Abstract:
A method and apparatus for transmitting/receiving a shared control channel message in an Orthogonal Frequency Division Multiple Access (OFDMA) wireless communication system are provided. The message transmission apparatus receives feedback information from a terminal; determines whether to transmit data by applying preceding; and transmits, in the shared control channel message, control information whose message type is differently set according to the application of the preceding. The message reception apparatus receives the shared control channel message from a base station; determines a message type of the shared control channel message; and if the message type is a Transmit Diversity (TD)-Forward Link Assignment Message (FLAM), demodulates data by at least one of Single Input Single Output (SISO) and Spatial Time Transmit Diversity (STTD) as indicated by the TD-FLAM.

Description:
PRIORITY 
     This application claims priority under 35 U.S.C. §119(a) to a Korean Patent Application filed in the Korean Intellectual Property Office on Dec. 22, 2006 and assigned Serial No. 2006-133210, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a wireless communication system using Orthogonal Frequency Division Multiple Access (OFDMA), and more particularly, to a method and apparatus for transmitting and receiving a shared control channel message in an OFDMA wireless communication system. 
     2. Description of the Related Art 
     In general, OFDMA is a system that supports multiple access technologies over different subcarriers using multiple orthogonal subcarriers. 
     Commonly, a forward link of the OFDMA system supports various transmission technologies using multiple transmit antennas, for data transmission. The various antenna technologies include a Single Input Single Output (SISO) technology, a Single Input Multi Output (SIMO) technology, a Transmit Diversity technology, and a Multi Input Multi Output (MIMO) technology. Generally, terminals transmit, to a base station, and feedback information for efficiently supporting the various transmission technologies in a reverse link. The feedback information includes a Channel Quality Indicator (CQI), a preferred precoder index, a preferred number of ranks, etc., based on the characteristic of the wireless channel estimated by the terminal. The term ‘precoder,’ as used herein, refers to the information including a weight(s) multiplied by the multiple antennas. The term ‘number of ranks,’ as used herein, refers to the number of data streams transmitted via a given number of antennas. 
     When MIMO is realized using multiple antennas, a precoding method is used for adaptively forming transmission beams according to the channel state. The term ‘preceding,’ as used herein, refers to an operation in which a transmitter pre-distorts a transmission signal before transmitting the signal via a transmit antenna. If the preceding is realized by linear combining, the precoding process can be expressed as Equation (1).
 
x=Es  (1)
 
where ‘s’ denotes a signal that the transmitter intends to transmit with a K×1 vector, and ‘x’ denotes a signal that the transmitter actually transmits with an M×1 vector. Here, ‘K’ denotes the number of symbols which are simultaneously transmitted with the same resources by MIMO, and ‘M’ denotes the number of transmit antennas. In addition, ‘E’ denotes an N×K precoding matrix. That is, Equation (1) expresses that a MIMO transmitter, with M transmit antennas, simultaneously transmits K signal streams by applying a precoding scheme, called E.
 
     The precoding matrix E is adaptively determined according to the transmission MIMO channel. However, when the transmitter cannot acquire information on the transmission MIMO channel, it performs precoding according to the feedback information reported by a receiver. To this end, a precoding codebook including a finite number of preceding matrixes E is preset between the transmitter and the receiver. The receiver selects its most-preferred precoding matrix E in the current channel state from the precoding codebook, and feeds it back to the transmitter, and the transmitter performs MIMO transmission by applying the precoding. 
     For the transmission signal of Equation (1), a signal received over a MIMO channel H is expressed as Equation (2).
 
 y=Hx+z=HEs+z   (2)
 
where ‘y’ and ‘z’ are each an N×1 vector, and denote signals and noises received at N receive antennas, respectively, and ‘H’ is an N×M matrix, and denotes a MIMO channel. The received signals undergo a reception combining process so as to improve a Signal-to-Interference and Noise Ratio (SINR) of transmission signal streams for each layer. The signal r that has undergone the reception combining process is expressed as Equation (3).
 
 r=Wy=WHx+Wz=WHEs+Wz   (3)
 
where ‘W’ is an N×N matrix, and denotes a reception combining process, and ‘r’ is an N×1 signal vector. To more correctly receive the transmission signal streams of each layer, it is possible to also use a reception technique such as interference cancellation and Maximum Likelihood (ML) reception.
 
     The reception technique can be classified into a Single-CodeWord (SCW) scheme and a Multi-CodeWord (MCW) scheme according to the number of coded packets from which multiple signal streams transmitted by the MIMO technique were generated. 
       FIG. 1  is a diagram illustrating a structure of an SCW MIMO transceiver. 
     The SCW MIMO transmitter includes a channel coding and modulation unit  101 , a demultiplexer  103 , a precoder  105 , transmission processors  107   a  to  107   m , and transmit antennas  109   a  to  109   m . The SCW MIMO receiver includes receive antennas  111   a  to  111   n , reception processors  113   a  to  113   n , a reception combiner  115 , a multiplexer  117 , and a demodulation and channel decoding unit  119 . 
     The channel coding and modulation unit  101  performs channel coding and modulation on a desired transmission data stream and converts it into one coded packet signal stream. The demultiplexer  103  demultiplexes the signal stream into K signal streams, for MIMO transmission. The precoder  105  linear-converts the demultiplexed K signal streams into M signal streams to be transmitted via the transmit antennas  109   a  to  109   m . Here, the K signal streams are transmitted with different transmission beams. The transmission processors  107   a  to  107   m  transmit the precoded M signal streams to the reception side via the transmit antennas  109   a  to  109   m . The transmission processors  107   a  to  107   m  each include not only the process of generating CDMA/OFDMA signals, but also the filtering or Radio Frequency (RF) processing process performed at each antenna. 
     The transmission signal is received at the reception processors  113   a  to  113   n  via N receive antennas  111   a  to  111   n . The reception processors  113   a  to  113   n  restore the signal received at the receive antennas  111   a  to  111   n  to a baseband signal. The reception combiner  115  combines the reception-processed signal, and outputs the combined signal to the multiplexer  117 . The multiplexer  117  multiplexes the combined signal, and outputs the multiplexed signal to the demodulation and channel decoding unit  119 . The demodulation and channel decoding unit  119  restores the multiplexed signal to the desired original transmission data stream. 
     According to the SCW MIMO characteristics, because the SCW MIMO transmitter generates multiple transmission signal streams with one channel coding and modulation unit  101 , it may receive only one feedback CQI. However, the number K of MIMO-transmitted transmission signal streams, i.e., the number K of transmitted MIMO layers, should be adjusted according to the channel state. Herein, the number K of transmitted MIMO layers is defined as ‘rank’. Therefore, the SCW MIMO feedback is composed of one CQI representative of the channel state of the transmission MIMO layer, and the number ‘rank’ of transmission layers. 
       FIG. 2  is a diagram illustrating a structure of an MCW MIMO transceiver. 
     In MCW MIMO, unlike in SCW MIMO, different coded packet signal streams are transmitted separately through MIMO layers. 
     A demultiplexer  201  first demultiplexes a desired transmission data stream into as many data stream as the rank. Channel coding and modulation units  101   a  to  101   k  each perform different channel coding and modulation on the demultiplexed signal streams, and output the signal streams associated with the MIMO layers. The next transmission process is equal to that of SCW MIMO, and the output signal streams proceed through a precoder  105  and each of transmission processors  107   a  to  107   m  associated with the transmit antennas  109   a  to  109   m , generating the signals to be transmitted via M transmit antennas  109   a  and  109   m . The MCW MIMO reception process is also equal to the SCW MIMO reception process in several steps immediately after the signal reception. Although the receiver structure of  FIG. 2  utilizes an interference canceller  205 , by way of example, it may use the other-type reception method. A signal received via N receive antennas  111   a  to  111   n  undergoes reception processors  113   a  to  113   n  and a reception combiner  115  in order, restoring transmission signals associated with the corresponding layers. The restored signals include their mutual interference. 
     In MCW MIMO, because the transmission signal underwent different channel coding and modulation separately for each layer, the receiver cancels the first restored signal of a particular layer, thereby removing the interference to the other layer caused by the signal. The use of the interference canceller  205  can improve the channel capacity of the MIMO layers, thereby facilitating transmission of more data by MCW MIMO transmission. An interference cancellation-based reception process is described in greater detail below. 
     If a one-layer signal is successfully restored by a demodulation and channel decoding unit  203 , the interference canceller  205  cancels interference using the restored signal. The interference-canceled signal stream  207  is input back to the demodulation and channel decoding unit  203 . The restoration and interference cancellation are repeated until signals of all layers are successfully restored, or there is no more layer signal to be restored. 
     A multiplexer  209  multiplexes the last restored signal streams associated with the multiple layers, thereby restoring one desired transmission data stream. 
     According to the MCW MIMO characteristics, because the MCW MIMO transmitter generates multiple transmission signal streams with multiple channel coding and modulation units  101   a  to  101   k  associated with the corresponding layers, it should receive feedback CQIs separately for the corresponding layers. 
     Meanwhile, the rank can be expressed in an immanent way by setting a predefined CQI value indicating ‘No Transmission’ among the CQI values, instead of separately. Therefore, the MCW MIMO feedback is composed of multiple CQIs representative of the channel states of the transmission MIMO layers. 
     In the common OFDMA system, the base station transmits pilots to the terminal for coherent demodulation (or coherent detection) of the data transmitted in the forward link, and for quality estimation of the forward channel. The pilots used for the data demodulation are classified into common pilots and dedicated pilots according to their form. 
       FIG. 3  is a diagram illustrating an example of common pilots. 
     In  FIG. 3 , a term ‘auxiliary pilot’ is used to distinguish a pilot of the first antenna from the pilots for the remaining antennas. The common pilots, transmitted by the base station, are commonly used by several users (or terminals) together. The common pilots can be used for both the data demodulation and the channel quality estimation. The common pilots are characterized in that they are transmitted over the fill available band of the system at fixed periods regardless of the data transmission and resource allocation. 
       FIG. 4  is a diagram illustrating an example of dedicated pilots. 
     As illustrated in  FIG. 4 , a bundle of 8 consecutive OFDM symbols and 16 consecutive subcarriers is commonly called one tile or Block Resource Channel (BRCH). As shown in  FIG. 4 , various patterns of dedicated pilots can be defined in one tile, and the reason for defining the various pilot patterns is to use an appropriate pilot pattern according to the number of ranks and the channel characteristic. The dedicated pilots, or those pilots transmitted to a particular user, are the pilots that one user, i.e., only the user receiving data over particular resources at a particular time, uses. Therefore, the dedicated pilots are characterized in that they are inserted into particular resources allocated to the user to which data is transmitted at an arbitrary time. 
     The common OFDMA system can be divided into (i) a system that supports only the common pilots as the pilots for data demodulation in the forward link, (ii) a system that supports only the dedicated pilots, and (iii) a system that supports both of the common pilots and the dedicated pilots. 
     In the case where the base station uses the common pilots, the base station, when it transmits data over the forward link, applies predetermined precoding for multiple antennas. Therefore, when the base station intends to form one or multiple beams and transmit data over the beams, the base station cannot apply the precoding appropriate for the particular user to the common pilots. This is because the common pilots are commonly utilized for several users. Therefore, when the base station uses the common pilots, and for data transmission, forms beams by applying precoding and transmit data over the beams, a receiver, or terminal, should have information indicating which precoding is applied to the data transmission, in order to perform channel estimation even on the received common pilots taking into account the precoding applied to the data transmission, and to demodulate the data depending thereon. 
     However, in the case where the base station uses the dedicated pilots, the base station, when it transmits data over the forward link, applies predetermined precoding for multiple antennas. Therefore, when the base station intends to form one or multiple beams and transmit data over the beams, the base station applies the precoding used for the data transmission even to the dedicated pilots in the same way. This is possible because the dedicated pilots are the pilots provided for a particular one user. The foregoing characteristics make the receiver have no need to acquire the information indicating which precoding the transmitter has applied in the process of performing data reception and demodulation to which precoding is applied. That is, because the same precoding is applied to the data and the pilots, the data receiver only needs to perform channel estimation over the pilots for the following reason. That is, because the channel estimation already includes the preceding, the intact channel estimation value can be used for the data demodulation. 
     The term ‘shared control channel’ as used herein refers to a channel that is transmitted together when data is transmitted to an arbitrary terminal at an arbitrary time. This channel is characterized in that it includes control information necessary for demodulation of the transmission data. A description of the control information is made using Table 1. Table 1 shows a message format of the shared control channel used in the prior art, and the message is transmitted over the shared control channel. 
     Referring to Table 1, ‘Block type’ is a field indicating a type of the message. ‘MAC ID’ is a field indicating an identifier (ID) of a terminal. That is, after receiving the shared control channel, the terminal checks the MAC ID included in the shared control channel and determines whether the received MAC ID is equal to the MAC ID previously agreed upon between the terminal itself and the base station, thereby determining whether there is any data being transmitted to the terminal itself. Although the MAC ID is included herein in the message of the shared control channel of Table 1, rather than being included in the message of the shared control channel, it can be transmitted by scrambling the message of the shared control channel using a MAC ID-specific scrambling sequence of the target user. A ‘Persistent’ field indicates whether the resources allocated to the terminal itself are persistent resources or non-persistent resources. ‘Channel Identifier (ChanID)’ is an ID for the allocated resource. ‘Packet Format (PF)’ is a field indicating a modulation order (QPSK, 8PSK, 16QAM, etc.) and a code rate used for data transmission. ‘Extended Transmission (Ext. Tx)’ is the information indicating a time length of the transmission data. ‘Rank’ indicates the number of data streams transmitted via multiple antennas. 
     In Table 1, Forward Link Assignment Message (FLAM) indicates that the corresponding message is a message for forward resource allocation. MCW indicates that the multiple data streams transmitted via multiple antennas are the data streams that underwent channel coding (for example, turbo coding) independently of each other. SCW indicates that the multiple data streams transmitted via multiple antennas are parts of the codeword that underwent one channel coding. 
     In Table 1, numerals shown in the shaded part indicate whether the message type includes a particular field. For example, Rank field is ‘0’ for FLAM, but Rank field is ‘1’ for SCW FLAM. Because the FLAM is a message type used for SIMO transmission, it has no Rank field used for transmission of multiple streams. However, because multiple streams can be transmitted, the SCW FLAM needs the rank information. 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Block 
                   
                   
                   
                   
                 Ext. 
                   
               
               
                 Field 
                 type 
                 MACID 
                 Persistent 
                 ChanID 
                 PF 
                 TX 
                 Rank 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 # bits 
                 3 
                 9-11 
                 1 
                 6-8 
                 4-6 
                 1 
                 2 
               
               
                 FLAM 
                 00 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
               
               
                 MCW 
                 01 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
               
               
                 FLAM1 
               
               
                 MCW 
                 10 
                 1 
                 0 
                 0 
                 3 
                 1 
                 0 
               
               
                 FLAM2 
               
               
                 SCW 
                 11 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 FLAM 
               
               
                   
               
             
          
         
       
     
     The foregoing conventional shared control channel&#39;s message format is not suitable for forward data transmission supporting various antenna technologies including the precoding technology. For example, in the system supporting the common pilots, the data receiver, or terminal, should have the information indicating which precoding is used for the data transmission. However, such information is not included in the message. In addition, when the data transmitter transmits data by applying SISO, Spatial Time Transmit Diversity (STTD), etc. without applying the precoding, the data receiver cannot detect the application of the SISO or STTD technology. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention provides an apparatus and method for efficiently transmitting/receiving a message of a forward shared control channel in an OFDMA wireless communication system that transmits data over a forward link using various antenna technologies. 
     Another aspect of the present invention provides an apparatus and method for transmitting/receiving a message of the forward shared control channel. 
     An additional aspect of the present invention provides an apparatus and method for transmitting/receiving a message of a forward shared control channel so as to identify Transmit Diversity (TD) technologies agreed upon between a base station and a terminal to determine which precoding is used for data transmission in an OFDMA wireless communication system. 
     A further aspect of the present invention is to provide an apparatus and method for transmitting/receiving a message of a forward shared control channel so as to distinguish that a data transmitter transmits data by applying SISO, STTD, etc. without applying precoding in an OFDMA wireless communication system. 
     According to one aspect of the present invention, a method for transmitting a shared control channel message in an OFDMA wireless communication system is provided. Feedback information is received from a terminal. It is determined whether to transmit data by applying precoding. Control information is transmitted in the shared control channel message. The control information message type is differently set according to the application of the precoding. 
     According to another aspect of the present invention, a method for receiving a shared control channel message in an OFDMA wireless communication system is provided. The shared control channel message is received from a base station. A message type of the shared control channel message is determined. Data is demodulated by at least one of SISO and STTD as indicated by the TD-FLAM, when the message type is a TD FLAM. 
     According to an additional aspect of the present invention, a method for transmitting a shared control channel message in an OFDMA wireless communication system is provided. It is determined whether to transmit data by applying precoding. Control information is transmitted in the shared control channel message over a TD FLAM when determining whether to transmit the data without applying the preceding. The TD-FLAM includes information indicating which TD is used. 
     According to a further aspect of the present invention, an apparatus is provided for transmitting a shared control channel message in an OFDMA wireless communication system. The message transmission apparatus includes a controller for determining whether to transmit data by applying precoding. When determining whether to transmit data without applying the preceding, the controller transmits control information in the shared control channel message over a TD-FLAM. The TD-FLAM includes information indicating which TD is used. 
     According to yet another aspect of the present invention, an apparatus is provided for receiving a shared control channel message in an OFDMA wireless communication system. The message reception apparatus includes a reception unit for receiving the shared control channel message from a base station. The message reception apparatus also includes a controller for determining a message type of the shared control channel message, and if the message type is a TD-FLAM, demodulating data as indicated by the TD-FLAM. The TD-FLAM includes information indicating which TD is used. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, 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 SCW MIMO transceiver; 
         FIG. 2  is a diagram illustrating a structure of an MCW MIMO transceiver; 
         FIG. 3  is a diagram illustrating an example of common pilots; 
         FIG. 4  is a diagram illustrating an example of dedicated pilots; 
         FIG. 5  is a flow diagram illustrating a method for transmitting a message of a forward shared control channel depending on various antenna technologies used for forward data transmission, according to an embodiment of the present invention; 
         FIG. 6  is a flow diagram illustrating a process in which to demodulate data transmitted over the forward link, a terminal receives a shared control channel, analyzes its message, and demodulates a data channel depending on the analysis result, according to an embodiment of the present invention; 
         FIG. 7  is a diagram illustrating a structure of a transmitter according to an embodiment of the present invention; and 
         FIG. 8  is a diagram illustrating a structure of a receiver according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are described in detail with reference to the accompanying drawings. It should be noted that similar components are designated by similar reference numerals although they are illustrated in different drawings. Detailed descriptions of constructions or processes known in the art may be omitted to avoid obscuring the subject matter of the present invention. 
     The present invention relates to a method and apparatus for configuring and transmitting/receiving a message of a Forward Shared Control Channel (F-SCCH) to support various antenna technologies for forward data transmission in a wireless communication system using OFDMA. Although the present invention will be described herein with reference to the system supporting both the common pilots and the dedicated pilots, it should be noted that the present invention can be applied to the systems supporting any one of the common pilots and the dedicated pilots. 
     In addition, although the message of the shared control channel proposed by the present invention includes even the particular fields not directly related to the present invention, such as ‘Persistent’ and ‘PF’ fields, by way of example, the message may include only the particular fields defined in an embodiment of the present invention, or may further include other fields used for other purposes. 
     Table 2 and Table 3 show message formats of the shared control channel according to a preferred embodiment of the present invention. Among them, Table 2 corresponds to a first embodiment and Table 3 corresponds to a second embodiment. 
     In Table 2 and Table 3, the underlined portions are newly proposed by the present invention. TD-FLAM is used in Table 2 and Table 3 rather than the conventional FLAM to indicate the use/nonuse of the TD technology for data transmission, and to specifically indicate which TD technology is used for the TD-FLAM. Although the term ‘TD-FLAM’ is used herein, the original term ‘FLAM’ can be used instead, or the term ‘Open Loop (OL)-FLAM’ can be used. The term ‘OL’ as used herein refers to an antenna technology that operates without receiving the precoding-related feedback from the terminal. This technology covers the case where the base station transmits data using a specific diversity technology without using the precoding fed back (or designated) by the terminal, even when the terminal transmits the precoding-related feedback. That is, ‘Rank’ in the example of Table 2 or ‘TD-scheme’ in the example of Table 3, is a field having the same function. This is a field for indicating whether SISO (which can be replaced with SIMO according to the number of receive antennas in the terminal) is used for forward data transmission, or a TD technology, for example, STTD technology, is used for forward data transmission. Further, this field is used for distinguishing even the information on rank-1 STTD, rank-2 STTD and rank-3 STTD divided from the STTD technology. With reference to  FIG. 5 , a detailed description is provided regarding how to use this field (‘Rank’ in Table 2 or ‘TD-scheme’ in Table 3). 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Block 
                   
                   
                   
                   
                 Ext. 
                   
               
               
                 Field 
                 type 
                 MACID 
                 Persistent 
                 ChanID 
                 PF 
                 TX 
                 Rank 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 # bits 
                 3 
                 9-11 
                 1 
                 6-8 
                 4-6 
                 1 
                 2 
               
               
                 TD-FLAM 
                 00 
                 1 
                 1 
                 1 
                 1 
                 1 
                 
                   1 
                 
               
               
                 MCW 
                 01 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
               
               
                 FLAM1 
               
               
                 MCW 
                 10 
                 1 
                 0 
                 0 
                 3 
                 1 
                 0 
               
               
                 FLAM2 
               
               
                 SCW 
                 11 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 FLAM 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Block 
                   
                 Persis- 
                   
                   
                 Ext. 
                   
                 TD- 
               
               
                 Field 
                 type 
                 MACID 
                 tent 
                 ChanID 
                 PF 
                 TX 
                 Rank 
                 Scheme 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 # 
                 3 
                 9-11 
                 1 
                 6-8 
                 4-6 
                 1 
                 2 
                 2 
               
               
                 bits 
               
               
                 TD- 
                 00 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 
                   1 
                 
               
               
                 FLAM 
               
               
                 MCW 
                 01 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
                 0 
               
               
                 FLAM1 
               
               
                 MCW 
                 10 
                 1 
                 0 
                 0 
                 3 
                 1 
                 0 
                 0 
               
               
                 FLAM2 
               
               
                 SCW 
                 11 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 0 
               
               
                 FLAM 
               
               
                   
               
             
          
         
       
     
       FIG. 5  is a flow diagram illustrating a method for transmitting a message of a forward shared control channel depending on various antenna technologies used for forward data transmission according to an embodiment of the present invention. 
     Referring to  FIG. 5 , a base station receives a variety of feedback information from a terminal in step  501 . The feedback information includes channel quality information, preceding information, etc. Reverse channels over which the feedback information is transmitted include Channel Quality Indicator Channel (CQICH), Beam Index Feedback Channel (BCH), MIMO Quality Indication Channel (MQICH), Subband Feedback Channel (SFCH), etc. 
     The CQICH is a channel used for feeding back forward channel quality information for a SISO channel. The CQICH is a channel used for feeding back channel quality information for the full available band of the system. The BFCH is a channel used for feeding back precoding (or beamforming)-related information, i.e., ID information for the preceding preferred by the terminal. The MQICH is a channel used for feeding back a plurality of channel quality information. The plurality of channel quality information indicates channel quality information for each of the layers or beams. The SFCH is a channel used for feeding back channel quality information for each subband. The SFCH transmits, along with a subband ID, channel quality information of a subband corresponding to the subband ID. Although the feedback channels can be configured such that all of the four types of the above-described feedback channels are transmitted from one terminal, it should be noted that only some of them can be enabled. The rule for determining which feedback channel the base station will enable and which feedback channel the base station will disable is commonly agreed upon between the base station and the terminal by Layer-3 signaling. 
     In step  502 , the base station performs scheduling using a variety of the other information necessary for scheduling, including the feedback information received in step  501 . The variety of information necessary for scheduling can include the amount (buffer information) of data that the base station should transmit to each user, and Quality of Service (QoS). The phrase ‘performing scheduling’ as used herein refers to an operation in which the base station determines data of which user it will transmit over which subcarrier, determines by which antenna technology it will transmit the data, and determines which modulation scheme and code rate it will use. 
     In step  503 , the base station determines whether it uses a common pilot or a dedicated pilot at a corresponding time. If it is determined that the base station uses the common pilot, the base station proceeds to step  504  where it determines whether the precoding-related feedback, i.e., BFCH, in the feedback from the terminal that intends to transmit data at the corresponding time according to the result of step  502 , is enabled. If it is determined in step  504  that the BFCH is enabled, the base station proceeds to step  505  where it determines whether during data transmission to the scheduled terminal, the base station transmits the data using the precoding scheme recently fed back by the terminal over the BFCH. If it is determined in step  505  that the base station transmits the data using the precoding scheme recently fed back, or received, from the terminal over the BFCH, the base station transmits, in step  506 , control information to the terminal using SCW-FLAM and MCW-FLAM. 
     However, if it is determined in step  505  that the base station does not transmit the data using the precoding scheme recently fed back by the terminal over the BFCH during data the transmission to the scheduled terminal, the base station transmits control information to the terminal using TD-FLAM in step  507 . The TD-FLAM is characterized in that it is defined to identify the TD technologies (including random beamforming) agreed upon between the base station and the terminal. As a detailed example, the 2-bit Rank field of Table 2 and the 2-bit TD-scheme field of Table 3 can be defined as follows. 
     Embodiment 1 for Meaning of 2-Bit TD-Scheme Field 
     00: SISO (replaceable with SIMO according to the number of receive antennas of terminal) 
     01: STTD rate 1 
     10: STTD rate 2 
     11: Spatial Multiplexing (SM) (for rank 4) 
     Embodiment 2 for Meaning of 2-Bit TD-Scheme Field 
     00: SISO (replaceable with SIMO according to the number of receive antennas of terminal) 
     01: STUD rate 1 
     10: STTD rate 2 
     11: STTD rate 3 
     Embodiment 3 for Meaning of 2-Bit TD-Scheme Field 
     00: STUD rate 1 
     01: STUD rate 2 
     10: STTD rate 3 
     11: SM (for rank 4) 
     In the foregoing description, STTD rate 1 indicates rank-1 STUD transmission, STTD rate 2 indicates rank-2 STTD transmission, and STTD rate 3 indicates rank-3 STUD transmission. In addition, SM for rank 4 refers to a technology for multiplexing 4 streams to 4 antennas. 
     If it is determined in step  504  that the precoding-related feedback, i.e., BFCH, is not enabled, the base station proceeds to step  508  where it determines whether it transmits data by applying the precoding, if any, previously agreed upon between the base station and the terminal. If the base station transmits data by applying the preceding, if any, previously agreed upon between the base station and the terminal, the base station proceeds to step  509  where it transmits control information using SCW-FLAM and MCW-FLAM. 
     However, if it is determined in step  508  that there is no preceding scheme previously agreed upon between the base station and the terminal or the base station does not transmit data by applying the agreed precoding, the base station proceeds to step  510  where it transmits control information using TD-FLAM. The TD-FLAM is characterized in that it is defined to identify the TD technologies (including random beamforming) agreed upon between the base station and the terminal. For meanings of the 2-bit TD-scheme field of the TD-FLAM, reference can be made to Embodiments 1 to 3 for Meaning of 2-bit TD-scheme Field. 
     If it is determined in step  503  that the base station uses the dedicated pilot rather than the common pilot as a pilot for data demodulation at the corresponding time, the base station proceeds to step  511  where it determines whether preceding is applied for the data transmission. If it is determined that the precoding is applied for the data transmission, the base station transmits control information using SCW-FLAM and MCW-FLAM in step  512 . However, if it is determined in step  511  that the precoding is not applied for the data transmission, the base station transmits control information using TD-FLAM in step  513 . The TD-FLAM is characterized in that it is defined to identify the TD technologies (including random beamforming) agreed upon between the base station and the terminal. For meanings of the 2-bit TD-scheme field of the TD-FLAM, reference can be made to Embodiments 1 to 3 for Meaning of 2-bit TD-scheme Field. 
       FIG. 6  is a flow diagram illustrating a process in which to demodulate data transmitted over the forward link, a terminal receives a shared control channel, analyzes its message, and demodulates a data channel depending on the analysis result, according to an embodiment of the present invention. 
     Referring to  FIG. 6 , a terminal transmits in step  601   a  variety of feedback information to a base station over the reverse link. The feedback information includes the feedback information described in  501  of  FIG. 5 . In step  602 , the terminal receives a shared control channel from the base station, and demodulates it to acquire a message. In step  603 , the terminal determines whether the base station uses the common pilot or uses the dedicated pilot at the corresponding time. If it is determined that the base station uses the common pilot, the terminal proceeds to step  604  where it determines whether the precoding-related feedback, i.e., BFCH, in the feedback channel of the terminal, is enabled. If the BFCH is enabled, the terminal proceeds to step  605  where it determines whether a message type (Block type in Table 2 and Table 3) of the received shared control channel is SCW-FLAM or MCW-FLAM. If the message type is SCW-FLAM or MCW-FLAM, the terminal receives and demodulates the data by applying the precoding in step  606 . 
     If it is determined in step  605  that the message type is not SCW-FLAM or MCW-FLAM, the terminal receives and demodulates the data in step  607  using the SISO or STTD technology as designated by the TD-scheme field of the TD-FLAM. For meanings of the 2-bit TD-scheme field of the TD-FLAM, reference can be made to Embodiments 1 to 3 for Meaning of 2-bit TD-scheme Field. 
     If it is determined in step  604  that the BFCH is not enabled, the terminal proceeds to step  608  where it determines whether a message type (Block type in Table 2 and Table 3) of the received shared control channel is SCW-FLAM or MCW-FLAM. If the message type is SCW-FLAM or MCW-FLAM, the terminal receives and demodulates the data by applying the preceding in step  609 . However, if it is determined in step  608  that the message type is not SCW-FLAM or MCW-FLAM, the terminal receives and demodulates in step  610  the data using the SISO or STTD technology as designated by the TD-scheme field of the TD-FLAM. For meanings of the 2-bit TD-scheme field of the TD-FLAM, reference can be made to Embodiments 1 to 3 for Meaning of 2-bit TD-scheme Field. 
     If it is determined in step  603  that the base station does not use the common pilot at the corresponding time, the terminal proceeds to step  611  where it determines whether a message type (Block type of Table 2 and Table 3) of the received shared control channel is SCW-FLAM or MCW-FLAM. If the message type (Block type of Table 2 and Table 3) of the received shared control channel is SCW-FLAM or MCW-FLAM, the terminal receives and demodulates the data by applying the precoding in step  612 . However, if it is determined in step  611  that the message type of the received shared control channel is not SCW-FLAM or MCW-FLAM, the terminal receives and demodulates in step  613  the data using the SISO or STTD technology as designated by the TD-scheme field of the TD-FLAM. For meanings of the 2-bit TD-scheme field of the TD-FLAM, reference can be made to Embodiments 1 to 3 for Meaning of 2-bit TD-scheme Field. 
       FIG. 7  is a diagram illustrating a structure of a transmitter according to an embodiment of the present invention. 
     Referring to  FIG. 7 , the transmitter includes a channel coding, modulation &amp; demultiplexing unit  701 , a transmission processor  702 , a precoder  703 , a controller  704 , a control information generator  705 , and a channel coding and modulation unit  706 . 
     The channel coding, modulation &amp; demultiplexing unit  701 , the transmission processor  702 , and the precoder  703  are equal in structure and operation to the corresponding elements described with reference to  FIGS. 1 and 2 . 
     The controller  704  receives, from the channel coding, modulation &amp; demultiplexing unit  701 , the transmission processor  702  and the precoder  703 , the information indicating which transmission scheme is used for data transmission, and controls a control information transmission method of the control information generator  705  and the channel coding and modulation unit  706  depending on the received information. Although the description of  FIG. 7  is directed to the example where the controller  704  acquires the information on the transmission scheme used for a data channel from the channel coding, modulation &amp; demultiplexing unit  701 , the transmission processor  702  and the precoder  703 , it should be noted that the same can be applied to another example where the controller  704  can directly acquire the information on the transmission scheme used for the data channel from a scheduler though it is not shown in  FIG. 7 . A detailed control operation of the controller  704  has been described in  FIG. 5 . The controller  704  controls the control information generator  705  to configure the control information as described above, and controls the channel coding and modulation unit  706  to perform a channel coding and modulation process on the generated control information and to transmit it over a control channel. 
       FIG. 8  is a diagram illustrating a structure of a receiver according to an embodiment of the present invention. 
     Referring to  FIG. 8 , the receiver includes a demodulation and channel decoding unit  802 , a control information extractor  803 , a controller  804 , a reception processor  805 , a reception combiner  806 , and a demodulation, channel decoding &amp; interference cancellation unit  807 . 
     A control channel reception unit composed of the demodulation and channel decoding unit  802  and the control information extractor  803  extracts control information through a demodulation and channel decoding process on the signal received over a specific control channel. The extracted control information is input to the controller  804 . The controller  804  controls a data channel reception unit composed of the reception processor  805 , the reception combiner  806  and the demodulation, channel decoding &amp; interference cancellation unit  807  using the method described in  FIG. 6 . A detailed description of the reception processor  805 , the reception combiner  806  and the demodulation, channel decoding &amp; interference cancellation unit  807  has been made in  FIGS. 1 and 2 . 
     As is apparent from the foregoing description, according to the present invention, the use of the message configuration method for the forward shared control channel can reduce the overhead of the shared control channel, and facilitate the efficient utilization of the various antenna technologies in the OFDMA packet data mobile communication system, thereby contributing to the expected increase in the capacity. 
     In addition, the present invention can identify the TD technologies agreed upon between the base station and the terminal to determine which precoding is used for data transmission in the system supporting the common pilots. 
     Further, according to the present invention, when the data transmitter transmits the data by applying the SISO or STTD technology without applying the preceding, the data receiver can detect the application of the SISO or STTD technology. 
     While the invention has been shown and described with reference to a certain preferred embodiments 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.