Patent Publication Number: US-7912146-B2

Title: Method and apparatus for transmitting data in a communication system

Description:
PRIORITY 
     This application claims the benefit under 35 U.S.C. §119(a) of an application filed in the Korean Intellectual Property Office on Oct. 12, 2005 and assigned Serial No. 2005-96267, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to signal transmission in a communication system, and in particular, to a data transmission method and apparatus capable of compensating for distortion caused by fast fading in a communication system that uses a Space-Frequency Block-Coded (SFBC) scheme and a single carrier. 
     2. Description of the Related Art 
     In the next generation multimedia communication system now under research, as there is an increasing demand for a high-speed communication system capable of processing and transmitting a variety of information such as video and wireless data beyond early voice-oriented services, it is necessary to increase efficiency of communication systems by using a proper channel coding scheme. In addition, communication systems should transmit signals over a channel at high efficiency and reliability. 
     Meanwhile, wireless channel environments in wireless communication systems, unlike wire channel environments, suffer a loss of information as errors occur due to various causes such as multi-path interference, shadowing, propagation attenuation, time-varying noise, interference, fading, etc. A Frequency-Domain Equalization (FDE) scheme has been proposed as a technique for removing interference in the wireless channel environments. 
     In addition, a single-carrier transmission scheme based on the FDE scheme has recently been adopted as a standard for the broadband wireless Metropolitan Area Network (MAN) system, such as Institute of Electrical and Electronics Engineers (IEEE) 802.16 and European Telecommunications Standards Institute (ETSI) Hiper MAN. Further, a Single Carrier Frequency-Domain Equalization (SC-FDE) scheme having the similar structure and performance to that of the Orthogonal Frequency Division Multiplexing (OFDM) scheme, is robust against non-linear distortion or synchronization of carriers, and can reduce system complexity of a user terminal for uplink transmission even through simple signal processing at a transmitter. 
     Also, there has been proposed a transmission diversity technique that can increase channel capacity and link reliability by spatially arranging several transmission antennas without increasing a frequency bandwidth or transmission power. Recently, an SC-FDE scheme to which a Space Time Block Code (STBC) scheme for providing a transmission diversity gain is applied has been proposed. 
       FIG. 1  shows an STBC transmission sequence used for transmitting signals via two antennas using an STBC scheme according to the prior art. Referring to  FIG. 1 , the STBC transmission sequence sequentially transmits symbol blocks  110 ,  120 ,  130  and  140  via two antennas  101  and  103  in the time domain, and inserts cyclic prefixes (CPs)  112 ,  122 ,  132  and  142  between the symbol blocks  110 ,  120 ,  130  and  140  as guard intervals. The channel state should be constant between two symbol blocks, i.e. an n th  block  110  (or  130 ) and an (n+1) th  block  120  (or  140 ), transmitted through each of the two antennas  101  and  103 . However, the SC-FDE scheme to which the STBC scheme is applied, can guarantee its performance because the constant channel state between symbol blocks is maintained in the slow fading environment, but the scheme has a limitation in performance guarantee in the fast fading environment. 
     However, the SFBC scheme, although it is robust against the fading environment as compared with the STBC scheme, cannot be directly applied to the single-carrier system because it is a multi-carrier scheme that applies block codes to adjacent sub-channels or adjacent sub-carriers. In particular, the channel state between adjacent sub-carriers should be constant, in order for the SFBC scheme to guarantee its performance. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a method and apparatus for transmitting data in a communication system. 
     It is another object of the present invention to provide a method and apparatus for transmitting data through a single carrier in a communication system using SFBC. 
     According to one aspect of the present invention, there is provided a method for transmitting data in a communication system. The method includes repeatedly processing an input signal a number of times; performing SFBC coding on the repeatedly processed input signals and outputting at least two signal blocks in parallel; and inserting a CP in the signal blocks and transmitting the CP-inserted signal blocks via associated transmission antennas using a single carrier. 
     According to another aspect of the present invention, there is provided an apparatus for transmitting data in a communication system. The apparatus includes a symbol mapper for mapping input information bits to a symbol; a repeater for repeatedly processing symbols output from the symbol mapper a number of times; a demultiplexer for demultiplexing symbols output from the repeater; a symbol processing module for processing parallel symbols output from the demultiplexer and outputting at least two SFBC-coded signal blocks in parallel; and a CP inserter for inserting a CP in signal blocks output in parallel from the symbol processing module. 
     According to further another aspect of the present invention, there is provided an apparatus for transmitting data in a communication system. The apparatus includes a repeater for repeatedly processing an input signal a number of times; an SFBC encoder for performing SFBC coding on the repeatedly processed input signals, and outputting at least two signal blocks in parallel; and a CP inserter for inserting a CP in the signal blocks and transmitting the CP-inserted signal blocks via associated transmission antennas using a single carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a diagram illustrating a structure of an STBC transmission sequence according to the prior art; 
         FIG. 2  is a diagram illustrating a configuration of a Single Carrier Frequency-Domain Equalization (SC-FDE) communication system with a single transmission antenna; 
         FIG. 3  is a diagram illustrating a structure of a transmitter in a communication system using an SFBC scheme; 
         FIG. 4  is a diagram illustrating a configuration of an SC-FDE communication system with a single transmission antenna according to the present invention; 
         FIG. 5  is a diagram illustrating symbols transmitted in a frequency band by the transmitter of  FIG. 4  according to the present invention; 
         FIG. 6  is a diagram illustrating a structure of a transmitter in a communication system according to of the present invention; 
         FIG. 7  is a diagram illustrating symbols transmitted in a frequency band by the transmitter of  FIG. 6  according to the present invention; and 
         FIG. 8  is a diagram illustrating a structure of a receiver in a communication system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness. 
     The present invention provides a method and apparatus for transmitting data in a communication system. In addition, the present invention provides a scheme for transmitting/receiving data with a single carrier in a communication system using a Space-Frequency Block-Coded (SFBC) scheme. In particular, the present invention provides a data transmission/reception scheme for compensating for distortion of data in the fast fading environment and allowing a transmitter to transmit data to a plurality of receivers without increasing complexity of the transmitter, thereby improving system performance. 
       FIG. 2  shows a Single Carrier Frequency-Domain Equalization (SC-FDE) communication system with a single transmission antenna according to the present invention. Referring to  FIG. 2 , the communication system includes a transmitter and a receiver. The transmitter includes a bit generator  201  for generating information bits upon receipt of data to be transmitted to a receiver, a symbol mapper  203  for mapping a bit stream output from the bit generator  201  to a fixed-length symbol, a cyclic prefix (CP) inserter  205  for inserting a CP in the symbol output from the symbol mapper  203 , a digital-to-analog (D/A) converter  207  for converting the digital signal output from the CP inserter  205  into an analog signal, and a radio frequency (RF) transmitter  209  for transmitting the signal output from the D/A converter  207  using an RF frequency. 
     The receiver includes an RF receiver  211  for receiving a signal from the transmitter over a wireless channel, an analog-to-digital (A/D) converter  213  for converting the analog signal output from the RF receiver  211  into a digital signal, a CP remover  215  for removing a CP from the digital signal output from the A/D converter  213 , a Fast Fourier Transform (FFT) unit  217  for performing an FFT process on the signal output from the CP remover  215 , an FDE unit  219  for performing an FDE process on the signal output from the FFT unit  217 , an Inverse Fast Fourier Transform (IFFT) unit  221  for performing an IFFT process on the signal output from the FDE unit  219 , a symbol demapper  223  for demapping the symbol output from the IFFT unit  221  into a bit stream, and a signal determiner  225  for determining a transmission signal for the bit stream output from the symbol demapper  223 . 
     A description will now be made of a single-carrier communication system with two transmission antennas and one reception antenna, which transmits/receives SFBC signals based on the FDE scheme shown in  FIG. 2 . 
       FIG. 3  shows a transmitter in a communication system with two antennas. Referring to  FIG. 3 , if the data to be transmitted to a user, i.e. the data to be transmitted to the receiver, is input to the bit generator  201  of the transmitter shown in  FIG. 2 , the bit generator  201  outputs a bit stream to the symbol mapper  203 . The symbol mapper  203  maps the bit stream to a fixed-length symbol and then delivers the mapped bit stream to a symbol generator  310 . The symbol generator  310  then outputs symbols. The symbols output from the symbol generator  310  are processed into two signal streams by a signal processor  320  including a pair of FFT units  321  and  323  and a pair of IFFT units  325  and  327  associated with the FFT units  321  and  323 . A CP is inserted in each signal stream by an associated CP inserter  331  and  333 ), and the CP-inserted signal stream is transmitted via an associated transmission antenna  341  and  343 ). 
     The signal transmission of the transmitter represents transmission in a time band other than a frequency band, and because the communication system processes the transmission sequence in the time band in such a way, the signal processor  320  introduces the concept in which the communication system generates single-carrier transmission signals in the time band using the SFBC scheme. Of the two signal streams output from the pair of the FFT units  321  and  323 , the signal stream X( 0 ), X( 1 ), . . . , X(n−2), X(n−1) corresponding to the first antenna  341  and the signal stream −X*( 1 ), X*( 0 ), . . . , −X*(n−1), X*(n−2) corresponding to the second antenna  343  are conjugate to each other. 
     If an n th  symbol of a signal block transmitted from an i th  antenna is denoted by x i (n), a symbol x 1 (n) transmitted via the first antenna  341  and a symbol x 2 (n) transmitted via the second antenna  343  can be expressed as Equation (1) 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             
                               
                                 
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     In Equation (1), x e (n) and x o (n) are defined as shown in Equation (2), and the x e (n) and the x o (n) have a period of N/2 for n. In addition, W N  is defined as 
               W   N     =       ⅇ       -   j     ⁢       2   ⁢           ⁢   π     N         .             x   e ( n )= x (2 n ),  x   o ( n )= x (2 n+ 1),  n= 0, 1, . . . ,  N/ 2−1  (2)
 
     In this way, the transmitter transmits the symbols shown in Equation (1) via the first antenna  341  and the second antenna  343  using a single carrier. From the symbols transmitted, in particular, via the second antenna  343 , the transmitter can determine that the communication system transmits signals using the SFBC scheme. 
       FIG. 4  shows a Single Carrier Frequency-Domain Equalization (SC-FDE) communication system with a single transmission antenna according to the present invention. Referring to  FIG. 4 , the communication system includes a transmitter and a receiver. The transmitter includes a bit generator  401  for generating information bits, a symbol mapper  403  for mapping a bit stream output from the bit generator  401  to a fixed-length symbol, a repeater  405  for repeatedly processing the symbols output from the symbol mapper  403  a number of times so the symbols are spaced apart at regular intervals and symbols of other information are inserted in the spaced intervals, a cyclic prefix (CP) inserter  407  for inserting a CP in the symbols output from the repeater  405 , a digital-to-analog (D/A) converter  409  for converting the digital signal output from the CP inserter  407  into an analog signal, and a radio frequency (RF) transmitter  411  for transmitting the signal output from the D/A converter  409  using an RF frequency. 
     The repeater  405  repeatedly processes a symbol block generated by collecting input symbols, and the number of repeated processes (hereinafter referred to as “the number of repetitions”) corresponds to the number of users whose signals the communication system can simultaneously process. The symbol block input to the repeater  405  and the symbol block output from the repeater  405  exist at the same time. That is, the repeater  405 , while repeatedly processing the symbol block, reduces a sample time of the samples constituting each symbol block by the number of repetitions so the input symbol block and the output symbol block of the repeater  405  may exist at the same time. 
     The receiver includes an RF receiver  413  for receiving a signal from the transmitter over a wireless channel, an analog-to-digital (A/D) converter  415  for converting the analog signal output from the RF receiver  413  into a digital signal, a CP remover  417  for removing a CP from the digital signal output from the A/D converter  415 , a Fast Fourier Transform (FFT) unit  419  for performing an FFT process on the signal output from the CP remover  417 , an FDE unit  421  for performing an FDE process on the signal output from the FFT unit  419 , an Inverse Fast Fourier Transform (IFFT) unit  423  for performing an IFFT process on the signal output from the FDE unit  421 , a symbol demapper  425  for demapping the symbol output from the IFFT unit  423  into a bit stream, and a signal determiner  427  for determining a transmission signal for the bit stream output from the symbol demapper  425 . 
     The communication system of  FIG. 4 , compared with the communication system of  FIG. 2 , further includes the repeater  405  in the transmitter, and the repeater  405  spaces symbols at regular intervals as described above. The repeater  405  arranges the symbols output from the symbol mapper  403  at regular intervals such that the symbols should not be adjacent to each other in the frequency band. In order to arrange the symbols in the frequency band at regular intervals, the repeater  405  repeatedly processes the input signal in the time band a predetermined number of times, and ‘0’ is inserted between transmission samples of the signal, received as many times as the number of repetitions of the repeater  405 . For example, if the number of repetitions of the repeater  405  is four, four ‘0’s are inserted in each interval between the transmission samples. If the transmission samples, between which ‘0’s are inserted in the time band, are represented as symbols in the frequency band, the symbols are arranged in such a way that they are spaced apart at regular intervals as described above. A regular interval occurs by the ‘0’s inserted between the samples in the time band, and transmission samples of another input signal can be inserted in the regular interval, i.e. in the positions where the ‘0’s are inserted. With reference to  FIG. 5 , a detailed description will now be made of the repeater  405 . 
       FIG. 5  shows symbols transmitted in a frequency band by the transmitter in the communication system of  FIG. 4  according to the present invention. It is assumed in  FIG. 5  that the transmitter transmits eight symbols in the frequency band. Referring to  FIG. 5 , if the data to be transmitted to a user  1  is input to the bit generator  401  as described in  FIG. 4 , the transmitter performs the above-described signal processing on the input data, and transmits eight symbols  510  through the RF transmitter  411  using an RF frequency. In addition, if the data to be transmitted to a user  2  is input to the bit generator  401 , the transmitter transmits eight symbols  520  through the RF transmitter  411  using an RF frequency. 
     The eight symbols  510  for the user  1  and the eight symbols  520  for the user  2  are transmitted over different spaces in the frequency band. That is, the transmitter divides the space into a space for the eight symbols  510  associated with the user  1  and a space for the eight symbols  520  associated with the user  2  in the same frequency band, and then transmits the eight symbols  510  and the eight symbols  520  over their associated divided spaces. The eight symbols  510  and the eight symbols  520  are spaced apart at regular intervals by the repeater  405  of the transmitter, and a spaced interval between the symbols is determined depending on the number of repetitions of the repeater  405 . More specifically, as the number of repetitions of the repeater  405  increases, the number of ‘0’s inserted between transmission samples in the time band increases as described above, and if the inserted ‘0’ is shown in the frequency band, it becomes the spaced interval between the symbols. As a result, the spaced interval between the symbols increases. The space where it can be divided in the frequency band increases due to the increased interval. As the space where it can be divided in the frequency band increases in this way, it is possible to transmit symbols corresponding to more users through the increased space in the frequency band. For example, if the number of repetitions of the repeater  405  is four, the number of ‘0’s inserted between transmission samples in the time band is four, and as the positions where ‘0’s are inserted are shown at regular intervals in the frequency band, eight symbols for four users can be inserted in the positions where ‘0’s can be inserted. 
     Because the space where it can be divided in the frequency band has a predetermined size, the symbols for the users, which can be transmitted in the frequency band, also have a predetermined size by increasing the number of repetitions of the repeater  405 . That is, if the number of symbols for one user in the frequency band is small, it is possible to transmit symbols corresponding to more users by increasing the number of repetitions of the repeater  405 . If the number of symbols for one user in the frequency band is large, because the number of repetitions of the repeater  405  is smaller than the former case, the number of users is also smaller than the former case. 
     In the following description, it will be assumed that a single-carrier communication system with two transmission antennas and one reception antenna transmits/receives SFBC signals based on the FDE scheme shown in  FIG. 4 . 
       FIG. 6  shows a transmitter in a communication system with two antennas. If the data to be transmitted to a user, i.e. the data to be transmitted to a receiver, is input to the bit generator  401  of the transmitter as shown in  FIG. 4 , the bit generator  401  outputs a bit stream to the symbol mapper  403 , and the symbol mapper  403  maps the bit stream to a fixed-length symbol, and then delivers the mapped bit stream to a symbol generator  610 . Then the symbol generator  610  outputs symbols. The symbols output from the symbol generator  610  are delivered to a repeater  620 , and the symbols are arranged at regular intervals by the repeater  620  such that they should not be adjacent to each other in the frequency band. The symbols output from the repeater  620  are processed into two signal streams by a signal processor  630  including a pair of FFT units  631  and  633  and a pair of IFFT units  635  and  637  associated with the FFT units  631  and  633 . A CP is inserted in each signal stream by an associated CP inserter  641  and  643 ), and the CP-inserted signal stream is transmitted via an associated transmission antenna  651  and  653 ). 
     The signal transmission of the transmitter represents transmission in a time band other than a frequency band, and because the communication system processes the transmission sequence in the time band in such a way, the signal processor  630  introduces the concept in which the communication system generates single-carrier transmission signals in the time band using the SFBC scheme. Of the two signal streams output from the pair of the FFT units  631  and  633 , the signal stream X( 0 ), X( 1 ), 0, . . . , X( 2 ), X( 3 ), 0, . . . , X(n−2), X(n−1), 0, . . . corresponding to the first antenna  651  and the signal stream −X*( 1 ), X*( 0 ), 0, . . . , −X*( 3 ), X*( 2 ), 0, . . . , −X*(n−1), X*(n−2), 0, . . . corresponding to the second antenna  653  are conjugate to each other. 
     ‘0’ in the two signal streams represents a regular interval between symbols by the repeater  620  when the symbols are transmitted via the first antenna  651  and the second antenna  653  in the frequency band. For example, when the symbols are transmitted via the first antenna  651  in the frequency band, symbols X( 0 ) and X( 1 ) are transmitted with adjacent sub-carriers, and symbols X( 2 ) and X( 3 ) are also transmitted with adjacent sub-carriers. A regular interval between the symbol pair X( 0 ) and X( 1 ) and the symbol pair X( 2 ) and X( 3 ) transmitted with the adjacent sub-carriers is a symbol of ‘0’ between the symbol pair X( 0 ) and X( 1 ) and the symbol pair X( 2 ) and X( 3 ) in the signal stream. That is, as the number of ‘0’s existing between signals in the signal stream is larger, the interval between symbols in the frequency band increases. 
     In order to arrange symbol pairs in the frequency band at regular intervals, the repeater  620  repeatedly processes a signal input in the time band a number of times, and ‘0’s are inserted between transmission sample pairs, i.e. a sample pair X( 0 ) and X( 1 ), a sample pair X( 2 ) and X( 3 ), . . . , a sample pair X(n−2) and X(n−1), and a sample pair −X*( 1 ) and X*( 0 ), a sample pair −X*( 3 ) and X*( 2 ), . . . , a sample pair −X*(n−1) and X*(n−2), of transmission symbols of the signal input as many times as the number of repetitions of the repeater  620 . For example, if the number of repetitions of the repeater  620  is 4, 4 pairs of ‘0’s, i.e. 8 ‘0’s, are inserted between the transmission sample pairs. If the transmission sample pairs between which ‘0’s are inserted in the time band are shown as symbols in the frequency band, the symbols are arranged between the symbol pairs at regular intervals as described above. Therefore, it is possible to insert input signals of other users in the positions of ‘0’s inserted in the transmission sample pairs before transmission. 
     If an n th  symbol of a signal block transmitted from an i th  antenna is denoted by x i (n), a symbol x 1 (n) transmitted via the first antenna  651  can be expressed as Equation (3) 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
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                                 2 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 L 
                               
                             
                             
                               
                                 - 
                                 n 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               l 
                             
                           
                           + 
                           
                             
                               1 
                               
                                 N 
                               
                             
                             ⁢ 
                             
                               W 
                               N 
                               
                                 - 
                                 n 
                               
                             
                             ⁢ 
                             
                               
                                 ∑ 
                                 
                                   l 
                                   = 
                                   0 
                                 
                                 
                                   
                                     N 
                                     
                                       2 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       L 
                                     
                                   
                                   - 
                                   1 
                                 
                               
                               ⁢ 
                               
                                 
                                   
                                     X 
                                     1 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     
                                       
                                         2 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         L 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         l 
                                       
                                       + 
                                       1 
                                     
                                     ) 
                                   
                                 
                                 · 
                                 
                                   W 
                                   
                                     N 
                                     
                                       2 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       L 
                                     
                                   
                                   
                                     
                                       - 
                                       n 
                                     
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     l 
                                   
                                 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           = 
                           
                             
                               1 
                               
                                 N 
                               
                             
                             ⁢ 
                             
                               ( 
                               
                                 
                                   
                                     x 
                                     e 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                                 + 
                                 
                                   
                                     W 
                                     N 
                                     
                                       - 
                                       n 
                                     
                                   
                                   ⁢ 
                                   
                                     
                                       x 
                                       o 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       n 
                                       ) 
                                     
                                   
                                 
                               
                               ) 
                             
                           
                         
                         , 
                         
                           n 
                           = 
                           0 
                         
                         , 
                         … 
                         ⁢ 
                         
                             
                         
                         , 
                         
                           N 
                           - 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     In Equation (3), Q denotes the number of symbols transmitted via one antenna. If the one antenna transmits symbols corresponding to a plurality of users, it indicates the number of symbols associated with each user. Further, L denotes an interval between symbols depending on the number of repetitions of the repeater  620 , i.e. depending on the symbols by the repeater  620 . Thus, L indicates the number of users associated with the symbols transmitted by the antenna. In addition, N denotes a size of the FFT unit pair  631  and  633 , and if N is defined as N=Q·L, W N  is defined as 
     
       
         
           
             
               W 
               N 
             
             = 
             
               
                 ⅇ 
                 
                   
                     - 
                     j 
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     
                       2 
                       ⁢ 
                       π 
                     
                     N 
                   
                 
               
               . 
             
           
         
       
     
     In addition, x e (n) and x(n) in Equation (3) are defined in Equation (4) as 
     
       
         
           
             
               
                 
                   
                     
                       
                         x 
                         e 
                       
                       ⁡ 
                       
                         ( 
                         n 
                         ) 
                       
                     
                     = 
                     
                       
                         ∑ 
                         
                           l 
                           = 
                           0 
                         
                         
                           
                             N 
                             
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               L 
                             
                           
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         
                           
                             X 
                             1 
                           
                           ⁡ 
                           
                             ( 
                             
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               L 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               l 
                             
                             ) 
                           
                         
                         · 
                         
                           W 
                           
                             N 
                             
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               L 
                             
                           
                           
                             
                               - 
                               n 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             l 
                           
                         
                       
                     
                   
                   , 
                   
                     
                       
                         x 
                         o 
                       
                       ⁡ 
                       
                         ( 
                         n 
                         ) 
                       
                     
                     = 
                     
                       
                         ∑ 
                         
                           l 
                           = 
                           0 
                         
                         
                           
                             N 
                             
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               L 
                             
                           
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         
                           
                             X 
                             1 
                           
                           ⁡ 
                           
                             ( 
                             
                               
                                 2 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 L 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 l 
                               
                               + 
                               1 
                             
                             ) 
                           
                         
                         · 
                         
                           W 
                           
                             N 
                             
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               L 
                             
                           
                           
                             
                               - 
                               n 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             l 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     The x e (n) and the x o (n) have a period of N/2 for n, and when the transmitter is actually implemented, the signal processor  630  separates the x e (n) and the x o (n) as shown in Equation (5) below, using a demultiplexer for demultiplexing the symbols output from the repeater  620 . 
     
       
         
           
             
               
                 
                   
                     
                       
                         x 
                         e 
                       
                       ⁡ 
                       
                         ( 
                         l 
                         ) 
                       
                     
                     = 
                     
                       x 
                       ⁡ 
                       
                         ( 
                         
                           2 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           l 
                         
                         ) 
                       
                     
                   
                   , 
                   
                     
                       
                         x 
                         o 
                       
                       ⁡ 
                       
                         ( 
                         l 
                         ) 
                       
                     
                     = 
                     
                       x 
                       ⁡ 
                       
                         ( 
                         
                           
                             2 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             l 
                           
                           + 
                           1 
                         
                         ) 
                       
                     
                   
                   , 
                   
                     l 
                     = 
                     0 
                   
                   , 
                   1 
                   , 
                   … 
                   ⁢ 
                   
                       
                   
                   , 
                   
                     
                       N 
                       
                         2 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         L 
                       
                     
                     - 
                     1 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Because the transmitter uses block coding for 2 adjacent sub-carriers and 2 transmission antennas at the rear stages of the FFT units  631  and  633  included in the signal processor  630 , time-band transmission samples of the transmission antennas  651  and  653 , output through the IFFT units  635  and  637 , can be generated using the output symbols of the repeater  620  through the symmetry property of FFT as shown in Equation (6) below.
 
 x *(− n ) N     X *( k ),  n, k= 0, 1, . . . ,  N− 1  (6)
 
     A symbol x 2 (n) transmitted via the second antenna  653  using Equation (4) to Equation (6) described in connection with Equation (3) indicating a symbol x 1 (n) transmitted via the first antenna  651  can be represented by Equation (7) 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           x 
                           2 
                         
                         ⁡ 
                         
                           ( 
                           n 
                           ) 
                         
                       
                       = 
                       
                         
                           
                             1 
                             
                               2 
                             
                           
                           ⁢ 
                           
                             
                               ( 
                               
                                 - 
                                 
                                   
                                     x 
                                     o 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     
                                       
                                         ( 
                                         
                                           - 
                                           n 
                                         
                                         ) 
                                       
                                       
                                         N 
                                         
                                           2 
                                           ⁢ 
                                           
                                               
                                           
                                           ⁢ 
                                           L 
                                         
                                       
                                     
                                     ) 
                                   
                                 
                               
                               ) 
                             
                             * 
                           
                         
                         + 
                         
                           
                             
                               W 
                               N 
                               
                                 - 
                                 n 
                               
                             
                             ⁡ 
                             
                               ( 
                               
                                 
                                   x 
                                   e 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       ( 
                                       
                                         - 
                                         n 
                                       
                                       ) 
                                     
                                     
                                       N 
                                       
                                         2 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         L 
                                       
                                     
                                   
                                   ) 
                                 
                               
                               ) 
                             
                           
                           * 
                         
                       
                     
                     ) 
                   
                   , 
                   
                     n 
                     = 
                     0 
                   
                   , 
                   1 
                   , 
                   … 
                   ⁢ 
                   
                       
                   
                   , 
                   
                     N 
                     - 
                     1 
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     That is, the symbols x 1 (n) and x 2 (n) transmitted via the first antenna  651  and the second antenna  653  can be represented by Equation (8) 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           x 
                           1 
                         
                         ⁡ 
                         
                           ( 
                           n 
                           ) 
                         
                       
                       = 
                       
                         
                           1 
                           
                             2 
                           
                         
                         ⁢ 
                         
                           ( 
                           
                             
                               
                                 x 
                                 e 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                   
                                     N 
                                     
                                       2 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       L 
                                     
                                   
                                 
                                 ) 
                               
                             
                             + 
                             
                               
                                 W 
                                 N 
                                 
                                   - 
                                   n 
                                 
                               
                               ⁢ 
                               
                                 
                                   x 
                                   o 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       ( 
                                       n 
                                       ) 
                                     
                                     
                                       N 
                                       
                                         2 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         L 
                                       
                                     
                                   
                                   ) 
                                 
                               
                             
                           
                           ) 
                         
                       
                     
                     , 
                     
                       n 
                       = 
                       0 
                     
                     , 
                     1 
                     , 
                     … 
                     ⁢ 
                     
                         
                     
                     , 
                     
                       N 
                       - 
                       1 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       
                         
                           x 
                           2 
                         
                         ⁡ 
                         
                           ( 
                           n 
                           ) 
                         
                       
                       = 
                       
                         
                           1 
                           
                             2 
                           
                         
                         ⁢ 
                         
                           ( 
                           
                             
                               - 
                               
                                 
                                   ( 
                                   
                                     
                                       x 
                                       o 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         
                                           ( 
                                           
                                             - 
                                             n 
                                           
                                           ) 
                                         
                                         
                                           N 
                                           2 
                                         
                                       
                                       ) 
                                     
                                   
                                   ) 
                                 
                                 * 
                               
                             
                             + 
                             
                               
                                 
                                   W 
                                   N 
                                   
                                     - 
                                     n 
                                   
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       x 
                                       e 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         
                                           ( 
                                           
                                             - 
                                             n 
                                           
                                           ) 
                                         
                                         
                                           N 
                                           
                                             2 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             L 
                                           
                                         
                                       
                                       ) 
                                     
                                   
                                   ) 
                                 
                               
                               * 
                             
                           
                           ) 
                         
                       
                     
                     , 
                     
                       n 
                       = 
                       0 
                     
                     , 
                     1 
                     , 
                     … 
                     ⁢ 
                     
                         
                     
                     , 
                     
                       N 
                       - 
                       1 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     x e (n) and x o (n) are defined by Equation (4), and 
               x   ⁡     (   n   )         N     2   ⁢           ⁢   L             
of above equations including Equation (8) is defined as
 
                   x   ⁡     (   n   )         N     2   ⁢           ⁢   L         =     x   ⁡     (   k   )         ,         
where k is defined as
 
             k   =     mod   ⁡     (     n   ,     N       2   ⁢   L     ⁢                 )             
and is a value obtained by performing a modulo operation on n with N/2L. In addition, Q, L and N of Equation (8) are equally defined as done in Equation (3).
 
     In this way, the transmitter transmits the symbols shown in Equation (8) via the first antenna  651  and the second antenna  653  with a single carrier. In particular, from the symbols transmitted via the second antenna  653 , the transmitter can determine that the communication system can transmits signals using the SFBC scheme. 
       FIG. 7  shows symbols transmitted in a frequency band by the transmitter in the communication system of  FIG. 6  according to the present invention. It is assumed that the first antenna  651  and the second antenna  653  of the transmitter each transmit four pairs of symbols through adjacent sub-carriers in the frequency band. 
     Referring to  FIG. 7 , if the data to be transmitted to a user is input to the symbol generator  610  as shown in  FIG. 6 , the transmitter performs the above-described signal processing on the input data, and transmits four pairs of symbols ( 711 ,  713 ,  715 ,  717 ) and ( 721 ,  723 ,  725 ,  727 ) via the first antenna  651  and the second antenna  653  using an RF frequency. The symbols ( 711 ,  713 ,  715 ,  717 ) and ( 721 ,  723 ,  725 ,  727 ) of the four pairs, transmitted via the first antenna  651  and the second antenna  653 , are symbols transmitted to one receiver, i.e. one user, and symbols of each pair (for example,  711  and  713 ) are transmitted through adjacent sub-carriers. In addition, the four pairs of symbols transmitted via each antenna are transmitted over the same space in the same frequency band. That is, symbols ( 711  and  721 ), ( 713  and  723 ), ( 715  and  725 ), and ( 717  and  727 ) of the corresponding pairs are transmitted over the same space and with the same adjacent sub-carriers in the frequency band, except that they are transmitted via different antennas. 
     In addition, the transmitter divides the symbols to be transmitted to one user into four symbol pairs  711 ,  713 ,  715  and  717  to be transmitted via the first antenna  651  and four symbol pairs  721 ,  723 ,  725  and  727  to be transmitted via the second antenna  653 , and symbols of the four pairs to be transmitted via the corresponding antenna by the repeater  620  of the transmitter are spaced apart at regular intervals. The spaced interval between the symbol pairs is determined depending on the number of repetitions of the repeater  620 . More specifically, as the number of repetitions of the repeater  620  increases, the number of ‘0’s inserted between transmission sample pairs in the time band increases as described above, and if the inserted ‘0’ is shown in the frequency band, it becomes the spaced interval between the symbol pairs. As a result, the spaced interval between the symbol pairs increases. The space where it can be divided in the frequency band increases due to the increased interval. As the space where it can be divided in the frequency band increases in this way, it is possible to transmit symbol pairs corresponding to more users through the increased space in the frequency band. For example, if the number of repetitions of the repeater  620  is four, it is possible to transmit four symbol pairs corresponding to the four users via each of the first antenna  651  and the second antenna  653  in the frequency band. 
     Because the space where it can be divided in the frequency band has a predetermined size, the symbol pairs for the users, which can be transmitted in the frequency band, also have a predetermined size by increasing the number of repetitions of the repeater  620 . That is, if the number of symbol pairs for one user in the frequency band is small, it is possible to transmit symbol pairs corresponding to more users via each of the first antenna  651  and the second antenna  653  by increasing the number of repetitions of the repeater  620 . If the number of symbol pairs for one user in the frequency band is large, because the number of repetitions of the repeater  620  is smaller than the former case, the number of users is also smaller than the former case. 
       FIG. 8  shows a receiver in a communication system according to the present invention. The receiver corresponds to the structure of the transmitters of  FIGS. 3 and 6 , and the communication system has two transmission antennas and one reception antenna. Referring to  FIG. 8 , the receiver includes a CP remover  801  for removing a CP of the signal output from the A/D converter  415 , received via the reception antenna and the RF receiver  413  as described in  FIG. 4 , a serial-to-parallel (S/P) converter  803  for S/P-converting the output signal of the CP remover  801 , a size-N FFT unit  805  for performing an FFT process on the parallel signal output from the S/P converter  803 , a signal detector  809  for detecting a transmission signal from the output signal of the FFT unit  805 , a demultiplexer (DEMUX)  813  for demultiplexing the signal detected by the signal detector  809 , a complex conjugate transposer  815  for performing complex conjugate transposition on (or for conjugating) the odd frequency band detection signal in the signal output from the demultiplexer  813 , a first size-N/2 IFFT unit  817  for performing an IFFT process on the even frequency band detection signal in the signal output from the demultiplexer  813 , a second size-N/2 IFFT unit  819  for performing an IFFT process on the output signal of the complex conjugate transposer  815 , and a multiplexer (MUX)  821  for multiplexing the output signals of the first IFFT unit  817  and the second IFFT unit  819 . 
     The signal detector  809  includes a linear combiner  807  for combining the output signals of the FFT unit  805 , and a Single Carrier FDE (SC-FDE) unit  811  for performing an FDE process on the output signal of the linear combiner  807 . The multiplexed signal is output as a bit stream through the symbol demapper  425 , and the signal determiner  427  for determining a transmission signal for the bit stream, outputs the transmission signal. 
     The linear combiner  807  of the signal detector  809  detects a signal using a Minimum Mean Square Error (MMSE) combining technique, and the detected signal is defined in Equation (9) as
 
 r=H   1   x   1   +H   2   x   2   +n   (9)
 
     In Equation (9), H 1  and H 2  are channel matrixes for the first antenna  651  and the second antenna  653  of  FIG. 6 , respectively. If the frequency band signal obtained by multiplying the r of Equation (9) by an FFT matrix W is divided into even and odd frequency components, they can be expressed in Equations (10) and (11) as 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           R 
                           ⁡ 
                           
                             ( 
                             
                               2 
                               ⁢ 
                               m 
                             
                             ) 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             
                               
                                 Λ 
                                 1 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   2 
                                   ⁢ 
                                   m 
                                 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 X 
                                 1 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   2 
                                   ⁢ 
                                   m 
                                 
                                 ) 
                               
                             
                           
                           + 
                           
                             
                               
                                 Λ 
                                 2 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   2 
                                   ⁢ 
                                   m 
                                 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 X 
                                 2 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   2 
                                   ⁢ 
                                   m 
                                 
                                 ) 
                               
                             
                           
                           + 
                           
                             N 
                             ⁡ 
                             
                               ( 
                               
                                 2 
                                 ⁢ 
                                 m 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           = 
                             
                           ⁢ 
                           
                             
                               
                                 
                                   Λ 
                                   1 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   ) 
                                 
                               
                               ⁢ 
                               
                                 
                                   X 
                                   1 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   ) 
                                 
                               
                             
                             - 
                             
                               
                                 
                                   Λ 
                                   2 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   ) 
                                 
                               
                               ⁢ 
                               
                                 
                                   X 
                                   1 
                                   * 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       2 
                                       ⁢ 
                                       m 
                                     
                                     + 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                             + 
                             
                               N 
                               ⁢ 
                               
                                 ( 
                                 
                                   2 
                                   ⁢ 
                                   m 
                                 
                                 ) 
                               
                             
                           
                         
                         , 
                       
                     
                   
                   
                     
                       
                         
                           m 
                           = 
                             
                           ⁢ 
                           0 
                         
                         , 
                         1 
                         , 
                         … 
                         ⁢ 
                         
                             
                         
                         , 
                         
                           
                             N 
                             / 
                             2 
                           
                           - 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         
                           R 
                           ⁡ 
                           
                             ( 
                             
                               
                                 2 
                                 ⁢ 
                                 m 
                               
                               + 
                               1 
                             
                             ) 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             
                               
                                 Λ 
                                 1 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   + 
                                   1 
                                 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 X 
                                 1 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   + 
                                   1 
                                 
                                 ) 
                               
                             
                           
                           + 
                           
                             
                               
                                 Λ 
                                 2 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   + 
                                   1 
                                 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 X 
                                 2 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   + 
                                   1 
                                 
                                 ) 
                               
                             
                           
                           + 
                         
                       
                     
                   
                   
                     
                       
                           
                         ⁢ 
                         
                           N 
                           ⁡ 
                           
                             ( 
                             
                               
                                 2 
                                 ⁢ 
                                 m 
                               
                               + 
                               1 
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               
                                 Λ 
                                 1 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   + 
                                   1 
                                 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 X 
                                 
                                   1 
                                   ⁢ 
                                   
                                       
                                   
                                 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   + 
                                   1 
                                 
                                 ) 
                               
                             
                           
                           + 
                           
                             
                               
                                 Λ 
                                 2 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     m 
                                   
                                   + 
                                   1 
                                 
                                 ) 
                               
                             
                             ⁢ 
                             
                               
                                 X 
                                 1 
                                 * 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   2 
                                   ⁢ 
                                   m 
                                 
                                 ) 
                               
                             
                           
                           + 
                           
                             N 
                             ⁡ 
                             
                               ( 
                               
                                 
                                   2 
                                   ⁢ 
                                   m 
                                 
                                 + 
                                 1 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     Assuming that channel information for two adjacent sub-carriers is constant, Equation (10) and Equation (11) can be rewritten as a determinant of Equation (12) below. 
     
       
         
           
             
               
                 
                   
                     R 
                     m 
                   
                   = 
                   
                     [ 
                     
                       
                         
                           
                             R 
                             ⁡ 
                             
                               ( 
                               
                                 2 
                                 ⁢ 
                                 m 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             
                               R 
                               * 
                             
                             ⁡ 
                             
                               ( 
                               
                                 
                                   2 
                                   ⁢ 
                                   m 
                                 
                                 + 
                                 1 
                               
                               ) 
                             
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     From Equation (12), the received signal can be expressed as a liner combination of the transmission signals. In addition, the signal detection is performed based on the Minimum Mean Square Error (MMSE) criterion. Accordingly, a similar formula of a reception diversity system using the Maximum Ratio Combining (MRC) of the path received from the finally found optimal two branches, i.e. two transmission antennas, can be expressed in Equation (13) as 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           Y 
                           m 
                         
                         = 
                         
                           
                             H 
                             m 
                             H 
                           
                           ⁢ 
                           
                             R 
                             m 
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           
                             X 
                             ^ 
                           
                           m 
                         
                         = 
                         
                           
                             [ 
                             
                               
                                 
                                   
                                     
                                       
                                         X 
                                         ^ 
                                       
                                       1 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         2 
                                         ⁢ 
                                         m 
                                       
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       
                                         X 
                                         ^ 
                                       
                                       1 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         
                                           2 
                                           ⁢ 
                                           m 
                                         
                                         + 
                                         1 
                                       
                                       ) 
                                     
                                   
                                 
                               
                             
                             ] 
                           
                           = 
                           
                             
                               
                                 ( 
                                 
                                   
                                     
                                       H 
                                       m 
                                       H 
                                     
                                     ⁢ 
                                     
                                       H 
                                       m 
                                     
                                   
                                   + 
                                   
                                     
                                       1 
                                       SNR 
                                     
                                     ⁢ 
                                     
                                       I 
                                       2 
                                     
                                   
                                 
                                 ) 
                               
                               
                                 - 
                                 1 
                               
                             
                             ⁢ 
                             
                               Y 
                               m 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           H 
                           m 
                         
                         = 
                         
                           [ 
                           
                             
                               
                                 
                                   
                                     H 
                                     1 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     
                                       2 
                                       ⁢ 
                                       m 
                                     
                                     ) 
                                   
                                 
                               
                               
                                 
                                   - 
                                   
                                     
                                       H 
                                       2 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         2 
                                         ⁢ 
                                         m 
                                       
                                       ) 
                                     
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     H 
                                     2 
                                     * 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     
                                       2 
                                       ⁢ 
                                       m 
                                     
                                     ) 
                                   
                                 
                               
                               
                                 
                                   
                                     H 
                                     1 
                                     * 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     
                                       2 
                                       ⁢ 
                                       m 
                                     
                                     ) 
                                   
                                 
                               
                             
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     In Equation (13), Y m  denotes a received signal corresponding to 2m th  and (2m+1) th  sub-carriers, i.e. adjacent sub-carriers, H m  denotes a value of the channel that the received signal experiences through 2m th  and (2m+1) th  sub-carriers, H 1 (2m) denotes, among H m , a value of the channel that the signal transmitted via the first antenna experiences, and H 2 (2m) denotes, among H m , a value of the channel that the signal transmitted via the second antenna experiences. In addition, H m   H  denotes a Hermitian operation of the H m . 
     Although the channel equalization performed in such a way by the linear combiner  807  and the SC-FDE unit  811  is performed in the frequency domain, the determined values are obtained in the time domain, so an estimated value for the symbol transmitted to the receiver can be represented by Equation (14) 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             
                               X 
                               ^ 
                             
                             e 
                           
                           = 
                           
                             
                               W 
                               
                                 N 
                                 2 
                               
                               H 
                             
                             ⁢ 
                             
                               
                                 X 
                                 ^ 
                               
                               e 
                             
                           
                         
                         , 
                       
                     
                   
                   
                     
                       
                         
                           
                             X 
                             ^ 
                           
                           o 
                         
                         = 
                         
                           
                             W 
                             
                               N 
                               2 
                             
                             H 
                           
                           ⁢ 
                           
                             
                               X 
                               ^ 
                             
                             o 
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           x 
                           ^ 
                         
                         = 
                         
                           
                             [ 
                             
                               
                                 
                                   
                                     x 
                                     ^ 
                                   
                                   e 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   0 
                                   ) 
                                 
                               
                               , 
                               
                                 
                                   
                                     x 
                                     ^ 
                                   
                                   o 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   0 
                                   ) 
                                 
                               
                               , 
                               
                                 
                                   
                                     x 
                                     ^ 
                                   
                                   e 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   1 
                                   ) 
                                 
                               
                               , 
                               
                                 
                                   
                                     x 
                                     ^ 
                                   
                                   o 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   1 
                                   ) 
                                 
                               
                               , 
                               … 
                               ⁢ 
                               
                                   
                               
                               , 
                               
                                 
                                   
                                     x 
                                     ^ 
                                   
                                   e 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       N 
                                       2 
                                     
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                               , 
                               
                                 
                                   
                                     x 
                                     ^ 
                                   
                                   o 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
                                       N 
                                       2 
                                     
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                             ] 
                           
                           T 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
     Through Equation (14), the receiver estimates the symbols transmitted by the transmitter via two transmission antennas, and then delivers the estimated values to the symbol demapper  425 . Then the symbol demapper  425  demaps the estimated values into bit streams, and delivers the bit streams to the signal determiner  427 , thereby performing predetermined signal processing. 
     As can be understood from the foregoing description, the present invention allows an SC-FDE system to use SFBC in the communication system, thereby securing the advantages of the SFBC and SC-FDE that they are robust against non-linear distortion or a carrier synchronization error and have a transmission diversity gain, and contributing to minimization of performance degradation even in the fast fading environment. 
     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.