Abstract:
[Problem] To provide a wireless communication system, a base station, and a control method, whereby it is possible for the base station to control an active antenna transmission beam wherein an upstream reference signal is used. [Solution] A wireless communication system comprises a first base station further comprising an active antenna, and a second base station which is adjacent to the first base station. Using an upstream reference signal from a wireless terminal, the second base station estimates a direction of the wireless terminal with respect to the second base station, and transmits direction information which is the estimated result and location information of the second base station to the first base station. The first base station receives the direction information and the location information of the second base station, and, on the basis of the direction information, the location information of the second base station, and location information of the first base station, controls a transmission beam of the active antenna of the first base station.

Description:
TECHNICAL FIELD 
       [0001]    The disclosure of the present description relates to a wireless communication system, a base station, and a control method, and relates particularly to control of a transmission beam of an active antenna. 
       BACKGROUND ART 
       [0002]    To increase wireless capacity and to improve throughput, the parallel use of multiple base stations, for example, a system combining transmission base stations, has been proposed (e.g., NPL 1). 
         [0003]    PTLs 1 and 2 each disclose a control method in which a base station including an active antenna system estimates the location of a terminal and controls an antenna beam so that the antenna beam is to be directed to the terminal, thereby reducing inter-beam interference in the downlink and consequently increasing the efficiency in communication with the terminal. 
       CITATION LIST 
     Patent Literature 
       [0004]    [PTL 1] Japanese Unexamined Patent Application Publication No. 2001-127699 
         [0005]    [PTL 2] Japanese Unexamined Patent Application Publication No. 
         [0006]    2008-294728 
       Non Patent Literature 
       [0007]    [NPL 1] Proposal for concept of “Small Cell Enhancements” for Release 12 put forward in 3GPP Workshop (3GPP Workshop on Release 12 and onwards Ljubljana, Slovenia, Jun. 11 to 12, 2012 “Requirements, Candidate Solutions &amp; Technology Roadmap for LTE Rel-12 Onward) URL: “http://www.3gpp.org/Future-Radio-in-3GPP-300-attend” 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    However, transmission base stations each including an active antenna normally do not have the function of carrying out transmission path estimation by receiving a reference signal of an uplink control channel. For this reason, it is difficult for such a transmission base station to control a transmission beam of the active antenna by way of transmission path measurement using an uplink reference signal. 
         [0009]    In view of the above problem, an aim of exemplary embodiments of the present invention is to provide a wireless communication system, a base station, and a control method that enable the base station including an active antenna to control a transmission beam of the active antenna by use of an uplink reference signal. Note that, however, the above-described aim is merely one of multiple aims that the exemplary embodiments disclosed in the present description attempt to achieve. The other aims, or other problems and new aspects, are made apparent through the following description and the accompanying drawings. 
       Solution to Problem 
       [0010]    A wireless communication system according to an exemplary embodiment includes: a first base station including an active antenna; and a second base station, which is an adjacent base station of the first base station. The second base station estimates, by use of an uplink reference signal from a wireless terminal, a direction of the wireless terminal with respect to the second base station, and transmits direction information, which is a result of the estimation, and location information of the second base station, to the first base station. The first base station receives the direction information and the location information of the second base station, and controls a transmission beam of the active antenna of the first base station on the basis of the direction information, the location information of the second base station, and location information of the first base station. 
         [0011]    A base station according to an exemplary embodiment includes: an active antenna; an interface connected to a second base station which is an adjacent base station of the base station; and an active antenna system configured to control a transmission beam of the active antenna. The interface receives, from the second base station, direction information of a wireless terminal with respect to the second base station, the direction information being estimated by the second base station by use of an uplink reference signal from the wireless terminal, and location information of the second base station. The control of the transmission beam of the active antenna is performed on the basis of the direction information, the location information of the second base station, and location information of the base station itself. 
         [0012]    A control method of a base station according to an exemplary embodiment controls a transmission beam of an active antenna included in the base station. In the control method, direction information of a wireless terminal with respect to a second base station, the direction information being estimated by the second base station by use of an uplink reference signal from the wireless terminal, and location information of the second base station are received from the second base station. In the control method, control of a transmission beam of the active antenna is performed on the basis of the direction information, the location information of the second base station, and location information of the base station itself. 
         [0013]    A wireless communication system according to an exemplary embodiment includes: a first base station including an active antenna; a second base station, which is an adjacent base station of the first base station; and a control device connected to the first base station and the second base station. The first base station transmits location information of the first base station to the control device. The second base station estimates, by use of an uplink reference signal from a wireless terminal, a direction of the wireless terminal with respect to the second base station, and transmits direction information, which is a result of the estimation, and location information of the second base station, to the control device. The control device receives the location information of the first base station, the direction information, and the location information of the second base station, estimates location of the wireless terminal on the basis of the direction information, the location information of the second base station, and the location information of the first base station, and transmits estimated location information, which is a result of the estimation, to the first base station. The first base station controls the transmission beam of the active antenna on the basis of the estimated location information. 
       Advantageous Effects of the Invention 
       [0014]    According to the exemplary embodiments of the present invention, by using direction information of a wireless terminal estimated by an adjacent base station by use of an uplink reference signal from the terminal, a base station, which is different from the adjacent base station, controls a transmission beam of an active antenna included in the base station itself. In this way, the base station can control a transmission beam of the active antenna by use of an uplink reference signal. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a configuration diagram illustrating a wireless communication system for explaining control of a transmission beam according to an exemplary embodiment. 
           [0016]      FIG. 2  is a block diagram illustrating a functional configuration of a base station in the wireless communication system according to the exemplary embodiment. 
           [0017]      FIG. 3  is a schematic diagram illustrating an example of a method of measuring location of a terminal according to the exemplary embodiment. 
           [0018]      FIG. 4  is a block diagram illustrating a functional configuration of a base station included in a wireless communication system according to another exemplary embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    Concrete exemplary embodiments are described below in detail with reference to the drawings. The same or corresponding elements are denoted by the same reference signs throughout the respective drawings, and, for clear illustration, explanation of such elements is omitted where appropriate to avoid overlap. 
         [0020]    The multiple exemplary embodiments described below may be implemented individually or by being combined appropriately. The multiple exemplary embodiments have new features which are different from each other. Hence, the multiple exemplary embodiments contribute to achieving different aims or solving different problems, and to bringing about different effects. 
         [0021]    According to one of the exemplary embodiments, a base station including an active antenna forms a transmission beam pattern of the active antenna by using incoming wave direction information of an uplink reference signal received by an adjacent base station from a terminal, the incoming wave direction information being shared by the base stations. This exemplary embodiment is described below in detail. 
       1. System Configuration 
       [0022]    As illustrated in  FIG. 1 , a wireless communication system according to the exemplary embodiment includes a base station  10 , a base station  20 , and a base station  30 . The base stations  10  and  20  are adjacent base stations that are adjacent to the base station  30 . The base station  10  controls a cell Ca, and has a geographical location La (coordinates) and a height ha from a reference height (height above the sea level in this example). Similarly, the base station  20  controls a cell Cb, and has a geographical location Lb (coordinates) and a height hb from the reference height (height above the sea level in this example). The base station  30  controls a cell Cc, and has a geographical location Lc (coordinates) and a height he from a reference height (height above the sea level in this example). The base station  30  may be a base station under the control of the adjacent base station  10  or  20 . The cell Cc of the base station  30  is a small cell that is smaller in size than each of the cells Ca and Cb of the base stations  10  and  20  and is also called a microcell or a picocell. 
         [0023]    Each of the base stations  10  and  20  includes a transceiver capable of transmitting and receiving control signals and data to and from a wireless communication terminal  40  (referred to as a terminal  40  below) movable in a cell or between cells. In contrast, the base station  30  is configured to operate in a downlink transmission mode. As is described later, the base station  30  can be used exclusively for downlink data transmission to the terminal  40  via the active antenna. As is also described later, the base stations  10 ,  20 , and  30  can communicate with each other via an exchange or a network. 
         [0024]    In  FIG. 2 , the base station  10  includes multiple antennas  100 , and includes a transceiver unit  101 , a demodulation processing unit  102 , a central processing control unit  103 , a network interface  104 , and an incoming wave estimation unit  105 . Note that, however,  FIG. 2  only illustrates the configuration related to this exemplary embodiment, and other components, for example, a scheduler and the like, are omitted here. The base station  20  also has a similar configuration to that of the base station  10 . Specifically, the base station  20  includes multiple antennas  200 , and includes a transceiver unit  201 , a demodulation processing unit  202 , a central processing control unit  203 , a network interface  204 , and an incoming wave estimation unit  205 . Note that, also in this case,  FIG. 2  only illustrates the configuration related to this exemplary embodiment, and other components, for example, a scheduler and the like, are omitted. Equivalent functions to those of the demodulation processing unit  102 , the central processing control unit  103 , and the incoming wave estimation unit  105  of the base station  10  may be implementable by executing a program stored in an unillustrated memory on a computer. Similarly, equivalent functions to those of the demodulation processing unit  202 , the central processing control unit  203 , and the incoming wave estimation unit  205  of the base station  20  may be implementable by executing a program stored in an unillustrated memory on a computer. 
         [0025]    The base station  30  includes an active antenna system (referred to as an AAS below)  301 , which adjusts an active antenna  300 , a modulation processing unit  302 , a central processing control unit  303 , a network interface  304 , a terminal location estimation unit  305 , and an AAS control unit  306 . 
         [0026]    The AAS  301  can form a beam pattern having desired directivity, by setting transmission radio frequency (RF) signals of multiple element antennas of the active antenna  300  to have certain phase differences and gain differences. Equivalent functions of the modulation processing unit  302 , the central processing control unit  303 , the terminal location estimation unit  305 , and the AAS control unit  306  of the base station  30  can be implemented by executing a program stored in an unillustrated memory on a computer. 
         [0027]    It is assumed that the base stations  10 ,  20 , and  30  can communicate with each other via a network  50 . Operations of the base stations  10 ,  20 , and  30  illustrated in  FIG. 2  are described below. 
       2. Operation for Controlling Transmission Beam Pattern 
       [0028]    In  FIG. 2 , the base station  10  receives a control channel from the terminal  40  via the multiple antennas  100  and the transceiver unit  101 . The modulation processing unit  102  extracts an uplink reference signal (or a pilot signal) from the received uplink control channel and outputs the uplink reference signal to the incoming wave estimation unit  105 . The incoming wave estimation unit  105  estimates the direction from which the uplink reference signal has arrived, and outputs incoming wave direction information of the signal to the central processing control unit  103 . The central processing control unit  103  transmits direction estimation information (Da, La, ha), which includes incoming wave direction information Da indicating the direction of the signal from the terminal  40 , and the location information La and the height information ha of the base station  10  itself, to the base station  30  via the network interface  104  and the network  50 . 
         [0029]    The basic configuration and operation of the base station  20  are similar to those of the base station  10 . The central processing control unit  203  transmits direction estimation information (Db, Lb, hb), which includes incoming wave direction information Db indicating the direction of the signal from the terminal  40 , and the location information Lb and the height information hb of the base station  20  itself, to the base station  30  via the network interface  204  and the network  50 . 
         [0030]    The base station  30  receives the direction estimation information (Da, La, ha) and the direction estimation information (Db, Lb, hb) from the base stations  10  and  20  via the network interface  304  and the network  50 , respectively. The central processing control unit  303  outputs the received direction estimation information (Da, La, ha) and direction estimation information (Db, Lb, hb) to the terminal location estimation unit  305 . 
         [0031]    The terminal location estimation unit  305  estimates the location and direction of the terminal  40  with respect to the base station  30  itself on the basis of the direction estimation information (Da, La, ha) from the adjacent base station  10  and the direction estimation information (Db, Lb, hb) from the adjacent base station  20  as well as the location information Lc and the height information he of the base station  30  itself, and outputs obtained estimation values to the AAS control unit  306 . The AAS control unit  306  generates an AAS control signal on the basis of the direction of the terminal  40  and the distance of the terminal  40  from the base station  30  itself and outputs the AAS control signal to the AAS  301 . The AAS  301  forms a directional beam pattern directed to the terminal  40  by setting transmission RF signals of the multiple element antennas of the active antenna  300  to have certain phase differences and gain differences, according to the AAS control signal. 
         [0032]    In this way, the base station  30  can form a directional beam pattern of the active antenna  300  so that the beam pattern is directed to the terminal  40 , on the basis of the geographical coordinates and heights above the sea level of the adjacent base stations  10  and  20  as well as the information on the directions of the respective adjacent base stations  10  and  20  with respect to the terminal  40 . Hence, the base station  30  is capable of controlling the directivity of the active antenna  300  by way of transmission path measurement using an uplink reference signal. 
         [0033]    The terminal location estimation unit  305  can estimate the terminal location on the triangulation principle. For example, assume, as illustrated in  FIG. 3 , that the distance between the base station  10  and the base station  20  is  1 , the angle of the incoming wave direction information Da of the base station  10  with respect to the direction in which the base station  20  is located is α, and the angle of the incoming wave direction information Db of the base station  20  with respect to the direction in which the base station  10  is located is β. In this case, the distance d of the terminal  40  from the straight line joining the base stations  10  and  20  is obtained according to Eq. (1) below. Eq. (1) can be turned into Eq. (3) by use of Eq. (2). 
         [0000]    
       
         
           
             
               
                 
                   
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         [0034]    The distance  1  between the base station  10  and the base station  20  can be calculated using the coordinates La and Lb of the base stations  10  and  20 , which are known. In other words, the location of the terminal  40  can be estimated only by detecting the directions a and  13  of the terminal  40  with respect to the respective adjacent base stations  10  and  20  on the basis of uplink reference signals. 
         [0035]    As described above, according to this exemplary embodiment, the base station  30  operating in the downlink transmission mode can control the active antenna  300  so as to form a beam pattern directed to the terminal  40 , by using the incoming wave estimation information obtained at the adjacent base stations  10  and  20 , the incoming wave estimation information being shared by the base stations. In other words, the base station  30  can control a transmission beam pattern of the active antenna without performing transmission path estimation based on a reference signal of an uplink control signal. Specifically, a base station including an active antenna and operating in the downlink transmission mode forms a transmission beam pattern of the active antenna so that the beam pattern is directed to the location of a terminal estimated on the basis of incoming wave direction information of an uplink reference signal received by an adjacent base station from the terminal, on the basis of the location of the terminal. In this way, a downlink base station can control antenna&#39;s directivity by use of an uplink reference signal. 
       3. Other Embodiments 
       [0036]    The above-described exemplary embodiment illustrates, as a general structure of base stations, the case in which the base stations  10 ,  20 , and  30  are connected to each other via the host network  50  as illustrated in  FIG. 2 . Alternatively, adjacent base stations may be connected, for example, by a dedicated line. Connection by a dedicated line reduces network delay, consequently enabling to form a beam pattern in such a manner as to be excellent in following performance with respect to the movement of the terminal  40 . 
         [0037]    In  FIG. 2 , the base station  30  shares the incoming wave direction information from the two adjacent base stations  10  and  20 . However, the present invention is not limited to this configuration. 
         [0038]    For example, the base station  30  may control the active antenna  300  so as to form a beam pattern directed to the terminal  40 , on the basis of the incoming wave estimation information obtained from at least one of the adjacent base stations  10  and  20 . This configuration is described in more detail. 
         [0039]    The base station  10  receives a control channel from the terminal  40  via the multiple antennas  100  and the transceiver unit  101 . The demodulation processing unit  102  extracts an uplink reference signal (or a pilot signal) from the received uplink control channel and outputs the uplink reference signal to the incoming wave estimation unit  105 . The incoming wave estimation unit  105  estimates the direction from which the uplink reference signal has arrived, and outputs the incoming wave direction information to the central processing control unit  103 . The central processing control unit  103  transmits direction estimation information (Da, La, ha) including the incoming wave direction information Da indicating the direction of the signal from the terminal  40 , and the location information La and the height information ha of the base station  10  itself to the base station  30  via the network interface  104  and the network  50 . 
         [0040]    The base station  30  receives the direction estimation information (Da, La, ha) from the base station  10  via the network interface  304  and the network  50 . The central processing control unit  303  outputs the received direction estimation information (Da, La, ha) to the terminal location estimation unit  305 . The terminal location estimation unit  305  estimates the location and direction of the terminal  40  with respect to the base station  30  itself on the basis of the direction estimation information (Da, La, ha) of the adjacent base station  10  as well as the location information Lc and height information he of the base station  30  itself, and outputs an obtained estimation value to the AAS control unit  306 . The AAS control unit  306  generates an AAS control signal on the basis of the direction of the terminal  40  and the distance of the terminal  40  from the base station  30  itself and outputs the AAS control signal to the AAS  301 . The AAS  301  forms a directional beam pattern directed to the terminal  40 , by setting transmission RF signals of the multiple element antennas of the active antenna  300  to have certain phase differences and gain differences, according to the AAS control signal. In this way, the base station  30  can form the directional beam pattern of the active antenna  300  so that the beam pattern is directed to the terminal  40 , on the basis of the geographical coordinates and the height above the sea level of the adjacent base station  10  and the information on the direction of the adjacent base station with respect to the terminal  40 . In other words, the base station  30  can control the directivity of the active antenna  300  by way of transmission path measurement using an uplink reference signal. 
         [0041]    The use of a larger number of adjacent base stations, for example, makes it possible to improve the accuracy of forming a beam directed to the terminal  40 . 
         [0042]    Alternatively, as illustrated in  FIG. 4 , a control device  60  may be connected to the network  50 . The control device  60  may receive direction estimation information (Da, La, ha) of the adjacent base station  10 , direction estimation information (Db, Lb, hb) of the adjacent base station  20 , and location information Lc and height information he of the base station  30 , estimates the location and direction of the terminal  40  with respect to the base station  30 , and transmits obtained estimation values to the base station  30 . In this case, the terminal location estimation unit  305  of the base station  30  is unnecessary. 
         [0043]    The invention of the present application is described above with reference to the exemplary embodiments. However, the invention of the present application is not limited to the above-described exemplary embodiments. Various changes understandable by those skilled in the art can be made to the configuration and details of the invention of the present application within the scope of the invention of the present application. 
         [0044]    (Supplementary Notes) 
         [0045]    The scope of the present invention is not limited to the exemplary embodiments illustrated in the drawings and described above and includes all the exemplary embodiments possible to bring about the effects equivalent to those aimed by the present invention. In addition, the scope of the present invention may be defined by desired combinations of certain ones of all the disclosed aspects. 
         [0046]    It is also possible to describe some of or all the above-described exemplary embodiments as in the following supplementary notes. Note, however, that each of the following supplementary notes is merely an example of the present invention, and the present invention is not limited only to the following cases. 
       (Supplementary Note 1) 
       [0047]    A wireless communication system including multiple base stations, wherein 
         [0048]    the wireless communication system includes a base station including an active antenna and configured to operate in a downlink transmission mode, and at least two adjacent base stations connected to the base station, 
         [0049]    each of the adjacent base stations estimates, by use of an uplink reference signal from a wireless terminal, a direction of the wireless terminal and notifies the base station of the estimated direction information of the wireless terminal together with location information of the adjacent base station, and 
         [0050]    the base station controls a transmission beam pattern of the active antenna of the base station so that the transmission beam pattern is to be directed to the wireless terminal, on the basis of the location information of each of the adjacent base stations and the base station, and the direction information of the wireless terminal estimated by each of the adjacent base stations. 
       (Supplementary Note 2) 
       [0051]    A method of controlling a transmission beam pattern in a wireless communication system including multiple base stations, wherein the wireless communication system includes a base station including an active antenna and configured to operate in a downlink transmission mode, and at least two adjacent base stations connected to the base station, 
         [0052]    the control method including: 
         [0053]    each of the adjacent base stations estimating, by use of an uplink reference signal from a wireless terminal, a direction of the wireless terminal and notifying the base station of the estimated direction information of the wireless terminal, and 
         [0054]    the base station controlling a transmission beam pattern of the active antenna of the base station so that the transmission beam pattern is to be directed to the wireless terminal, on the basis of the location information of each of the adjacent base stations and the base station, and the direction information of the wireless terminal estimated by each of the adjacent base stations. 
       (Supplementary Note 3) 
       [0055]    A base station configured to operate in a downlink transmission mode in a wireless communication system, the base station including: 
         [0056]    an active antenna; 
         [0057]    a communication means that receives, from each of at least two adjacent base stations, direction information of a wireless terminal estimated by each of the adjacent base stations by use of an uplink reference signal from the wireless terminal; 
         [0058]    a terminal location estimation means that estimates location of the wireless terminal on the basis of location information of each of the adjacent base stations and the base station, and the direction information of the wireless terminal estimated by each of the adjacent base stations; and 
         [0059]    an active antenna control means that controls a transmission beam pattern of the active antenna so that the transmission beam pattern is to be directed to the wireless terminal, on the basis of the estimated location information of the wireless terminal. 
       (Supplementary Note 4) 
       [0060]    A method of controlling a transmission beam pattern of a base station including an active antenna and configured to operate in a downlink transmission mode, the method including: 
         [0061]    receiving, from each of at least two adjacent base stations, direction information of a wireless terminal estimated by the adjacent base station by use of an uplink reference signal from the wireless terminal; 
         [0062]    estimating location of the wireless terminal on the basis of location information of each of the adjacent base stations and the base station, and the direction information of the wireless terminal estimated by each of the adjacent base stations; and 
         [0063]    controlling a transmission beam pattern of the active antenna so that the transmission beam pattern is to be directed to the wireless terminal, on the basis of the estimated location information of the wireless terminal. 
       (Supplementary Note 5) 
       [0064]    A program for causing a computer to function as a base station including an active antenna and configured to operate in a downlink transmission mode, the program causing the computer to implement: 
         [0065]    a communication function of receiving, from each of at least two adjacent base stations, direction information of a wireless terminal estimated by each of the adjacent base stations by use of an uplink reference signal from the wireless terminal; 
         [0066]    a terminal location estimation function of estimating location of the wireless terminal on the basis of location information of each of the adjacent base stations and the base station, and the direction information of the wireless terminal estimated by each of the adjacent base stations; and 
         [0067]    an active antenna control function of controlling a transmission beam pattern of the active antenna so that the transmission beam pattern is to be directed to the wireless terminal, on the basis of the estimated location information of the wireless terminal. 
       (Supplementary Note 6) 
       [0068]    A wireless communication system in which multiple base stations are connected to a network, the wireless communication system including: 
         [0069]    a base station including an active antenna and configured to operate in a downlink transmission mode; 
         [0070]    at least two adjacent base stations connected to the base station; and 
         [0071]    a control device connected to the network, wherein 
         [0072]    each of the adjacent base stations estimates a direction of a wireless terminal by use of an uplink reference signal from the wireless terminal and notifies the control device of the estimated direction information of the wireless terminal together with location information of the adjacent base station, 
         [0073]    the base station notifies the control device of location information of the base station itself, 
         [0074]    the control device estimates location of the wireless terminal on the basis of the location information of each of the adjacent base stations and the base station, and the direction information of the wireless terminal estimated by each of the adjacent base stations, and notifies the base station of the estimated location information, and 
         [0075]    the base station controls a transmission beam pattern of the active antenna so that the transmission beam pattern is to be directed to the wireless terminal, on the basis of the estimated location information of the wireless terminal notified by the control device. 
       (Supplementary Note 7) 
       [0076]    A method of controlling a transmission beam pattern in a wireless communication system including multiple base stations, wherein the wireless communication system includes a base station including an active antenna and configured to operate in a downlink transmission mode, at least two adjacent base stations connected to the base station, and a control device connected to the network, the control method including: 
         [0077]    each of the adjacent base stations estimating a direction of a wireless terminal by use of an uplink reference signal from the wireless terminal, and notifying the control device of the estimated direction information of the wireless terminal together with location information of the adjacent base station, 
         [0078]    the base station notifying the control device of location information of the base station itself, 
         [0079]    the control device estimating location of the wireless terminal on the basis of the location information of each of the adjacent base stations and the base station, and the direction information of the wireless terminal estimated by each of the adjacent base stations, and notifying the base station of the estimated location information, and 
         [0080]    the base station controlling a transmission beam pattern of the active antenna so that the transmission beam pattern is to be directed to the wireless terminal, on the basis of the estimated location information of the wireless terminal notified by the control device. 
         [0081]    The present application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-144536, filed on Jul. 10, 2013, the disclosure of which is incorporated herein in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0082]    The exemplary embodiments of the present invention are each applicable to a mobile communication system in which multiple base stations are located. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10 ,  20  base station (adjacent base station) 
           30  base station (base station for downlink) 
           40  terminal 
           50  network 
           101 ,  201  transceiver unit 
           102 ,  202  demodulation processing unit 
           103 ,  203  central processing control unit 
           104 ,  204  network interface 
           105 ,  205  incoming wave estimation unit 
           301  AAS (active antenna system) 
           302  modulation processing unit 
           303  central processing control unit 
           304  network interface 
           305  terminal location estimation unit 
           306  AAS control unit