Abstract:
Provided are a mobile communication apparatus including an antenna array and a mobile communication method. The mobile communication apparatus has a base station and a mobile station. The mobile station measures the downlink characteristics, detects physical space information and approximate long-term information, produces short-term informatio, transforms the short-term information and the physical space information into a feedback signal, and transmits the feedback signal to the base station. The base station receives the feedback signal, extracts weighted information, beamforms dedicated physical channel signals, combines pilot channel signals with the result of the beamforming, and transmits the results of the combinations to the mobile station via the antenna array. The physical space information denotes space information about the location of the mobile station with respect to the base station, and the approximate long-term information denotes long-term information. Accordingly, degradation of the performance of communications caused by a great amount of information to be fed back station can be prevented while keeping a beamforming gain.

Description:
BACKGROUND OF THE INVENTION 
     This application claims the benefit of Korean Patent Application Nos. 2002-9288 and 2003-9495 filed on Feb. 21, 2002 and on Feb. 14, 2003 respectively, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference. 
     1. Field of the Invention 
     The present invention relates to a mobile communication apparatus including an antenna array, by which interference of a received signal between users can be removed by massing the beams of a signal to be transmitted to individual users in order to minimize the influence of fading, interference, and noise in a mobile communication environment, and a mobile communication method performed in the mobile communication apparatus, and more particularly, to a mobile communication apparatus capable of improving the performance of a mobile communication system by reducing the amount of feedback information in order to make the mobile communication system insensitive to feedback errors or feedback delays, in contrast with an eigen beamforming method proposed by Siemens, in which eigenvectors are directly,quantized, and the quantized eigenvectors are fed by a mobile station to a base station, and a mobile communication method performed in the mobile communication apparatus. 
     2. Description of the Related Art 
     A next-generation mobile communication system is required to transmit information faster than existing mobile communication systems such as personal communication services (PCSs). Europe and Japan have already adopted a wideband code division multiple access (W-CDMA) system as a wireless access standard, while the North America has already adopted a CDMA-2000 (multi-carrier code division multiple access) system. 
     In a general mobile communication system, several mobile stations communicate with one another through a base station. In order to transmit data at a high speed, a mobile communication system should minimize loss due to the characteristics of a mobile communication channel, such as fading, and user interference. In particular, diversity systems are used to prevent communication from becoming unstable due to fading. A space diversity system, which is a type of diversity system, uses multiple antennas, that is, an antenna array. 
     In order to achieve fast data transmission, a general mobile communication system should overcome fading having the most serious effect on the performance of the mobile communication system, because fading reduces the amplitude of a received signal to several dB or several tens of dB. Here, the fading is one of the channel characteristics of the mobile communication system. As described above, fading can be overcome by several diversity techniques. A representative example of the diversity techniques is a rake receiver for performing the diversity using the delay or spread of a channel in a CDMA technique. A rake receiver performs a diversity reception technique for receiving a multi-path signal. However, the diversity technique does not operate diversity when a delay spread is low. 
     Another example of the diversity techniques is a time diversity system using interleaving and coding, which is used in a Doppler spread channel. However, the time diversity system is not suitable for a low-speed Doppler channel. In a room channel with a low delay spread and a pedestrian channel corresponding to a low Doppler channel, a space diversity system is used in order to overcome fading. A space diversity system uses at least two antennas. If a signal received via one antenna is attenuated by fading, the space diversity system receives the signal via another antenna. The space diversity is classified into a reception antenna diversity using a reception antenna and a transmission antenna diversity using a transmission antenna. As it is difficult for a mobile station to install the reception antenna diversity in respect of area and costs, it is recommended that a base station use the transmission antenna diversity. 
     In the transmission antenna diversity, there are a closed loop transmission antenna diversity getting feedback of a downlink channel information from a mobile station to the base station, and an open loop transmission antenna diversity getting no feedback from a mobile station to the base station. In the transmission antenna diversity, a mobile station searches for an optimal weighted value by measuring the phase and magnitude of a downward channel formed from a base station to a mobile station and transmits the searched information to the base station. In order to measure the magnitude and phase of the moving channel, a base station must send different orthogonal pilot signals for different transmission antennas. A mobile station receives the pilot signals, measures the magnitude and phase of a channel using the received pilot signals, and searches for an optimal weighted value for a transmission antenna diversity from the measured channel magnitude and phase information. 
     For the transmission antenna diversity, if the number of transmission antennas of the base station increases, the diversity effect and the signal-to-noise ratio still improve, but the amount/speed of improvement in the diversity effect continuously decreases. Accordingly, to obtain a slightly-improved diversity effect while sacrificing a lot cost is not preferable. Hence, it is preferable that the number of antennas used in a base station increases to minimize the power of an interference signal and maximize the signal-to-noise ratio of an internal signal, instead of improving the diversity effect. 
     A transmission adaptive antenna array system invented in consideration of a beamforming effect that minimizes the influence that interference and noise as well as diversity effect have upon an internal signal is referred to as a downlink beamforming system. A system using feedback information like a transmission diversity is referred to as a closed loop downlink beamforming system. The closed loop downlink beamforming system, which uses information fed back from a mobile station to a base station, may degrade the performance of communications by failing to properly reflect changes in channel information if a feedback channel does not have a sufficient bandwidth. 
     The first and second TxAA modes standardized in a W-CDMA system, which is a European IMT-2000have the following problems when the number of antennas and the characteristics of a space-time channel vary. If the number of antennas increases, a weighted value for each antenna must be fed back, and hence a lot of information to be fed back is created. Thus, depending on the movement speed of a mobile station, the first and second TxAA modes degrade the communication performance. That is, generally, if the movement speed of a mobile station increases in a fading channel, a change in the space-time channel becomes serious. Thus, the feedback speed of channel information must increase. However, if the feedback speed is limited, feedback information increasing with an increase in the number of antennas consequently degrades the performance of communications. If the distance between antennas is not sufficient, the correlation between channels in each antenna increases. If the correlation between channels increases, the information amount of a channel matrix decreases. The effective use of a feedback method prevents performance degradation in a high-speed moving body environment even if the number of antennas increases. However, since the first and second TxAA modes are constructed under the assumption that the channels of two antennas that constitute the space-time channels are completely independent from each other, they cannot be used effectively when the number of antennas and the characteristics of the space-time channel change. In addition, the first and second TxAA modes have never been applied to an environment using more than 2 antennas and cannot provide excellent performance even when using 3 or more antennas. 
     Because of the above reasons, a beamforming antenna system is formed in case three or more antennas are used. A beamforming technique uses the difference in a direction between individual users and is suitable for an environment having a great correlation between channels of individual transceiving antennas. In particular, Siemens suggests that the 3GPP adopts an eigen beamforming technique which combines a diversity with a beam-forming. However, the eigen beamforming technique provides a lot of feedback information because it simply quantizes eigenvectors for beamforming and feeds the quantized eigenvectors back to a sender. Such a feedback of information in a large amount causes feedback information during transmission to be sensitive to generated errors and delays, thereby degrading the performance of mobile communication systems. 
     SUMMARY OF THE INVENTION 
     The present invention provides a mobile communication apparatus including an antenna array, by which the amount of information that is necessary for a beamforming and is fed from a mobile station back to a base station is reduced, thus increasing the performance of communication. 
     The present invention also provides a mobile communication method performed in the mobile communication apparatus including an antenna array, by which the amount of information that is necessary for a beamforming and is fed from a mobile station back to a base station is reduced, thus increasing the performance of communications. 
     According to an aspect of the present invention, there is provided a mobile communication apparatus having a mobile station and a base station including an antenna array. The mobile station measures the downlink characteristics of a channel of individual antennas from a signal received from the base station, detects physical space information and approximate long-term information from the measured downlink characteristics, produces short-term information from the approximate long-term information and the downlink characteristics, transforms the short-term information and the physical space information into a feedback signal, and transmits the feedback signal to the base station. The base station receives the feedback signal, extracts weighted information from the short-term information and the physical space information, which are restored from the received feedback signal, beamforms a dedicated physical channel signal using the weighted information, combines pilot channel signals with the results of the beamforming, and transmits the results of the combinations to the mobile station via the antenna array. The physical space information denotes space information about the location of the mobile station with respect to the base station, and the approximate long-term information denotes long-term information that is the most similar to long-term information in which the correlation characteristics of a channel of individual antennas are reflected. 
     According to another aspect of the present invention, there is provided a mobile communication method performed in a mobile communication apparatus having a mobile station and a base station including an antenna array. The mobile communication method includes step of measuring the downlink characteristics of a channel of individual antennas from a signal received from the base station, detecting physical space information and approximate long-term information from the measured downlink characteristics, producing short-term information using approximate long-term information and the downlink characteristics, transforming the short-term information and the physical space information into a feedback signal, and transmitting the feedback signal to the base station, and step of receiving the feedback signal, extracting weighted information from the short-term information and physical space information, which are restored from the received feedback signal, beamforming a dedicated physical channel signal using the weighted information, combining the beamforming results with pilot channel signals, and transmitting the results of the combinations to the mobile station via the antenna array. The physical space information denotes space information about the location of the mobile station with respect to the base station, and the approximate long-term information denotes long-term information that is the most similar to long-term information in which the correlation characteristics of a channel of individual antennas are reflected. 
     In a conventional mobile communication apparatus and a conventional mobile communication method, eigenvectors, which represent long-term information among information representing the downlink characteristics of a channel generated by multiple transmission antennas, are directly quantized, and the quantization result is fed by a mobile station to a base station. Hence, the amount of information to be fed by the mobile station to the base station increases, and the time taken to feed information back to the base station increases. Thus, if the speed at which a channel changes is higher than the speed at which long-term information is updated, the performance of mobile communications is degraded, and a load upon a backward channel formed from a mobile station to a base station increases. Consequently, the amount of data to be transmitted via the backward channel is reduced. However, in the mobile communication apparatus including an antenna array according to the present invention and the mobile communication method according to the present invention, because physical space information instead of long-term information is fed by a mobile station  20 ,  22 , . . . , or  24  to a base station  10 , the amount of information to be fed back to the base station  10  is reduced by 50% or greater. Accordingly, the updating speed of long-term information can be increased, and a fast mobile can adapt a fast channel change, that is, can quickly and smoothly respond to a change in a channel according to the speed. Also, the capacity of a backward channel that can be used to transmit data is increased because the amount of information to be fed back is reduced, and a received signal to noise ratio required by a mobile station can be significantly reduced as in the conventional mobile communication apparatus including an antenna array and the conventional mobile communication method. Therefore, the mobile communication apparatus and method according to the present invention have the effect that degradation of the performance of communications caused by a great amount of information to be fed back can be prevented while keeping a beamforming gain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a schematic block diagram of a mobile communication apparatus including an antenna array, according to the present invention; 
         FIG. 2  is a flowchart for illustrating a mobile communication method according to the present invention, performed in the mobile communication apparatus of  FIG. 1 ; 
         FIG. 3  is a flowchart for illustrating a preferred embodiment of the present invention of step  30  of  FIG. 2 ; 
         FIG. 4  is a block diagram of a preferred embodiment of the present invention of the k-th mobile station of  FIG. 1 ; 
         FIG. 5  is a flowchart for illustrating a preferred embodiment of the present invention of step  44  of  FIG. 3 ; 
         FIG. 6  is a block diagram of an embodiment of the present invention of the long-term space information producer of  FIG. 4 ; 
         FIG. 7  is a table of an embodiment of the present invention of the first lookup table of  FIG. 6 ; 
         FIG. 8  is a flowchart for illustrating a preferred embodiment of the present invention of step  80  of  FIG. 5 ; 
         FIG. 9  is a block diagram of a preferred embodiment of the present invention of the address producer of  FIG. 6 ; 
         FIG. 10  is a block diagram of a preferred embodiment of the present invention of the address producer of  FIG. 9 ; 
         FIG. 11  is a flowchart for illustrating a preferred embodiment of the present invention of step  46  of  FIG. 3 ; 
         FIG. 12  is a block diagram of a preferred embodiment of the present invention of the short-term information producer of  FIG. 4 ; 
         FIG. 13  is a flowchart for illustrating an embodiment of the present invention of step  32  of  FIG. 2 ; 
         FIG. 14  is a block diagram of an embodiment of the present invention of the base station of  FIG. 1 ; 
         FIG. 15  is a flowchart for illustrating an embodiment of the present invention of step  200  of  FIG. 13 ; 
         FIG. 16  is a block diagram of an embodiment of the present invention of the weighted information producer of  FIG. 14 ; 
         FIG. 17  is a flowchart for illustrating an embodiment of the present invention of step  264  of  FIG. 15 ; and 
         FIG. 18  is a block diagram of an embodiment of the present invention of the information combiner of  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The structure and operations of embodiments of a mobile communication apparatus including an antenna array according to the present invention and a mobile communication method performed in the mobile communication apparatus will be described hereinafter with reference to the accompanying drawings. 
       FIG. 1  is a schematic block diagram of a mobile communication apparatus including an antenna array, according to the present invention. The mobile communication apparatus is composed of a base station  10  and first, second, . . . , and K-th mobile stations  20 ,  22 , . . . , and  24 . Here, K denotes a positive integer. 
       FIG. 2  is a flowchart for illustrating a mobile communication method according to the present invention, performed in the mobile communication apparatus of  FIG. 1 . This mobile communication method includes step  30  of obtaining a feedback signal and step  32  of extracting weighted information from the feedback signal. 
     In step  30 , a k-th (1≦k≦K) mobile station among the first, second, . . . , and K-th mobile stations  20 ,  22 , . . . , and  24  of  FIG. 1  measures the downlink characteristics H DL  of a channel for each of the antennas of the antenna array included in the base station  10  from a signal received from the base station  10 , and detects physical space information and approximate long-term information from the measured downlink characteristics H DL . Hereinafter, bold characters denote vectors, and non-bold characters denote scalars. Still in step  30 , the k-th mobile station also produces short-term information from the approximate long-term information and the downlink characteristics H DL , transforms the physical space information and the short-term information into a feedback signal, and transfers the feedback signal to the base station  10 . Here, H DL  denotes a matrix. The column components of the matrix H DL  are obtained with respect to the space, and the row components are obtained with respect to the time. The physical space information denotes space information about the location of the k-th mobile station  20 ,  22 , . . . , or  24  with respect to the base station  10 . For example, the physical space information may be a direction of arrival (DOA) and an angle spread. The approximate long-term information denotes long-term information the most approximate to long-term information, which reflect the correlations between channels for individual antennas. 
     Embodiments of step  30  and an embodiment of the k-th mobile station  20 ,  22 , . . . , or  24  will now be described with reference to attached drawings. 
       FIG. 3  is a flowchart for illustrating step  30 A, which is a preferred embodiment of the present invention of step  30  of  FIG. 2 . In step  40 , the downlink characteristics H DL  of a channel are measured. In steps  42 ,  44 , and  46 , the physical space information, the approximate long-term information, and the short-term information of a channel are determined from the measured downlink characteristics H DL . In step  48 , the determined physical space information and the short-term information are transformed into a feedback signal. 
       FIG. 4  is a block diagram of the k-th mobile station  20 ,  22 , . . . , or  24  of  FIG. 1  according to a preferred embodiment of the present invention. As shown in  FIG. 4 , the k-th mobile station  20 ,  22 , . . . , or  24  includes an antenna  60 , a channel characteristics measurer  62 , a long-term information determiner  64 , a long-term space information producer  66 , a short-term information producer  68 , and mobile station signal transformer  70 . 
     In step  40 , the channel characteristics measurer  62  of  FIG. 4  receives a signal from the base station  10  via the antenna  60 , measures the downlink characteristics H DL  of a channel of individual antennas from the received signal, and outputs the measured downlink characteristics H DL  to the short-term information producer  68  and either of the long-term information determiner  64  or the long-term space information producer  66 . Here, the downlink characteristics H DL  of a channel denotes the phase and magnitude of a channel transferred from the base station  10  to the k-th mobile station  20 ,  22 , . . . , or  24 . 
     According to an embodiment of the present invention, as shown in  FIGS. 3 and 4 , in step  42 , the long-term information determiner  64  produces eigenvectors v 1 , . . . , and v ant , which denote eigen beams, from the channel downlink characteristics H DL  temporally and spatially measured by the channel characteristics measurer  62 , using an eigenvalue decomposition (EVD) method, selects effective (i.e., usable) eigenvectors v 1  through V Nbeam  out of the produced eigenvectors v 1  through v ant , determines the selected effective eigenvectors as long-term information, and outputs the long-term information to the long-term space information producer  66 . Here, ‘ant’ denotes the number of antennas in an antenna array included in the base station  10 , and ‘Nbeam’ denotes the number of effective eigenvectors. The EVD method is disclosed in a book written by ‘G. Golub’ and ‘C. Van. Loan’ with the title of “Matrix Computation” and published in 1996 by the Johns Hopkins University publishing company located in London. Next, in step  44 , the long-term space information producer  66  detects physical space information and produces approximate long-term information from the long-term information, that is, the effective eigenvectors v 1  through V Nbeam , received from the long-term information determiner  64  and outputs the detected physical space information to the mobile station signal transformer  70  and the produced approximate long-term information to the short-term information producer  68 . 
     According to another embodiment of the present invention, step  30 A of  FIG. 3  may not include step  42 , and the mobile station of  FIG. 4  may not include the long-term information determiner  64 . In this alternative, after step  40 , the long-term space information producer  66  detects physical space information and approximate long-term information from the channel downlink characteristics H DL  received from the channel characteristics measurer  62 , in step  44 . 
     In the case where step  30 A of  FIG. 3  includes step  42  and the mobile station of  FIG. 4  includes the long-term information determiner  64 , preferred embodiments of the present invention of step  44  and the long-term space information producer  66  will be described hereinafter. 
       FIG. 5  is a flowchart for illustrating step  44 A, which is a preferred embodiment of the present invention of step  44  of  FIG. 3 . Step  44 A includes steps  80  and  82  of detecting physical space information and producing approximate long-term information. 
       FIG. 6  is a block diagram of a long-term space information producer  66 A, which is a preferred embodiment of the present invention of the long-term space information producer  66  of  FIG. 4 . The long-term space information producer  66 A includes an address producer  84  and a first lookup table (LUT)  86 . 
     Referring to  FIG. 6 , after step  42 , the address producer  84  detects approximate long-term information that is the most approximate to the long-term information (i.e., the effective eigenvectors v 1  through V Nbeam ) received from the long-term information determiner  64  via an input terminal IN 1  and outputs the detected approximate long-term information to the short-term information producer  68  via an output terminal OUT 1  while addresses for the approximate long-term information are produced and output to the first LUT  86 , in step  80 . Thereafter, in step  82 , the first LUT  86  outputs physical space information stored in the addresses received from the address producer  84  to the mobile station signal transformer  70  via an output terminal OUT 2 . 
       FIG. 7  shows a table of an embodiment of the present invention of the first LUT  86  of  FIG. 6 , which includes DOAs, angle spread (AS), predetermined effective eigenvectors, and indices (or addresses). 
     If the minimum unit of a DOAs (θ) and a possibility of occurrence of AS (φ) are restricted, the first LUT  86  of  FIG. 7  produces a total of 60 effective eigenvectors as shown in Equation 1:
 
[λ 1  V 1  λ 2  V 2  . . . λ N     B    V N     B   ]=EVD eff (R(θ,φ)  (1)
 
wherein EVD eff  denotes a function for searching for effective eigenvectors and eigenvalues from the results of EVD, λ i  an eigenvalue, v j  denotes an eigenvector, and R(,) denotes a channel correlation matrix that is produced using DOAs (θ) and AS(φ) using Equation 2:
 
     
       
         
           
             
               
                 
                   
                     R 
                     ⁡ 
                     
                       ( 
                       
                         θ 
                         , 
                         ϕ 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       1 
                       
                         Q 
                         + 
                         1 
                       
                     
                     ⁢ 
                     
                       
                         ∑ 
                         
                           q 
                           = 
                           
                             
                               - 
                               Q 
                             
                             / 
                             2 
                           
                         
                         
                           Q 
                           / 
                           2 
                         
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           a 
                           ⁡ 
                           
                             ( 
                             
                               θ 
                               + 
                               
                                 ϕ 
                                 ⁢ 
                                 
                                   q 
                                   Q 
                                 
                               
                             
                             ) 
                           
                         
                         ⁢ 
                         
                           
                             a 
                             H 
                           
                           ⁡ 
                           
                             ( 
                             
                               θ 
                               + 
                               
                                 ϕ 
                                 ⁢ 
                                 
                                   q 
                                   Q 
                                 
                               
                             
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     wherein a direction vector a(θ) is [1 exp(jψ) exp(j2Ψ) . . . exp(j(B−1)Ψ)], where Ψ=πsin (θ). 
     If physical space information is read out from the first LUT  86  of  FIG. 7 , the mobile station signal transformer  70  can express all eigenvectors included in the physical space information read from the first LUT  86  using a 6-bit feedback signal. 
     If the DOA (−80°&lt;θ&lt;80°) is quantized in units of 10° (i.e., a resolution of 10°), and the AS (φ) is expressed as 0°, 5°, 10°, and 20°, a total of 8 bits of information is required to feed one eigenvector back to a base station, and a total of 16 bits of information is enough to feed two eigenvectors back. If the first LUT  86  of  FIG. 7  is used, the amount of information fed from the k-th mobile station  20 ,  22 , . . . , or  24  back to the base station  10  is only 30% of 54-bit long-term information proposed by Siemens. 
       FIG. 8  is a flowchart for illustrating step  80 A, which is a preferred embodiment of the present invention of step  80  of  FIG. 5 . Step  80 A is comprised of step  90  of calculating a distance between vectors and step  92  of obtaining an address and approximate long-term information. 
       FIG. 9  is a block diagram of an address producer  84 A, which is a preferred embodiment of the present invention of the address producer  84  of  FIG. 6 . The address producer  84 A includes a distance calculator  100  and a maximum value searcher  102 . 
     After step  42 , the distance calculator  100  applies norms to the differences between each of at least one of the effective eigenvectors v 1 , v 2 , . . . , and v x  (where x corresponds to Nbeam and is a positive integer), which are long-term information determined by the long-term determiner  64  of  FIG. 4 , and predetermined effective eigenvectors v 1 ´, v 2 ´, . . . , and v y ´, square each of the norms, and determines t results of the squaring as inter-eigenvector distances, in step  90 . 
     Thereafter, in step  92 , the maximum value searcher  102  determines as an address the order of the greatest distance in the inter-vector distances received from the distance calculator  100 , which are calculated with respect to each of the effective eigenvectors corresponding to the determined long-term information, and outputs addresses to the first LUT  86  via an output terminal OUT 3 . Still in step  92 , the maximum value searcher  102  determines a predetermined effective eigenvector corresponding to the greatest inter-vector distance as approximate long-term information, which is approximate to the determined effective eigenvector, and outputs the approximate long-term information to the short-term information producer  68  via an output terminal OUT 4 . 
     To facilitate understanding of the present invention, the structure and operation of the address producer  84 A of  FIG. 9  will be described on the assumption that x is 2. 
       FIG. 10  is a block diagram of a preferred embodiment of the present invention of the address producer  84 A of  FIG. 9 , which includes an address calculator  1  OOA and a maximum value searcher  102 A. 
     To perform step  90 , the distance calculator  100 A includes first through y-th subtractors  110 ,  112 , . . . , and  114 , (y+1)th through 2y-th subtractors  116 ,  118 , . . . , and  120 , and first through 2y-th operation units  122 ,  124 , . . . , and  132 . 
     The first through y-th subtractors  110 ,  112 , . . . , and  114  of  FIG. 10  subtract the effective eigenvector v 1  received from the long-term information determiner  64  from each of the predetermined effective eigenvectors v 1 ´, v 2 ´, . . . , and v y ´ outputs the results of the subtractions to the first through y-th operation units  122 ,  124 , . . . , and  126 . The first through y-th operation units  122 ,  124 , . . . , and  126  apply norms to the subtraction results received from the first through y-th subtractors  110 ,  112 , . . . , and  114 , square the norms, and output the squared results as inter-vector distances to a first maximum value searcher  134 . In  FIG. 10 , ∥ 0  ∥ denotes a norm. Similarly, the (y+1)th through 2y-th subtractors  116 ,  118 , . . . , and  120  subtract the effective eigenvector v 2  received from the long-term information determiner  64  from each of the predetermined effective eigenvectors v 1 ´, v 2 ´, . . . , and v y ´ and outputs the results of the subtractions to the (y+1)th through 2y-th operation units  128 ,  130 , . . . , and  132 . The (y+1)th through 2y-th operation units  128 ,  130 , . . . , and  132  apply norms to the subtraction results received from the (y+1)th through 2y-th subtractors  116 ,  118 , . . . , and  120 , square the norms, and output the squared results as inter-vector distances to a second maximum value searcher  136 . 
     To perform step  92 , the maximum value searcher  102 A includes the first and second maximum value searchers  134  and  136 . For the effective eigenvector v 1  determined as long-term information, the first maximum value searcher  134  searches for the greatest distance from the inter-vector distances that are received from the first through y-th operation units  122 ,  124 , . . . , and  126 , determines the order of the greatest distance to be an address, and outputs the address via an output terminal OUT 5 . Also, the first maximum value searcher  134  determines as approximate long-term information with respect to the determined long-term information a predetermined effective eigenvector used in obtaining the greatest distance and outputs the determined approximate long-term information to the short-term information producer  68  via an output terminal OUT 6 . If the inter-vector distance output from the second operation unit  124 , which is the second one from the first through y-th operation units  122 ,  124 , . . . , and  126 , has the greatest value, a number 2 is determined as an address and output to the first LUT  86  via an output terminal OUT 5 . At this time, among the predetermined effective eigenvectors v 1 ´, v 2 ´, . . . , and v y ´, the predetermined effective eigenvector v 2 ´ used in calcula inter-vector distance output from the second operation unit  124  is determined as approximate long-term information the most similar to the long-term information v 1  and output via an output terminal OUT 6 . 
     Similarly, for the effective eigenvector v 2  determined as long-term information, the second maximum value searcher  136  searches for the greatest distance from the inter-vector distances that are received from the (y+1)th through 2y-th operation units  128 ,  130 , . . . , and  132 , determines the order of the greatest distance to be an address, and outputs the address via an output terminal OUT 7 . Also, the second maximum value searcher  136  determines as approximate long-term information with respect to the determined long-term information a predetermined effective eigenvector used in obtaining the greatest distance and outputs the approximate long-term information to the short-term information producer  68  via an output terminal OUT 8 . For example, if the inter-vector distance output from the 2y-th operation unit  132 , which is the y-th one from the (y+1)th through 2y-th operation units  128 ,  130 , . . . , and  132 , that is, the order of which is y, has the greatest value among the inter-vector distances output from the (y+1)th through the 2y-th operation units  128 ,  130 , . . . , and  132 , the order y is determined as an address and output to the first LUT  86  via an output terminal OUT 7 . At this time, among the predetermined effective eigenvectors v 1 ´, v 2 ´, . . . , and v y ´, the predetermined effective eigen v y ´ used in calculating the inter-vector distance output from the 2y-th operation unit  132  is determined as approximate long-term information with respect to the determined long-term information v 2  and output to the short-term information producer  68  via an output terminal OUT 8 . 
     After step  44 , the short-term information producer  68  produces short-term information using the downlink characteristics H DL  received from the channel characteristics measurer  62  and the approximate long-term information received from the long-term space information producer  66  and outputs the short-term information to the mobile station signal transformer  70 , in step  46 . 
     Preferred embodiments of the present invention of step  46  and the short-term information producer  68  will be described hereinafter with reference to attached drawings. 
       FIG. 11  is a flowchart for illustrating step  46 A, which is a preferred embodiment of the present invention of step  46  of  FIG. 3 . The step  46 A includes steps  140  and  142  of obtaining reception power values using determined weighted vectors and step  144  of determining short-term information using the maximum power value among the reception power values. 
       FIG. 12  is a block diagram of a short-term information producer  68 A, which is a preferred embodiment of the present invention of the short-term information producer  68  of  FIG. 4 . The short-term information producer  68 A includes a basisvector combiner  150 , a reception power calculator  152 , and a maximum power detector  154 . 
     After step  44 , the basisvector combiner  150  combines all predetermined weighted constants a 1 , a 2 , . . . , and a NB  (where NB denotes the number of effective eigenvectors and is the same as Nbeam) received via an input terminal IN 3  with the approximate long-term information received from the long-term space information producer  66  via the input port IN 4  and outputs the combination results as weighted vectors w 0 , w 1 , . . . , and w B′-1  (where B′ denotes the number of pieces of predetermined short-term information) to the reception power calculator  152 , in step  140 . 
     Thereafter, in step  142 , the reception power calculator  152  multiplies the weighted vectors w 0 , w 1 , . . . , and w B′-1  received from the basisvector combiner  150  by the downlink characteristics H DL  received from the channel characteristics measurer  62 , applies a square of norm to the results of the multiplications, and outputs a plurality of reception power value, which are the results of the squaring, to the maximum power detector  154 . 
     The reception power calculator  152  is comprised of (2y+1)th through (2y+B′)th operation units  160 ,  162 , . . . , and  164 , which multiply the weighted vectors w 0 , w 1 , . . . , and w B′-1  by the downlink characteristics H DL , apply norms to the multiplication results, square the norms, and outputs the squaring results as a plurality of reception power values to the maximum power detector  154 . 
     After step  142 , the maximum power detector  154  detects as maximum reception power the greatest value among the plurality of reception power values received from the reception power calculator  152 , determines, as short-term information, indices where coefficients used to obtain the weighted vector used to calculate the maximum reception power are located, and outputs the determined short-term information b to the mobile station signal transformer  70 , in step  144 . 
     After step  46 , the mobile station signal transformer  70  transforms the short-term information obtained by the short-term information producer  68  and the physical space information obtained by the long-term space information producer  66  into a feedback signal, in step  48 . The feedback signal is transmitted to the base station  10  via an antenna  60 . For that, the mobile station signal transformer  70  includes a physical space information formatter  72 , a mobile station short-term information formatter  74 , and a time division multiplexer  76 . The physical space information formatter  72  formats the physical space information received from the long-term space information producer  66  such that the physical space information can be properly fed back to the base station  10 , and outputs the formatted physical space information to the time division multiplexer  76 . In the meantime, the mobile station short-term information formatter  74  formats the short-term information received from the short-term information producer  68  and outputs the formatted short-term information to the time division multiplexer  76 . The time division multiplexer  76  performs time division multiplexing on the formatted physical space information received from the physical space information formatter  72  and the formatted short-term information received from the mobile station short-term information formatter  74  and outputs the time division multiplexed results in the form of a feedback signal to the antenna  60 . 
     According to the present invention, the formatted physical space information received from the physical space information formatter  72  is less frequently multiplexed than the formatted short-term information received from the mobile station short-term information formatter  74 . 
     After step  30 , the base station  10  receives a feedback signal from the k-th mobile station  20 ,  22 , . . . , or  24 , extracts weighted information from physical space information and short-term information which are restored from the received feedback signal, beamforms a dedicated physical channel signal using weighted information, adds pilot channel signals CPICH 1 , CPICH 2 , CPICH 3 , . . . , and CPICH ant  to the beamformed dedicated physical channel signal, and outputs the results of the additions to the mobile station via an antenna array, in step  32 . 
     Embodiments of the present invention of step  32  and the base station  10  will now be described with reference to attached drawings. 
       FIG. 13  is a flowchart for illustrating step  32 A, which is a preferred embodiment of the present invention of step  32  of  FIG. 2 . Step  32 A includes step  200  of producing weighted information and steps  202  and  204  of adding pilot channel signals to the beamforming results obtained using the weighted information. 
       FIG. 14  is a block diagram of a base station  10 A, which is a preferred embodiment of the present invention of the base station  10  of  FIG. 1 . The base station  10 A includes a first multiplier  220 , a first adder  222 , an antenna array  224 , and a weighted information producer  226 . 
     After step  30 , the weighted information producer  226  receives a feedback signal transmitted from the k-th mobile station  20 ,  22 , . . . , or  24 , restores short-term information and physical space information from the received feedback signal, transforms the restored physical space information into approximate long-term information, and combines the approximate long-term information and the restored short-term information to produce weighted information, in step  200 . 
     The antenna array  224  of  FIG. 14  includes antennas  248 ,  250 ,  252 , . . . , and  254 , the number of which is ant. According to one embodiment of the present invention, each of the antennas  248 ,  250 ,  252 , . . . , and  254  receives a feedback signal transmitted from the k-th mobile station  20 ,  22 , . . . , or  24  of  FIG. 1  and outputs the received feedback signal to the weighted information producer  226 . According to another embodiment of the present invention, instead of receiving the feedback signal via the antenna array  224  as shown in  FIG. 14 , the weighted information producer  226  may receive the feedback signal via extra reception antennas (not shown) not via the antenna array  224  of  FIG. 14 . 
     Preferred embodiments of the present invention of step  200  of  FIG. 13  and the weighted information producer  226  of  FIG. 14  will now be described with reference to attached drawings. 
       FIG. 15  is a flowchart for illustrating step  200 A, which is a preferred embodiment of the present invention of step  200  of  FIG. 13 . Step  200 A includes step  260  of restoring physical space information and a feedback signal and steps  262  and  264  of obtaining approximate long-term information and combining the same with the short-term information. 
       FIG. 16  is a block diagram of a weighted information producer  226 A, which is a preferred embodiment of the present invention of the weighted information producer  226  of  FIG. 14 . The weighted information producer  226 A includes an information restorer  280 , an information transformer  282 , and an information combiner  284 . 
     After step  30 , the information restorer  280  restores short-term information and physical space information from the feedback signal received via the input terminal IN 5  and outputs the restored short-term information to the information combiner  284  and the restored physical space information to the information transformer  282 , in step  260 . 
     After step  260 , in step  262 , the information transformer  282  transforms the restored physical space information received from the information restorer  280  into approximate long-term information and outputs the transformed approximate long-term information to the information combiner  284 . To do this, the information transformer  282  can be implemented as a second LUT  286 . The second LUT  286  receives the restored physical space information from the information restorer  280  to serve as an address, reads out approximate long-term information corresponding to the address, and outputs the read-out approximate long-term information to the information combiner  284 . The outputs/inputs of the second LUT  286  correspond to inputs/outputs of the first LUT  86 . For that, the first and second LUTs  86  and  286  are produced in advance using above-described Equations 1 and 2 by a mobile communication apparatus. In other words, the second LUT  286  uses the physical space information restored by the information restorer  280  as an address and reads out approximate long-term information corresponding to the address. 
     After step  262 , the information combiner  284  combines the transformed approximate long-term information received from the information transformer  282  with short-term information restored by the information restorer  280  and outputs the combination result as weighted information to the first multiplier  220  via an output terminal OUT 9 , in step  264 . 
     Embodiments of the present invention of step  264  of  FIG. 15  and the information combiner  284  of  FIG. 16  will now be described with reference to attached drawings. 
       FIG. 17  is a flowchart for illustrating step  264 A, which is a preferred embodiment of the present invention of step  264  of  FIG. 15 . Step  264 A includes step  300  of multiplying approximate effective eigenvectors by predetermined weighted constants and step  302  of summing the results of the multiplications. 
       FIG. 18  is a block diagram of an information combiner  284 A, which is a preferred embodiment of the present invention of the information combiner  284  of  FIG. 16 . The information combiner  284 A includes a second multiplier  310  and a second adder  312 . 
     After step  262 , the second multiplier  310  multiplies approximate effective eigenvectors {tilde over (v)} 1 , {tilde over (v)} 2 , . . . , and {tilde over (v)} N     B   . which correspond to the approximate long-term information transformed by the information transformer  282 , by the restored predetermined weighted constants ã 1 , ã 2 , . . . , and ãN N     B   , which correspond to the short-term information restored by the information restorer  280 , and outputs the results of the multiplications to the second adder  312 , in step  300 . Here, the predetermined weighted constants ã 1 , ã 2 , . . . , and ãN N     B   , are the results of restoration executed on predetermined weighted constants a 1 , a 2 , . . . , and a NB . To perform step  300 , the second multiplier  310  can be comprised of N B  multiplication units  320 ,  322 , . . . , and  324 , which multiply the approximate effective eigenvectors {tilde over (v)} 1 , {tilde over (v)} 2 , . . . , and {tilde over (v)} N     B    and the restored weighted constants ã 1 , ã 2 , . . . , and ã N     B    . 
     After step  300 , in step  302 , the second adder  312  adds the results of the multiplications executed in the second multiplier  310 , determines the results of the addition as weighted information, and outputs the determined weighted information via an output terminal OUT 10  to the first multiplier  220 . 
     After step  200 , the first multiplier  220  multiplies a Dedicated Physical CHannel signal (DPCH) by the weighted information received from the weighted information producer  226  and outputs the result of the multiplication as the results of beamforming to the first adder  222 , in step  202 . To perform step  202 , the first multiplier  220  includes multiplication units  230 ,  232 ,  234 , . . . , and  236 , the number of which is ant. The multiplication units  230 ,  232 ,  234 , . . . , and  236  multiply weighted values w 1 , w 2 , w 3 , . . . , and w ant , which are included in the weighted information received from the weighted information producer  226 , by the Dedicated Physical CHannel signal (DPCH). 
     After step  202 , the first adder  222  adds pilot channel signals to the beamforming results received from the first multiplier  220  and outputs the results of the additions to the antenna array  224 , in step  204 . To perform step  204 , the first adder  222  can include addition units  240 ,  242 ,  244 , . . . , and  246 , the number of which is ant. The addition units  240 ,  242 ,  244 , . . . , and  246  add the pilot channel signals to the results of the multiplications executed by the ant multipliers  230 ,  232 ,  234 , . . . , and  236 . Here, the pilot channel signals [P i (k)] (1≦i≦ant) are Common Pllot CHannel signals (CPICH) as shown in  FIG. 14 . However, the pilot channel signals may be Dedicated CPICH (DCPICH) signals or secondary CPICH (SCPICH) signals unlike  FIG. 14 . For example, if the pilot channel signals [P i (k)] are Common Pilot CHannel signals (CPICH), P i (k) is CPICH i . 
     Each of the antennas  248 ,  250 ,  252 , . . . , and  254  of the antenna array  224  transmits the results of the addition performed by the corresponding addition unit among the addition units  240 ,  242 ,  244 , . . . , and  246  of the first adder  222  to the k-th mobile station  20 ,  22 , . . . , or  24  of  FIG. 1 . 
     As described above, each of the antennas  248 ,  250 ,  252 , . . . , and  254  of the antenna array  224  can both play the role of signal-transmission of transmitting the results of the addition performed by the addition unit  240 ,  242 ,  244 , . . . , or  246  and the role of signal-reception of receiving a feedback signal transmitted from the k-th mobile station  20 ,  22 , . . . , or  24 . 
     Alternatively, each of the antennas  248 ,  250 ,  252 , . . . , and  254  of the antenna array  224  may only transmit the results of the additions performed by the addition units  240 ,  242 ,  244 , . . . , and  246 . In this case, extra antennas for receiving a feedback signal transmitted from the k-th mobile station  20 ,  22 , . . . , or  24  are included in the base station  10 . 
     To sum up, in a mobile communication apparatus and a mobile communication method according to the present invention, the k-th mobile station  20 ,  22 , . . . , or  24  feeds physical space information instead of long-term information back to the base station  10 . Thus, the amount of feedback information is reduced. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.