Abstract:
A space code block coding and spreading apparatus for transmission diversity, a Code Division Multiple Access (CDMA) diversity transmitter using it, and a CDMA mobile station receiver for receiving a transmission diversity signal, which are capable of improving the performance of system in wireless channel environments by allowing a transmission diversity to be made within one symbol interval in a CDMA communication system. The apparatus includes an encoder for generating a predetermined number of different transmission data with respect to a plurality of modulation symbols inputted during one modulation symbol interval, an orthogonal code generator for producing orthogonal codes, a spreader for spreading each of the transmission data generated from the encoder using the orthogonal codes generated from the orthogonal code generator, and a combining unit for combining the transmission data spread at the spreader to provide combined data for each transmission antenna path.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a space code block coding and spreading apparatus and method for transmission diversity and a Code Division Multiple Access (CDMA) diversity transmitter and a CDMA mobile station receiver using the same. More particularly, the invention is directed to a space code block coding and spreading apparatus and method for transmission diversity, and a CDMA diversity transmitter and a CDMA mobile station receiver using it, which are capable of improving the performance of a system in wireless channel environments by allowing a transmission diversity to be made within one symbol interval in a CDMA communication system. 
     DESCRIPTION OF RELATED ART 
       FIG. 1  shows a view describing the concept of a conventional transmission diversity method using a space time block coding technique. 
     One of the conventional transmission diversity techniques is “Space Time Block Coding (STBC)” proposed in “IEEE Journal on select areas in communications” by Siavash M. Alamouti in 1998. Such an STBC scheme is a scheme that performs a diversity encoding with respect to data to be transmitted in space (antenna) and time domains and then transmits it, as shown in  FIG. 1 . 
     In other words, in a basic mode where the number of transmission antenna is one, if a modulation symbol transmitted at an arbitrary timeslot t  101  is s 0  and a modulation symbol transmitted at its adjacent timeslot t+T  102  is s 1 , the transmission diversity technique using the STBC encoding method proposed by Alamouti transmits the first symbol s 0  via a first antenna (antenna  0 ) at a timeslot t  111  and its conjugate complex s 0 * via a second antenna (antenna  1 ) at its adjacent timeslot t+T  122 , as can be seen from  FIG. 1 . The second symbol s 1  is transmitted via the second antenna (antenna  1 ) at a timeslot t  121  and its negative conjugate complex −s 1 * via the first antenna (antenna  0 ) at its adjacent timeslot t+T  112 . Namely, the Alamouti&#39;s STBC encoding method is a method which acquires a diversity gain by transmitting each modulation symbol at two adjacent time intervals via different antennas. 
       FIG. 2   a  is a circuitry diagram showing a configuration of a transmitter that implements a conventional STBC transmission diversity method in Multi Carrier-CDMA (MC-CDMA) system. That is,  FIG. 2   a  represents a configuration of a base station transmitter where one channelization code is assigned to an arbitrary kth user, in the MC-CDMA system to which the Alamouti&#39;s STBC encoding method is applied. 
     Specifically, channel-encoded data is first modulated at a modulator  201  using Quadrature Phase Shift Keying (QPSK) or M-ary Quadrature Amplitude Modulation (QAM) and then applied to an STBC encoder  202 . 
     The STBC encoder  202  gets two symbols every two Orthogonal Frequency Division Multiplexing (OFDM) symbol intervals and performs STBC encoding to obtain an encoded symbol for each of two diversity antennas, as shown in  FIG. 2   a . In other words, during a first symbol interval, s k,0  and s k,1  are outputted to paths for a first and a second antennas, respectively, while, during a second symbol interval, −s* k,1  and s* k,0  are provided to the paths for the first and the second antennas, respectively. Here, the asterisk “*” represents a conjugate complex. 
     The two outputs from the STBC encoder  202  are duplicated at each of duplicators  203   a  and  203   b  by N every symbol interval; and then each of the duplicated values is multiplied by an orthogonal code with the length of N assigned to a current channel at each of orthogonal code multipliers  204   a  and  204   b . Here, the orthogonal codes multiplied with respect to the two antenna paths are C (k,0) =[C 0   (k,0) C 1   (k,0)  . . . C N−1   (k,0) ] T  which is given as the same one. And, k indicates a kth user and T represents a transposition matrix. 
     The N symbols with respect to each of the antenna paths multiplied by the orthogonal codes are combined with symbols of other channels at channel combiners  205   a  and  205   b , respectively. Outputs from the channel combiners  205   a  and  205   b  are multiplied by scrambling codes at scramblers  206   a  and  206   b  and then converted into time domain signals at parallel/serial converters  208   a  and  208   b  via Inverse Fast Fourier Transformers (IFFTs)  207   a  and  207   b . Thereafter, Cyclic Prefix (CP) is inserted into the signals at CP inserters  209   a  and  209   b ; and then the CP-inserted signals are amplified and converted into RF signals at IF/RF processors  210   a  and  210   b  to transmit via antennas  211   a  and  211   b.    
     As described above, the conventional STBC diversity method acquires the diversity gain by transmitting the arbitrary one symbol to the different antennas via the two paths at the two adjacent symbol intervals, that is, two. different time intervals. 
       FIG. 2   b  is a view describing the concept of a conventional STBC transmission diversity method in MC-CDMA system. 
     As shown in  FIG. 2 , a modulation symbol s k,0  is transmitted via a first antenna (antenna  0 ) at a time T 0  (OFDM symbol interval  0 ) and then its conjugate complex s* k,0  via a second antenna (antenna  1 ) at a time T 1  (OFDM symbol interval  1 ). Conversely, a modulation symbol s k,1  is transmitted via the second antenna (antenna  1 ) at the time T 0  (OFDM symbol interval  0 ) and then its negative conjugate complex −s* k,1  via the first antenna (antenna  0 ) at the time T 1  (OFDM symbol interval  1 ). 
     At a receiver of the transmitter using the conventional STBC diversity method, s k,0  and s k,1  are recovered using the symbols received at the two adjacent time intervals. 
     In other words, signals received at each of the intervals T 0  and T 1  are transformed by taking Fast Fourier Transform (FFT) and then descrambled. If symbols obtained by adding the descrambled signals to a signal despread to C (k,0)  are r 0  and r 1 , respectively, the symbols may be represented as:
 
 r   0 =α 0 ( T   0 ) s   k,0 +α 1 ( T   0 ) s   k,1   +n   0 
 
 r   1 =−α 0 ( T   1 ) s*   k,1 +α 1 ( T   1 ) s*   k,0   +n   0   Eq. (1)
 
     In Eq. (1) above, α α (T e ) implies a channel component of signal received via an ath reception antenna at an interval T e , which generally has a Rayleigh distribution. And, n i  represents a reception noise component of despread and added signal. For example, if a speed of a mobile station is very slow, it satisfies the following equality: α α (T 0 )≅α α (T 1 ). Further, if the above equality is given by α α , the result of STBC decoding may be defined as follows:
 
 ŝ   0   =r   0 α* 0   +r*   1 α 1 =|α 0 | 2   s   0   +n   0 α* 0   +n*   1 α 1 
 
 ŝ   1   =r   0 α* 1   −r*   1 α 0 =|α 1 | 2   s   1   +n   0 α* 1   −n*   1 α 0   Eq. (2)
 
     If the speed of mobile station is slow, the result of the STBC decoding may be given as Eq. (2) above; and but, if the speed of mobile station is fast, α α (T 0 )≠α α (T 1 ), and thus Eq. (2) above is not satisfied. This causes any interference in each determinant variable. Consequently, as the speed of the mobile station is faster, the interference increases, thereby giving a reason that greatly lowers the performance of system. 
       FIG. 3  is a circuitry diagram of a transmitter that implements a conventional MC-CDMA diversity method using a multi-code when a data transmission rate is twice. Particularly,  FIG. 3  represents an MC-CDMA base station transmitter employing a general STBC transmission diversity technique when two channelization codes are assigned to an arbitrary user. 
     Here, the meaning that the two channelization codes are assigned is that the data transmission rate is twice compared to an instance of assigning a single code, as in  FIG. 1 . That is, if it is assumed that the data transmission rate of the example shown in  FIG. 1  is a basic data transmission rate R, the data transmission rate of the example in  FIG. 3  becomes 2R. 
     As can be seen from  FIG. 3 , two pairs of modulation symbols assigned to each of two codes, s k,0  and s k,1 , and s k,2  and s k,3 , are first processed at a serial/parallel converter  301  for their serial to parallel conversions and then each of them is STBC-encoded at STBC encoders  302   a  and  302   b . A more easy description thereof will be given below with reference to  FIG. 4 . The pair of symbols s k,0  and s k,1  is STBC-encoded and then spread to C (k,0) =[C 0   (k,0) C 1   (k,0)  . . . C N−1   (k,0) ] T ; and the pair of symbols s k,2  and s k,3  is STBC-encoded and then spread to C (k,1) =[C 0   (k,1) C 1   (k,1)  . . . C N−1   (k,1) ] T . 
     In this case, the arbitrary one symbol is also transmitted to different antennas via two paths at two adjacent symbol intervals, i.e., different time intervals; and therefore, the performance of system is very lowered in high speed mobile station environments. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide a space code block coding and spreading apparatus and method for transmission diversity and a CDMA diversity transmitter using it, which are capable of improving the performance of system in wireless channel environments by allowing a transmission diversity to be made within one symbol interval in CDMA communication system. 
     Another object of the present invention is to provide a CDMA mobile station receiver for receiving a transmission diversity signal transmitted through the CDMA diversity transmitter and method thereof. 
     In accordance with one aspect of the present invention, there is provided a Space Code Block Coding (SCBC) and spreading apparatus for transmission diversity in a Code Division Multiple Access (CDMA) communication system, the apparatus comprising: an encoding means for generating a predetermined number of different transmission data with respect to a plurality of modulation symbols inputted during one modulation symbol interval; an orthogonal code generation means for producing orthogonal codes; a spreading means for spreading each of the transmission data generated from the encoding means using the orthogonal codes generated from the orthogonal code generation means; and a combining means for combining the transmission data spread at the spreading means to provide combined data for each transmission antenna path so that a transmission diversity is made within said one modulation symbol interval. 
     In accordance with another aspect of the present invention, there is provided an SCBC and spreading method for transmission diversity in a CDMA communication system, the method comprising the steps of: (a) generating a predetermined number of different transmission data with respect to a plurality of modulation symbols inputted during one modulation symbol interval; (b) spreading each of the transmission data generated at said step (a) using orthogonal codes; and (c) combining the transmission data spread at said step (b) to ,provide a baseband signal for each transmission antenna path so that a transmission diversity is made within said one modulation symbol interval. 
     In accordance with still another aspect of the present invention, there is provided a CDMA diversity transmitter for a CDMA communication system, comprising: a modulation means for modulating channel-coded symbol data; a serial/parallel conversion means for converting a plurality of modulation symbols inputted every modulation symbol interval from the modulation means to provide pairs of modulation symbols made every predetermined number of modulation symbols in parallel; a plurality of SCBC and spreading means for generating and spreading a predetermined number of different transmission data every each of the pairs of modulation symbols provided by the serial/parallel conversion means, and combining the spread transmission data so that a transmission diversity is made within one modulation symbol interval; a combining means for combining the outputs from each of the plurality of SCBC and spreading means to generate a baseband signal for each antenna path; and a wireless signal processing means for converting each of the baseband signals into a wireless signal. 
     In addition, the CDMA diversity transmitter further comprises an Inverse Fast Fourier Transform (IFFT) means for transforming each of the baseband signals in the frequency domain generated from the combining means for each antenna path into a time domain signal, in case where the CDMA communication system employs a Multi-Carrier CDMA (MC-CDMA) scheme, wherein each of the SCBC and spreading means performs the spreading process in the frequency domain. 
     Furthermore, the CDMA diversity transmitter further comprises a scrambling means for scrambling the outputs from the combining means for each antenna path; and a Cyclic Prefix (CP) insertion means for inserting CP into each of the outputs from the IFFT means. 
     Moreover, the CDMA diversity transmitter further comprises a multiplexing means for providing modulation symbols of two user channels to be transmitted within one modulation symbol interval to the serial/parallel conversion means alternately, in case where the number of transmission antennas of the transmitter are two and one orthogonal code is assigned to each of a plurality of user channels. 
     In accordance with still yet another aspect of the present invention, there is provided a CDMA mobile station receiver for receiving a diversity signal transmitted in a CDMA communication system, comprising: a wireless signal processing means for converting a wireless signal received via a reception antenna into a baseband signal; a despreading means for despreading the baseband signal using orthogonal codes; a channel estimation means for estimating a channel value for a wireless path between a transmission antenna of the CDMA communication system and the reception antenna from the despread signal from the despreading means; an SCBC decoding means for recovering a transmitted signal by performing SCBC decoding using the channel estimated value from the channel estimation means and the despread signal from the despreading means; and a bit calculation means for calculating a bit value from the output from the SCBC decoding means. 
     In addition, the CDMA mobile station receiver further comprises a Fast Fourier Transform (FFT) means for transforming the baseband signal into a frequency domain signal in case where the CDMA communication system employs MC-CDMA scheme. 
     Moreover, the CDMA mobile station receiver further comprises: a CP removal means for removing a CP from the baseband signal outputted from the wireless signal processing means; a descrambling means for descrambling the frequency domain signal from the FFT means to provide it to the SCBC decoding means and the channel estimation means; and a channel decoding means for performing channel decoding with respect to the output from the bit calculation means. 
     The other objectives and advantages of the invention will be understood by the following description and will also be appreciated by the embodiments of the invention more clearly. Further, the objectives and advantages of the invention will readily be seen that they can be realized by the means and its combination specified in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the instant invention will become apparent from the following description, of preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view describing the concept of a conventional transmission diversity method using a space time block coding technique; 
         FIG. 2   a  is a circuitry diagram showing a configuration of a transmitter that implements a conventional STBC transmission diversity method in an MC-CDMA system; 
         FIG. 2   b  is a view describing the concept of a conventional STBC transmission diversity method in an MC-CDMA system; 
         FIG. 3  is a circuitry diagram of a transmitter that implements a conventional MC-CDMA diversity method using a multi-code when a data transmission rate is twice; 
         FIG. 4  is a view describing the concept of a conventional MC-CDMA diversity method using a multi-code when a data transmission rate is twice; 
         FIG. 5   a  is a circuitry diagram showing a configuration of one embodiment of a Space Code Block Coding (SCBC) and spreading apparatus for transmission diversity in accordance with the present invention; 
         FIG. 5   b  is a conceptual view describing a SCBC and spreading method for transmission diversity in accordance with the present invention; 
         FIG. 6   a  is a circuitry diagram showing a configuration of one embodiment of a multi-code (e.g., two codes) MC-CDMA diversity transmitter using SCBC in accordance with the present invention; 
         FIG. 6   b  is a view describing the concept of the SCBC transmission diversity in the MC-CDMA diversity transmitter shown in  FIG. 6   a  in accordance with the present invention; 
         FIG. 7  shows a view explaining the concept of an SCBC transmission diversity method where 2M codes are assigned to an arbitrary user in accordance with the present invention; 
         FIG. 8  is a circuitry diagram showing a configuration of one embodiment of an MC-CDMA diversity transmitter using SCBC in case where 2M codes are assigned to an arbitrary user in accordance with the present invention; 
         FIG. 9  is a view describing the concept of a transmission diversity method where one orthogonal code is assigned to each of arbitrary two users&#39; channels in accordance with the present invention; 
         FIG. 10  is a circuitry diagram showing a configuration of one embodiment of a CDMA mobile station receiver with respect to the transmission diversity in accordance with the present invention; 
         FIG. 11   a  is a circuitry diagram depicting a configuration of one embodiment of a DS-CDMA diversity transmitter using SCBC in case where 2M codes are assigned to an arbitrary user in accordance with the present invention; and 
         FIG. 11   b  is a circuitry diagram illustrating a configuration of the SCBC and spreading unit in accordance with the invention shown in  FIG. 11   a.    
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The above-mentioned objectives, features, and advantages will be more apparent from the following detailed description in association with the accompanying drawings; and based on this, the invention will be readily conceived by those skilled in the art to which the invention belongs. Further, in the following description, well-known arts will not be described in detail if it seems that they could obscure the invention in unnecessary detail. Hereinafter, a preferred embodiment of the present invention will be set forth in detail with reference to the accompanying drawings. 
       FIG. 5   a  is a circuitry diagram showing a configuration of one embodiment of an SCBC and spreading apparatus for transmission diversity in accordance with the present invention, and  FIG. 5   b  is a conceptual view describing a SCBC and spreading method for transmission diversity in accordance with the present invention. Here, a method for performing the diversity encoding in space (antenna) and code domain is presented. 
     As shown in  FIG. 5   a , the SCBC and spreading apparatus  500  in accordance with the present invention comprises an SCBC encoder  501 , orthogonal code generators  502   a  and  502   b , spreaders  503   a  to  503   d  composed of multipliers, and combiners  504   a  and  504   b  composed of adders. 
     The SCBC encoder  501  simultaneously outputs four symbols, e.g., s 0 , s 1 , −s 1 *, s 0 *, as transmission data, with respect to two input symbols s 0  and s 1  at arbitrary one modulation symbol interval. That is, the SCBC  501  simultaneously provides four symbols s 0 , s 1 , −s 1 *, s 0 * in response to the two input symbols s 0  and s 1  in parallel. The four output symbols include the two input symbols s 0  and s 1 , the input symbol&#39;s conjugate complex s 0 *, and the input symbol&#39;s negative conjugate complex −s 1 *. 
     Among the four output symbols from the SCBC encoder  501 , two, e.g., s 0  and −s 1 *, are spread by binary orthogonal code C (j) =[c 0   (j) c 1   (j) c 2   (j)  . . . c N−1   (j) ] T , and the remaining two symbols, i.e., s 1  and s 0 * are spread by another binary orthogonal code C (k) =[c 0   (k) c 1   (k) c 2   (k)  . . . . c N−1   (k) ] T . Here, T indicates a transposition matrix. And, the two orthogonal codes are orthogonal codes whose cross correlations are “0”. Further, the orthogonal codes in the invention are used as direct sequence spread spectrum codes on the frequency axis in case of MC-CDMA or Frequency-Hopping MC-CDMA (FH-MC-CDMA), while being used as direct sequence spread spectrum codes on the time axis in case of Direct Sequence-CDMA (DS-CDMA)(see  FIG. 11   a ). 
     The orthogonal code generators  502   a  and  502   b  generate desired binary orthogonal codes, and the multipliers  503   a  to  503   d  multiply the symbols outputted from the SCBC encoder  501  by the corresponding orthogonal codes, respectively. Outputs from the multipliers  503   a  to  503   d  are added at the adders  504   a  and  504   b  and then transmitted to antennas. 
     Hereinafter, the concept of the SCBC and spreading method in accordance with the present invention will be described in more detail with reference to  FIG. 5   b.    
     A signal s 0 C (j)  created by spreading the symbol s 0  to the orthogonal code C (j)  is added to a signal s 1 C (k)  produced by spreading the symbol s 1  to the orthogonal code s 1 C (k)  to output an added signal to a path for the first antenna (antenna  0 ). And, a signal S 0 *C (k)  created by spreading the symbol s 0 * to the orthogonal code C (k)  is added to a signal −s 1 *C (j)  obtained by spreading the symbol −s 1 * to the orthogonal code C (j)  to provide an added signal to a path for the second antenna (antenna  1 ). 
     As a result, a baseband signal transmitted via the first transmission antenna (antenna  0 ) at the arbitrary transmission symbol interval becomes S 0 C (j) +s 1 C (k) , and a baseband signal transmitted via the second transmission antenna (antenna  1 ) at the arbitrary transmission symbol interval becomes S 0 *C (k) −s 1 *C (j) . These two signals are transmitted at one symbol interval concurrently. This feature is the greatest difference of the SCBC transmission diversity method of the invention, which is distinguishable from the conventional STBC transmission diversity method. 
     Namely, the SCBC and spreading method of the invention performs the space code block coding with respect to the modulated symbols in such a way that the transmission diversity is made within one symbol interval every fixed number of modulated symbols (e.g., two, s 0  and s 1 , in  FIGS. 5   a and  5   b ). 
     The present invention may be applied to the DS-CDMA system that performs the direct sequence spread spectrum on the time axis, and also to the MC-CDMA system or FH-MC-CDMA system that carries out the direct sequence spread spectrum on the frequency axis or two-dimensional spread spectrum on both of the time and frequency axes. 
       FIG. 6   a  is a circuitry diagram showing a configuration of one embodiment of a multi-code (e.g., two codes) MC-CDMA diversity transmitter using the SCBC in accordance with the present invention, which represents a configuration of a base station transmitter in case where the SCBC transmission diversity method is applied to the MC-CDMA system that performs the direct sequence spread spectrum on the frequency axis. 
     In case where a data transmission rate is R when the number of symbols to be transmitted is one within one modulation symbol interval,  FIG. 6   a  shows an example where a data transmission rate of a kth channel is 2R. 
     In  FIG. 6   a , encoded data of the kth channel with the data transmission rate of 2R is first modulated at a modulator  601  and then two modulated symbols s k,0  and s k,1  are applied to an SCBC encoder  6021  every symbol interval. Then, the SCBC encoder  6021  provides four outputs s k,0 , s k,1 , −s* k,1 , and s* k,0  using the inputted two modulation symbols s k,0  and s k,1 , wherein each output symbol is duplicated at duplicators  6022   a  to  6022   d  by N. 
     Orthogonal code multipliers  6023   a  to  6023   d  multiply each of the four outputs s k,0 , s k,1 , −s* k,1 , and s* k,0  by a corresponding orthogonal code. Through such multiplication operation, each of the four outputs s k,0 , s k,1 , −s* k,1 , and s* k,0  is spread by any of two orthogonal codes, i.e., C (k,0) =[c 0   (k,0) c 1   (k,0) c 2   (k,0)  . . . c N−1   (k,0) ] T  and C (k,1) =[C 0   (k,1) c 1   (k,1) c 2   (k,1)  . . . c N−1   (k,0) ] T  assigned to the kth channel on the frequency axis. 
     Among the spread signals, the signals s k,0 C (k,0)  and s k,1 C (k,1)  are added at an adder  6024   a  for each subcarrier to output an added signal to a path for a first antenna  609   a , and the signals S* k,0 C (k,1)  and −S* k,1 C (k,0)  are added at an adder  6024   b  for each subcarrier to provide an added signal to a path for a second antenna  609   b . The signals s 0  outputted are again added to signals of other channels at adders  603   a  and  603   b  for each antenna and subcarrier and then multiplied by scrambling codes at scramblers  604   a  and  604   b . In the forgoing, s k,0 C (k,0) , s k,1 C (k,1) , s* k,0 C (k,1) , −s* k,1 C (k,0)  are all vectors. 
     The outputs from the scramblers  604   a  and  604   b  are IFFT-transformed at IFFT units  605   a  and  605   b  and then processed at parallel/serial converters  606   a  and  606   b  to provide arranged serial data. And then, CP is inserted into each of the outputs from the parallel/serial converters  606   a  and  606   b  at CP inserters  607   a  and  607   b ; and the CP-inserted signals are multiplied by a given gain and then converted into RF wireless signals at IF/RF processors  608   a  and  608   b  to transmit via the antennas  609   a  and  609   b.    
     Meanwhile,  FIG. 6   b  shows a view describing the concept of the SCBC transmission diversity in the MC-CDMA diversity transmitter shown in  FIG. 6   a.    
     It can be seen from  FIG. 6   b  that the outputs from the modulator  601 , s k,0  and s k,1 , are SCBC-processed and spread to transmit s k,0 C (k,0) +s k,1 C (k,1)  to the antenna  0   609   a  and s* k,0 C (k,1) −s* k,1 C (k,0)  to the antenna  1   609   b . In other words, it can be found that the transmission diversity can be made within one symbol interval. 
       FIG. 7  shows a view explaining the concept of an SCBC transmission diversity method where 2M codes are assigned to an arbitrary user in accordance with the present invention. That is,  FIG. 7  presents an example where the transmission diversity method in accordance with the present invention is applied in case where 2M orthogonal codes are assigned to a kth user. 
     Among 2M modulation symbols, each pair of two symbols is SCBC-encoded, spread by an orthogonal code corresponding to each symbol, added for each antenna, and then transmitted simultaneously, within one modulation symbol interval. 
     For instance, if 2mth symbol and (2m+1)th symbol among the 2M modulation symbols are s k,2m  and s k,2m+1 , respectively, each pair of two symbols is SCBC-encoded, wherein m is 0, 1, 2, . . . , M−1. And then, each of the SCBC-encoded symbols is spread by C (k,2m) =[c 0   (k,2m) c 1   (k,2m) c 2   (k,2m)  . . . c N−1   (k,2m) ] T  and C (k,2m+1) =[c 0   (k,2m+1) c 1   (k,2m+1) c 2   (k,2m+1)  . . . c N−1   (k,2m+1) ] T , respectively, added for each antenna and then outputted. 
     Hence, a component transmitted to the first antenna (antenna  0 ) becomes 
               ∑     m   =   0       M   -   1       ⁢           ⁢     (         s     k   ,     2   ⁢   m         ⁢     C     (     k   ,     2   ⁢   m       )         +       s     k   ,       2   ⁢   m     +   1         ⁢     C     (     k   ,       2   ⁢   m     +   1       )           )           
and a component to the second antenna (antenna  1 ) becomes
 
               ∑     m   =   0       M   -   1       ⁢           ⁢       (         s     k   ,     2   ⁢   m       *     ⁢     C     (     k   ,       2   ⁢   m     +   1       )         -       s     k   ,       2   ⁢   m     +   1       *     ⁢     C     (     k   ,     2   ⁢   m       )           )     .           
And, since the number of the orthogonal codes used is 2M, the data transmission rate becomes 2MR.
 
       FIG. 8  is a circuitry diagram showing a configuration of one embodiment of an MC-CDMA diversity transmitter using SCBC in case where 2M codes are assigned to an arbitrary user in accordance with the present invention. That is,  FIG. 8  offers a structure of an MC-CDMA transmitter employing a transmission diversity technology in accordance with the present invention in case where 2M orthogonal codes are assigned to a kth user. 
     At first, encoded data of a kth channel is modulated at a modulator  801  and then 2M modulation symbols are applied to a serial/parallel converter  802  at each transmission modulation symbol interval. Then, the serial/parallel converter  802  simultaneously outputs total M symbol pairs in parallel. 
     Each of the M symbol pairs, e.g., s k,0  and s k,1 , etc., is provided to an SCBC and spreading unit  803  wherein two vector signals s k,2m C (k,2m) +s k,2m+1 C (k,2m+1)  and s* k,2m C (k,2m+1)s*   k,2m+1 C (k,2m)  are outputted from each of SCBC and spreading units  803 - 1  to  803 -M. 
     The output vector signals from the M SCBC and spreading units  803 - 1  to  803 -M are combined at combiners  804   a  and  804   b  for antenna paths composed of adders. Hence, an output from the combiner  804   a  for the first antenna becomes 
               ∑     m   =   0       M   -   1       ⁢           ⁢     (         s     k   ,     2   ⁢   m         ⁢     C     (     k   ,     2   ⁢   m       )         +       s     k   ,       2   ⁢   m     +   1         ⁢     C     (     k   ,       2   ⁢   m     +   1       )           )           
and an output from the combiner  804   b  for the second antenna becomes
 
     
       
         
           
             
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     The outputs from the combiners  804   a  and  804   b  for the antenna paths are applied to channel combiners  805   a  and  805   b  to add to channel signals of other users. And then, the added signals are scrambled by multiplying by scrambling codes at scramblers  806   a  and  806   b.    
     The outputs from the scramblers  806   a  and  806   b  are IFFT-transformed at IFFT units  807   a  and  807   b , that is, the frequency domain signals are transformed into corresponding time domain signals, and then processed at parallel/serial converters  808   a  and  808   b  to obtain converted serial signals. 
     Thereafter, CP is inserted into each of the outputs from the parallel/serial converters  808   a  and  808   b  at CP inserters  809   a  and  809   b ; and then the CP-inserted signals are amplified and converted into RF signals at IF/RF processors  810   a  and  801   b  to transmit them via corresponding antennas  811   a  and  811   b.    
       FIG. 9  shows a view describing the concept of a transmission diversity method where one orthogonal code is assigned to each of arbitrary two users&#39; channels in accordance with the present invention. That is,  FIG. 9  presents a transmission diversity method in accordance with the present invention in case where one orthogonal code is assigned to an arbitrary user channel, i.e., the data transmission rate is R. 
     In this case, a transmitter of the present invention multiplexes modulation .symbols of arbitrary two channels whose data transmission rate is R at a multiplexer  901 , and then SCBC-encodes and spreads the multiplexed symbols using two orthogonal codes assigned to each channel at an SCBC and spreading unit  902  to transmit spread signals. 
     Details of the transmitter will be given below. 
     For example, if modulation signals of kth and uth users&#39; channels are s k,0  and s u,0  at an arbitrary transmission interval, respectively, the multiplexed signal from the multiplexer  901  becomes s k,0  s u,0  which is then applied to the SCBC and spreading unit  902 , wherein the signal is SCBC-encoded and spread to orthogonal codes C (k)  and C (u)  assigned to each channel to output s k,0 C (k) +s u,0 C (u)  to the first antenna and also provide s* k,0 C (u) −s u,0 C (k)  to the second antenna. 
     With respect to the diversity transmission signals as described early, a mobile station receiver performs SCBC decoding and then takes only corresponding users&#39; channel symbols excepting other users&#39; channel symbols. 
       FIG. 10  is a circuitry diagram showing a configuration of one embodiment of a CDMA mobile station receiver with respect to the transmission diversity of the present invention, which represents a structure of a mobile station receiving end in case where the transmission diversity technique of the present invention is applied to the MC-CDMA base station transmitting end. 
     As shown in  FIG. 10 , the MC-CDMA mobile station receiver of the invention comprises an antenna  1001 , an RF/IF processor  1002 , a CP remover  1003 , an FFT block  1004 , a descrambler  1005 , a despreader  1006 , a channel estimator  1007 , a channel equalization and SCBC decoder  1008 , a soft bit calculator  1009 , and a channel decoder  1010 . Each of the elements will be described below in detail. 
     A wireless signal is first received via the antenna  1001  and then amplified and converted into a baseband signal at the RF/IF processor  1002 . 
     The CP remover  1003  serves to remove CP from the output signal provided from the RF/IF processor  1002 , and the FFT  1004  transforms the time domain signal from the CP remover  1003  into a corresponding frequency domain signal. And then, the descrambler  1005  descrambles the frequency domain signal from the FFT  1004 . 
     The despreader  1006  despreads the descrambled signal to an orthogonal signal; and the channel estimator  1007  conducts channel estimation with respect to two wireless paths between two base station transmission antenna and mobile station reception antenna from the descrambled signal. 
     The channel equalization and SCBC decoder  1008  performs channel equalization and SCBC decoding using the outputs from the despreader  1006  and the channel estimator  1007 , that is, the despread reception symbols and channel estimation values to thereby recover a transmitted signal 
     Thereafter, the soft bit calculator  1009  receives the output from the channel equalization and SCBC decoder  1008  and calculates a soft bit value to be provided to the channel decoder  1010 . 
     And then, the channel decoder  1010  conducts the channel decoding and offers the decoded result to an upper layer. 
     Hereinafter, a more detailed description of the receiver will be provided. 
     For instance, if a transmitting end utilizes 2M orthogonal codes for kth user channel as shown in  FIG. 8  (that is, if a data transmission rate is 2M that is twice a basic transmission rate R), the despreader  1006  of the mobile station receiver as shown in  FIG. 10  outputs results that are despread to the 2M orthogonal codes assigned to the kth user channel every symbol interval. 
     Then, the channel equalization and SCBC decoder  1008  receives the 2M outputs from the despreader  1006  at each symbol interval and performs the SCBC decoding therefore. 
     In other words, in case where a wireless channel estimated value between the first transmission antenna (base station transmission antenna) and the mobile station reception antenna is α 0 , and a wireless channel estimated value between the second transmission antenna (base station transmission antenna) and the mobile station reception antenna is α 1  at an arbitrary symbol interval, if the symbol values despread by the orthogonal codes C (k+2m)  and C (k+2m+1)  (where m=0, 1, 2 , . . . , M−1) are r 2m  and r 2m+1 , respectively, the output from the channel equalization and SCBC decoder  1008  may be as follows:
 
 ŝ   2m   =r   2m α* 0   +r*   2m+1 α 1  
 
 ŝ   2m+1   =r   2m α* 1   −r*   2m+1 α 0   Eq. (3)
 
where m=0, 1, 2, . . . , M−1
 
     On the other hand, if a transmitting end multiplexes and SCBC-encodes with respect to each of two users&#39; channels to which only one orthogonal code is assigned and then transmits the results at the transmitter as shown in  FIG. 9 , the despreader  1006  of the mobile station receiver as shown in  FIG. 10  despreads to the orthogonal code C (k)  assigned to the kth user channel and to the orthogonal code C (u)  assigned to the uth user channel. 
     Then, using the two symbols r k  and r u  despread at the despreader  1006  and the output values α 0  and α 1  from the channel estimator  1007 , the channel equalization and SCBC decoder  1008  provides a signal obtained by taking the following equation 4 when the current mobile station is for the kth user channel and a signal derived by taking the following equation 5 when the current mobile state is for the uth user channel.
 
 ŝ   k   =r   k α* 0   +r*   u α 1   Eq. (4)
 
 ŝ   u   =r   k α* 1   −r*   u α 0   Eq. (5)
 
       FIG. 11   a  is a circuitry diagram depicting a configuration of one embodiment of a DS-CDMA diversity transmitter using SCBC in case where 2M codes are assigned to an arbitrary user in accordance with the present invention, and  FIG. 11   b  is a circuitry diagram illustrating a configuration of the SCBC and spreading unit of the invention shown in  FIG. 11   a.    
     The basic concept of the DS-CDMA diversity transmitter (base station transmitter) as shown in  FIGS. 11   a  and  11   b  is the same as that of the MC-CDMA as shown in  FIG. 8  except that the spreading process is carried out on the time axis. Details thereof will be presented hereinafter. 
     Firstly, encoded data every channel is modulated at a modulator  1101  and then 2M modulation symbols are applied to a serial/parallel converter  1102  at each transmission modulation symbol interval. Then, the serial/parallel converter  1102  simultaneously outputs a total M number of symbol pairs in parallel. Each of the M symbol pairs, e.g., s k,0  and s k,1 , etc., is provided to an SCBC and spreading unit  1103  wherein two vector signals are outputted from each of SCBC and spreading units  1103 - 1  to  1103 -M. For example, an (m+1)th SCBC and spreading unit  1103 -(m+1) included in the SCBC and spreading unit  1103  provides s k,2m C (k,2m) +s k,2m+1 C (k,2m+1)  and s* k,2m C (k,2m+1 −s* k,2m+1 C (k,2m)  (see  FIG. 11   b ). 
     The output vector signals from the M SCBC and spreading units  1103 - 1  to  1103 -M are added at adders  1104   a  and  1104   b  for each antenna path. Hence, an output from the adder  1104   a  for a first antenna path becomes 
               ∑     m   =   0       M   -   1       ⁢           ⁢     (         s     k   ,     2   ⁢   m         ⁢     C     (     k   ,     2   ⁢   m       )         +       s     k   ,       2   ⁢   m     +   1         ⁢     C     (     k   ,       2   ⁢   m     +   1       )           )           
and an output from the adder  1104   b  for a second antenna path becomes
 
     
       
         
           
             
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     The outputs from the adders  1104   a  and  1104   b  are applied to channel combiners  1105   a  and  1105   b  to add to channel signals of other users. And then, the added signals are scrambled by multiplying by scrambling codes at scramblers  1106   a  and  1106   b.    
     The outputs from the scramblers  1106   a  and  1106   b  are amplified and converted into RF signals at IF/RF processors  1107   a  and  1107   b  to transmit them via corresponding antennas. 
     As can be seen from the drawing, since the DS-CDMA base station transmitter performs the spreading process on the time axis, it doesn&#39;t include the IFFTs  807   a  and  807   b , the parallel/serial converters  808   a  and  808   b , and the CP inserters  809   a  and  809   b , which are involved in the MC-CDMA as shown in  FIG. 8 . 
     Meanwhile, a description will be given below in detail with respect to the (m+1)th SCBC and spreading unit  1103 -(m+1) in the SCBC and spreading unit  1103 . 
     The outputs from the serial/parallel converter  1102 , s k,2m  and s k,2m+1 , are provided to an SCBC encoder  11031 ; and the outputs therefrom are then spread by multiplying by orthogonal codes at a spreader  11032 . Lastly, outputted from an adding unit  11033  are a baseband signal to be s k,2m+1 C (k,2m) +s k,2m+1 C (k,2m+1)  to be transmitted via a first transmission antenna and a baseband signal s* k,2m C (k,2m+1) −s* k,2m+1 C (k,2m)  to be transmitted via a second transmission antenna. 
     As a result, the present invention allows the antenna diversity to be conducted within one symbol interval, thereby improving the performance of system in wireless channel environments where Doppler effect exists, compared to a conventional STBC transmission diversity method which makes the antenna diversity performed over two symbol intervals. 
     The method of the present invention as mentioned above may be implemented by a software program and stored in a computer-readable storage medium such as CD-ROM, RAM, ROM, floppy disk, hard disk, optical magnetic disk, etc. This process may be readily carried out by those skilled in the art; and therefore, details of thereof are omitted here. 
     The present application contains subject matter related to Korean patent application No. 2005-48940, filed with the Korean Intellectual Property Office on Jun. 8, 2005, the entire contents of which are incorporated herein by reference. 
     While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.