Abstract:
Provided are a beamforming receiving/transmitting function and a beamforming receiving/transmitting structure, which are optimized for a given basic system in order to provide advanced performance in consideration of a wireless mobile communication system through a ultra-high performance CDMA array antenna based on continuously orthogonal spreading codes and a pre-rake scheme for non-interference communication. Also, there is provided a chip-level/symbol-level beamforming receiving/transmitting apparatus based on a multiple-input multiple-output (MIMO) system on a forward/backward link in order to be applied to various advanced wireless mobile communication applications by improving the performance and capacity of a Code Division Multiple Access (CDMA) array antenna system based on continuously orthogonal spreading codes and a pre-rake scheme for non-interference communication, and a forward and backward link automatic beamforming method. Accordingly, a ultra-high performance base station and terminal having no-interference reception performance as well as achieving high hardware and power efficiency may be realized.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Applications No. 10-2010-0100514, filed on Oct. 14, 2010, and No. 10-2011-0104946, filed on Oct. 14, 2011, the entire disclosures of which are incorporated herein by reference for all purposes. 
       BACKGROUND 
     1. Field 
       [0002]    The following description relates to a Code Division Multiple Access (CDMA) array antenna system for providing a forward and backward link automatic beamforming function using an array antenna in order to implement an adaptive beamforming system capable of improving the performance and capacity of a CDMA base station system based on continuously orthogonal spreading codes and a pre-rake scheme for non-interference communication and enhancing the performance of a terminal, and a forward and backward link automatic beamforming method. 
         [0003]    2. Description of the Related Art 
         [0004]    A conventional rake receiver needs L matched filters and L searchers for processing L multiple paths. A pre-rake system transmits signals through a pre-rake combiner based on channel information at a transmitter, and a receiver which receives the signals needs a matched filter for extracting a peak signal from the received signals. Such a pre-rake method can simplify the structure of a rake receiver compared to the existing rake receiver. However, L-path signals having a rake effect are diverged into (2L−1)-th path signals when passing through a channel, so that signals finally received by a receiver have double Multiple Access Interference (MAI) and Multi-Path Interference (MPI). That is, since the performance of the pre-rake system is greatly influenced by the amount of interference that depends on an increase in number of multiple paths, an increase of MAI an MPI may deteriorate the performance of the pre-rake system compared to when the conventional rake-receiver is utilized. This is because Walsh codes have low orthogonality. 
         [0005]    Meanwhile, a pre-rake based system has low reception performance due to channel fading, interference, etc., compared to the conventional rake receiver, and its performance degradation becomes significant as the number of users increases. In order to overcome the problem, a method of reducing interference and improving reception performance by combining the pre-rake based system with a multiple antenna technology has been proposed. 
         [0006]    The multiple antenna technology has marked a quantum leap forward in mobile communication technologies by significantly increasing reception performance, a data transfer rate, etc. A multiple-input multiple-output (MIMO) system reduces influences by main problems in mobile communication, such as fading, delay spread, co-channel interference, etc. The MIMO system mainly uses a beamforming scheme and a space diversity scheme. Recently, with an increase of requirements for high-quality, broadband communication, a shortage of frequency resources used for mobile communication is predicted in the near feature. In order to increase reuse of frequencies, a beamforming scheme using antennas having spatial directivity is noted. The beamforming scheme is mainly implemented by using a smart antenna capable of adaptively adjusting beam patterns. 
         [0007]    The MIMO system has been introduced in 3G WCDMA, WiMAX, etc., and is expected that it will be actively applied to 4th generation communication systems in the near future. However, channel interference that is a basic problem in mobile communication will be more serious as the number of downtowns and the number of users increase. IS-95 or IMT-2000 which is a commercialized CDMA system is exposed to various interference environments that degrade system performance. Also, a beamforming CDMA method based on pre-rake can make hardware simplified, but never avoid performance degradation due to interference. 
       SUMMARY 
       [0008]    The following description relates to a chip-level/symbol-level beamforming receiving/transmitting apparatus on a forward and backward links, capable of being applied to various advanced wireless mobile communication applications by improving the performance and capacity of a Code Division Multiple Access (CDMA) array antenna system based on continuously orthogonal spreading codes and a pre-rake scheme for non-interference communication, and a forward and backward link automatic beamforming method. 
         [0009]    The following description relates to a beamforming receiving/transmitting function and a beamforming receiving/transmitting structure, which are optimized for a given basic system in order to provide advanced performance in consideration of a wireless mobile communication system through a ultra-high performance CDMA array antenna based on continuously orthogonal spreading codes and a pre-rake scheme for non-interference communication. 
         [0010]    In one general aspect, there is provided a base station which receives a signal through a multi-path channel using a plurality of antennas in a communication system, the base station including: a beamforming unit configured to perform chip-level reception beamforming with respect to a pre-raked combined signal received through the plurality of antennas by multiplying the pre-rake combined signal by a plurality of weight vectors corresponding to the respective antennas; and a despreading unit configured to perform matched filtering on the pre-rake combined signal subject to the chip-level reception beamforming, thereby demodulating a user signal. 
         [0011]    In another general aspect, there is provided a terminal which receives a signal through a multi-path channel using a plurality of antennas in a communication system, the terminal including: a beamforming unit configured to perform chip-level reception beamforming with respect to a pre-raked combined signal received through the plurality of antennas by multiplying the pre-rake combined signal by a plurality of weight vectors corresponding to the respective antennas; and a despreading unit configured to perform matched filtering on the pre-rake combined signal subject to the chip-level reception beamforming, thereby demodulating a user signal. 
         [0012]    In another general aspect, there is provided a base station which receives a signal through a multi-path channel using a plurality of antennas, the base station including: a despreading unit configured to perform matched filtering on a plurality of pre-rake combined signals received through the plurality of antennas, thereby demodulating a user signal; and a beamforming unit configured to perform symbol-level reception beamforming with respect to the user signal by multiplying the user signal by a plurality of weight vectors corresponding to the respective antennas. 
         [0013]    In another general aspect, there is provided a terminal which receives a signal through a multi-path channel using a plurality of antennas, the terminal including: a despreading unit configured to perform matched filtering on a plurality of pre-rake combined signals received through the plurality of antennas, thereby demodulating a user signal; and a beamforming unit configured to perform symbol-level reception beamforming with respect to the user signal by multiplying the user signal by a plurality of weight vectors corresponding to the respective antennas. 
         [0014]    In another general aspect, there is provided a method in which a base station receives a signal through a multi-path channel using a plurality of antennas in a communication system, the method including: performing chip-level reception beamforming with respect to a pre-raked combined signal received through the plurality of antennas by multiplying the pre-rake combined signal by a plurality of weight vectors corresponding to the respective antennas; and performing matched filtering on the pre-rake combined signal subject to the chip-level reception beamforming, thereby demodulating a user signal. 
         [0015]    In another general aspect, there is provided a method in which a base station receives a signal through a multi-path channel using a plurality of antennas, the method including: performing matched filtering on a plurality of pre-rake combined signals received through the plurality of antennas, thereby demodulating a user signal; and performing symbol-level reception beamforming with respect to the user signal by multiplying the user signal by a plurality of weight vectors corresponding to the respective antennas. 
         [0016]    In another general aspect, there is provided a base station which transmits a signal using a plurality of antennas in a communication system, the base station including: a spreading unit configured to spread-modulate a user signal using continuously orthogonal spreading codes having a characteristic of being continuously orthogonal for a predetermined time interval to generate a spreading signal; a pre-rake combiner configured to perform pre-rake combining of the spreading signal and to generate a pre-rake combined signal; and a beamforming unit configured to perform chip-level transmission beamforming by multiplying the pre-rake combined signal by a plurality of weight vectors corresponding to the respective antennas. 
         [0017]    As described above, by providing a transmitting/receiving apparatus for chip-level/symbol-level beamforming based on a multiple antenna system on a forward and backward links and providing a chip-level/symbol-level beamforming method, it is possible to increase the system performance and capacity. Accordingly, a ultra-high performance base station and terminal having no-interference reception performance as well as achieving high hardware and power efficiency may be realized. 
         [0018]    Therefore, by applying the pre-rake scheme and continuously orthogonal spreading codes to a CDMA system with an array antenna, the configuration of the CDMA system can become significantly simple. The pre-rake scheme significantly reduces the number of required matched filters and the continuously orthogonal spreading codes perform complete interference cancellation, thereby making it possible to prevent performance deterioration due to an increase in number of users. 
         [0019]    Interference cancellation is first performed by beamforming and then more complete interference cancellation is performed through spreading/despreading by continuously orthogonal spreading codes. Accordingly, Multiple Access Interference (MAI) and Multi-Path Interference (MPI) unavoidably following wireless communication may be cancelled so that a beamforming system can guarantee a complete array gain. 
         [0020]    Accordingly, it is possible to achieve high hardware efficiency through the pre-rake scheme, to ensure optimal performance of a beamforming system through the interference cancellation capacity of continuously orthogonal spreading codes, to guarantee price competitiveness of a terminal as well as a base station, and to achieve equipment compactness and low power consumption. 
         [0021]    Furthermore, by simplifying the hardware structure of a CDMA beamforming system and reducing the amount of data processing of the CDMA beamforming system as well as enhancing its performance, price competitiveness may be ensured and power consumption may be reduced. In particular, when the CDMA beamforming system is applied to a terminal, a compact device size can be achieved through hardware simplification, and a battery problem is overcome through low power consumption. 
         [0022]    The above features of satisfying all of high efficiency, economical efficiency, and excellent performance can be applied to a variety of mobile wireless communication applications. 
         [0023]    Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a diagram illustrating an example of a communication system. 
           [0025]      FIG. 2  is a diagram illustrating a configuration example of a terminal that can perform multiple-input multiple-output (MIMO) beamforming. 
           [0026]      FIG. 3  is a diagram illustrating a configuration example of a transmitter of the terminal in the case where the terminal has a single antenna. 
           [0027]      FIG. 4  is a diagram illustrating a configuration example of a receiver of a base station which performs chip-level reception beamforming to receive signals from a terminal. 
           [0028]      FIG. 5  is a diagram illustrating a configuration example of a receiver of the base station where channel estimation is performed upon chip-level reception beamforming 
           [0029]      FIG. 6  is a diagram illustrating a configuration example of a receiver of a base station which performs symbol-level reception beamforming to receive signals from a terminal. 
           [0030]      FIG. 7  is a diagram illustrating a configuration example of a receiver of the base station where channel estimation is performed upon symbol-level reception beamforming. 
           [0031]      FIG. 8  is a diagram illustrating a configuration example of a transmitter of a base station which performs forward transmission beamforming to transmit signals to a terminal 
           [0032]      FIG. 9  is a diagram illustrating a configuration example of a receiver of a terminal with a single antenna, which can perform multiple-input signal-output (MISO) beamforming. 
           [0033]      FIG. 10  is a diagram illustrating a configuration example of a receiver of a terminal with multiple antennas, which can perform chip-level MIMO beamforming. 
           [0034]      FIG. 11  is a diagram illustrating a configuration example of the receiver of the terminal with multiple antennas, which can perform chip-level MIMO beamforming, when channel estimation is performed. 
           [0035]      FIG. 12  is a diagram illustrating a configuration example of a receiver of a terminal with multiple antennas, which can perform symbol-level MIMO beamforming. 
           [0036]      FIG. 13  is a diagram illustrating a configuration example of the receiver of the terminal with multiple antennas, where channel estimation is performed upon symbol-level reception beamforming. 
           [0037]      FIG. 14  is a flowchart illustrating an example of a method in which a base station receives signals transmitted through a multi-path channel using a plurality of antennas. 
           [0038]      FIG. 15  is a flowchart illustrating an example of a method in which a terminal receives signals transmitted through a multi-path channel using a plurality of antennas. 
           [0039]      FIG. 16  is a flowchart illustrating an example of another method in which a base station receives signals transmitted through a multi-path channel using a plurality of antennas. 
           [0040]      FIG. 17  is a flowchart illustrating an example of another method in which a terminal receives signals transmitted through a multi-path channel using a plurality of antennas. 
           [0041]      FIG. 18  is a flowchart illustrating an example of a method in which a terminal transmits signals through a multi-path channel using a plurality of antennas. 
           [0042]      FIG. 19  is a flowchart illustrating an example of a method in which a base station transmits signals through a multi-path channel using a plurality of antennas. 
       
    
    
       [0043]    Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
       DETAILED DESCRIPTION 
       [0044]    The following description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness. 
         [0045]      FIG. 1  is a diagram illustrating an example of a communication system  110   
         [0046]    Referring to  FIG. 1 , the communication system  110 , which is a Code Division Multiple Access (CDMA) beamforming system based on a pre-rake scheme and continuously orthogonal spreading codes, includes a terminal  110  and a base station  120 . 
         [0047]    The terminal  110  and the base station  120  may function as a transmitting apparatus and a receiving apparatus, respectively. The terminal  110  and the base station  120  may be connected to each other via a multi-path channel. The terminal  110  includes a transmitter  112  for transmitting signals through antennas  1  through N and a receiver  114  for receiving signals through the antennas  1  through N. The base station  120  includes a transmitter  122  for transmitting signals through antennas  1  through M and a receiver  124  for receiving signals through the antennas  1  through M. 
         [0048]    On a backward link, the transmitter  112  of the terminal  110  may spread-modulate an input signal (or a user signal) using continuously orthogonal spreading codes having a characteristic of being continuously orthogonal for a predetermined time interval and then perform pre-rake combining of the spread-modulated input signal to thereby transmit the pre-rake combined signal. The receiver  124  of the base station  120  may receive a signal transmitted from the terminal  110  via a multi-path channel and then restore the signal of the terminal  110  from the received signal. Upon such backward reception beamforming, in order to efficiently receive signals from the terminal  110 , the base station  120  may obtain a weight vector for forming a reception beam corresponding to the terminal  110  to use the weight vector for forward transmission beamforming or to modulate and use the weight vector for forward transmission beamforming. 
         [0049]    Likewise, on a forward link, the transmitter  122  of the base station  120  may spread-modulate an input signal using continuously orthogonal spread codes and then perform pre-rake combining of the input signal to thereby transmit the pre-rake combined signal. The receiver  114  of the terminal  110  may receive the signal transmitted from the base station  120  via a multi-path channel and then restore the signal of the base station  120  from the received signal. A conventional technology related to pre-rake and continuously orthogonal spreading codes has been disclosed in detail in Korean Patent Application No. 10-2007-0042510. 
         [0050]    Since existing Walsh codes lose orthogonality and generate large deterioration when they fail to be synchronized, the current example uses continuously orthogonal spreading codes having a characteristic of being completely continuously orthogonal between signals received for a predetermined chip interval. 
         [0051]    The continuously orthogonal spreading codes are spread codes having a characteristic of being continuously orthogonal for a predetermined time interval, and have an auto-correlation function value of 0 and a cross-correlation function value of 0 for the predetermined time period. Here, the predetermined time period may be a length capable of covering a main delay path length of multi-path interference. The continuously orthogonal spreading codes may include multi-phase and multi-level continuously orthogonal codes. The continuously orthogonal spreading codes may include any one of zero correlation duration (ZCD), zero correlation zone (ZCZ), and large area synchronous (LAS). By using such continuously orthogonal spreading codes instead of Walsh codes, interference, such as MAI and MPI, may be cancelled, wherein the MAI is multi-access interference, that is, multi-user interference, and MPI is multi-path interference, that is, self-interference. 
         [0052]    The terminal  110  may include N antennas, and the base station  120  may include M antennas, wherein N is a natural number equal to or greater than 1, and M is a natural number equal to or greater than 2. In the case where the terminal  110  has two or more antennas, a multiple-input multiple-output (MIMO) beamforming system may be implemented, and if the terminal has a single antenna, a single input multiple output (SIMO) or multiple input single output (MISO) beamforming system may be implemented. 
         [0053]    That is, in the case of the backward link from the terminal  110  to the base station  120 , a SIMO or MIMO beamforming system may be implemented, and in the case of the forward link from the base station  120  to the terminal, a MISO or MIMO beamforming system may be implemented. 
         [0054]    The N antennas of the terminal  110  can be understood as components of the transmitter  112  and the receiver  114 . Likewise, the M antennas of the base station  120  can be understood as components of the transmitter  122  and the receiver  124 . 
         [0055]    When the base station  120  has a multiple antenna system and the terminal  110  has a single antenna system, forward and backward signal flows are as follows. 
         [0056]    1. Backward Signal Flow 
         [0057]    First, backward signal flow from the terminal  110  to the base station  120  can be expressed as equation 1 below. 
         [0058]    When a signal S k (t) generated by the terminal  110  is transmitted to the base station  120 , the signal S k (t) is subject to reception beamforming by multiple antennas of the base station  120  and the base station  120  receives the resultant signal x(t) which is expressed by equation  1  below. 
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         [0000]    where n(t) is a white noise vector generated by each antenna of the base station  120 , b k,l  and exp(jγ k,l ) are the amplitude (or a path gain) and phase of a user signal (or a data symbol), respectively, which depend on a path via a channel, K is a total number of users who use the corresponding communication system, L is a total number of paths that are used in the communication system, and a(θ k,l ) is a vector corresponding to each signal received by each antenna element of the base station  120 , the vector generated due to a different reception timing. Reception timing differences may be expressed as a delay time and make phase differences between signals received by the individual antennas of the base station  120 . T c  corresponds to one chip period of a spreading code. 
         [0059]    a(θ k,l ) may be generalized to an array response vector or an array steering vector for a k-th user and a l-th path, which is written as equation 2 below. 
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         [0000]    where d represents an antenna interval and is λ/2 as in a general beam forming system, and 2 is the wavelength of a signal. 
         [0060]    The base station  120  extracts a part that is to be compared to a reference signal from the received signal x(t) (equation 1), and applies a beamforming algorithm to the extracted part together with the reference signal to calculate a weight vector w k   H . The weight vector w k   H  is multiplied by the received signal x(t), thereby completing reception beamforming. 
         [0000]        y   k ( t )= w   k   H ×( t )   (3)
 
         [0061]    Equation (3) is a signal before being despreaded by a matched filter (not shown) of the receiver  122  of the base station  120 . 
         [0062]    Upon despreading, the matched filter generates a spreading code C k , (L−1)(t) at a chip time (L−1)T c  at which a peak signal exists with respect to a reception signal from a user k, thereby performing despreading. 
         [0063]    In order to obtain a weight vector, a reference signal is needed and in the case of TDD, the following midamble is used. The midamble has been already known to the receiver  124  of the base station  120 , and can be expressed as equation  4  below. 
         [0000]        {circumflex over (d)}   k(L−1) ( n )=[ m   I   (k) ( n )+ jm   Q   (k) ( n )]δ( n−T   k,(L−1) )   (4)
 
         [0000]    where the meaning of (L−1) in and is that a reference signal (that is, a midamble) is generated at a chip time (L−1)Tc at which a peak signal exists with respect to a reception signal from a user k. Here, since it is assumed that a multi-path consisting of L paths is provided and path indexes are expressed as l=0, . . . , L−1, the chip time (L−1)Tc is substantially a L-th time. m I   (k) (n) represents an in-phase component of the midamble, and represents a quadrature component of the midamble. 
         [0064]    2. Forward Signal Flow 
         [0065]    Now, forward signal flow from the base station  120  to the terminal  110  can be expressed as equation 5 below. A signal z(t) generated by multiple antennas of the base station  120  through transmission beamforming can be expressed as equation 5 below. 
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         [0000]    where w k * is a conjugate vector of a weight vector for a transmission signal from a user k. A forward weight vector may be decided based on a backward weight vector. 
         [0066]    A method of deciding a forward weight vector includes a method of using a backward weight vector as a forward weight vector, a method of using an inverse matrix of a backward weight vector as a forward weight vector, etc. The present invention is a system invention that is a superordinate concept of the methods. Here, the norm of the weight vector has to be normalized to “1” in order to maintain Signal to Noise Ratio (SNR) for transmission. The normalization can be expressed by equation 6 below. 
         [0000]      w k           w k /|w k |  (6)
 
         [0067]    Equation 6 makes the magnitude of the weight vector normalized to “1” while maintaining the phase of the weight vector. The normalized weight vector is used for beamforming. 
         [0068]    z(t) of equation (5) represents a multiuser signal generated by the multiple antennas of the base station  120 , and when the multiuser signal z(t) is received by an i-th user&#39;s terminal  110  having a single antenna, the received signal r j (t) can be expressed as equation 7 below. 
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         [0000]    where the signal r i (t) is a signal of the i-th user before being despread by a matched filter (not shown) included in the receiver  114  of the terminal  110 , α T (θ i,l ) represents an array response vector for a l-th path of the i-th user&#39;s terminal  110 , and b i,l  and exp(jγ i,l ) represent the amplitude (or a path gain) and phase of each data symbol, which vary according to a path via a channel 
         [0069]    Upon despreading, a matched filter (not shown) for despreading generates a synchronized spreading code C k (L−1)(t) at a chip time (L−1)Tc at which a peak signal exists with respect to a reception signal from a user k, thereby performing despreading. 
         [0070]    Hereinafter, the operation of the communication system  100  will be described in regard of forward and backward transmission. 
         [0071]      FIGS. 2 through 7  illustrate configuration examples of the terminal  110  and the base station  120  (see  FIG. 1 ) for backward transmission in the communication system  100 . 
         [0072]      FIG. 2  is a diagram illustrating a configuration example of the terminal  110  that can perform MIMO beamforming. 
         [0073]    A transmitter  112 A of the terminal  110  may transmit signals to the base station  120  through transmission beamforming using multiple antennas. In this case, the terminal  110  performs transmission beamforming and the base station  120  performs reception beamforming. That is, backward MIMO beamforming is performed. 
         [0074]    The transmitter  112 A includes a normalizer  205 , a spreading unit  210 , a pre-rake combiner  220 , a beamforming unit  230 , a weight vector converter  240 , a weight vector generator  250 , a plurality of RF transceivers  260 - 1  through  260 -N, and an array antenna consisting of a plurality of antenna elements  265 - 1  through  265 -N. 
         [0075]    The normalizer  205  normalizes a data sequence b k , which is a user signal of a user k to be transmitted, to a normalization vector Q. The data sequence b k  may be a signal obtained by modulating original user data using a digital modulation method, such as phase shift keying (PSK), quadrature phase shift keying (QPSK), quadrature amplitude modulation (QAM), etc. 
         [0076]    The spreading unit  210  performs spread spectrum modulation on the user signal using a continuously orthogonal spreading code, thus generating a spreading signal. The spreading unit  210  may include a continuously orthogonal code generator  212  for generating the continuously orthogonal spreading code and a multiplier  214  for multiplying the continuously orthogonal spreading code by the user signal b k  that is to be transmitted. 
         [0077]    The pre-rake combiner  220  performs pre-rake combining of the spreading signal subject to the spread spectrum modulation, thus generating a pre-rake combined signal. In other words, the pre-rake combiner  220  combines the spreading signal with a channel impulse response for a multi-path channel based on channel information acquired during previous data transmission/reception, thereby obtaining a pre-rake combined signal. The combining of the spreading signal with the channel impulse response is to apply a complex conjugate value of the time-inverted value of the channel impulse response to the spreading signal. The beamforming unit  230  multiplies the pre-rake combined signal by weight vectors provided by the weight vector  240  to generate chip-level transmission beams. 
         [0078]    The RF transceivers  260 - 1  through  260 -N may modulate the chip-level transmission beams to carrier frequencies. By transmitting signals via the RF transceivers  260 - 1  through  260 -N, peak signals having a RAKE effect while passing through a channel are obtained. The receiver  114  of the base station  120  illustrated in  FIG. 1  needs a single matched filter for obtaining a (L−1)-th signal having a RAKE effect among a plurality of signals. Accordingly, a receiver (or the base station  120 ) which receives a signal transmitted from the transmitter  112 A of the terminal  110  may use a reference signal (expressed by equation 4) synchronized with a reception signal on a (L−1)-th path to obtain weight vectors upon reception beamforming. That is, a reference signal that can be expressed by equation 4 may be used to obtain weight vectors corresponding to a peak path that can be expressed by equation 3. 
         [0079]    The weight vector converter  240  provides weight vectors that are supplied to the beamforming unit  230 . The weight vector converter  240  may provide weight vectors provided by the weight vector generator  250  to the beamforming unit  230 . The weight vector generator  250  may generate weight vectors acquired from the base station  120 , wherein the weight vectors have been decided by weight vector generators ( 430 ,  530 - 1  through  530 -N in  FIGS. 4 and 5 , which will be described later) included in the base station  120  upon a previous communication between the terminal  110  and the base station  120 . 
         [0080]    There are methods of using weight vectors obtained in a previous time slot for a predetermined time slot interval, of predicting weight vectors based on previously calculated weight vectors and using the predicted weight vectors as weight vectors for a next time slot interval, of using weight vectors obtained in a current time slot without any conversion, etc. However, a method of using the weight vectors is not limited to the methods mentioned above. The operation of the weight vector converter  240  may depend on which one among the above-mentioned method is used. 
         [0081]      FIG. 3  is a diagram illustrating a configuration example of a transmitter  112 B of the terminal  110  illustrated in  FIG. 1  in the case where the terminal  110  has a single antenna. 
         [0082]    The transmitter  112 B includes a normalizer  305 , a spreading unit  310 , a pre-rake combiner  320 , an RF transceiver  330 , and a single antenna  335 . 
         [0083]    The normalizer  305  normalizes a user signal b k  of a user k, which is to be transmitted, to a normalization factor Q, and transfers the normalized user signal to the spreading unit  310 . The spreading unit  310  includes a continuously orthogonal code generator  312  and a multiplier  314 . The continuously orthogonal code generator  312  generates a continuously orthogonal spreading code, and the multiplier  314  multiplies the normalized user signal by the continuously orthogonal spreading code to spread-modulate the normalized user signal, thereby generating a spreading signal The spreading unit  310  transfers the spreading signal to the pre-rake combiner  320 . 
         [0084]    The pre-rake combiner  320  converts the spread-modulated spreading signal to a pre-rake combined signal. The pre-rake combined signal is transmitted through the signal antenna  335  via the RF transceiver  330 . 
         [0085]    The pre-rake combined signal transmitted from the transmitter  112 B of the terminal  110  may be received by the base station  120  through reception beamforming by the base station  120 . In this case, SIMO beamforming may be performed. 
         [0086]      FIG. 4  is a diagram illustrating a configuration example of a receiver  124 A of the base station  120  (see  FIG. 1 ) which performs chip-level reception beamforming to receive signals from the terminal  110 . 
         [0087]    Referring to  FIG. 4 , the receiver  124 A of the base station  120  may be configured to receive signals transmitted from the transmitter  112 A or  112 B (see  FIGS. 2 and 3 ) of the terminal  110  through chip-level reception beamforming. Referring to  FIG. 4 , the receiver  124 A of the base station  120  includes an array antenna consisting of a plurality of antennas  401 - 1  through  401 -M, a plurality of RF transceivers  405 - 1  through  405 -M, a beamforming unit  410 , a first demultiplexing unit  420 , a plurality of weight vector generators  430 - 1  through  430 -K, a plurality of reference signal generators  440 - 1  through  440 -K, a plurality of second demultiplexing units  450 - 1  through  450 -K, and a plurality of despreading units  460 - 1  through  460 -K. The beamforming unit  410  may include a plurality of beamforming elements  410 - 1  through  410 -K. In the current example, the numbers of the beamforming elements  410 - 1  through  410 -K, the weight vector generators  430 - 1  through  430 -K, the reference signal generators  440 - 1  through  440 -K, the second demultiplexing units  450 - 1  through  450 -K, and the despreading units  460 - 1  through  450 -K may be a total number of users included in the corresponding communication system. 
         [0088]    Pre-rake combined signals transmitted from the terminal  110  are received by the individual antennas  401 - 1  through  401 -M via a multi-path channel. The signals received by the individual antennas  401 - 1  through  401 -M are input to the RF transceivers  405 - 1  through  405 -M. The RF-transceivers  405 - 1  through  405 -M may convert the individual signals received through the array antenna  401 - 1  through  401 -M to base-band signals. 
         [0089]    The beamforming elements  410 - 1  through  410 -K multiply the signals received through the RF transceivers  405 - 1  through  405 -M by weight vectors, respectively, and perform chip-level reception beamforming on the received pre-rake combined signals for each user (that is, for each terminal). The signal before being multiplied by a weight vector may be expressed as equation 1 above. 
         [0090]    The weight vector generators  430 - 1  through  430 -K generate beamforming vectors according to a beamforming algorithm for each user, and provide the beamforming vectors to the beamforming elements  410 - 1  through  410 -K. The weight vector generators  430 - 1  through  430 -K may apply a predetermined algorithm to reference signals extracted from signals received by the antenna elements  401 - 1  through  401 -M via a channel for each user and original reference signals generated by the reference signal generators  440 - 1  through  440 -K, thereby acquiring weight vectors. The first demultiplexing unit  420  may extract reference signals from the signals received by the array antenna  401 - 1  through  401 -M via a channel. 
         [0091]    The reference signals may be midambles in the case of a time division duplex (TDD) system and pilot signals in the case of a frequency division duplex (FDD) system. As illustrated in  FIG. 4 , if the number of antennas is M, M×1 weight vectors are generated. 
         [0092]    In the case of the TDD system, a procedure of obtaining weight vectors is as follows. Midamble parts of the base-band signals converted by the RF transceivers  405 - 1  through  405 -M are subject to demultiplexing by the first demultiplexing unit  420  and then input to the weight vector generators  430 - 1  through  430 -K. The weight vector generators  430 - 1  through  430 -M apply a beamforming algorithm to calculate weight vectors. 
         [0093]    The beamforming algorithm includes an Optimal/Sub-optimal method, a reference signal-based beamforming method, etc., specifically, Minimum Mean Square Error (MMSE), Normalized Least Mean Square (NLMS), Least Mean Square (LMS), Recursive Least Square (RLS), etc. The above-mentioned algorithms have their own unique characteristics, however, have a common characteristic of considering signals from other users as interference, suppressing the interference, and then generating weight vectors for beamforming to have an array gain in receiving a signal from a desired user. 
         [0094]    However, the weight vector generators  430 - 1  through  430 -M may use another beamforming algorithm that is within the scope not departing from the technical concept of the system. As described above, there are methods of using weight vectors obtained in a previous time slot for a predetermined time slot interval, of predicting weight vectors based on previously calculated weight vectors and using the predicted weight vectors as weight vectors for a next time slot interval, of using weight vectors obtained in a current time slot without any conversion, etc. However, a method of using the weight vectors is not limited to the methods mentioned above. 
         [0095]    As described above, the received signals passed through the RF transceivers  405 - 1  through  405 -M are respectively multiplied by the weight vectors for each array in the beamforming unit  410 . The resultant signals multiplied by the weight vectors for each array are added to each other, as expressed as equation 3. 
         [0096]    The signals expressed as equation  3  are respectively input to the second demultiplexing units  450 - 1  through  450 -K, and the second demultiplexing units  450 - 1  through  450 -K extract user data parts from the signals except for the reference signals (or the midambles) and transfer the user data parts to the despreading unit  460 . The despreading unit  460  matched-filters the pre-rake combined signals subject to reception beamforming, thus demodulating a plurality of user signals. 
         [0097]    For this operation, the despreading unit  460  may include a plurality of matched filters  460 - 1  through  460 -K to process signals received through the individual antennas  401 - 1  through  401 -M. Each of the matched filters  460 - 1  through  460 -K may be configured to match each reference signal to a code having an interval corresponding to one code cycle. The matched filters  460 - 1  through  460 -K perform matched filtering on a (L−1)-th signal, thereby demodulating a plurality of user signals. 
         [0098]    A plurality of determining units  470 - 1  through  470 -N determine signals output from the individual matched filters  460 - 1  through  460 -K and output the user data sequence b k  that has been sent from the terminal  110 . 
         [0099]      FIG. 5  is a diagram illustrating a configuration example of a receiver  124 B of the base station  120  (see  FIG. 1 ) where channel estimation is performed upon chip-level reception beamforming. 
         [0100]    Referring to  FIG. 5 , the receiver  124 B of the base station  120  includes an array antenna consisting of a plurality of antenna elements  501 - 1  through  501 -M, a plurality of RF transceivers  505 - 1  through  505 -M, a plurality of beamforming elements  510 - 1  though  501 -M, a first demultiplexing unit  520 , a plurality of weight vector generators  530 - 1  through  530 -K, a plurality of reference signal generators  540 - 1  through  540 -K, a plurality of second demultiplexing units  550 - 1  through  550 -K, a plurality of despreading units  560 - 1  through  560 -N, and a plurality of channel estimators  570 - 1  through  570 -K. 
         [0101]    The receiver  124 B illustrated in  FIG. 5  has a configuration similar to that of the receiver  124 A illustrated in  FIG. 4 , except that the receiver  124 B includes the channel estimators  570 - 1  through  570 -K. For this, the second demultiplexing units  550 - 1  through  550 -K may be configured to extract user data parts from received signals by excluding reference signals from the received signals and output the user data parts to the despreading units  560 - 1  through  560 -K, and to output the reference signals to a multiplier  545 . 
         [0102]    The reference signal generators  540 - 1  through  540 -K generates a plurality of reference signals that are synchronized with a received signal on a (L−1)-th path among a plurality of pre-rake combined signals received for each user. The reference signals generated by the reference signal generators  540 - 1  through  540 -K are respectively input to the channel estimators  580 - 1  through  580 K via the multiplier  545 . Each of the channel estimators  580 - 1  through  580 -K perform channel estimation for each user, based on a reference signal part of a signal received via a channel and a reference signal that is synchronized with the received signal on a (L−1)-th path and generated by the reference signal generators  540 - 1  through  540 -K. At this time, the channel estimators  580 - 1  through  580 -K may perform channel estimation using one of various channel estimation methods. The user data parts of the received signals, which have been output from the matched filters  560 - 1  through  560 -K, are compensated using the channel estimated values, and then determined by the determining units  570 - 1  through  570 -K. The channel estimators  580 - 1  through  580 -K and the configuration for processing the reference signals for channel estimation may be selectively used. 
         [0103]      FIG. 6  is a diagram illustrating a configuration example of a receiver  124 C of the base station  120  (see  FIG. 1 ) which performs symbol-level reception beamforming to receive signals from the terminal  110 . 
         [0104]    The receiver  124 C of the base station  120  illustrated in  FIG. 6  is configured to perform symbol-level reception beamforming on the pre-rake combined signal received from the terminal  110  illustrated in  FIG. 3  to receive a signal from the terminal  110 . The receiver  124 C of the base station  120  illustrated in  FIG. 6  includes an array antenna consisting of a plurality of antenna elements  601 - 1  through  601 -M, a plurality of RF transceivers  605 - 1  through  605 -M, a plurality of demultiplexing units  610 - 1  through  610 -M, a despreading unit  620 , a plurality of beamforming elements  630 - 1  through  630 -K, a plurality of weight vector generators  640 - 1  through  640 -K, a plurality of reference signal generators  650 - 1  through  650 -K, and a plurality of determining units  660 - 1  through  660 -K. In the current example, the numbers of the beamforming elements  630 - 1  through  630 -K, the weight vector generators  640 - 1  through  640 -K, the reference signal generators  650 - 1  through  650 -K, and the determining units  660 - 1  through  660 -K may be configured to numbers corresponding to a total number of users included in the communication system. 
         [0105]    For symbol-level beamforming, adversely from signal processing for chip-level beamforming of passing signals through the beamforming elements  410 - 1  through  410 -K and then despreading the resultant signals using the despreading units  460 - 1  through  460 -K, as illustrated in  FIG. 4 , a plurality of pre-rake combined signals are despreaded by the despreading unit  620  and then symbol-level reception beamforming is performed for each user by the beamforming units  630 - 1  through  630 -K. As such, the signal processing flow by the receiver  124 C illustrated in  FIG. 6  performs the operations with the same equations as in the signal processing illustrated in  FIG. 4 . 
         [0106]    Referring to  FIG. 6 , pre-rake combined signals received through the RF transceivers  605 - 1  through  605 -M are divided into user data parts and reference signal parts by the demultiplexing units  610 - 1  through  610 -M. Then, the user data parts are despreaded using continuously orthogonal spreading codes by the despreading unit  620 . The despreading unit  620  includes a plurality of matched filters  620 - 1  through  620 - 1 K, . . . ,  620 -M 1  through  620 -MK for each array that perform despreading. The matched filters  620 - 11  through  620 - 1 K, . . . ,  620 -M 1  through  620 -MK perform matched filtering in synchronization with a signal on a (L−1)-th path according to the characteristics of a pre-rake system, thereby performing despreading on user data parts. 
         [0107]    Also, the demultiplexing units  610 - 1  through  610 -M transfer the reference signal parts among the received signals to the weight vector generators  640 - 1  through  640 -K. The weight vector generators  640 - 1  through  640 -K apply a specific beamforming algorithm to reference signals received from the demultiplexing units  610 - 1  through  610 -M and reference signals that are synchronized to a signal on a (L−1)-th path and generated by the reference signal generators  650 - 1  through  650 -K, thus generating weight vectors. 
         [0108]    After the weight vectors are generated, the beamforming elements  630 - 1  through  630 -K perform symbol-level reception beamforming by multiplying symbol-level user data parts despreaded by the individual matched filters  620 - 11  through  620 - 1 K and  621 -M 1  through  621 -MK of the despreading unit  620  by the respective weight vectors. Thereafter, the user data parts calculated for individual arrays are added to a single signal for each array, respectively. 
         [0109]    The weight vector generators  640 - 1  through  640 -K may use methods of using weight vectors obtained in a previous time slot for a predetermined time slot interval, of predicting weight vectors based on previously calculated weight vectors and using the predicted weight vectors as weight vectors for a next time slot interval, of using weight vectors obtained in a current time slot without any conversion, etc. However, a method of using weight vectors is not limited to the methods mentioned above. 
         [0110]    The resultant signals subject to the symbol-level reception beamforming by the beamforming units  630 - 1  through  630 -K are input to the determining units  660 - 1  through  660 -K, and the determining units  660 - 1  through  660 -K determine data values of the signals and then output them. 
         [0111]      FIG. 7  is a diagram illustrating a configuration example of a receiver  124 D of the base station  120  (see  FIG. 1 ) where channel estimation is performed upon symbol-level reception beamforming. 
         [0112]    The receiver  124 D of the base station  120  illustrated in  FIG. 7  includes an array antenna consisting of a plurality of antenna elements  701 - 1  through  701 -M, a plurality of RF transceivers  705 - 1  through  705 -M, a plurality of demultiplexing units  710 - 1  through  710 -M, a despreading unit  720 , a plurality of beamforming elements  730 - 1  through  730 -K, a plurality of weight vector generators  740 , a plurality of reference signal generators  750 - 1  through  750 -K, a plurality of determining units  760 - 1  through  760 -K, and a plurality of channel estimators  770 - 1  through  770 -K. 
         [0113]    The receiver  124 D of the base station  120  illustrated in  FIG. 7  has a configuration similar to the receiver  124 C of the base station  120  illustrated in  FIG. 6 , except that the receiver  124 D includes a plurality of channel estimators  770 - 1  through  770 -K. 
         [0114]    The channel estimators  770 - 1  through  770 -K extract reference signal parts from among signals subject to reception beamforming by the beamforming elements  730 - 1  through  730 -K, and perform channel estimation for each user, based on the extracted reference signal parts and reference signals that are synchronized with a reception signal on a (L−1)-th path and generated by the reference signal generators  750 - 1  through  750 -K. The channel estimators  770 - 1  through  770 -K may estimate a channel for each user using one of various estimation methods. 
         [0115]    A channel state estimated by the channel estimators  770 - 1  through  770 -K is applied to the signal subject to reception beamforming by the beamforming elements  730 - 1  through  730 -K to perform channel compensation on the signal, and then the channel compensated signal is output via the determining units  760 - 1  through  780 -K. 
         [0116]      FIGS. 8 through 13  illustrate configuration examples of the terminal  110  and the base station  120  for forward signal transmission. 
         [0117]      FIG. 8  is a diagram illustrating a configuration example of a transmitter  212  of the base station  120  which performs forward transmission beamforming to transmit signals to a terminal. 
         [0118]    As described above, in the case of forward transmission, the base station  120  having multiple antennas may perform MISO or MIMO beamforming with respect to the terminal  110  having a single antenna or multiple antennas. 
         [0119]    The transmitter  212  of the base station  120  illustrated in  FIG. 8  includes a plurality of normalizers  805 - 1  through  805 -K, a plurality of spreading units  810 - 1  through  810 -K, a plurality of multiplexing units  820 - 1  through  820 -K, a reference signal generator  830 , a plurality of pre-rake combiners  840 - 1  through  840 -K, a beamforming unit  850 , a weight vector converter  860 , a weight vector generator  870 , a plurality of RF transceivers  880 - 1  through  880 -M, and an array antenna consisting of a plurality of antenna elements  885 - 1  through  885 -M. 
         [0120]    The spreading units  810 - 1  through  810 -K spread user data that is to be transmitted using a continuously orthogonal spreading code for each user to generate a spreading signal. 
         [0121]    The multiplexing units  820 - 1  through  820 -K perform multiplexing on a reference signal for each user generated by the reference signal generator  830  and a signal corresponding to a user data part for the user, thus outputting a signal for the user. 
         [0122]    The pre-rake combiners  840 - 1  through  840 -K performing pre-rake combining of a multiplexed signal for each user to generate pre-rake combined signals. 
         [0123]    The beamforming unit  850  performs chip-level transmission beamforming for each user by multiplying weight vectors provided by the weight vector converter  860  by the pre-rake combined signals. The weight vectors may be decided by each terminal  110  that receives signals transmitted from the base station  120 , and acquired from the terminal  110 . 
         [0124]    If signals output from the pre-rake combiners  840 - 1  through  840 -K are s k (t), the signals s k (t) are multiplied by weight vectors while passing through the beamforming unit  850 , and the resultant signals may be expressed as equation 5 above. That is, signals z(t) resulting from multiplying the signals s k (t) by conjugate values of weight vectors normalized by equation 6 are transmitted to a channel via the RF transceivers  880 - 1  through  880 -M of the individual antennas elements. 
         [0125]    The weight vector converter  860  and the weight vector generator  870  may perform operations corresponding to the weight vector converter  240  and the weight vector generator  250  of the terminal  120  illustrated in  FIG. 2 . The weight vector converter  860  may provide a weight vector corresponding to a pre-rake combined signal for each user, and the weight vector generator  870  may generate a weight vector for each user and provide the weight vector to the weight vector converter  860 . 
         [0126]    A receiver that receives the signals z(t) may be a terminal having multiple antennas for chip-level reception beamforming, as illustrated in  FIG. 10  or  11 , or may be a terminal having multiple antennas for symbol-level reception beamforming, as illustrated in  FIG. 12  or  13 . Also, a receiver that receives the signals z(t) may be a terminal having a single antenna, as illustrated in  FIG. 9 , in order to enhance hardware efficiency of a terminal and achieve low power consumption. That is, in this specification, the number of antennas included in a base station or terminal is not limited. 
         [0127]      FIG. 9  is a diagram illustrating a configuration example of a receiver  114 A of the terminal  110  (see  FIG. 1 ) with a single antenna, which can perform MISO beamforming. 
         [0128]    The receiver  114 A of the terminal  110  illustrated in  FIG. 9  includes a single antenna  910 , an RF transceiver  905 , a matched filter  910 , and a determining unit  920 . 
         [0129]    When signals are received by the terminal  110  with the single antenna  910  via a multi-path fading channel, the receiver  114  of the terminal  110  needs to have only one matched filter  910  since the signals have been already subject to the pre-rake effect upon transmission. 
         [0130]    Meanwhile, a signal received by a receiver in a specific direction is a combined signal of signals transmitted respectively from an array antenna of a transmitter. Thus, a time difference exists between signals transmitted from the individual antennas according to an antenna direction of a receiver, and the time difference becomes a phase difference. The phase difference is called an array response, and the array response which is represented as a vector value is multiplied by signals transmitted from individual antennas. Accordingly, a signal received by a receiver at a specific direction is a signal multiplied by a specific array response and passed through a multi-path channel The signal can be expressed as equation 7 above. As seen in equation 7, white noise, instead of a vector value, is added since the receiver has been assumed to have a single antenna, and the signal is subject to despreading using a continuously orthogonal spreading code in the matched filter  910  of the receiver  114 A. 
         [0131]      FIG. 10  is a diagram illustrating a configuration example of a receiver  114 B of the terminal  110  (see  FIG. 1 ) with multiple antennas, which can perform chip-level MIMO beamforming. 
         [0132]    Referring to  FIG. 10 , the receiver  114 B of the terminal  110  includes an array antenna consisting of a plurality of antenna elements  1001 - 1  through  1001 -N, a plurality of RF transceivers  1005 - 1  through  1005 -M, a beamforming unit  1010 , a first demultiplexing unit  1020 , a weight vector generator  1030 , a reference signal generator  1040 , a second demultiplexing unit  1050 , a despreading unit  1060 , and a determining unit  1070 . 
         [0133]    A plurality of pre-rake combined signals transmitted from the base station are received by the antennal elements  1001 - 1  through  1001 -M via a multi-path channel, and then input to the beamforming unit  1010  via the RF transceivers  1005 - 1  through  1005 -M. 
         [0134]    The beamforming unit  1010  performs chip-level reception beamforming by multiplying the received signals received through the individual RF transceivers  1005 - 1  through  1005 -N by weight vectors. The resultant signals multiplied by the weight vectors are added to each other and then output to the second demultiplexing unit  1050 . 
         [0135]    The weight vector generator  1030  may generate beamforming vectors according to a beamforming algorithm and provide the beamforming vectors to the beamforming unit  1010 . The weight vector generator  1030  may obtain weight vectors for targets by applying a specific algorithm to reference signals extracted from signals received by the individual antennas  1001 - 1  through  1001 -N through a channel and reference signals that are synchronized with a reception signal on a (L−1)-th path and generated by the reference signal generator  1040 . 
         [0136]    The reference signals may be midambles in the case of the TDD system and pilot signals in the case of the FDD system. As illustrated in  FIG. 10 , if the number of antennas is N, N×1 weight vectors are generated. 
         [0137]    In the case of the TDD system, a procedure of obtaining weight vectors is as follows. 
         [0138]    Signals received by the antenna elements  1001 - 1  through  1001 -M are input to the first demultiplexing unit  1020  through the RF transceivers  1005 - 1  through  1005 -M, and the first demultiplexing unit  1020  performs demultiplexing on the midamble parts of the signals and transfers the demultiplexed midamble parts to the weight vector generator  1030 . The weight vector generator  1030  uses a beamforming algorithm stored therein to calculate weight vectors. 
         [0139]    The second demultiplexing unit  1050  extracts user data parts from the signals subject to reception beamforming, which are output from the beamforming unit  1010 , except for the midamble parts, and then transfers the user data parts to the despreading unit  1010  that has been synchronized with a (L−1)-th signal. The despreading unit  1010  performs despreading of the user data parts. The despreading unit  1060  may be a matched filter for performing matched filtering on the received signals with respect to the (L−1)-th signal. 
         [0140]    The determining unit  1070  may determine a signal output from the matched filter  1060  and output a user data sequence b k  that has been sent from the base station  120 . 
         [0141]      FIG. 11  is a diagram illustrating a configuration example of a receiver  114  of the terminal  110  (see  FIG. 1 ) with multiple antennas, which can perform chip-level MIMO beamforming, when channel estimation is performed. 
         [0142]    Referring to  FIG. 11 , the receiver  114 C of the terminal  110  includes an array antenna consisting of antenna elements  1101 - 1  through  1101 -N, a plurality of RF transceivers  1105 - 1  through  1105 -N, a beamforming unit  1110 , a first demultiplexing unit  1120 , a weight vector generator  1130 , a reference signal generator  1140 , a second demultiplexing unit  1150 , a despreading unit  1160 , a determining unit  1170 , and a channel estimator  1180 . 
         [0143]    The receiver  114 C of the terminal  110  illustrated in  FIG. 11  has a configuration similar to the receiver  114 B of the terminal  110  illustrated in  FIG. 10 , except that the receiver  11 C of the terminal  110  includes a channel estimator  1180 . Also, the second demultiplexing unit  1150  outputs user data parts of received signals to the despreading unit  1160 , and reference signals of the received signals to the multiplier  1145 . 
         [0144]    Each reference signal that is synchronized with a reception signal on a (L−1)-th path and generated by the reference signal generator  1140  is input to the channel estimator  1180  through the multiplier  1145 . The channel estimator  1180  estimates a channel, using a reference signal output from the second demultiplexing unit  1150 , which is a reference signal part of a signal received through a channel, and a reference signal generated by the reference signal generator  1140 . The channel estimator  1180  may perform channel estimation using one of various estimation methods. A channel estimation value that represents a channel state estimated by the channel estimator  1180  is applied to a user data part output from the despreading unit  1160 , subject to channel compensation, and then output via the determining unit  1170 . 
         [0145]      FIG. 12  is a diagram illustrating a configuration example of a receiver  114 D of the terminal  110  (see  FIG. 1 ) with multiple antennas, which can perform symbol-level MIMO beamforming. 
         [0146]    The receiver  114 D of the terminal  110  includes an array antenna consisting of a plurality of antenna elements  1201 - 1  through  1201 -N, a plurality of RF transceivers  1205 - 1  through  1205 -N, a plurality of demultiplexing units  1210 - 1  through  1210 -N, a despreading unit  1220 , a beamforming unit  1230 , a weight vector generator  1240 , a reference signal generator  1250 , and a determining unit  1260 . The despreading unit  1220  includes a plurality of matched filters  1220 - 1  through  1220 -N. 
         [0147]    For symbol-level beamforming, adversely from signal processing for chip-level beamforming of passing signals through the beamforming unit  1110  and then despreading the resultant signals using the despreading unit  1160 , as illustrated in  FIG. 11 , received signals are despreaded by the despreading unit  1220  and demodulated, and then symbol-level reception beamforming is performed by the beamforming unit  1230 . As such, the signal processing flow performs the operations with the same equations as in the signal processing illustrated in  FIG. 11 . 
         [0148]    Referring to  FIG. 12 , the received signals passed through the RF transceivers  1205 - 1  through  1205 -N are divided into user data parts and reference signal parts by the demultiplexing units  1210 - 1  through  1210 -N for each array. Then, the user data parts are despreaded using a continuously orthogonal spreading code by the despreading unit  1230 . The matched filters  1220 - 1  through  1220 -N that perform despreading perform matched filtering on the user data parts in synchronization with a reception signal on a (L−1)-th path according to the characteristics of the pre-rake system, thereby performing despreading. 
         [0149]    Also, the demultiplexing units  1210 - 1  through  1210 -N transfer the reference signal parts of the received signals to the weight vector generator  1240 . The weight vector generator  124  applies a specific beamforming algorithm to a reference signal received from the demultiplexing unit  1210  and a reference signal that is generated by the reference signal generator  1250  and synchronized with a reception signal on a (L−1)-th path, thereby generating weight vectors. 
         [0150]    After weight vectors are generated, the beamforming unit  1230  performs symbol-level beamforming by multiplying symbol-level user data parts divided and despreaded by the respective matched filters of the despreading unit  1220  by the weight vectors and then adding the data parts calculated for each array to each other to generate a single signal. 
         [0151]    The weight vector generator  1240  may use one among methods of using weight vectors obtained in a previous time slot for a predetermined time slot interval, of predicting weight vectors based on previously calculated weight vectors and using the predicted weight vectors as weight vectors for a next time slot interval, of using weight vectors obtained in a current time slot without any conversion, etc. However, a method of using weight vectors is not limited to the methods mentioned above. 
         [0152]      FIG. 13  is a diagram illustrating a configuration example of a receiver  114 E of the terminal  110  (see  FIG. 1 ) with multiple antennas, where channel estimation is performed upon symbol-level reception beamforming. 
         [0153]    The receiver  114 E of the terminal  110  illustrated in  FIG. 13  includes an array antenna consisting of a plurality of antenna elements  1301 - 1  through  1301 -N, a plurality of RF transceivers  1305 - 1  through  1305 -N, a plurality of demultiplexing units  1310 - 1  through  1310 -N, a despreading unit  1320 , a beamforming unit  1330 , a weight vector generator  1340 , a reference signal generator  1350 , a determining unit  1360 , and a channel estimator  1370 . 
         [0154]    The receiver  114 E of the terminal  110  has a configuration similar to the receiver  114 D of the terminal  110  illustrated in  FIG. 12 , except that the receiver  114 E includes a channel estimator  1370 . 
         [0155]    The channel estimator  1370  performs channel estimation using a reference signal part of a signal received through a channel and an original reference signal generated by the reference signal generator  1350 . A channel state estimated by the channel estimator  1370  may be applied to a signal subject to reception beamforming by the beamforming unit  133 , subject to channel compensation, and then output via the determining unit  1360 . 
         [0156]    In the case where the terminal  110  has multiple antennas as illustrated in  FIGS. 10 through 13 , the terminal  110  that receives signals subject to transmission beamforming performs reception beamforming through the weight vector generator and the beamforming unit, resulting in a greater array gain and an improved interference reduction effect. Also, through the interference cancellation capacity of continuously orthogonal spreading codes, deterioration due to interference may little occur in spite of an increase in number of users. 
         [0157]      FIG. 14  is a flowchart illustrating an example of a method in which the base station  120  (see  FIG. 1 ) receives signals transmitted through a multi-path channel using a plurality of antennas. 
         [0158]    The base station  120  receives a plurality of pre-rake combined signals through the plurality of antennas ( 1410 ). The base station  120  may receive the pre-rake combined signals from a terminal having multiple antennas, as described above with reference to  FIG. 2 , or from a terminal having a single antenna, as described above with reference to  FIG. 3 . 
         [0159]    Then, the base station  120  performs chip-level reception beamforming with respect to the pre-rake combined signals for each user by multiplying the pre-rake combined signals by weight vectors corresponding to the respective antennas ( 1420 ). The base station  120  performs matched filtering on the pre-rake combined signals subject to the reception beamforming to despread the pre-rake combined signals, thereby demodulating a plurality of user signals ( 1430 ). 
         [0160]    The base station  120  may extract reference signal parts from the signals subject to the reception beamforming, and perform channel estimation using the extracted reference signal parts and reference signals generated by a reference signal generator. Then, the base station  120  may correct user data parts of the demodulated user signals using channel estimation values obtained through channel estimation. 
         [0161]      FIG. 15  is a flowchart illustrating an example of a method in which the terminal  110  receives signals transmitted through a multi-path channel using a plurality of antennas. 
         [0162]    The terminal  110  receives a plurality of pre-rake combined signals through a plurality of antennas ( 1510 ). The terminal  110  may receive the pre-rake combined signals from a base station as described above with reference to  FIG. 8 . 
         [0163]    Then, the terminal  110  performs chip-level reception beamforming with respect to the pre-rake combined signals by multiplying the pre-rake combined signals by weight vectors corresponding to the respective antennas ( 1520 ). Successively, the terminal  110  performs matched filtering on the pre-rake combined signal subject to reception beamforming to despread the pre-rake combined signals, thereby demodulating a user signal of the terminal  110  ( 1530 ). 
         [0164]    Then, the terminal  110  extracts reference signal parts from the signals subject to the reception beamforming, and estimate a channel using the extracted reference signal parts and reference signals generated by a reference signal generator. Next, the terminal  110  may correct user data parts of the demodulated user signals using channel estimation values obtained through channel estimation. 
         [0165]      FIG. 16  is a flowchart illustrating an example of another method in which the base station  120  receives signals transmitted through a multi-path channel using a plurality of antennas. 
         [0166]    The base station  120  receives a plurality of pre-rake combined signals through a plurality of antennas ( 1610 ). The base station  120  may receive the pre-rake combined signals from a terminal having multiple antennas, as described above with reference to  FIG. 2 , or from a terminal having a single antenna, as described above with reference to  FIG. 3 . 
         [0167]    The base station  120  performs matched filtering on the pre-rake combined signals received through the antennas, thus demodulating a plurality of user signals. The base station  120  performs symbol-level reception beamforming with respect to the user signals for each user by multiplying the user signals by weight vectors corresponding to the respective antennas ( 1630 ). 
         [0168]    Then, the base station  120  extracts reference signal parts from among the signals subject to the reception beamforming, estimates a channel for each user using the extracted reference signal parts and reference signals generated by a reference signal generator, and corrects the signal subject to the reception beamforming for each user using channel estimation values obtained through channel estimation. 
         [0169]      FIG. 17  is a flowchart illustrating an example of another method in which the terminal  110  receives signals transmitted through a multi-path channel using a plurality of antennas. 
         [0170]    The terminal  110  receives a plurality of pre-rake combined signals transmitted through a multi-path channel using a plurality of antennas ( 1710 ). The terminal  110  may receive the pre-rake combined signals from a base station as described above with reference to  FIG. 8 . 
         [0171]    The terminal  110  performs matched filtering on the pre-rake combined signals received through the antennas, thereby demodulating its user signal ( 1720 ). Then, the terminal  110  performs symbol-level reception beamforming by multiplying the user signal signal by weight vectors corresponding to the respective antennas ( 1730 ). 
         [0172]    The terminal  110  extracts reference signal parts from the signals subject to the reception beamforming, performs channel estimation using the extracted reference signal parts and reference signals generated by a reference signal generator, and then correct the signal subject to the reception beamforming using channel estimation values obtained through channel estimation. 
         [0173]      FIG. 18  is a flowchart illustrating an example of a method in which the terminal  110  (see  FIG. 1 ) transmits signals through a multi-path channel using a plurality of antennas. 
         [0174]    The terminal  110  spread-modulates a user signal using continuously orthogonal spreading codes having a characteristic of being continuously orthogonal for a predetermined time interval, thus generating a spreading signal ( 1810 ). 
         [0175]    Then, the terminal  110  performs pre-rake combining of the spreading signal to generate a pre-rake combined signal ( 1820 ). 
         [0176]    Successively, the terminal  110  performs chip-level transmission beamforming by multiplying the pre-rake combined signal by weight vectors corresponding to the respective antennas ( 1830 ). 
         [0177]      FIG. 19  is a flowchart illustrating an example of a method in which the base station  120  transmits signals through a multi-path channel using a plurality of antennas. 
         [0178]    The base station  120  spread-modulates a plurality of user signals using continuously orthogonal spreading codes having a characteristic of being continuously orthogonal for a predetermined time interval to generate spreading signals for individual users ( 1910 ). 
         [0179]    Then, the base station  120  performs pre-rake combining of the spreading signals to generate a plurality of pre-rake combined signals. ( 1920 ). 
         [0180]    Successively, the base station  120  performs chip-level transmission beamforming by multiplying the pre-rake combined signals by weight vectors corresponding to the respective antennas for individual users ( 1930 ). 
         [0181]    The examples as described above relate to the case where the TDD system is used, however, can be applied to the FDD system where channel information of a receiver is fed back to a transmitter so that the transmitter can use the channel information. Generally, the TDD system uses midambles as reference signals, while the TDD system uses pilot signals as reference signals. 
         [0182]    The present invention can be implemented as computer readable codes in a computer readable record medium. The computer readable record medium includes all types of record media in which computer readable data are stored. Examples of the computer readable record medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage. Further, the record medium may be implemented in the form of a carrier wave such as Internet transmission. In addition, the computer readable record medium may be distributed to computer systems over a network, in which computer readable codes may be stored and executed in a distributed manner 
         [0183]    A number of examples have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.