Patent Publication Number: US-7590045-B2

Title: Apparatus and method for transmitting fast feedback information in a wireless communication system

Description:
PRIORITY 
     This application claims the benefit under 35 U.S.C. § 119(a) of an application entitled “Apparatus and Method for Transmitting Fast Feedback Information in a Wireless Communication System” filed in the Korean Intellectual Property Office on Jan. 11, 2005 and assigned Serial No. 2005-2700 and an application entitled “Apparatus and Method for Transmitting Fast Feedback Information in a Wireless Communication System” filed in the Korean Intellectual Property Office on Jun. 4, 2005 and assigned Serial No. 2005-48138, the entire contents of both of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an apparatus and method for transmitting control information in a wireless communication system, and in particular, to an apparatus and method for transmitting fast feedback information in a Broadband Wireless Access (BWA) communication system. 
     2. Description of the Related Art 
     A mobile communication system is a typical wireless communication system. The mobile communication system is gradually evolving into a system capable of providing wireless packet data service based on voice service. The 3 rd  Generation (3G) mobile communication system that can provide wireless packet data service is developing into a system capable of providing various multimedia services at a high rate. The 3G mobile communication system identifies users using a Code Division Multiple Access (CDMA) scheme. The CDMA scheme can transmit data by allocating different orthogonal codes or transmission data to users. 
     However, the 3G system cannot provide data at a higher rate with higher quality due to a lack of codes. That is, the 3G system is limited in data rate due to a restriction of available codes. In order to address this problem, mobile communication system developers are taking into consideration a 4 th  Generation (4G) BWA communication system, referred to as the next generation communication system. The 4G system can classify users or user data using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme before transmission. The 4G system can increase data rate up to about 100 Mbps. Therefore, compared with the 3G system, the 4G system can provide services with various Qualities-of-Service (QoS). 
     Research on the 4G system now focuses on the BWA communication system such as a wireless Local Area Network (LAN) system and a wireless Metropolitan Area Network (MAN) system. The BWA communication system is evolving into a system capable of guaranteeing QoS, providing mobility which is the characteristic of a wireless communication system. An Institute of Electrical and Electronics Engineers (IEEE) 802.16a communication system and an IEEE 802.16e communication system are typical BWA communication systems. In addition, various other systems are being developed using the OFDMA scheme. 
     The BWA communication system is developing into a system that basically uses the OFDMA scheme and can guarantee mobility. For data transmission, the BWA communication system transmits Orthogonal Frequency Division Multiplexing (OFDM) symbols basically using a Time Division Duplexing (TDD) scheme. In transmitting OFDM symbols, the BWA communication system divides the OFDM symbols into a downlink and an uplink in a period of a particular time domain because it uses the TDD scheme. Each of the downlink and the uplink transmits OFDM symbols in particular slots. Such a BWA communication system can distinguish the OFDM symbols as physical channels having a separate particular purpose in the uplink and the downlink. 
     The OFDMA-based communication system has physical channels for fast feedback in the uplink. Information included in the physical channels for fast feedback includes perfect signal-to-noise ratio (SNR) information, per-band differential SNR information, fast Multi-Input Multi-Output (MIMO) feedback information, mode selection feedback information, MIMO feedback information, etc. The perfect SNR information refers to an SNR for a full band. Such fast feedback information for the uplink requires a guarantee of high reliability because it is very important for application of a communication system although it is large in quantity. 
     In transmitting the fast feedback information in the uplink, the conventional technology transmits 6-bit information using one uplink subchannel. However, transmitting only the fixed 6-bit information using one uplink subchannel causes a lack of application flexibility for a system requiring various feedback information, for example, for a MIMO system that has multiple antennas and requires feedback information for each individual antenna or stream. This is because the multi-antenna transmission system requires information on various wireless channels in order to acquire optimal performance while using a plurality of transmission antennas. 
     Therefore, the multi-antenna transmission system requires diverse feedback information according to a multi-antenna transmission algorithm. However, presently there is no proposed scheme for a method capable of providing the diverse information. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an apparatus and method for transmitting diverse fast feedback information on an uplink in a wireless communication system. 
     It is another object of the present invention to provide an apparatus and method for transmitting more fast feedback information in a wireless communication system. 
     It is further another object of the present invention to provide an apparatus and method for performing efficient communication through diverse fast feedback information from an uplink in a wireless communication system. 
     It is yet another object of the present invention to provide an apparatus and method for correctly delivering feedback information on an uplink in a BWA communication system. 
     It is still another object of the present invention to provide an apparatus and method for securing flexibility of feedback information delivered on an uplink in a BWA communication system. 
     According to one aspect of the present invention, there is provided an apparatus for transmitting uplink fast feedback information in a wireless communication system. The apparatus includes a channel encoder for generating uplink fast feedback information to transmit, and outputting 3-bit codewords being set such that a minimum Hamming distance defined in a system setup process becomes maximized according to the fast feedback information; a noncoherent modulator for modulating transmission symbols corresponding to the codewords using a noncoherent modulation scheme, and allocating the modulated transmission symbols to each of subcarrier bundles; and an inverse fast Fourier transform (IFFT) unit for IFFT-processing a transmission signal comprised of the subcarrier bundles before transmission. 
     According to another aspect of the present invention, there is provided an apparatus for receiving uplink fast feedback information in a wireless communication system. The apparatus includes a reception device for receiving fast feedback information transmitted from a transmission apparatus through an uplink fast feedback channel, extracting 3-bit fast feedback information or 6-bit fast feedback information from the fast feedback information received from the transmission apparatus, and using the extracted fast feedback information in transmitting information at a next time. 
     According to further another aspect of the present invention, there is provided an apparatus for transmitting uplink fast feedback information in a wireless communication system. The apparatus includes an encoder for generating an uplink fast feedback information bit stream to transmit, and encoding the fast feedback information bit steam using a coding scheme predefined in a system setup process. The fast feedback information bit stream includes at least one fast feedback information comprised of a predetermined number of bits according to a system condition. 
     According to yet another aspect of the present invention, there is provided a method for transmitting uplink fast feedback information in a wireless communication system. The method includes: generating uplink fast feedback information to transmit, and outputting 3-bit codewords being set such that a minimum Hamming distance defined in a system setup process becomes maximized according to the fast feedback information; modulating transmission symbols corresponding to the codewords using a noncoherent modulation scheme, and allocating the modulated transmission symbols to each of subcarrier bundles; and performing an inverse fast Fourier transform (IFFT) process on a transmission signal comprised of the subcarrier bundles before transmission. 
     According to still another aspect of the present invention, there is provided a method for receiving uplink fast feedback information in a wireless communication system. The method includes: receiving fast feedback information transmitted from a transmission apparatus through an uplink fast feedback channel; extracting 3-bit fast feedback information or 6-bit fast feedback information from the fast feedback information received from the transmission apparatus; and controlling information transmission at a next time using the extracted fast feedback information. 
     According to still another aspect of the present invention, there is provided a method for transmitting uplink fast feedback information in a wireless communication system. The method includes: generating an uplink fast feedback information bit stream to transmit; and encoding the fast feedback information bit steam using a coding scheme predefined in a system setup process. The fast feedback information bit stream includes at least one fast feedback information comprised of a predetermined number of bits according to a system condition. 
    
    
     
       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 schematically illustrating a structure of a transmitter for transmitting fast feedback information in an OFDMA communication system according to an embodiment of the present invention; 
         FIG. 2  is a diagram schematically illustrating a structure of a receiver for receiving fast feedback information in an OFDMA communication system according to an embodiment of the present invention; 
         FIG. 3  is a diagram illustrating time-frequency resources allocated for transmission of uplink fast feedback information in an OFDMA communication system according to an embodiment of the present invention; 
         FIG. 4  is a diagram illustrating time-frequency resources allocated for transmission of uplink fast feedback information in an OFDMA communication system according to another embodiment of the present invention; and 
         FIG. 5  is a block diagram schematically illustrating a structure for transmitting fast feedback information using a Downlink Interval Usage Code (DIUC) scheme according to an embodiment of 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. 
       FIG. 1  is a diagram schematically illustrating a structure of a transmitter for transmitting fast feedback information in an OFDMA communication system according to the present invention. In particular,  FIG. 1  schematically illustrates partial blocks of a mobile terminal (MS) transmitter for transmitting fast feedback information on an uplink according to the present invention. 
     Referring to  FIG. 1 , the transmitter includes an M-ary channel encoder  101  for encoding information data bits  100  of uplink fast feedback information, a noncoherent modulator  103  for modulating the information data bits using a noncoherent scheme, and an Inverse Fast Fourier Transform (IFFT) unit  105  for IFFT-processing a transmission signal before transmission. 
     As illustrated in  FIG. 1 , the information data bits  100  represent fast feedback information. The fast feedback information includes information data bits output from a controller (not shown in  FIG. 1 ). A detailed description of the fast feedback information will be given below. The fast feedback information is input to the M-ary channel encoder  101 . 
     If there are information data bits  100  to transmit, the M-ary channel encoder  101  encodes the information data bits  100  into a codeword corresponding thereto, and outputs the codeword to the noncoherent modulator  103 . The M-ary channel encoder  101  can be implemented with a binary channel encoder or an M-ary block encoder according to input bits. 
     The noncoherent modulator  103  receives the codeword output from the M-ary channel encoder  101 , modulates transmission symbols corresponding thereto using a noncoherent modulation scheme, and outputs the modulated symbols to the IFFT unit  105 . Herein, the noncoherent modulator  103  can use a predetermined modulation scheme, for example, orthogonal modulation. 
     The IFFT unit  105  IFFT-processes the modulation symbols received from the noncoherent modulator  103 , generating OFDM transmission symbols. Although the OFDM symbol generally includes a cyclic prefix (CP), a structure thereof and a structure for transmission in a wireless band are omitted in  FIG. 1 , for simplicity. 
       FIG. 2  is a diagram schematically illustrating a structure of a receiver for receiving fast feedback information in an OFDMA communication system according to the present invention. In particular,  FIG. 2  schematically illustrates a structure of a base station (BS) receiver for receiving uplink fast feedback information according to the present invention. 
     Referring to  FIG. 2 , the receiver includes a Fast Fourier Transform (FFT) unit  201  for FFT-processing a time-domain reception signal  200  into a frequency-domain reception signal, a noncoherent demodulator  203  for demodulating the frequency-domain reception signal, and an M-ary channel decoder  205  for decoding the demodulated reception symbols into information data bits of fast feedback information. 
     A process of processing a signal received through a wireless channel and removing a CP from the received signal is omitted in  FIG. 2 , for simplicity. Therefore, the reception signal  200  corresponds to a signal that underwent signal processing and CP removing process. The reception signal  200  is input to the FFT unit  201 . 
     The FFT unit  201  converts the reception signal  200  received from the transmitter into a time-domain reception signal by performing an FFT process thereon, and outputs the time-domain reception signal to the noncoherent demodulator  203 . 
     The noncoherent demodulator  203  noncoherently demodulates the reception symbols received from the FFT unit  201  by acquiring a soft decision value for the time-band reception symbols, for example, by squaring an absolute value of a correlation value between the reception symbols. The noncoherent demodulator  203  outputs the demodulated symbols to the M-ary channel decoder  205 . 
     The M-ary channel decoder  205  determines which codeword was transmitted from the transmitter by analyzing the soft decision value received from the noncoherent demodulator  203 , and outputs data bits corresponding thereto. Herein, the M-ary channel decoder  205  can be implemented with a binary channel decoder or an M-ary channel decoder according to input bits. 
     The output information corresponds to the fast feedback information transmitted by the MS transmitter, if it was normally received without an error in its transmission process or demodulation and decoding process. Therefore, the fast feedback information is used for a scheduling process and an information transmission process at a next time by a controller (not shown) or a scheduler (also not shown) included in the BS. 
     A description will now be made of a method for transmitting/receiving uplink fast feedback information in the MS transmitter and the BS receiver. 
       FIG. 3  is a diagram illustrating time-frequency resources in which six 3×3 subcarrier bundles are allocated for transmission of uplink fast feedback information in an OFDMA communication system according to the present invention. 
     As illustrated in  FIG. 3 , an embodiment of the present invention will be described with reference to a method for transmitting fast feedback information by allocating six 3×3 subcarrier bundles to subchannels on a time-frequency domain on an uplink in an OFDM communication system. However, the present invention is not limited to this embodiment, and the uplink subchannels should not necessarily include the six 3×3 subcarrier bundles. For example, the uplink subchannels may include six 4×3 subcarrier bundles. 
     Referring to  FIG. 3 , reference numeral  300  represents a set of subchannels in a particular time domain. Therefore, the subchannel set  300  includes a plurality of subchannels therein. Each of the subchannels includes one or more subcarriers. In  FIG. 3 , hatched parts  310 ,  320 ,  330 ,  340 ,  350  and  360  represent uplink subcarrier bundles (or tiles), and one uplink subchannel includes six subcarrier bundles. That is, reference numerals  310 ,  320 ,  330 ,  340 ,  350  and  360  represent a fast feedback channel. 
     One uplink subchannel includes six 3×3 subcarrier bundles in a time-frequency domain, each of which is configured as shown by reference numeral  330 . In the shown subcarrier bundle, a horizontal axis represents a time or a symbol, and a vertical axis represents a frequency or a subcarrier. 
     Information data bits, for example, fast feedback information, are transmitted through one uplink subchannel, i.e., fast feedback channel, as shown in  FIG. 3 . The information data bits, as described with reference to  FIG. 1 , pass through an M-ary channel encoder  101 . It will be assumed herein that the number of the information data bits is 6 and an M (=8)-ary channel encoder is used. Therefore, the subchannel  330 , as can be understood from its internal structure, carries information output from the 8-ary channel encoder in its 8 boundary zones shown by reference numerals  331 ,  332 ,  333 ,  334 ,  336 ,  337 ,  338  and  339 , and carries a pilot symbol in the center zone shown by reference numeral  335 . 
     Table 1 below shows 64 possible codewords output from the 8-ary channel encoder. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 Codeword 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
                 10 
                 11 
                 12 
                 13 
                 14 
                 15 
               
               
                   
               
               
                 A0 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 2 
                 3 
                 0 
                 1 
                 6 
                 7 
                 4 
                 5 
               
               
                 A1 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 4 
                 5 
                 6 
                 7 
                 0 
                 1 
                 2 
                 3 
               
               
                 A2 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 3 
                 2 
                 1 
                 0 
                 7 
                 6 
                 5 
                 4 
               
               
                 A3 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 6 
                 7 
                 4 
                 5 
                 2 
                 3 
                 0 
                 1 
               
               
                 A4 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
               
               
                 A5 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 5 
                 4 
                 7 
                 6 
                 1 
                 0 
                 3 
                 2 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 Codeword 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 16 
                 17 
                 18 
                 19 
                 20 
                 21 
                 22 
                 23 
                 24 
                 25 
                 26 
                 27 
                 28 
                 29 
                 30 
                 31 
               
               
                   
               
               
                 A0 
                 4 
                 5 
                 6 
                 7 
                 0 
                 1 
                 2 
                 3 
                 3 
                 2 
                 1 
                 0 
                 7 
                 6 
                 5 
                 4 
               
               
                 A1 
                 3 
                 2 
                 1 
                 0 
                 7 
                 6 
                 5 
                 4 
                 6 
                 7 
                 4 
                 5 
                 2 
                 3 
                 0 
                 1 
               
               
                 A2 
                 6 
                 7 
                 4 
                 5 
                 2 
                 3 
                 0 
                 1 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
               
               
                 A3 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
                 5 
                 4 
                 7 
                 6 
                 1 
                 0 
                 3 
                 2 
               
               
                 A4 
                 5 
                 4 
                 7 
                 6 
                 1 
                 0 
                 3 
                 2 
                 1 
                 0 
                 3 
                 2 
                 5 
                 4 
                 7 
                 6 
               
               
                 A5 
                 1 
                 0 
                 3 
                 2 
                 5 
                 4 
                 7 
                 6 
                 2 
                 3 
                 0 
                 1 
                 6 
                 7 
                 4 
                 5 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 Codeword 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 32 
                 33 
                 34 
                 35 
                 36 
                 37 
                 38 
                 39 
                 40 
                 41 
                 42 
                 43 
                 44 
                 45 
                 46 
                 47 
               
               
                   
               
               
                 A0 
                 6 
                 7 
                 4 
                 5 
                 2 
                 3 
                 0 
                 1 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
               
               
                 A1 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
                 5 
                 4 
                 7 
                 6 
                 1 
                 0 
                 3 
                 2 
               
               
                 A2 
                 5 
                 4 
                 7 
                 6 
                 1 
                 0 
                 3 
                 2 
                 1 
                 0 
                 3 
                 2 
                 5 
                 4 
                 7 
                 6 
               
               
                 A3 
                 1 
                 0 
                 3 
                 2 
                 5 
                 4 
                 7 
                 6 
                 2 
                 3 
                 0 
                 1 
                 6 
                 7 
                 4 
                 5 
               
               
                 A4 
                 2 
                 3 
                 0 
                 1 
                 6 
                 7 
                 4 
                 3 
                 4 
                 5 
                 6 
                 7 
                 0 
                 1 
                 2 
                 3 
               
               
                 A5 
                 4 
                 5 
                 6 
                 7 
                 0 
                 1 
                 2 
                 3 
                 3 
                 2 
                 1 
                 0 
                 7 
                 6 
                 5 
                 4 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 Codeword 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 48 
                 49 
                 50 
                 51 
                 52 
                 53 
                 54 
                 55 
                 56 
                 57 
                 58 
                 59 
                 60 
                 61 
                 62 
                 63 
               
               
                   
               
               
                 A0 
                 5 
                 4 
                 7 
                 6 
                 1 
                 0 
                 3 
                 2 
                 1 
                 0 
                 3 
                 2 
                 5 
                 4 
                 7 
                 6 
               
               
                 A1 
                 1 
                 0 
                 3 
                 2 
                 5 
                 4 
                 7 
                 6 
                 2 
                 3 
                 0 
                 1 
                 6 
                 7 
                 4 
                 5 
               
               
                 A2 
                 2 
                 3 
                 0 
                 1 
                 6 
                 7 
                 4 
                 5 
                 4 
                 5 
                 6 
                 7 
                 0 
                 1 
                 2 
                 3 
               
               
                 A3 
                 4 
                 5 
                 6 
                 7 
                 0 
                 1 
                 2 
                 3 
                 3 
                 2 
                 1 
                 0 
                 7 
                 6 
                 5 
                 4 
               
               
                 A4 
                 3 
                 2 
                 1 
                 0 
                 7 
                 6 
                 5 
                 4 
                 6 
                 7 
                 4 
                 5 
                 2 
                 3 
                 0 
                 1 
               
               
                 A5 
                 6 
                 7 
                 4 
                 5 
                 2 
                 3 
                 0 
                 1 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
               
               
                   
               
            
           
         
       
     
     Upon receiving information data bits, the 8-ary channel encoder in a transmitter outputs one of the possible 64 codewords shown in Table 1 to a noncoherent modulator. Herein, the 8-ary channel encoder is set such that the minimum Hamming distance between codewords becomes maximized for the given number and length of codewords. The term “Hamming distance” refers to the number of inconsistent bits between binary codes having the same number of bits. 
     The minimum Hamming distance, a factor that mainly affects a codeword error rate in this transmission method, becomes 5. For example, for a codeword “32” among the 64 possible codewords, a pattern of codeword indexes A0, A1, A2, A3, A4 and A5 for its subcarrier bundles becomes “675124,” and for a codeword “40,” a pattern of codeword indexes A0, A1, A2, A3, A4 and A5 for its subcarrier bundles becomes “751243,” so the minimum Hamming distance between the two codewords “32” and “40” becomes 5. The minimum Hamming distance being 5 indicates that a Hamming distance between two of all the possible codewords is greater than or equal to 5. 
     The foregoing transmission method can also be replaced with a method of transmitting 5 bits using 32 codewords. 
     Thereafter, in order to transmit the allocated codeword through a fast feedback channel, the noncoherent modulator performs orthogonal modulation on the codeword received from the 8-ary channel encoder. That is, the noncoherent modulator modulates the information data bits encoded by the 8-ary channel encoder using the orthogonal modulation scheme. Orthogonal vectors used for the orthogonal modulation are shown in Table 2 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Subcarrier Modulation per Codeword 
               
               
                   
                 Vector Index 
                 Subcarrier 0, Subcarrier 1, . . . , Subcarrier 7 
               
               
                   
                   
               
             
            
               
                   
                 0 
                 P0, P1, P2, P3, P0, P1, P2, P3 
               
               
                   
                 1 
                 P0, P3, P2, P1, P0, P3, P2, P1 
               
               
                   
                 2 
                 P0, P0, P1, P1, P2, P2, P3, P3 
               
               
                   
                 3 
                 P0, P0, P3, P3, P2, P2, P1, P1 
               
               
                   
                 4 
                 P0, P0, P0, P0, P0, P0, P0, P0 
               
               
                   
                 5 
                 P0, P2, P0, P2, P0, P2, P0, P2 
               
               
                   
                 6 
                 P0, P2, P0, P2, P2, P0, P2, P0 
               
               
                   
                 7 
                 P0, P2, P2, P0, P2, P0, P0, P2 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 2, the orthogonal vectors to be used for the orthogonal modulation can be represented by P0, P1, P2 and P3, and when the orthogonal vectors are modulated into Quadrature Phase Shift Keying (QPSK) modulation symbols, the modulation symbols generated by a QPSK modulation scheme can be defined as Equation (1): 
     
       
         
           
             
               
                 
                   
                     
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     Herein, the 8 boundary subcarriers of a 3×3 subcarrier bundle transmit data symbols shown in Table 2, and the center subcarrier transmits a pilot symbol. That is, in  FIG. 3 , the subcarriers indicated by reference numerals  331 ,  332 ,  333 ,  334 ,  336 ,  337 ,  338  and  339  transmit symbols shown in Table 2, and the center subcarrier indicated by reference numeral  335  transmits a pilot symbol. Herein, the pilot symbol can be randomly established. 
     For example, if 6 information data bits to be transmitted are given, the transmitter determines a codeword depending on Table 1. Thereafter, according to the determined codeword, the transmitter transmits orthogonal vectors of a pattern, i.e., a vector index, corresponding to a codeword index A0 through a first 3×3 subcarrier bundle, transmits orthogonal vectors of a pattern, i.e., a vector index, corresponding to a codeword index A1 through a second 3×3 subcarrier bundle, and in the same manner, finally transmits orthogonal vectors of a pattern, i.e., a vector index corresponding to a codeword index A5 through a sixth 3×3 subcarrier bundle, using the method shown in Table 2. More specifically, if a vector index for the first 3×3 subcarrier bundle is 4, its data symbol values are set as P0, P0, P0, P0, P0, P0, P0, P0 corresponding to the vector index 4. If a vector index for the second 3×3 subcarrier bundle is 7, its data symbol values are set as P0, P2, P2, P0, P2, P0, P0, P2 corresponding to the vector index 7. If a vector index for the third 3×3 subcarrier bundle is 2, its data symbol values are set as P0, P0, P1, P1, P2, P2, P3, P3 corresponding to the vector index 2. 
     A description will now be made of a reception method. 
     Upon receiving the transmission signal from the transmitter, an FFT unit in a receiver performs an FFT process on the received signal, and outputs the FFT-processed signal to a noncoherent demodulator. The noncoherent demodulator calculates a square for an absolute value of a correlation value between 8 possible orthogonal vectors for each of six 3×3 subcarrier bundles, and outputs the calculation result to an M-ary channel decoder. The M-ary channel decoder calculates a sum of squares for absolute values of correlation values between orthogonal vectors, for each of all 64 possible codewords. Thereafter, the receiver determines that the transmitter transmitted the information data bits corresponding to a codeword having the maximum value among the calculated values. 
     An embodiment of the present invention has been described with reference to an exemplary transmission method of transmitting 6 information data bits. A description will now be made of an exemplary transmission method of transmitting 3 information data bits according to the present invention. 
       FIG. 4  is a diagram illustrating time-frequency resources in which six 3×3 subcarrier bundles are allocated for transmission of uplink fast feedback information in an OFDMA communication system according to the present invention. 
     Fast feedback information transmission shown in  FIG. 4  is equal to the fast feedback information transmission shown in  FIG. 3  in that one uplink subchannel is comprised of six 3×3 subcarrier bundles. The 3-bit fast feedback information transmission method proposed in  FIG. 4  will be described with reference to an exemplary transmission method in which six 3×3 subcarrier bundles are allocated to 3 subchannels in a time-frequency domain on an uplink in an OFDMA communication system. However, the present invention is not limited to this embodiment, and the uplink subchannels should not necessarily include the six 3×3 subcarrier bundles. For example, the uplink subchannels may include six 4×3 subcarrier bundles. 
     Referring to  FIG. 4 , reference numeral  400  represents a set of subchannels in a particular time domain. Therefore, the subchannel set  400  includes a plurality of subchannels therein. Each of the subchannels includes one or more subcarriers. In  FIG. 4 , hatched parts  410 ,  420 ,  430 ,  440 ,  450  and  460  represent uplink subcarrier bundles (or tiles), and one uplink subchannel includes six subcarrier bundles. That is, reference numerals  410 ,  420 ,  430 ,  440 ,  450  and  460  represent a fast feedback channel. 
     One uplink subchannel includes six 3×3 subcarrier bundles in a time-frequency domain, each of which is configured as shown by reference numeral  420 . In the shown subcarrier bundle, a horizontal axis represents a time or a symbol, and a vertical axis represents a frequency or a subcarrier. 
     In  FIG. 4 , information data bits, for example, fast feedback information, are transmitted through three uplink subchannels, i.e., fast feedback channels. In  FIG. 4 , among the subchannels  410 ,  420 ,  430 ,  440 ,  450  and  460 , even subchannels  410 ,  420  and  430  constitute one fast feedback channel, and odd subchannels  440 ,  450  and  460  constitute another fast feedback channel. Therefore, an embodiment of the present invention as shown in  FIG. 4  can generate two fast feedback subchannels. 
     The present invention has been described with reference to an exemplary method of generating two fast feedback subchannels using three subchannels. However, the present invention is not so limited, and it would be obvious to those skilled in the art that the present invention can also be applied to another exemplary method of generating, for example, three fast feedback subchannels using two subchannels. 
     The 3-bit fast feedback information transmitted using one of the fast feedback channels can transmit low-quantity information such as an antenna group index, an antenna selection index and a precoding index for a multi-antenna transmission technology, for example, Multi-Input Multi-Output (MIMO) technology. 
     The information data bits pass through an M-ary channel encoder  101  shown in  FIG. 1 . It will be assumed herein that the number of the information data bits is 3 and an M (=8)-ary channel encoder is used. Therefore, the subchannel  420 , as can be understood from its internal structure, carries information output from the 8-ary channel encoder in its 8 boundary zones, and carries a pilot symbol in the center zone. 
     Table 3 below shows 8 possible codewords output from the 8-ary channel encoder for 3 input information data bits. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Fast Feedback Vector Index per Tile 
               
               
                   
                   
                 Even = {tile (0), tile (2), tile (4)}, 
               
               
                   
                 3 bit payload 
                 Odd = {tile (1), tile (3), tile (5)} 
               
               
                   
                   
               
             
            
               
                   
                 0b000 
                 0, 0, 0 
               
               
                   
                 0b001 
                 1, 1, 1 
               
               
                   
                 0b010 
                 2, 2, 2 
               
               
                   
                 0b011 
                 3, 3, 3 
               
               
                   
                 0b100 
                 4, 4, 4 
               
               
                   
                 0b101 
                 5, 5, 5 
               
               
                   
                 0b110 
                 6, 6, 6 
               
               
                   
                 0b111 
                 7, 7, 7 
               
               
                   
                   
               
            
           
         
       
     
     It is possible to generate two 3-bit fast feedback channels with one uplink subchannel by dividing 3×3 subcarrier bundles (tiles) into three odd subcarrier bundles and three even subcarrier bundles as shown in Table 3. 
     Referring to Table 3, upon receiving the information data bits, the 8-ary channel encoder in a transmitter outputs a selected one of the 8 possible codewords, shown in Table 3, to a noncoherent modulator. Herein, the 8-ary channel encoder is set such that the minimum Hamming distance between codewords becomes maximized for the given number and length of codewords. The term “Hamming distance” refers to the number of inconsistent bits between binary codes having the same number of bits. 
     The minimum Hamming distance, a factor that mainly affects a codeword error rate in this transmission method, is maximized to 6. The vector index for each of the codewords generated in this manner is mapped to its associated subcarriers in a conventional method shown in  FIG. 5 , and transmitted in the method described with reference to  FIG. 1 . 
       FIG. 5  is a block diagram schematically illustrating a structure for transmitting fast feedback information using a Downlink Interval Usage Code (DIUC) scheme according to the present invention. 
     The transmission method of  FIG. 1  is designed such that it can guarantee stable reception quality for feedback information even in a bad wireless channel environment, making it possible to transmit a maximum of 6 information bits in one uplink subchannel. However, the 6 information bits are insufficient to efficiently increase cell capacity in a multi-antenna transmission system, because the system requires as much wireless channel information as possible. For this structure, there is a possible method for allocating several fast feedback channels to provide as much information as possible. However, this method uses excessive uplink resources. 
     In order to solve this problem, the present invention allows an MS having a good wireless channel environment to transmit many feedback information bits by applying the conventional data transmission scheme shown in  FIG. 5 . Although allocation of the fast feedback channels is achieved in the conventional method, it is preferable to use a coding scheme predefined between the system and the MS, for example, QPSK and 16-ary Quadrature Amplitude Modulation (16 QAM), for a transmission method. The MS, when it supports MIMO transmission, can use space-time coding such as space-time block coding (STBC) in order to guarantee stable transmission in the DFUC scheme. 
     With reference to  FIG. 5 , a description will now be made of a process of transmitting a fast feedback information bit stream  500 . 
     Referring to  FIG. 5 , the transmitter includes an encoder  501  for encoding an information data bit stream  500  for uplink fast feedback information, a modulator  503  for modulating the information data bits using a predetermined coding scheme, and an IFFT unit  505  for IFFT-processing a transmission signal before transmission. 
     The fast feedback information bit stream  500  uses a 3-bit fast feedback scheme proposed in an embodiment of the present invention, and such a DIUC scheme and the 6-bit fast feedback scheme described above can indicate an MS by transmitting a field shown in Table 4 through downlink control information. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Indication Field 
                 Length (bits) 
                 Contents 
               
               
                   
                   
               
             
            
               
                   
                 CQICH type 
                 2 
                 00 = 6 bit CQI, 
               
               
                   
                   
                   
                 01 = DIUC-CQI 
               
               
                   
                   
                   
                 10 = 3 bit CQI (even) 
               
               
                   
                   
                   
                 11 = 3 bit CQI (odd) 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 4, in an indication field, CQICH type=‘00’ indicates a 6-bit fast feedback scheme, CQICH type=‘01’ indicates a DIUC scheme for transmitting much more information to an MS having a good wireless channel environment, CQICH type=‘10’ indicates even subcarrier bundles for an uplink subchannel allocated in a 3-bit fast feedback scheme, and CQICH type=‘11’ indicates odd subcarrier bundles for the uplink subchannel allocated in the 3-bit fast feedback scheme. In addition, it is also possible to increase the number of fast feedback channels by increasing a length of a CQICH type value of the indication field and decreasing the number of information bits transmitted over the fast feedback channels. The fast feedback information bit stream  500  is input to the encoder  501  as shown in  FIG. 5 . The fast feedback information bit stream  500  is an information bit stream output from a controller not shown in  FIG. 5 . 
     If there is a fast feedback information bit stream  500  to transmit, the encoder  501  encodes the fast feedback information bit stream  500  according to a coding scheme predefined in a system setup process, and outputs the coding result to the modulator  503 . Herein, the encoder  501  can use various coding schemes such as Convolution Turbo Code (CTC), Convolutional Code (CC) and Space Time Block Code (STBC), as the coding scheme predefined in the system setup process. 
     The modulator  503  modulates the coded symbols output from the encoder  501  into modulation symbols using a modulation scheme predefined in the system setup process, and outputs the modulation symbols to the IFFT unit  505 . Herein, the modulator  503  can use, for example, M-order QAM modulation as the predefined modulation scheme. 
     The IFFT unit  505  IFFT-processes the modulation symbols received from the modulator  503 , generating OFDM symbols to transmit. Generally, the OFDM symbol includes a CP. However, a structure thereof and a structure for transmission in a wireless band are omitted in  FIG. 5 , for simplicity. 
     As can be understood from the foregoing description, the present invention can generate fast feedback information in various formats to efficiently transmit channels in a BWA communication system, making it possible to obtain correct and various feedback information. In addition, in transmitting uplink fast feedback information using given time-frequency resources, the BWA communication system maps various types of fast feedback information of 3 bits, 5 bits or 6 bits to transmission information data bits, thereby contributing to correct information delivery and stable system operation. 
     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.