Abstract:
An apparatus and method for allocating dedicated pilots for supporting MIMO and setting MIMO-only interlace slots in a CDMA  2000  Nx-EV-DO compatible system. The method includes determining whether a current interlace is a particular interlace in which a Multiple Input Multiple Output (MIMO) signal for channel estimation in a receiver is inserted; and inserting the MIMO signal into the particular interlace when the current interlace is the particular interlace and then transmitting the MIMO signal according to a predetermined transmission scheme. By the apparatus and method, it is possible to effectively use the MIMO in a system in which EV-DO users, MIMO EV-DO users, OFDM users, MIMO-OFDM users co-exist.

Description:
PRIORITY  
       [0001]     This application claims the benefit under 35 U.S.C. §119(a) of an application filed in the Korean Industrial Property Office on Jan. 25, 2006 and assigned Serial No. 2006-7981, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention generally relates to an apparatus and a method for transmitting/receiving data in a High Rate Packet Data (HRPD) system, and more particularly to a transmission/reception apparatus and method for supporting an Orthogonal Frequency Division Multiplexing (OFDM) scheme and a Multiple Input Multiple Output (MIMO) technology as well as an Evolution Data Only (EV-DO) transmission scheme in an HRPD system.  
         [0004]     2. Description of the Related Art  
         [0005]     With rapid development of communication technology, current mobile communication systems are providing not only ordinary voice communication services but also high rate data services which enable transmission of large-capacity digital data, such as moving images, as well as transmission of an e-mail or a still image, by using a Mobile Station (MS).  
         [0006]     Representative examples of mobile communication systems currently providing high rate data services include an EV-DO system, an OFDM system, etc. An EV-DO system uses one of the high rate data service standards proposed by the Qualcomm company of the United States for transmission of large-capacity digital data and has been one-step evolved from a conventional Code Division Multiple Access (CDMA) 2000 1× in order to provide a forward transmission speed of 2.4 Mbps. An EV-DO system is also called an “HRPD system.” 
         [0007]     Further, one of representative wireless communication systems employing a multi-carrier transmission scheme is an OFDM system. According to an OFDM scheme, a serial symbol sequence is converted into parallel symbol sequences and the parallel symbol sequences are modulated with a plurality of mutually orthogonal sub-carriers before being transmitted. OFDM schemes have come into the spotlight since the beginning of the 1990&#39;s according to development of Very Large Scale Integration (VLSI) technology.  
         [0008]     According to an OFDM transmission scheme, data is modulated with multiple sub-carriers, and the sub-carriers maintain orthogonality between them. Therefore, an OFDM transmission scheme is stronger against a frequency selective multi-path fading channel and is more proper for HRPD services, such as a broadcasting service, than a conventional single carrier modulation scheme.  
         [0009]     A slot structure and a transmitter structure in a forward link of a typical HRPD system will now be briefly described.  
         [0010]     A forward link of an HRPD system uses a Time Division Multiple Access (TDMA) technology for multiple access, and uses a Time Division Multiplexing (TDM)/Code Division Multiplexing (CDM) scheme for multiplexing.  
         [0011]      FIG. 1  shows a slot structure of a forward link in a conventional HRPD system. One slot has a structure including repeated one-half slots. Each of the one-half slots includes a pilot signal  103  or  108  having an N pilot  hip length, which is inserted at a center thereof and is used in channel estimation of the forward link in a receiver of an MS. Medium Access Control (MAC) signals  102 ,  104 ,  107 , and  109 , each of which has an N MAC  chip length and includes reverse power control information and resource allocation information, are located at both sides of associated pilot signals  103  and  108 . Further, actual transmission data  101 ,  105 ,  106 , and  110 , each of which has an N Data  chip length, are located at opposite outer sides of associated MAC signals  102 ,  104 ,  107 , and  109 . In an HRPD system as described above, a slot of a forward link has been multiplexed according to a TDM scheme in which a pilot, MAC information, data, etc. are transmitted at different time points.  
         [0012]     In the slot structure shown in  FIG. 1 , the MAC information and the data are multiplexed according to a CDM scheme using Walsh codes, and the pilot signal, the MAC signal, and a small block unit of data have been set to have sizes such that N pilot =96 chips, N MAC =64 chips, and N Data =400 chips, respectively, in the forward link of the HRPD system.  
         [0013]      FIG. 2  shows a transmitter of a conventional HRPD system. Packet data of a data channel passes through a channel encoder  201  for channel-encoding the packet data, a channel interleaver  202  for interleaving the encoded data, and a modulator  203  for modulating the interleaved packet data. Data of a MAC channel passes through a channel encoder  204 . The pilot tone, the MAC signal, and the data pass through a TDM multiplexer (MUX)  206  and then forms a physical link having a slot structure of  FIG. 1 . The data output from the TDM MUX  206  is transmitted to users through an antenna (not shown) after passing through a sub-carrier modulator  207 . Reference numeral  208  in  FIG. 2  denotes an HRPD processor for compatibility with an HRPD system, which includes the channel encoder  204 , the TDM MUX  206 , and the sub-carrier modulator  207 .  
         [0014]     However, an HRPD system having the above-described structure is insufficient for adequate support of wideband data transmission and efficient use of frequency resources, which are used by next generation systems, such as broadcasting service systems. In order to support wideband data transmission and efficient use of frequency resources, a need exists to provide a solution for high speed data transmission and efficient use of frequency resources by using multiple antennas and a proper data modulation scheme.  
       SUMMARY OF THE INVENTION  
       [0015]     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a transmission/reception apparatus and method for supporting an OFDM scheme and a MIMO technology as well as an EV-DO transmission scheme in an HRPD system.  
         [0016]     It is another object of the present invention to provide a transmission/reception apparatus and method for supporting an OFDM scheme and an EV-DO transmission scheme and supporting the MIMO technology by allocating a position of a data symbol to a fixed interlace in an HRPD system.  
         [0017]     In order to accomplish this object, there is provided a transmitter for transmitting packet data in a forward link of an HRPD system, the transmitter including a transmission unit for modulating physical layer packet data to a transmission signal according to a transmission scheme and transmitting the transmission signal to a wireless network; a MIMO signal inserter for inserting a MIMO signal for channel estimation in a receiver into a particular interlace of a slot in which the transmission signal is transmitted; and a MIMO interlace selector for controlling an operation of the MIMO signal inserter to insert the MIMO signal into the particular interlace.  
         [0018]     In accordance with another aspect of the present invention, there is provided a method for transmitting packet data in a forward link of an HRPD system, the method including determining when a current interlace is a particular interlace in which a MIMO signal for channel estimation in a receiver is inserted; and inserting the MIMO signal into the particular interlace when the current interlace is the particular interlace and then transmitting the MIMO signal according to a transmission scheme.  
         [0019]     In accordance with another aspect of the present invention, there is provided a receiver for receiving packet data in a forward link of an HRPD system, the receiver including a MIMO signal extractor for extracting a MIMO signal for channel estimation from a particular interlace of a slot in which a wireless signal is transmitted; and a reception unit for receiving the wireless signal according to a transmission scheme, performing channel estimation by using the MIMO signal, and demodulating the packet data from the wireless signal, wherein information about the particular interlace is included in at least one of information promised in advance between a transmitter for transmitting the packet data and the receiver and control information transmitted from the transmitter to the receiver  
         [0020]     In accordance with another aspect of the present invention, there is provided a method for receiving packet data in a forward link of an HRPD system, the method including extracting a MIMO signal for channel estimation from a particular interlace of a slot in which a wireless signal is transmitted; receiving the wireless signal according to a transmission scheme, and performing channel estimation by using the MIMO signal; and demodulating the packet data from the wireless signal based on a result of the channel estimation wherein information about the particular interlace is included in at least one of information promised in advance between a transmitter for transmitting the packet data and a receiver and control information transmitted from the transmitter to the receiver. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0022]      FIG. 1  illustrates a slot structure of a forward link in a conventional HRPD system;  
         [0023]      FIG. 2  illustrates a structure of a transmitter of a conventional HRPD system;  
         [0024]      FIG. 3  illustrates a slot structure of a forward link in an HRPD system according to the present invention, in which OFDM symbols are inserted in data transmission periods;  
         [0025]      FIG. 4  illustrates a structure of a transmitter in an HRPD system according to the present invention;  
         [0026]      FIG. 5A  illustrates an example of arrangement of MIMO pilot tones when using an OFDM transmission scheme supporting the MIMO in a forward link of an HRPD system according to the present invention;  
         [0027]      FIGS. 5B and 5C  illustrate examples of arrangement of MIMO pilots when using the EV-DO transmission scheme supporting the MIMO in a forward link of an HRPD system according to the present invention;  
         [0028]      FIG. 6A  is a view in order to illustrate the reason why interlaces for the MIMO users are fixedly allocated in the forward link of an HRPD system according to the present invention;  
         [0029]      FIG. 6B  illustrates an example in which interlaces are fixedly allocated exclusively for the MIMO in the forward link of an HRPD system according to the present invention;  
         [0030]      FIG. 7  is a flow diagram of a transmission process when MIMO interlaces have been allocated in the forward link of an HRPD system according to the present invention;  
         [0031]      FIG. 8  is a block diagram illustrating a structure of a receiver when using a non-MIMO EV-DO transmission scheme in a forward link of an HRPD system according to the present invention;  
         [0032]      FIG. 9  is a block diagram illustrating a structure of a receiver when using a MIMO EV-DO transmission scheme in a forward link of an HRPD system according to the present invention;  
         [0033]      FIG. 10  is a block diagram illustrating a structure of a receiver when using a non-MIMO OFDM transmission scheme in a forward link of an HRPD system according to the present invention; and  
         [0034]      FIG. 11  is a block diagram illustrating a structure of a receiver when using a MIMO OFDM transmission scheme in a forward link of an HRPD system according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations will be omitted when it may make the subject matter of the present invention rather unclear.  
         [0036]      FIG. 3  shows a slot structure of a forward link in a High Rate Packet Data (HRPD) system according to the present invention, in which Orthogonal Frequency Division Multiplexing (OFDM) symbols are inserted in data transmission periods.  
         [0037]     In an HRPD system according to the present invention, locations and sizes of a pilot signal and a Medium Access Control (MAC) signal for maintaining compatibility with a forward link are the same as those in the slot structure of the conventional forward link shown in  FIG. 1 . Therefore, a pilot signal  303  or  308  having an N pilot  chip length is located at a center of each one-half slot, and MAC signals  302 ,  304 ,  307 , and  309  each having an N MAC  chip length are located at both sides of associated pilot signals  303  and  308 . Therefore, even a typical HRPD Mobile Station (MS), which does not support an OFDM transmission scheme, can perform channel estimation through the pilot signals  303  and  308  and can receive the MAC signals  302 ,  304 ,  307 , and  309 . In the remaining regions, that is, in the data transmission periods, OFDM symbols  301 ,  305 ,  306 , and  310  are inserted.  
         [0038]     In the forward link of an ordinary HRPD system, a data transmission period is set to have a size so N Data =400 chips. According to an OFDM transmission scheme, a Cyclic Prefix (CP) is attached to the front of an OFDM symbol to be transmitted, in order to prevent self-interference of a time-delayed incoming signal through a multi-path. That is, one OFDM symbol includes a CP  301   b  and OFDM data  301   a  obtained through Inverse Fast Fourier Transform (IFFT) of packet data information.  
         [0039]     The CP  301   b  has a size of N CP  chips and is obtained by copying a signal as much as the N CP  chips from the rear portion of the OFDM data and the attaching the copied signal to the front of the OFDM data. Therefore, the OFDM data has a size of (N Data -N CP ), wherein N CP  is determined according to how much the time delay causing self-interference will be allowed. When N CP  is large, more delayed incoming signals can be demodulated without causing interference. However, the size of the OFDM data is reduced just as much, thus the quantity of information to be transmitted is also reduced. In contrast, when N CP  is small, the information to be transmitted can be increased. However, the probability of occurrence of self-interference in an environment having a severe multi-path fading increases, thereby degrading the reception quality.  
         [0040]     All of N Data  number of tones cannot be used in the data symbol transmission. Some tones located in the periphery of a used frequency band should be used as guard tones in order to reduce the influence by the interference of signals out of the used frequency band. The pilot signals  303  and  308  used in the forward link of the conventional HRPD system are also used for the channel estimation of the OFDM symbol. However, dedicated signals are additionally necessary for the channel estimation of a multi-antenna system for Multiple Input Multiple Output (MIMO) users. To this end, some tones may be used in order to transmit signals for use in channel estimation. As used herein, such tones will be called “MIMO pilot tones.” 
         [0041]      FIG. 4  shows a transmitter in an HRPD system according to the present invention. The transmitter includes a channel encoder  401  for channel-encoding packet data, a channel interleaver  402  for interleaving the encoded packet data, a modulator  403  for modulating the interleaved packet data, a guard tone inserter  404  for inserting guard tones in order to reduce the influence of interference by the signals out of the band, and a MIMO pilot tone inserter  405  for inserting MIMO pilot tones for channel estimation of a multi-antenna in a receiver mobile station of a MIMO user.  
         [0042]     The transmitter shown in  FIG. 4  also includes a spreader  406 , an IFFT processor  407  for converting a time-domain signal into a frequency-domain signal, a CP inserter  408  for inserting a CP into a front part of OFDM data, an HRPD processor  415  for compatibility with a transmission scheme of the HRPD system, an EV-DO transmitter  411 , and a MIMO pilot inserter  410  for inserting a MIMO pilot for an HRPD system. The spreader  406  may be, for example, a Quadrature Phase Shift Keying (QPSK) spreader.  
         [0043]     The transmitter shown in  FIG. 4  also includes a MIMO interlace selector  412  and an OFDM/EV-DO selector  413 . The MIMO interlace selector  412  selects and operates the MIMO pilot tone inserter  405  in order to transmit a MIMO pilot tone by a dedicated pilot when an OFDM transmission scheme supporting the MIMO is used, and selects and operates the MIMO pilot inserter  410  in order to transmit a MIMO pilot by a dedicated pilot when an Evolution Data Only (EV-DO) transmission scheme supporting the MIMO is used. The OFDM/EV-DO selector  413  controls a multiplexer (MUX)  409  so the MUX  409  outputs an OFDM signal or EV-DO signal according to the transmission scheme, thereby selecting transmission of the OFDM signal or EV-DO signal.  
         [0044]     When the MIMO is not supported for a non-MIMO interlace, the MIMO interlace selector  412  controls the operation of the MIMO pilot tone inserter  405  and the MIMO pilot inserter  410  to prevent the MIMO pilot tone or the MIMO pilot from being inserted into the pilot dedicated for the MIMO. The transmitter shown in  FIG. 4  follows a typical OFDM transmission scheme or EV-DO transmission scheme. Therefore, in a system including both users of the OFDM or EV-DO transmission schemes using the MIMO or users of the OFDM or EV-DO transmission schemes not using the MIMO, it is preferable to fixedly locate an interlace for allocation of the MIMO pilot or a MIMO pilot tone for support of the MIMO.  
         [0045]     Further, a controller  414  controls the operation of the MIMO interlace selector  412  by checking whether the MIMO interlace has been allocated, and controls the operation of the OFDM/EV-DO selector  413  by checking whether the current slot is for the transmission for the OFDM users or the EV-DO users.  
         [0046]     Hereinafter, a process of transmission by a Base Station (BS) for the OFDM transmission scheme or MIMO-OFDM transmission scheme according to the present invention will be described.  
         [0047]     Physical layer packet data generated in a higher layer is input to and encoded by the channel encoder  401 , and the channel-encoded bit stream is interleaved by the channel interleaver  402  in order to obtain a diversity gain. The interleaved bit stream is input to and modulated into a modulation signal by the modulator  403 . The modulation signal is located at the data tone of the data transmission period in the slot construction shown in  FIG. 3 .  
         [0048]     Further, the guard tone inserter  404  places the guard tones at the band periphery of the signal output from the modulator  403 . For a MIMO-OFDM transmission scheme, the MIMO interlace selector  412  of the transmitter inserts a MIMO pilot tone into an allocated interlace by controlling the operation of the MIMO pilot tone inserter  405 . For a typical OFDM transmission scheme, the insertion of the MIMO pilot tone is omitted. When using a typical OFDM transmission scheme, the HRPD processor  415  inserts and transmits only the pilot signal of a typical EV-DO system.  
         [0049]     When signals to be transmitted have been allocated to all tones according to the operation described above, the spreader  406  performs, for example, QPSK spreading, through which different complex Pseudo Noise (PN) streams of BS signals transmitting different information are multiplied by each other. The complex PN streams refer to a complex number stream in which both the real number components and the imaginary number components are PN codes. The modulation signals having been subjected to the QPSK spreading are IFFTed by the IFFT processor  407 , so they are located at the positions of desired frequency tones. Further, the CP inserter  408  generates an OFDM symbol by inserting a CP into the IFFTed OFDM data in order to prevent self-interference due to the multi-path fading. The OFDM symbol having the MIMO pilot tone inserted therein is transferred through the MUX  409  to the HRPD processor  415  under the control of the OFDM/EV-DO selector  413 .  
         [0050]     Further, the HRPD processor  415  performs the compatibility processing of the HRPD system in order to multiplex the pilot signals  303  and  308  and the MAC signals  302 ,  304 ,  307 , and  309  together with the transmission data by the TDM scheme according to the slot structure shown in  FIG. 3 . Therefore, the wireless signal finally transmitted through the transmitter shown in  FIG. 4  has the slot structure as shown in  FIG. 3 .  
         [0051]     Hereinafter, a process of transmission by a base station for a typical EV-DO transmission scheme or an EV-DO transmission scheme supporting the MIMO according to the present invention will be described.  
         [0052]     When an EV-DO transmission scheme supporting the MIMO is used, the MIMO interlace selector  412  of the transmitter inserts a MIMO pilot into an allocated interlace by controlling the operation of the MIMO pilot tone inserter  405  having received a transmission signal from the EV-DO transmitter  411 . The signal having the MIMO pilot inserted therein is transferred through the MUX  409  to the HRPD processor  415  under the control of the OFDM/EV-DO selector  413 . Further, the HRPD processor  415  performs the compatibility processing of the HRPD system in order to multiplex the pilot signals  303  and  308  and the MAC signals  302 ,  304 ,  307 , and  309  together with the transmission data by the TDM scheme according to the slot structure shown in  FIG. 3 . When a typical OFDM transmission scheme is used, the insertion of the MIMO pilot tone by the MIMO pilot tone inserter  405  is omitted. That is, when using a typical OFDM transmission scheme, the HRPD processor  415  inserts and transmits only the pilot signal of a typical EV-DO system.  
         [0053]     Meanwhile, it is possible to construct a transmitter, which has a fixed interlace in which, for example, a MIMO pilot tone or a MIMO pilot is inserted, further to the transmitter structure shown in  FIG. 4 , and uses one of the MIMO OFDM scheme and MIMO EV-DO scheme as a transmission scheme dedicated for the MIMO.  
         [0054]     Hereinafter, a scheme for arranging MIMO pilot tones and MIMO pilots in the case of using an EV-DO transmission scheme and an OFDM transmission scheme supporting the MIMO in an HRPD system according to the present invention will be described with reference to  FIGS. 5A  to  5 C.  
         [0055]      FIG. 5A  shows an example of arrangement of MIMO pilot tones when using an OFDM transmission scheme supporting the MIMO in a forward link of an HRPD system according to the present invention.  
         [0056]     When using a typical EV-DO or OFDM transmission scheme, the pilot signals inserted by the HRPD processor  415  can be used as they are, as described above. However, when a Mobile Station (MS) supports the MIMO, since it is impossible to estimate the channel of a multi-antenna by the existing pilot signal  502 , the present invention places a MIMO pilot tone  504  dedicated for the MIMO in the data transmission region in which is the data tone  503  is located. The MIMO pilot tone  504  can be used in various forms in the time domain and the frequency domain within one slot.  
         [0057]     The arrangement shown in  FIG. 5A  is intended to improve the frequency diversity. However, it is possible to arrange the MIMO pilot tones  504  in various forms in the time domain and the frequency domain. The present invention may also be applied to arrangements where the pilot tones are exclusively arranged for the MIMO.  
         [0058]      FIGS. 5B and 5C  show examples of arrangement of MIMO pilots when using the EV-DO transmission scheme supporting the MIMO in a forward link of an HRPD system according to the present invention.  FIG. 5B  corresponds to an arrangement in which the MIMO pilots  505  are inserted in the existing pilot signal region  502  after being subjected to the Code Division Multiplexing (CDM), and  FIG. 5C  corresponds to an arrangement in which the MIMO pilots  507  are inserted in the existing pilot signal region  506  after being subjected to the CDM.  
         [0059]      FIG. 6A  shows a reason why interlaces for the MIMO users are fixedly allocated in the forward link of an HRPD system according to the present invention.  
         [0060]     In the HRPD system according to the present invention in which an OFDM system and EV-DO system supporting the MIMO and a typical OFDM system and EV-DO system co-exist, it is possible to use feedback (Channel Quality Information (CQI)) information  601  for the multi-antenna, which is transmitted to a BS from an MS of a MIMO user, as shown in  FIG. 6A . By receiving the feedback (CQI) information  601  from the MS, the transmitter of the BS can control the power of the MIMO pilot and the MIMO pilot tone in the next transmission.  
         [0061]     When fixedly allocated interlaces are used for transmission of the MIMO pilots and the MIMO pilot tones, the BS can support the MIMO user in an easy and simple manner without using a complex higher control signal. That is, the BS can inform the MS of the interlace to be exclusively used for the MIMO through the control signal, and the BS transmits data of the MIMO user by using the dedicated fixed interlace. Further, the MS receives data through an interlace allocated to the MS itself by using the received control signal from the BS.  
         [0062]      FIG. 6B  shows an example in which interlaces are fixedly allocated exclusively for the MIMO in the forward link of an HRPD system according to the present invention. Interlace # 0   602  has been allocated exclusively for the MIMO, and the other interlaces # 1 , # 2 , and # 3   603 ,  604 , and  605  have been allocated for data transmission for typical OFDM users using the existing pilot signals transmitted by the TDM, for example, typical EV-DO rev. A/B users or typical OFDM users. Therefore, through interlace # 0   602 , it is possible to transmit data of the OFDM or EV-DO user supporting the MIMO.  
         [0063]     In  FIG. 6B , reference numerals  606  to  608  denote slot structures transmitted through interlace # 0   602 , in which the MIMO pilot tones or MIMO pilots are inserted according to the arrangements shown in  FIGS. 5A  to  5 C, respectively. Further, in  FIG. 6B , reference numerals  609  and  610  denote slot structures in which the pilot signals for a typical OFDM user and EV-DO user are transmitted by the TDM as in the existing structure, respectively.  
         [0064]      FIG. 7  shows a transmission process according to whether MIMO interlaces have been allocated in the forward link of an HRPD system according to the present invention. In step  710 , the controller  414  of the transmitter determines whether the current slot to be transmitted is a MIMO interlace slot. When the current slot to be transmitted is a MIMO interlace slot, the controller  414  determines in step  702  whether the transmission is for a MIMO-OFDM user or a MIMO EV-DO user, in order to perform an operation according to a corresponding transmission scheme. When the transmission has been determined as transmission for the EV-DO user in step  702 , the transmitter proceeds to step  703  in which the transmitter performs general EV-DO transmission. Then, in step  704 , under the control of the controller  414 , the MIMO interlace selector  412  operates the MIMO pilot inserter  410  in order to insert a MIMO pilot into a transmission signal. The MIMO interlace selector  412  may insert the MIMO pilot  505  in the existing pilot signal region  502  after code division multiplexing the pilot or may insert the MIMO pilot  507  in the existing data region  506  according to a CDM scheme. Thereafter, under the control of the OFDM/EV-DO selector  413 , the MUX  409  outputs a signal in which the MIMO pilot has been inserted, and the HRPD processor  415  of the transmitter performs compatibility processing in order to TDM transmit a data channel, a MAC channel, and a pilot channel as designated by reference numeral  208  of  FIG. 2  for the compatibility with the HRPD system in step  705 , and then transmits the TDMed signal by a sub-carrier to a radio network in step  706 .  
         [0065]     Meanwhile, when it is determined in step  702  that the transmission is for the OFDM user, the transmitter proceeds to step  707  in which the transmitter encodes, interleaves, and modulates data to be transmitted, thereby generating a data tone. Thereafter, the guard tone inserter  404  of the transmitter inserts a guard tone into a portion near to a band periphery of the modulation signal in step  708 , and the MIMO pilot tone inserter  405  inserts the MIMO pilot tone in the interlace allocated under the control of the MIMO interlace selector  412 , for example, as shown in  FIG. 5A . Then, when signals to be transmitted have been allocated to all tones, the spreader  406  performs, for example, QPSK spreading in step  710 , so the modulation signals having been subjected to the spreading are placed at desired locations of desired frequency tones through IFFT by the IFFT processor  407 . Then, in step  711 , the CP inserter  408  inserts a CP into the IFFTed OFDM data in order to prevent the self-interference, thereby generating an OFDM symbol. Thereafter, under the control of the OFDM/EV-DO selector  413 , the MUX  409  outputs an OFDM signal having a MIMO pilot tone inserted therein, and the HRPD processor  415  of the transmitter performs compatibility processing in order to TDM transmit a data channel, a MAC channel, and a pilot channel for the compatibility with the HRPD system in step  712 , and then transmits the TDMed signal by a sub-carrier to a radio network in step  713 .  
         [0066]     Meanwhile, when it is determined in step  701  that the current slot to be transmitted is not a MIMO interlace slot, the transmitter of the BS determines in step  714  whether the transmission is for an OFDM user or an EV-DO user, in order to perform an operation according to a corresponding transmission scheme. The operation in steps  718  to  723  corresponding to a transmission process for a non-MIMO OFDM user is the same as the operation the operation in steps  707  to  713  except for the operation of MIMO pilot tone insertion in step  709  of  FIG. 7 , and the operation in steps  715  to  717  corresponding to a transmission process for a non-MIMO EV-DO user is the same as the operation in steps  715  to  717  except for the operation of MIMO pilot insertion in step  704  of  FIG. 7 , so detailed description will be omitted.  
         [0067]     Hereinafter, a structure of a receiver according to the present invention will be described with reference to FIGS.  8  to  11  for each transmission scheme. The receivers shown in FIGS.  8  to  11  correspond to receivers using a non-MIMO EV-DO scheme, a MIMO EV-DO scheme, a non-MIMO OFDM scheme, and a MIMO OFDM scheme, respectively. When an actual MS is implemented, at least one of the four types of receivers can be implemented within the MS. Then, the MS can receive a forward signal through a corresponding receiver according to a transmission scheme indicated by a control signal of a BS or according to a transmission scheme promised in advance between the MS and the BS.  
         [0068]      FIG. 8  shows a receiver in the case of using a non-MIMO EV-DO transmission scheme in a forward link of an HRPD system according to the present invention. An HRPD processor  801  operates in a process inverse to the operation of the HRPD processor  415  of  FIG. 4 . Specifically, the HRPD processor  801  demultiplexes TDMed data channel, MAC channel, and pilot channel signals and then transfers the demultiplexed signals. An EV-DO demodulator  802  receives the data channel from among the demultiplexed signals from the HRPD processor  801  and demodulates the data according to, for example, an EV-DO rev. A/B scheme. The EV-DO demodulator  802  is well-known in the art, so a detailed description will be omitted.  
         [0069]      FIG. 9  shows a receiver when using a MIMO EV-DO transmission scheme in a forward link of an HRPD system according to the present invention. An HRPD processor  901  operates in a process inverse to the operation of the HRPD processor  415  of  FIG. 4 . Specifically, the HRPD processor  901  demultiplexes TDMed data channel, MAC channel, and pilot channel signals and then transfers the demultiplexed signals. A MIMO pilot extractor  902  performs channel estimation by using a MIMO pilot inserted in the data channel region or pilot channel region from among the demultiplexed signals as shown in  FIG. 5B  or  5 C and outputs a signal corresponding to the data. Further, the EV-DO demodulator  903  demodulates the received data according to, for example, an EV-DO rev. A/B scheme.  
         [0070]      FIG. 10  shows a receiver when using a non-MIMO OFDM transmission scheme in a forward link of an HRPD system according to the present invention. An HRPD processor  1001  operates in a process inverse to the operation of the HRPD processor  415  of  FIG. 4 . Specifically, the HRPD processor  1001  demultiplexes TDMed data channel, MAC channel, and pilot channel signals and then transfers the demultiplexed signals. From among the transferred demultiplexed signals, a pilot signal is transferred to a channel estimator  1007  and a data signal is transferred to a CP remover  1002 . The CP remover  1002  eliminates the CP contaminated due to the propagation delay, the multi-path, etc., from the received signal. An FFT processor  1003  converts the input time domain signal to a frequency domain signal, and a QPSK de-spreader  1004  de-spreads the frequency domain signal and outputs tones of each signal. This is based on an assumption that the signal transmitted by the transmitter is spread before being transmitted. Therefore, when the transmitter uses a different spreading scheme, the receiver is equipped with a de-spreader corresponding to the used spreading scheme.  
         [0071]     The de-spread tones of each signal are transferred to the data tone extractor  1006 , which extracts data tones from the received signal tones. Meanwhile, the channel estimator  1007  estimates the channel from the received pilot signal, and transfers the channel-estimation value to a demodulator  1008 . The demodulator  1008  performs demodulation of the data tones by using the received channel estimation value, and the demodulated signal is de-interleaved by a de-interleaver  1009  and is then input to a decoder  1010 . The decoder  1010  decodes the input signal, thereby restoring the originally transmitted signal.  
         [0072]      FIG. 11  shows a receiver in the case of using a MIMO OFDM transmission scheme in a forward link of an HRPD system according to the present invention. The same components of the receiver shown in  FIG. 11  as those of the receiver shown in  FIG. 10  have the same functions as those of latter, so detailed description will be omitted.  
         [0073]     In the receiver of  FIG. 11 , an HRPD processor  1101  operates in a process inverse to the operation of the HRPD processor  415  of  FIG. 4 . Specifically, the HRPD processor  1101  demultiplexes TDMed data channel, MAC channel, and pilot channel signals and then transfers the demultiplexed signals. From among the transferred demultiplexed signals, a pilot signal is transferred to a channel estimator  1108  and a data signal is transferred to a MIMO interlace selector  1102 . The MIMO interlace selector  1102  determines whether the received signal corresponds to a fixedly allocated interlace, and then transfers the received signal to a CP remover  1103 . Then, the CP remover  1103  eliminates the CP contaminated due to the propagation delay, the multi-path, etc. from the received signal. An FFT processor  1104  converts the input time domain signal to a frequency domain signal, and a QPSK de-spreader  1105  QPSK de-spreads the frequency domain signal and outputs tones of each signal. This is based on an assumption that the signal transmitted by the transmitter is QPSK spread before being transmitted. Therefore, when the transmitter uses a different spreading scheme, the receiver is equipped with a de-spreader corresponding to the used spreading scheme.  
         [0074]     The receiver of  FIG. 11  is equipped with a MIMO pilot extractor  1106  for channel estimation, and the de-spread tones of each signal are transferred to the MIMO pilot extractor  1106 . The MIMO pilot extractor  1106  extracts a MIMO pilot tone inserted in a data channel region as shown in  FIG. 5A  from the interlace allocated exclusively for the MIMO-OFDM and transmits the extracted MIMO pilot tone to the channel estimator  1108 .  1107   k  extracts data tones except for the MIMO pilot tone from the data region and transfers the extracted data tones to a demodulator  1109  for restoration of the originally transmitted signal.  
         [0075]     As described above, the present invention uses an HRPD system and a transmission technology based on an EV-DO scheme and an OFDM scheme while maintaining compatibility between them and transmits a MIMO-only pilot/pilot tone by a fixedly allocated MIMO interlace. Therefore, according to the present invention, it is possible to effectively use the MIMO in a system in which EV-DO users, MIMO EV-DO users, OFDM users, MIMO-OFDM users co-exist.  
         [0076]     While the invention has been shown and described with reference to 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. For example, the arrangement of the MIMO pilot tones or MIMO pilots shown in  FIG. 5A  to  5 C is only an example, and the present invention is applicable various types of different arrangements. Further, in allocation of the interlaces, the identifications and the number of fixedly allocated interlaces may become different according to the number of MIMO-OFDM users within a base station. Therefore, the scope of the present invention should not be limited to the described embodiments and should be determined by the attached claims and equivalents thereof.