACH, etc. 
     Furthermore, the baseband signal processing section  208  notifies the mobile station  100  of the rotational Walsh code assigned to the mobile station  100  for code multiplexing of PHICH and phase rotation information on the downlink control channel. In addition, the invention is not limited thereto when the mobile station  100  beforehand stores the rotational Walsh code and phase rotation information as code multiplexing parameters of the PHICH as known information. 
     The transmission/reception section  206  performs frequency conversion processing for converting the baseband signal output from the baseband signal processing section  208  into a signal of a radio frequency band, and then, the signal is amplified in the amplifying section  204 , and is transmitted from the transmission/reception antenna  202 . 
     Meanwhile, with respect to the data transmitted from the mobile station  100  to the base station apparatus  200  in uplink, a radio frequency signal received in the transmission/reception antenna  202  is amplified in the amplifying section  204 , undergoes frequency conversion in the transmission/reception section  206 , is thereby converted into a baseband signal, and is input to the baseband signal processing section  208 . 
     The baseband signal processing section  208  performs FFT processing, MLD processing, IDFT processing, error correcting decoding, reception processing of MAC retransmission processing, and reception processing of RLC layer and PDCP layer on the user data included in the input baseband signal, and the data is transferred to the access gateway apparatus  300  via the transmission path interface  212 . In the MLD processing, the section  208  decodes the PUSCH subjected to code multiplexing using the phase rotational (DFT) sequences based on the phase rotation amount information, and performs maximum likelihood detection. The phase rotation amount information of the PUSCH may be of a scheme of signaling from the mobile station  100 , or a scheme of signaling from the base station  200  to the mobile station  100 . Alternately, instead of the signaling scheme, the phase rotation amount information of the PUSCH may be of a scheme of beforehand storing as code multiplexing parameters of the PUSCH of the base station  200  and mobile station  100 . 
     The call processing section  210  performs call processing such as setting and release of the communication channel, status management of the radio base station  200 , and management of radio resources. 
       FIG. 7  contains configuration diagrams of the baseband signal processing section  208  of the radio base station  200 , where  FIG. 7( a )  shows functional blocks of a transmission processing series, and  FIG. 7( b )  shows functional blocks of a reception processing series. 
     The transmission processing series is provided with a channel coding section  31  that applies error correction and interleaving to downlink transmission data, a data modulation section  32  that performs data modulation on coded data with a predetermined modulation scheme (for example, QPSK), a phase rotation giving section  33  that gives different phase rotation for each symbol sequence, a spreading/multiplexing section  34  that spreads information symbols using the rotational Walsh code and that multiplexes spread symbols, a mapping section  35  that maps code-multiplexed symbols onto the frequency domain, an Inverse Fast Fourier Transform section  36  that performs Inverse Fast Fourier Transform on coded multiplexed symbols, and a CP adding section  37  that adds a cyclic prefix. The configuration of the transmitter as shown in  FIG. 1  corresponds to the phase rotation giving section  33 , spreading/multiplexing section  34 , mapping section  35  and Inverse Fast Fourier Transform section  36  in the transmission processing series. In this Embodiment, the input data of the channel coding section  31  is transmission data transmitted on the PHICH, and the spreading/multiplexing section  34  gives phase rotation to information symbols using the rotational Walsh code recursively defined by Eq. (3) to spread. The mapping section  35  assigns multiplexed spread symbols to subcarriers respectively undergoing independent fading variations. 
     The reception processing series is provided with a CP removing section  41  that removes a cyclic prefix from a reception signal, a Fast Fourier Transform section  42  that performs Fast Fourier Transform on the reception signal, a demapping section  43  that demaps the signal in the frequency domain transformed by Fourier Transform, an MLD reception section  44  that performs signal detection on a demapped reception symbol according to maximum likelihood detection, an IDFT section  45  that despreads (IDFT) the reception symbol detected in the MLD reception section  44 , and a channel decoding section  46  that deinterleaves a despread reception symbol sequence to perform channel decoding. In this Embodiment, the reception signal is reception data transmitted on the PUSCH, and the mobile station  100  provides transmission symbols with phase rotation, and performs code-multiplexing using the phase rotational (DFT) code. The MLD reception section  44  considers phase rotation provided on the transmission side (mobile station) to specify signal points according to the phase rotation information provided on the transmission side, and estimates reception symbols. The reception signal detected in the MLD reception section  44  is despread in the IDFT section  45 , and output to the channel decoding section  46 . 
     As described above, the radio base station  200  provides the transmission data transmitted on the PHICH with phase rotation for each symbol sequence, spreads the resultant using the Walsh code in the spreading/multiplexing section  34 , and performs code-multiplexing to transmit in downlink, and it is thereby possible to obtain the maximum frequency diversity effect and improve transmission characteristics. 
     The mobile station  100  according to the Embodiment of the invention will be described with reference to  FIG. 10 . In  FIG. 10 , the mobile station  100  is provided with a transmission/reception antenna  102 , amplifying section  104 , transmission/reception section  106 , baseband signal processing section  108 , and application section  110 . 
     With respect to data in downlink, a radio frequency signal received in the transmission/reception antenna  102  is amplified in the amplifying section  104 , subjected to frequency conversion in the transmission/reception section  106 , and converted into a baseband signal. The baseband signal processing section  108  performs FFT processing, MLD processing, error correcting decoding, reception processing of retransmission control and the like on the baseband signal. In the data in downlink, the user data (speech data, transmission data) in downlink is transferred to the application section  110 . The application section  110  performs processing concerning layers higher than the physical layer and MAC layer. Further, in the data in downlink, the broadcast information is also transferred to the application section  110 . 
     Meanwhile, the user data in uplink is input to the baseband signal processing section  108  from the application section  110 . The baseband signal processing section  108  performs transmission processing of retransmission control (H-ARQ (Hybrid ARQ)), channel coding, DFT processing, IFFT processing and the like on the data to transfer to the transmission/reception section  106 . The transmission/reception section  106  performs frequency conversion processing for converting the baseband signal output from the baseband signal processing section  108  into a signal with a radio frequency band, and then, the signal is amplified in the amplifying section  104 , and is transmitted from the transmission/reception antenna  102 . 
       FIG. 11  contains configuration diagrams of the baseband signal processing section  108  of the mobile station  100 , where  FIG. 11( a )  shows functional blocks of a transmission processing series, and  FIG. 11( b )  shows functional blocks of a reception processing series. 
     The transmission processing series is provided with a channel coding section  131  that applies error correction and interleaving to uplink transmission data, a data modulation section  132  that performs data modulation on coded data with a predetermined modulation scheme (for example, QPSK), a phase rotation giving section  133  that gives different phase rotation for each symbol sequence, a DFT coding section  134  that spreads information symbols using the rotational phase (DFT) code and that multiplexes spread symbols, a mapping section  135  that maps code-multiplexed symbols onto the frequency domain, an Inverse Fast Fourier Transform section  136  that performs Inverse Fast Fourier Transform on coded multiplexed symbols, and a CP adding section  137  that adds a cyclic prefix. The configuration of the transmitter as shown in  FIG. 1  corresponds to the phase rotation giving section  133 , DFT coding section  134 , mapping section  135  and Inverse Fast Fourier Transform section  136  in the transmission processing series. In this Embodiment, the input data of the channel coding section  131  is transmission data transmitted on the PUSCH, and the DFT coding section  134  spreads the resultant with DFT that is the phase rotational (DFT) code. The mapping section  135  maps the multiplexed spread symbol to a single carrier comprised of consecutive subcarriers. 
     In the reception processing series, a reception signal output from the transmission/reception section  106  is input to a CP removing section  141  and the cyclic prefix is removed. A Fast Fourier Transform section  142  performs Fast Fourier Transform on the CP-removed reception signal, and converts time-series signal components into a string of frequency components. A subcarrier demapping section  143  performs subcarrier demapping to divide into a reference signal transmitting a RS sequence signal, control channel (for example, PHICH, PDCCH) for transmitting the downlink control information, and shared channel (for example, PDSCH) for transmitting the user data. 
     The reception symbol of the PHICH is input to an MLD reception section  144 . The MLD reception section  144  performs signal detection on the demapped reception symbol according to the maximum likelihood detection method. A channel decoding section  145  deinterleaves the reception symbol sequence detected in the MLD reception section  144  to perform channel decoding. 
     As described above, the mobile station  100  provides the transmission data transmitted on the PUSCH with phase rotation for each symbol sequence, then spreads (DFT) the resultant using the phase rotational (DFT) code, and performs code-multiplexing to transmit in uplink, and it is thereby possible to obtain the maximum frequency diversity effect and improve transmission characteristics. 
     As described above, it is possible to apply the code multiplexing transmission method using rotational orthogonal codes to the coexisting physical channels (PHICH, PUSCH) on which code multiplexing transmission is performed and the coexisting physical channel (PUCCH) on which spreading transmission is performed in the LTE system. Further, as a substitute for the rotational orthogonal code, it is possible to apply the code multiplexing transmission method using QAM codes. 
     Further, it is possible to apply the code multiplexing transmission method using rotational orthogonal codes or QAM codes of the invention to coexisting physical channels on which code multiplexing is not defined in LTE. For example, in LTE, spreading transmission using CAZAC sequences is defined on the physical channel (PUCCH) for transmitting CQI, and ACK/NACK in uplink (no code multiplexing in a single user), and it is possible to apply the code multiplexing transmission method using a plurality of cyclic shifts (phase rotational sequences in the frequency domain) for the CAZAC sequences. Furthermore, it is possible to apply the code multiplexing transmission method using rotational orthogonal codes or QAM codes of the invention to physical channel (PDCCH) for transmitting the L1/L2 control information in downlink. 
     In the further, it is conceivable that the feedback information and L1/L2 control information will increase due to the widened band, and it is expected to be effective measures applying the code multiplexing transmission method using rotational orthogonal codes or QAM codes of the invention capable of obtaining the maximum frequency diversity effect and improving transmission characteristics. 
     The present invention is not limited to the above-mentioned Embodiment, and is capable of being carried into practice with various modifications thereof without departing from the subject matter of the invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to radio communication systems. 
     The present application is based on Japanese Patent Application No. 2009-049802 filed on Mar. 3, 2009, entire content of which is expressly incorporated by reference herein.