Abstract:
The present disclosure relates to a pre-5 th -Generation (5G) or 5G communication system to be provided for supporting higher data rates beyond 4 th -Generation (4G) communication system such as Long Term Evolution (LTE). Embodiments of the present invention provide a method and an apparatus for adaptively determining a beam sweeping pattern of a base station in a beamforming-based wireless communication system. An embodiment of the present invention provides an operating method of a serving base station in a wireless communication system, the operating method comprising: receiving, from at least one terminal, beam collision information indicating a collision between beams received from the serving base station and at least one neighboring base station adjacent to the serving base station; and adjusting a beam sweeping pattern of a beam transmitted to the at least one terminal on the basis of the received beam collision information. Various other embodiments of the present invention are also disclosed.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a wireless communication system using a beamforming technology. 
       BACKGROUND ART 
       [0002]    To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. 
         [0003]    The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. 
         [0004]    In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. 
         [0005]    In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed. 
         [0006]    A wireless communication system supporting beamforming is one of the next generation communication technologies for processing heavily increasing wireless data traffic. The beamforming-based wireless communication system uses a high frequency area when transmitting a signal and, accordingly, may integrate a plurality of antennas into a base station and a terminal. The base station and the terminal may perform beamforming to make a big beamforming gain in a particular direction through a large number of antennas. The beamforming-based wireless communication system may perform a beam sweeping operation of transmitting or receiving signals while changing a plurality of beams. 
       DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
       [0007]    Accordingly, embodiments of the present invention have been made to provide a method and an apparatus for adaptively determining a beam sweeping pattern of a base station in a beamforming-based wireless communication system. 
         [0008]    Embodiments of the present invention have been made to provide a method and an apparatus for dynamically adjusting a beam sweeping pattern in order to reduce beam interference between base stations in a beamforming-based wireless communication system. 
         [0009]    Embodiments of the present invention have been made to provide a method and an apparatus for adaptively determining a beam sweeping pattern of a base station to improve accuracy of channel estimation and increase a success rate of channel reception in a beamforming-based wireless communication system. 
       Technical Solution 
       [0010]    According to an embodiment of the present invention, an operation method of a serving base station in a wireless communication system includes: receiving beam collision information indicating a collision of beams received from the serving base station and at least one neighboring base station adjacent to the serving base station from at least one terminal; and adjusting a beam sweeping pattern of a beam transmitted to the at least one terminal based on the received beam collision information. 
         [0011]    According to another embodiment of the present invention, an operation method of a serving base station in a wireless communication system includes: receiving beam collision information indicating a collision of beams received from the serving base station and at least one neighboring base station adjacent to the serving base station from at least one terminal; detecting a beam collision based on the received beam collision information; transmit a request for adjusting a beam sweeping pattern to a central control station when the beam collision is detected; receiving a result of the adjustment of the beam sweeping pattern from the central control station in response to the request; and transmitting the result of the adjustment of the beam sweeping pattern to the at least one terminal. 
         [0012]    According to another embodiment of the present invention, an operation method of a central control station in a wireless communication system includes: receiving, from a serving base station, a request for adjusting a beam sweeping pattern indicating that a collision between beams received from the serving base station and at least one neighboring base station among a plurality of base stations is detected, by at least one terminal; adjusting a beam sweeping pattern of a beam transmitted to the at least one terminal in response to the request for adjusting the beam sweeping pattern; and transmitting a result of the adjustment of the beam sweeping pattern to the serving base station and the neighboring base station. 
         [0013]    According to another embodiment of the present invention, an operation method of at least one terminal in a wireless communication system includes: generating beam collision information indicating a collision between beams received from a serving base station and at least one neighboring base station adjacent to the serving base station; and transmitting the generated beam collision information to the serving base station. 
         [0014]    According to another embodiment of the present invention, a serving base station apparatus of a wireless communication system includes: a transmitter; a receiver; and a controller. The receiver receives, from at least one terminal, beam collision information indicating a collision of beams received from the serving base station and at least one neighboring base station adjacent to the serving base station. The controller adjusts the beam sweeping pattern of the beam transmitted to at least one terminal based on the received beam collision information. 
         [0015]    According to another embodiment of the present invention, a serving base station apparatus of a wireless communication system includes: a transmitter; a receiver; and a controller. The receiver receives, from at least one terminal, beam collision information indicating a collision of beams received from the serving base station and at least one neighboring base station adjacent to the serving base station. The controller detects the beam collision based on the received beam collision information and, when the beam collision is detected, transmit a request for adjusting the beam sweeping pattern to a central control station. The receiver receives a result of the adjustment of the beam sweeping pattern from the central control station in response to the request. The transmitter transmits the result of the adjustment of the beam sweeping pattern to at least one terminal. 
         [0016]    According to another embodiment of the present invention, a central control station apparatus of a wireless communication system includes: a transmitter; a receiver; and a controller. The receiver receives, from the serving base station, a beam sweeping pattern adjusting request indicating that the collision between beams received from the serving base station and at least one neighboring base station adjacent to the serving base station among a plurality of base stations is detected in at least one terminal. The controller adjusts the beam sweeping pattern of the beam transmitted to at least one terminal in response to the beam sweeping pattern adjusting request. The transmitter transmits the beam sweeping pattern adjusting request to the serving base station and the neighboring base station. 
         [0017]    According to another embodiment of the present invention, at least one terminal apparatus of a wireless communication system includes: a transmitter; a receiver; and a controller. The controller generates beam collision information indicating a collision of beams received from the serving base station and at least one neighboring base station adjacent to the serving base station. The transmitter transmits the generated beam collision information to the serving base station. 
       Effects of the Invention 
       [0018]    According to embodiments of the present invention, it is possible to improve accuracy of channel station estimation using a reference signal and to increase a success rate of reception of a synchronization channel or a broadcast channel by adaptively determining a beam sweeping pattern in a beamforming-based wireless communication system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The following description is made with reference to the accompanying drawings for a more complete understanding of the present invention and effects thereof, and the same reference numerals indicate the same parts. 
           [0020]      FIG. 1  illustrates an example in which a base station operates different beams in a beamforming-based wireless communication system; 
           [0021]      FIGS. 2A to 2C  illustrate examples of resources which can be used when a signal is carried on a particular beam and transmitted in the beamforming-based wireless communication system; 
           [0022]      FIG. 3  illustrates an example of a transmission frame structure in the beamforming-based wireless communication system; 
           [0023]      FIGS. 4 to 5  illustrate examples of a collision between base station beams received by a terminal; 
           [0024]      FIGS. 6A and 6B  illustrate examples of a distributed beam sweeping pattern adjusting procedure according to an embodiment of the present invention; 
           [0025]      FIG. 7  illustrates an example of a processing flow of the base station for the procedure of adjusting the distributed beam sweeping pattern according to an embodiment of the present invention; 
           [0026]      FIG. 8  illustrates an example of a processing flow of the terminal for the distributed beam sweeping pattern adjusting procedure according to an embodiment of the present invention; 
           [0027]      FIGS. 9A and 9B  illustrate examples of the centralized beam sweeping pattern adjusting procedure according to another embodiment of the present invention; 
           [0028]      FIG. 10  illustrates an example of a processing flow of the base station for the centralized beam sweeping pattern adjusting procedure according to another embodiment of the present invention; 
           [0029]      FIG. 11  illustrates an example of a processing flow of the central control station for the centralized beam sweeping pattern adjusting procedure according to another embodiment of the present invention; 
           [0030]      FIGS. 12A and 12B  illustrate examples of a block diagram of the base station for the beam sweeping pattern adjusting procedure according to embodiments of the present invention; 
           [0031]      FIG. 13  illustrates an example of a block diagram of the terminal for the beam sweeping pattern adjusting procedure according to embodiments of the present invention; and 
           [0032]      FIG. 14  illustrates an example of a block diagram of the central control station for the beam sweeping pattern adjusting procedure according to embodiments of the present invention. 
       
    
    
     MODE FOR CARRYING OUT THE INVENTION 
       [0033]    In this patent specification,  FIGS. 1 to 14  used for describing principles of the present invention are merely for examples and should not be interpreted to limit the scope of the present invention. Those skilled in the art can understand that the principles of the present invention can be implemented in any properly arranged beamforming-based wireless communication system. 
         [0034]    In the beamforming-based wireless communication system, a base station and a terminal operate a plurality of beams. At this time, the base station helps the terminal in measuring a channel state of each beam by transmitting a reference signal for each beam. For example, when the terminal informs the base station of an optimum transmission beam index of the base station, the base station transmits data to the corresponding terminal through the optimum transmission beam. 
         [0035]    A synchronization channel corresponds to a channel for synchronization between the base station and the terminal. For example, the terminal may synchronize frames/subframes and orthogonal frequency division multiplexing (OFDM) symbols with the base station through the synchronization channel. In the beamforming system, the same synchronization channel may be transmitted in different directions through a plurality of transmission beams. 
         [0036]    A broadcast channel corresponds to a channel that makes the terminal acquire system information from the base station. Similar to the synchronization channel, the broadcast channel may be transmitted in different directions through a plurality of transmission beams in the beamforming-based wireless communication system. 
         [0037]    As a special example of the beamforming-based wireless communication system, a system using a fixed beam when transmitting a data channel may be considered. That is, the base station may map in advance each beam for the data channel to a particular resource (time, frequency, orthogonal code, or the like) and then use the beam but does not dynamically change the mapped beam. 
         [0038]    If beam directions of the reference signal, the synchronization channel, the broadcast channel, the data channel, and the like beamformed and transmitted by a plurality of neighboring base stations overlap each other, an error of channel state information measured in the reference signal may become large and a failure probability of a decoding of information on the synchronization channel and the broadcast channel may increase. Accordingly, if possible beams between base stations should not overlap each other. 
         [0039]    Meanwhile, in the next generation communication system, the base station may be irregularly installed and a lot of small cells may exist. Particularly, the base station may be frequently turned off or on in a self-organizing network (SON) environment and, in this case, an interference environment between beams may change. As described above, in an environment in which a network dynamically changes, it is difficult to find and fix an optimum beam sweeping pattern of each base station. Accordingly, it is required to dynamically adjust a beam sweeping pattern of each base station to make an amount of inter-beam interference minimal. 
         [0040]    Hereinafter, a method and an apparatus for adaptively determining a beam sweeping pattern of a base station to reduce inter-base station beam interference in the beamforming-based wireless communication system will be described according to embodiments of the present invention. 
         [0041]    In the description of embodiments of the present invention, the beam is defined by elements such as a beam width, a beam direction (or an array antenna element weight), beam power, and the like, and the beam sweeping pattern refers to mapping between the beam and resources used for carrying signals on one or more beams to transmit the signals. Resources used for carrying a signal on a particular beam to transmit the signal include a time, frequency, orthogonal code, and the like. 
         [0042]      FIG. 1  illustrates an example in which a base station operates different beams in a beamforming-based wireless communication system. 
         [0043]    Referring to  FIG. 1 , a base station  100  operates three different beams  11 A,  11 B, and  11 C. The beam  11 A is defined by a beam width (proportional to a length of reference numeral  12 ) of the beam, a beam direction (a direction of reference numeral  13 ), and beam power (proportional to a length of reference numeral  13 ). The beam  11 B and the beam  11 C are also defined in the same way. 
         [0044]      FIGS. 2A to 2C  illustrate examples of resources which can be used when a signal is carried on a particular beam and transmitted in the beamforming-based wireless communication system.  FIG. 2A  illustrates a case  20  where the resources are divided by the time,  FIG. 2B  illustrates a case  30  where the resources are divided by the frequency, and  FIG. 2C  illustrates a case where the resources are divided by the orthogonal code. 
         [0045]    Referring to  FIG. 2A , the base station transmits a total of six different beams to different time symbols  21 ,  22 ,  23 ,  24 ,  25 , and  26  of a corresponding subframe. 
         [0046]    Referring to  FIG. 2B , the base station transmits a total of six different beams to a corresponding subframe by using different subcarriers  31 ,  32 ,  33 ,  34 ,  35 , and  36 . 
         [0047]    Referring to  FIG. 2C , the base station transmits a total of six different beams to a corresponding subframe by using different orthogonal codes  41 ,  42 ,  43 ,  44 ,  45 , and  46 . 
         [0048]      FIG. 3  illustrates an example of a transmission frame structure  50  in the beamforming-based wireless communication system. 
         [0049]    Referring to  FIG. 3 , the frame  50  including a beam reference signal  51 , a synchronization channel  52 , and a broadcast channel  53  has a beam sweeping pattern. The beam reference signal  51  uses a total of six different beams, and the beams occupy different time-frequency domains in the frame  50 . The synchronization channel  52  and the broadcast channel  53  use a total of four different beams, and the beams occupy different time-frequency domains in the frame  50 . The type and number of transmission beams operated according to each signal or channel may be different. 
         [0050]      FIGS. 4 to 5  illustrate examples of collision between base station beams received by the terminal. 
         [0051]    Referring to  FIG. 4 , a beam collision between base stations  100  and  110  occurs. A serving base station  100  of a terminal  200  carries and transmits a downlink signal according to a particular beam sweeping pattern. When the serving base station  100  transmits a beam  61 , the neighboring base station  110  transmits a beam  62  at the same time. If resources (time, frequency, orthogonal code, or the like) used by the beams  61  and  62  are the same, a signal of the beam  62  transmitted by the neighboring base station  110  acts as interference when the terminal  200  receives a signal of the beam  61  transmitted by the serving base station  100 . At this time, if an amount of the interference is large and thus a performance of the terminal  200  significantly deteriorates, it may be considered that a collision occurs between the beam  61  of the base station  100  and the beam  62  of the base station  110 . 
         [0052]    Referring to  FIG. 5 , when the terminal  200  performs reception beamforming, a beam collision between base stations occurs. Reference numeral  100  refers to a serving base station, and reference numerals  110  and  120  refer to adjacent (or neighboring) base stations of the terminal  200 . Each base station carries a downlink signal on a beam to transmit the downlink signal according to a particular beam sweeping pattern. The serving base station  100  transmits a beam  71 , and the adjacent base stations  110  and  120  transmit beams  72  and  73 , respectively, at the same time. The terminal  200  uses an optimum reception beam  74  according to the beam  71  transmitted by the serving base station  100 . At this time, while a signal carried on the beam  73  transmitted by the adjacent base station  120  hardly influences a received signal of the terminal  200 , a signal carried on the beam  72  transmitted by the adjacent base station  110  heavily influences the received signal of the terminal  200 . If an amount of the interference is large and thus a performance of the terminal  200  significantly deteriorates, it may be considered that a collision occurs between the beam  71  of the base station  100  and the beam  72  of the base station  110 . 
         [0053]    The terminal experiencing the beam collision may have deterioration in a synchronization detection performance, a broadcast channel decoding performance, and a beam channel state estimation performance. Accordingly, it is required to adjust the beam sweeping pattern of each base station to minimize the beam collision between base stations. According to embodiments of the present invention, a method of adjusting a beam sweeping pattern includes a distributed type and a centralized type. The distributed beam sweeping pattern adjusting method corresponds to a method by which each base station individually adjusts the beam sweeping pattern. The centralized beam sweeping pattern adjusting method corresponds to a method by which a central control station adjusts beam sweeping patterns of a plurality of base stations. At this time, the central control station may be one of the plurality of base stations or may be an independent control station which is not the base station. In the following description of embodiments, base stations of which beams may generate the collision are base station 1   100 , base station 2   110 , and base station 3   120 , and it is assumed that terminal 1   200  and terminal 2   210  are connected to base station 1   100 . Although it is described that the number of base stations which may generate the beam collision is three herein, two or more base stations are enough as the number of base stations which may generate the beam collision. 
         [0054]      FIGS. 6A and 6B  illustrate examples of a distributed beam sweeping pattern adjusting procedure according to an embodiment of the present invention. Flows illustrated in  FIGS. 6A and 6B  merely correspond to examples for describing the present invention and can be variously changed, and thus should not be interpreted to limit the protection scope of the present invention. 
         [0055]    Referring to  FIG. 6A , base station 1   100  determines whether it is required to adjust a beam sweeping pattern in step S 110 , and starts adjusting the beam sweeping pattern according to a result of the determination. According to an embodiment, base station 1   100  determines that it is required to adjust the beam sweeping pattern when the terminal  200  informs base station 1   100  that a degree of a collision between a particular beam of base station 1   100  and a particular beam of another base station is higher than or equal to a predefined value. According to another embodiment, base station 1   100  determines that it is required to adjust the beam sweeping pattern when the terminal  200  informs base station 1   100  that a possibility of a collision between a particular beam of base station 1   100  and a particular beam of another base station is higher than or equal to a predefined number of times and that a degree of the collision is higher than or equal to a predefined value. Such an example corresponds to an example illustrated in  FIG. 6B . For example, the degree of the collision between beams may be defined by equation (4) described below, and the predefined value may be a threshold value TH B  in equation (4). 
         [0056]    According to another embodiment, base station 1   100  starts adjusting the beam sweeping pattern even when the terminal  200  does not inform base station 1   100  of generation of a beam collision event. Another embodiment may include one of the cases shown in Table 1 below. 
         [0000]    
       
         
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 (i) A case where a base station is installed and a beam sweeping pattern 
               
               
                 is never adjusted. 
               
               
                 (ii) A case where the corresponding base station is turned off from a 
               
               
                 turned on state 
               
               
                 (iii) A case where one or a plurality of neighboring base stations of the 
               
               
                 corresponding base station is turned off 
               
               
                 (iv) A case where one or a plurality of neighboring base stations of the 
               
               
                 corresponding base station is turned on 
               
               
                 (v) A case where one or a plurality of neighboring base stations of the 
               
               
                 corresponding base station changes a beam sweeping pattern 
               
               
                 (vi) A case where a predetermined time elapses after the corresponding 
               
               
                 base station has adjusted the beam sweeping pattern 
               
               
                 (vii) A case where a request for adjusting the beam sweeping pattern is 
               
               
                 received from another base station 
               
               
                   
               
             
          
         
       
     
         [0057]    When it is determined that the sweeping pattern needs to be adjusted, base station 1   100  transmits a beam sweeping pattern adjustment start notification message to neighboring base stations (for example, base station 1   100  and base station 3   120 ) that operate beams which may generate the beam collision with the beam operated by base station 1   100  in operation S 120 . Base station 2   110  and base station 3   120  having received the beam sweeping pattern adjustment start notification message do not change their own beam sweeping pattern until base station 1   100  transmits a beam sweeping pattern adjustment end notification message after ending the beam sweeping pattern adjustment. The reason for this is that base station 1   100  may incorrectly adjust the beam sweeping pattern if base station 2   110  or base station 3   120  changes the beam sweeping pattern while base station 1   100  performs a procedure for adjusting the beam sweeping pattern. 
         [0058]    In step S 130 , base station 1   100  transmits a request for beam collision information to terminal 1   200  and terminal 2   210  connected to base station 1   100 . According to an embodiment, base station 1   100  transmits a request for beam collision information to all terminals connected to base station 1   100 . According to another embodiment, base station 1   100  transmits a request for beam collision information only to a particular terminal which may experience the beam collision. For example, the particular terminal which may experience the beam collision may be a terminal located at a cell boundary. 
         [0059]    Terminal  1   200  and terminal 2   210  having received the request for the beam collision information generate the beam collision information in step S 140 A and step S 140 B, respectively, and report the generated beam collision information to base station 1   100  in step S 150 . 
         [0060]    In step S 160 , base station 1   100  detects whether there is a beam which may generate the collision with beams operated by other base stations among the beams operated by base station 1   100  by using the beam collision information reported from terminal 1   200  and terminal 2   210 . When the beam collision is detected, base station 1   100  adjust the beam sweeping pattern in step S 170 . 
         [0061]    When the adjustment of the beam sweeping pattern is completed, base station 1   100  transmits a beam sweeping pattern adjustment result message to terminal 1   200  and terminal 2   210  in step S 180 . According to an embodiment, base station 1   100  transmits the beam sweeping pattern adjustment result message only to terminals which participate in a procedure of generating the beam collision information and reporting the beam collision information. According to another embodiment, base station 1   100  transmits the beam sweeping pattern adjustment result message also to terminals which do not participate in the procedure of generating the beam collision information and reporting the beam collision information according to a determination of the base station. 
         [0062]    Further, when the adjustment of the beam sweeping pattern is completed, base station 1   100  transmits the beam sweeping pattern adjustment end notification message to base station 2   110  and base station 3   120  in step S 190 . The beam sweeping pattern adjustment end notification message may include some or all of the information shown in Table 2 below. 
         [0000]    
       
         
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                 (i) Fact that the adjustment of the beam sweeping pattern of base station1 
               
               
                 ends 
               
               
                 (ii) Whether base station1 has changed the beam sweeping pattern or not 
               
               
                 (iii) Information on the beam sweeping pattern changed by base station1 
               
               
                   
               
             
          
         
       
     
         [0063]    Referring to  FIG. 6B , when the beam collision event is generated in step S 102 , terminal 1   200  reports the generation of the beam collision event to base station 1   100  as beam collision information in step S 104 . The beam collision event refers to generation of a possibility of the collision between the particular beam of base station 1   100  and the particular beam of the other base station. Base station 1   100  determines whether it is required to adjust the beam sweeping pattern according to a result of the report, and starts adjusting the beam sweeping pattern according to a result of the determination. Here, it is assumed that base station 1   100  starts adjusting the beam sweeping pattern immediately as terminal 1   200  reports the beam collision information by a predetermined number of times. 
         [0064]    Base station 1   100  transmits the beam sweeping pattern adjustment start notification message to neighboring base stations (for example, base station 2   110  and base station 3   120 ) that operate beams which may generate the beam collision with the beam operated by base station 1   100  in step S 120 . Base station 2   110  and base station 3   120  having received the beam sweeping pattern adjustment start notification message do not change their own beam sweeping pattern until base station 1   100  transmits a beam sweeping pattern adjustment end notification message after ending the beam sweeping pattern adjustment. 
         [0065]    In step S 135 , base station 1   100  transmits a request for beam collision information to terminal 1   200  and terminal 2   210  connected to base station 1   100 . Terminal 2   210  having received the request for the beam collision information generates the beam collision information in step S 140 B, and reports the generated beam collision information to base station 1   100  in step S 155 . 
         [0066]    In step S 160 , base station 1   100  detects whether there is a beam which may generate the collision with beams operated by other base stations among the beams operated by base station 1   100  by using the beam collision information reported from terminal  1   200  in step S 104  and the beam collision information reported from terminal 2   210  in step S 155 . When the beam collision is detected, base station 1   100  adjust the beam sweeping pattern in step S 170 . 
         [0067]    When the adjustment of the beam sweeping pattern is completed, base station 1   100  transmits a beam sweeping pattern adjustment result message to terminal 1   200  and terminal 2   210  in step S 180 . Further, when the adjustment of the beam sweeping pattern is completed, base station 1   100  transmits the beam sweeping pattern adjustment end notification message to base station 2   110  and base station 3   120  in step S 190 . 
         [0068]      FIG. 7  illustrates an example of a processing flow of the base station for the distributed beam sweeping pattern adjusting procedure according to an embodiment of the present invention. The processing flow may be performed by base station 1   100  illustrated in  FIGS. 6A and 6B . The flow illustrated in  FIG. 7  merely corresponds to an example for describing the present invention and can be variously changed, and thus should not be interpreted to limit the protection scope of the present invention. 
         [0069]    Referring to  FIG. 7 , base station 1   100  that determines to adjust the beam sweeping pattern transmits a beam sweeping pattern adjustment start message to neighboring base stations in step S 210 . Base station 1   100  transmits a request for beam collision information to the terminal in step  220 , and receives the beam collision information from the terminal in step S 230 . When the beam collision information is received from the terminal, base station 1   100  performs a beam collision detection procedure by using the received information in step S 240 . 
         [0070]    When the beam collision is not detected, base station 1   100  does not change the beam sweeping pattern in step S 260 , transmits a beam sweeping adjustment result message indicating that the beam sweeping pattern has not been changed to the terminal in step S 270 , and transmits a beam sweeping pattern adjustment end message to neighboring base stations to inform that the beam sweeping pattern has not been changed in step S 280 . At this time, a procedure of transmitting the message indicating that the beam sweeping pattern has not been changed to the terminal may be omitted according to cases. 
         [0071]    When the beam collision is detected, base station 1   100  finds an optimum beam sweeping pattern and changes the beam sweeping pattern in step S 260 . At this time, the beam sweeping pattern may not be changed because there is no proper beam sweeping pattern. When the beam sweeping pattern is changed, base station 1   100  transmits a beam sweeping adjustment result message to the terminal in step S 270 , and transmit a beam sweeping pattern adjustment end message to the neighboring base stations in step S 280 . According to an embodiment, the beam sweeping adjustment result message may include only the fact that the beam sweeping pattern has been changed. According to another embodiment, the beam sweeping adjustment result message may include information on the beam sweeping pattern after the change. The beam sweeping pattern adjustment result message may include some or all of the information shown in Table 3 below. 
         [0000]    
       
         
               
             
           
               
                 TABLE 3 
               
               
                   
               
             
             
               
                 (i) Whether a beam sweeping pattern of a base station has been changed 
               
               
                 or not 
               
               
                 (ii) Information on the changed beam sweeping pattern of the base station 
               
               
                 (iii) A time point when the change in the beam sweeping pattern of the 
               
               
                 base station is applied 
               
               
                   
               
             
          
         
       
     
         [0072]      FIG. 8  illustrates an example of a processing flow of the terminal for the distributed beam sweeping pattern adjusting procedure according to an embodiment of the present invention. The processing flow may be performed by terminal  1   200  illustrated in  FIGS. 6A and 6B . The processing flow may be performed equally for the centralized beam sweeping pattern adjusting procedure according to another embodiment of the present invention described below. The flow illustrated in  FIG. 8  merely corresponds to an example for describing the present invention and can be variously changed, and thus should not be interpreted to limit the scope of the present invention. 
         [0073]    Referring to  FIG. 8 , in step S 305 , terminal 1   200  receives a request for beam collision information from a serving base station (for example, base station 1   100 ). When the request for the beam collision information is received from the serving base station, terminal 1   200  estimates signal quality of beams transmitted from the serving base station and neighboring base stations in step S 310 . One of the targets shown in Table 4 below may be determined as the neighboring base station of which the signal quality is estimated. 
         [0000]    
       
         
               
             
           
               
                 TABLE 4 
               
               
                   
               
             
             
               
                 (i) One or a plurality of neighboring base stations specified when a base 
               
               
                 station transmits a request for “beam collision information” 
               
               
                 (ii) Some or all of the base stations included in a neighboring base station 
               
               
                 list (neighboring cell list) broadcasted by the base station 
               
               
                   
               
             
          
         
       
     
         [0074]    For example, the signal quality may be some or a combination of a channel quality indication (CQI), a signal-to-noise ratio (SNR), a signal-to-interference ratio (SIR), a signal-to-interference and noise ratio (SINR), a reference signal received power (RSRP), a reference signal received quality (RSRQ), a reference signal strength indicator (RSSI), and the like. The signal quality may be an instantaneous value or a value averaged for a predetermined time. 
         [0075]    In step S 315 , terminal  1   200  finds a beam having the best signal quality among the beams transmitted by the serving base station and defines the signal quality as S 1 . In step  320 , terminal 1   200  estimates signal quality of beams transmitted by other neighboring base stations at the same resource location as that of resources (time, frequency, orthogonal code, and the like) when the beam having the best signal quality is transmitted by the serving base station to find the best beam, and defines the signal quality as S 2 . 
         [0076]    If the signal quality S 1  is smaller than a predefined threshold value TH A  (No of step S 325 ), terminal 1   200  does not report the beam collision information to base station 1   100  in step S 335 , and waits for receiving a beam sweeping pattern adjustment result from base station 1   100  in step S 340 . 
         [0077]    If the signal quality S 1  is larger than the threshold value TH A  (Yes of step S 325 ), terminal 1   200  determines whether a condition shown in equation (1) below is met in step S 330 . 
         [0000]      ( S   1   −S   2 )/ S   1   &lt;TH   B   (1)
 
         [0078]    When the condition of equation (1) above is met (Yes of step S 330 ), terminal 1   200  transmits the beam collision information to base station 1   100  in step S 335 . In contrast, when the condition of equation (1) above is not met (No of step S 330 ), terminal  1   200  does not transmit the beam collision information to base station 1   100  in step S 335 . 
         [0079]    According to another embodiment, equation (2), equation (3), and equation (4) below may be used instead of equation (1). 
         [0000]      ( S   1   −S   2 )/ S   2   &lt;TH   B   (2)
 
         [0000]        S   1   −S   2   &lt;TH   B   (3)
 
         [0000]        S   2   /S   1   &gt;TH   B   (4)
 
         [0080]    For example, the beam collision information may be one of the information shown in Table 5 below. 
         [0000]    
       
         
               
             
           
               
                 TABLE 5 
               
               
                   
               
             
             
               
                 (i) A quantized value of S 1  and S 2   
               
               
                 (ii) Indexes indicating values of S 1  and S 2   
               
               
                 (iii) A quantized value of (S 1  − S 2 )/S 1 , (S 1  − S 2 )/S 2 , or S 1  − S 2   
               
               
                 (iv) An index indicating a value of (S 1  − S 2 )/S 1 , (S 1  − S 1 )/S 2 , or S 1  − S 2   
               
               
                 (v) A beam index corresponding to S 1   
               
               
                 (vi) A beam index corresponding to S 2  and a neighboring base station 
               
               
                 index 
               
               
                 (vii) A metric indicating a degree of beam collision expressed by a 
               
               
                 predetermined function f(S 1 , S 2 ) of S 1  and S 2   
               
               
                   
               
             
          
         
       
     
         [0081]    According to an embodiment, the threshold voltage TH A  may be determined according to a minimum signal quality value that the terminal having received the request for the beam collision information requires. The threshold value TH A  corresponds to a reference to determine the beam collision. When the value is too large, the beam collision may be determined even though an amount of interference between base stations is small. When the value is too small, the beam collision may not be determined even though an amount of interference between base stations is large. Accordingly, the two threshold values TH A  and TH B  may be determined to minimize overhead due to the beam sweeping pattern adjustment in consideration of the performance of the terminal, a distance between cells, a minimally required signal quality, and the like. 
         [0082]    According to another embodiment, the terminal having received the request for the beam collision information may transmit the beam collision information to base station 1   100  unconditionally without a comparison with the threshold value TH A  or TH B . 
         [0083]    In step S 340 , terminal 1   200  waits for receiving a beam sweeping pattern adjustment result message for a predetermined time. When the beam sweeping pattern adjustment result message is received, terminal 1   200  determines whether the beam sweeping pattern is changed in step S 345 . 
         [0084]    When it is determined that the beam sweeping pattern is changed, terminal 1   200  changes a relevant operation of the terminal according to the changed beam sweeping pattern in step  350 . For example, terminal 1   200  may average signal qualities of the beams over a plurality of symbols or frames. When the beam sweeping pattern of the base station is changed, terminal 1   200  properly changes an interval in which the signal qualities are averaged. 
         [0085]      FIGS. 9A and 9B  illustrate examples of the centralized beam sweeping pattern adjusting procedure according to another embodiment of the present invention. Flows illustrated in  FIGS. 9A and 9B  merely correspond to examples for describing the present invention and can be variously changed, and thus should not be interpreted to limit the scope of the present invention. 
         [0086]    Referring to  FIG. 9A , base station 1   100  determines whether it is required to adjust a beam sweeping pattern in step S 310 , and starts adjusting the beam sweeping pattern according to a result of the determination. According to an embodiment, base station 1   100  determines that it is required to adjust the beam sweeping pattern when the terminal  200  informs base station 1   100  that a possibility of a collision between a particular beam of base station 1   100  and a particular beam of another base station is higher than or equal to a predetermined value. Such an example corresponds to an example illustrated in  FIG. 9B . According to another embodiment, base station 1   100  starts adjusting the beam sweeping pattern even when the terminal  200  does not inform base station 1   100  of generation of a beam collision event. Another embodiment may include one of the cases shown in Table 1 described above. 
         [0087]    When it is determined that the sweeping pattern needs to be adjusted, base station 1   100  transmits a beam sweeping pattern adjustment start notification message to the central control station  300  and neighboring base stations (for example, base station 2   110  and base station 3   120 ) that operate beams which may generate the beam collision with the beam operated by base station 1   100  in step 320 . 
         [0088]    In step S 330 , base station 1   100  transmits a request for beam collision information to terminal 1   200  and terminal 2   210  connected to base station 1   100 . According to an embodiment, base station 1   100  transmits a request for beam collision information to all terminals connected to base station 1   100 . According to another embodiment, base station 1   100  transmits a request for beam collision information only to a particular terminal which may experience the beam collision. For example, the particular terminal which may experience the beam collision may be a terminal located at a cell boundary. 
         [0089]    Terminal 1   200  and terminal 2   210  having received the request for the beam collision information generate the beam collision information in step S 340 A and step S 340 B, respectively, and report the generated beam collision information to base station 1   100  in step S 350 . 
         [0090]    In step S 360 , base station 1   100  detects whether there is a beam which may generate the collision with beams operated by other base stations among the beams operated by base station 1   100  by using the beam collision information reported from terminal 1   200  and terminal 2   210 . When the beam collision is detected, base station 1   100  transmits a request for adjusting the beam sweeping pattern to the central control station  300  in step S 365 . The beam sweeping pattern adjustment request message may include some or all of the information shown in Table 6 below. 
         [0000]    
       
         
               
             
           
               
                 TABLE 6 
               
               
                   
               
             
             
               
                 (i) A beam index of base station1 from which the beam collision is 
               
               
                 detected 
               
               
                 (ii) A beam index of another base station from which the beam collision 
               
               
                 with the beam of base station1 is detected 
               
               
                 (iii) Metric indicating a degree of the beam collision 
               
               
                   
               
             
          
         
       
     
         [0091]    In step S 370 , the central control station  300  adjusts the beam sweeping pattern according to the request of base station 1   100 . For example, the central control station  300  adjusts the beam sweeping pattern by using beam sweeping pattern information of base station 1   100 , base station 2   110 , and base station 3   120 , beam collision information received from each base station, stored past beam collision information, and stored past beam sweeping pattern adjustment information. Beam sweeping patterns of one base station or a plurality of base stations may be changed according to the beam sweeping pattern adjustment result of the central control station  300 . In step S 375 , the central control station  300  informs each of the base stations  100 ,  110 , and  120  of the beam sweeping pattern adjustment result. 
         [0092]    When the beam sweeping pattern adjustment result is received from the central control station  300 , base station 1   100  transmits a beam sweeping pattern adjustment result message to terminal 1   200  and temrinal 2   210  in step S 380 . According to an embodiment, base station 1   100  transmits the beam sweeping pattern adjustment result message only to terminals which participate in a procedure of generating the beam collision information and reporting the beam collision information. According to another embodiment, base station 1   100  transmits the beam sweeping pattern adjustment result message also to terminals which do not participate in the procedure of generating the beam collision information and reporting the beam collision information according to a determination of the base station. 
         [0093]    Further, when the beam sweeping pattern adjustment result is received from the central control station  300 , base station 1   100  transmits a beam sweeping pattern adjustment end notification message to base station 2   110 , base station 3   120 , and the central control station  300  in step  390 . The beam sweeping pattern adjustment end notification message may include some or all of the information shown in Table 2 below. 
         [0094]    Referring to  FIG. 9B , when a beam collision event is generated in step S 302 , terminal 1   200  reports the generation of the beam collision event to base station 1   100  as beam collision information in step S 304 . The beam collision event refers to generation of a possibility of the collision between the particular beam of base station 1   100  and the particular beam of the other base station. Base station 1   100  determines whether it is required to adjust the beam sweeping pattern according to a result of the report, and starts adjusting the beam sweeping pattern according to a result of the determination. Here, it is assumed that base station 1   100  starts adjusting the beam sweeping pattern immediately as terminal 1   200  reports the beam collision information by a predetermined number of times. 
         [0095]    When it is determined that the beam sweeping pattern needs to be adjusted, base station 1   100  transmits a beam sweeping pattern adjustment start notification message to the central control station  300  and neighboring base stations (for example, base station 2   110  and base station 3   120 ) that operate beams which may generate the beam collision with the beam operated by base station 1   100  in step  320 . 
         [0096]    In step S 335 , base station 1   100  transmits a request for beam collision information to terminal 2   210  connected to base station 1   100 . Terminal 2   210  having received the request for the beam collision information generates the beam collision information in step S 340 B, and reports the generated beam collision information to base station 1   100  in step S 355 . 
         [0097]    In step S 360 , base station 1   100  detects whether there is a beam which may generate the collision with beams operated by other base stations among the beams operated by base station 1   100  by using the beam collision information reported from terminal 1   200  in step S 304  and the beam collision information reported from terminal 2   210  in step S 355 . When the beam collision is detected, base station 1   100  transmits a request for adjusting the beam sweeping pattern to the central control state  300  in step S 365 . The beam sweeping pattern adjustment request message may include some or all of the information shown in Table 6 below. 
         [0098]    In step S 370 , the central control station  300  adjusts the beam sweeping pattern according to the request of base station 1   100 . For example, the central control station  300  adjusts the beam sweeping pattern by using beam sweeping pattern information of base station 1   100 , base station 2   110 , and base station 3   120 , beam collision information received from each base station, stored past beam collision information, and stored past beam sweeping pattern adjustment information. Beam sweeping patterns of one base station or a plurality of base stations may be changed according to the beam sweeping pattern adjustment result of the central control station  300 . In step S 375 , the central control station  300  informs each of the base stations  100 ,  110 , and  120  of the beam sweeping pattern adjustment result. 
         [0099]    When the beam sweeping pattern adjustment result is received from the central control station  300 , base station 1   100  transmits a beam sweeping pattern adjustment result message to terminal 1   200  and temrinal 2   210  in step S 380 . According to an embodiment, base station 1   100  transmits the beam sweeping pattern adjustment result message only to terminals which participate in a procedure of generating the beam collision information and reporting the beam collision information. According to another embodiment, base station 1   100  transmits the beam sweeping pattern adjustment result message also to terminals which do not participate in the procedure of generating the beam collision information and reporting the beam collision information according to a determination of the base station. 
         [0100]    Further, when the beam sweeping pattern adjustment result is received from the central control station  300 , base station 1   100  transmits a beam sweeping pattern adjustment end notification message to base station 2   110 , base station 3   120 , and the central control station  300  in step  390 . The beam sweeping pattern adjustment end notification message may include some or all of the information shown in Table 2 mentioned above. 
         [0101]      FIG. 10  illustrates an example of a processing flow of the base station for the centralized beam sweeping pattern adjusting procedure according to another embodiment of the present invention. The processing flow may be performed by base station 1   100  illustrated in  FIGS. 9A and 9B . The flow illustrated in  FIG. 10  merely corresponds to an example for describing the present invention and can be variously changed, and thus should not be interpreted to limit the scope of the present invention. 
         [0102]    Referring to  FIG. 10 , base station 1   100  transmits a beam sweeping pattern adjustment start message to neighboring base stations and the central control station in step S 410 . In step S 420 , base station 1   100  transmits a request for beam collision information to the terminal. In step S 430 , base station 1   100  receives the beam collision information from the terminal. In step S 440 , base station 1   100  performs a beam collision detection procedure by using the beam collision information. 
         [0103]    If the beam collision is detected, base station 1   100  transmits a request for adjusting the beam sweeping pattern to the central control station in step S 450 . In step S 460 , base station 1   100  receives a beam sweeping pattern adjustment result from the central control station. 
         [0104]    When the beam sweeping adjustment result is received, base station 1   100  notifies the terminal of the beam sweeping pattern adjustment result in step S 470 . Further, in step S 480 , base station 1   100  transmits a beam sweeping pattern adjustment end message to the neighboring base stations and the central control station. 
         [0105]      FIG. 11  illustrates an example of a processing flow of the central control station for the centralized beam sweeping pattern adjusting procedure according to another embodiment of the present invention. The processing flow may be performed by central control station  300  illustrated in  FIGS. 9A and 9B . The flow illustrated in  FIG. 11  merely corresponds to an example for describing the present invention and can be variously changed, and thus should not be interpreted to limit the scope of the present invention. 
         [0106]    Referring to  FIG. 11 , in step S 510 , the central control station  300  receives a beam sweeping pattern adjustment request from the base station. When the beam sweeping pattern adjustment request is received, the central control station  300  changes the beam sweeping pattern in step S 520 . In step S 530 , the central control station  300  transmits a beam sweeping pattern adjustment result to the base station. 
         [0107]    As described above, according to embodiments of the present invention, base station 1   100  performs an operation of detecting beam collision by using the beam collision information received from the terminal. 
         [0108]    It is assumed that base station 1   100  operates four beams b 1,1 , b 1,2 , b 1,3 , and b 1,4 , and the beam sweeping pattern is P 1 =(b 1,1 , b 1,2 , b 1,3 , b 1,4 ). Further, it is assumed that the beam sweeping patterns of base station 2   110  and base station 3   120  are P 2 =(b 2,3 , b 2,1 , b 2,4 , b 2,2 ) and P 3 =(b 3,4 , b 3,1 , b 3,3 , b 3,2 ), respectively. Base station 1   100  transmits the beams b 1,1 , b 1,2 , b 1,3 , and b 1,4  in time slots t 1 , t 2 , t 3 , and t 4 , respectively, according to the beam sweeping pattern P 1 . The beam frequently reported as the beam corresponding S 1  or S 2  in the beam collision information received from the terminal may have a high probability of the beam collision. For example, when the number of reports is larger than or equal to a predetermined value, base station 1   100  determines that the corresponding beam has a high probability of the collision with a beam of another base station. When it is assumed the beams b 1,2  and b 1,3  among the beams operated as base station 1   100  are reported as beams corresponding to S 1  by a predetermined number of times or more, the beam b 1,2  has a probability of the collision with the beam b 2,1  or the beam b 3,1 . Further, the beam b 1,3  has a possibility of the beam collision with the beam b 2,4  or the beam b 3,3 . According to an embodiment, when the existence of the beam collision is determined, only the number of reports of the beam corresponding to S 1  or S 2  may be considered According to another embodiment, when the existence of the beam collision is determined, a value of S 1 , a value of (S 1 −S 2 )/S 1 , or metric of a degree of the beam collision expressed by a predetermined function f(S 1 , S 2 ) of S 1  and S 2  may be used. 
         [0109]    As described above, according to embodiments of the present invention, when the beam collision is detected, base station 1   100  or the central control station  300  performs an operation of changing the beam sweeping pattern. 
         [0110]    The central control station  300  may adjust beam sweeping patterns of base stations to minimize performance deterioration of the network due to the beam collision between the base stations by using the beam collision information and past beam collision information received from other several base stations, past beam sweeping pattern change information, and the like. 
         [0111]    Base station 1   100  should change the beam sweeping pattern to minimize a beam collision possibility when the beam collision is detected. Base station 1   100  may have the beam collision information in advance as shown in Table 7 below. 
         [0000]    
       
         
               
             
           
               
                 TABLE 7 
               
               
                   
               
             
             
               
                 Beam which may cause beam collision in time slot t 1 : b 1, 2   
               
               
                 Beam which may cause beam collision in the time slot t2: b 1, 1   
               
               
                 Beam which may cause beam collision in time slot t 3 : b 1, 4   
               
               
                 Beam which may cause beam collision in time slot t 4 : b 1, 1  and b 1, 3   
               
               
                   
               
             
          
         
       
     
         [0112]    If the beam collision is detected in the beam b 1,2  and b 1,3  that are transmitted in the time slots t 2  and t 3 , base station 1   100  may know the beam which may cause the beam collision as shown in Table 8 below. Further, base station 1   100  may know that the beam b 1,3  should be allocated to one of the time slots t 1  and t 2 . 
         [0000]    
       
         
               
             
           
               
                 TABLE 8 
               
               
                   
               
             
             
               
                 Beam which may cause beam collision in the time slot t 2 : b 1, 1  and b 1, 2   
               
               
                 Beam which may cause beam collision in time slot t 3 : b 1, 3  and b 1, 4   
               
               
                   
               
             
          
         
       
     
         [0113]    A new beam sweeping pattern which may avoid the beam collision may be various. According to an embodiment, base station 1   100  may select a beam sweeping pattern through one of the methods shown in Table 9 below. 
         [0000]    
       
         
               
             
           
               
                 TABLE 9 
               
               
                   
               
             
             
               
                 (i) randomly select one of the available beam sweeping patterns 
               
               
                 (ii) select a beam sweeping pattern which makes the number of changed 
               
               
                 beams minimal among the available beam sweeping patterns 
               
               
                 (iii) select a beam sweeping pattern which makes a total sum or a 
               
               
                 maximum value of an amount of interference that the base station receives 
               
               
                 minimal among the available beam sweeping patterns 
               
               
                   
               
             
          
         
       
     
         [0114]    A new beam sweeping pattern that may avoid the beam collision may not exist. In this case, base station 1   100  may select a beam sweeping pattern from all beam sweeping patterns which can be used in spite of the beam collision according to the method (ii) or the method (iii) shown in Table 9 above. For example, in the above described example, base station 1   100  may change the beam sweeping pattern to be P 1 =(b 1,4 , b 1,3 , b 1,1 , b 1,2 ). Base station 1   100  performs the aforementioned next procedure according to the changed beam sweeping pattern information. 
         [0115]      FIGS. 12A and 12B  illustrate examples of a block diagram of the base station for the beam sweeping pattern adjusting procedure according to embodiments of the present invention. For example, base station 1   100  illustrated in  FIGS. 6A, 6B, 9A, and 9B  may be configured in such a form. Elements illustrated in  FIGS. 12A and 12B  merely correspond to examples for describing the present invention and can be variously changed, and thus should not be interpreted to limit the scope of the present invention. 
         [0116]    Referring to  FIG. 12A , the base station  100  includes a controller  1000 , a transmitter  1100 , a receiver  1200 , and an antenna unit  1300 . The controller  1000  controls the general operation of the base station  100 . The transmitter  1100  processes a transmission signal. For example, the transmitter  1100  may include a plurality of channel encoders, a plurality of modulators, a multi-input multi-output (MIMO) encoder, a precoder, and a plurality of radio frequency (RF) transmission processing block. Each RF transmission processing block processes streams provided from the precoder according to a predetermined transmission scheme (for example, orthogonal frequency division multiple access (OFDMA)) and outputs an RF signal to be transmitted. Each RF transmission processing block may include an inverse fast Fourier transform (IFFT) calculator, a parallel to serial (P/S) converter, a cyclic prefix (CP) adder, and a digital to analog converter (DAC). 
         [0117]    The antenna unit  1300  transmits a transmission signal processed by the transmitter  1100  to the outside, receives a signal from the outside, and provides the received signal to the receiver  1200 . The antenna unit  1300  may include a beamforming block and an antenna array to make beamforming-based signal transmission/reception possible. The beamforming block receives a plurality of signals from the plurality of RF transmission processing blocks included in the transmitter  1100  and forms a beam transmitted in a particular direction through a control of phase and amplitude for a plurality of antenna components. The antenna array may include a plurality of antenna components, which are grouped. 
         [0118]    The receiver  1200  processes a reception signal. The receiver  1200  includes elements corresponding to an inverse process of the transmitter  1100 . For example, the receiver  1200  may include a plurality of RF reception processing blocks, a MIMO decoder, a plurality of demodulators, and a plurality of channel decoders. Each RF reception processing block may include an analog to digital converter (ADC), a CP remover, a serial to parallel (S/P) converter, and a fast Fourier transform (FFT) calculator. 
         [0119]    The controller  1000  includes a beam sweeping pattern adjustment necessity determiner  1010 , a beam collision detector  1020 , and a beam sweeping pattern adjustor  1030 . The beam sweeping pattern adjustment necessity determiner  1010  determine whether the adjustment of the beam sweeping pattern is necessary. When it is determined that the adjustment of the beam sweeping pattern is necessary, the beam collision detector  1020  detect whether the beam collision occurs in the terminal based on the beam collision information received from at least one terminal. The beam sweeping pattern adjustor  1030  adjusts the beam sweeping pattern when the beam collision is detected by the beam collision detector  1020 . 
         [0120]    The above elements perform the distributed beam sweeping pattern adjusting operation according to an embodiment of the present invention. 
         [0121]    The receiver  1200  collects, from at least one terminal, beam collision information indicating the collision of beams received from the serving base station and at least one neighboring base station adjacent to the serving base station. According to an embodiment, the beam collision information includes information determined based on a signal quality of a beam having the best signal quality among the beams transmitted to at least one terminal from the serving base station and a signal quality of a beam having the best signal quality among the beams transmitted to at least one terminal from the neighboring base station. 
         [0122]    When it is determined that the adjustment of the beam sweeping pattern is necessary, the transmitter  1100  transmits a start notification message indicating the start of the adjustment of the beam sweeping pattern to the neighboring base station. 
         [0123]    The transmitter  1100  transmits a result of the adjustment of the beam sweeping pattern to at least one terminal. According to an embodiment, the result of the adjustment of the beam sweeping pattern includes at least one of whether the beam sweeping pattern of the serving base station is changed, information on the changed beam sweeping pattern of the serving base station, and a time point when the change in the beam sweeping pattern of the serving base station is applied. 
         [0124]    The transmitter  1100  transmits an end notification message indicating that the adjustment of the beam sweeping pattern ends to the neighboring base station. According to an embodiment, the end notification message includes at least one of whether the adjustment of the beam sweeping pattern of the serving base station ends, whether the beam sweeping pattern of the serving base station is changed, and information on the changed beam sweeping pattern. 
         [0125]    The controller  1000  adjusts the beam sweeping pattern of the beam transmitted to at least one terminal based on the received beam collision information. 
         [0126]    The controller  1000  determines whether the adjustment of the beam sweeping pattern is necessary through the beam sweeping pattern adjustment necessity determiner  1010  and, when it is determined that the adjustment of the beam sweeping pattern is necessary, transmits a request for beam collision information to at least one terminal. 
         [0127]    According to an embodiment, when the serving base station receives a report on a possibility of the collision between the beam transmitted from the serving base station and the beam transmitted from the neighboring base station by a predetermined number of times or more, the beam sweeping pattern adjustment necessity determiner  1010  of the controller  1000  determines that the adjustment of the beam sweeping pattern is necessary. 
         [0128]    According to another embodiment, in at least one of the cases where the serving base station is turned off from a turned on state, the neighboring base station is turned off, the neighboring base station is turned on, the neighboring base station changes the beam sweeping pattern, a predefined time elapses after the beam sweeping pattern is adjusted, and a request for adjusting the beam sweeping pattern is received, the beam sweeping pattern adjustment necessity determiner  1010  of the controller  1000  determines that the adjustment of the beam sweeping pattern is necessary. 
         [0129]    The beam collision detector  1020  of the controller  1000  detects the beam collision based on the received beam collision information. The beam sweeping pattern adjustor  1030  of the controller  1000  adjusts the beam sweeping pattern of the beam transmitted to at least one terminal by changing the beam sweeping pattern of the beam transmitted to at least one terminal when the beam collision is detected. 
         [0130]    According to an embodiment, the beam sweeping pattern adjustor  1030  adjusts the beam sweeping pattern through at least one of a process of randomly selecting one of a plurality of beam sweeping patterns, a process of selecting a beam sweeping pattern which makes the number of changed beams minimal among the plurality of beam sweeping patterns, and a process of selecting a beam sweeping pattern which makes a total sum or a maximum value of an amount of interference which the serving base station receives minimal among the plurality of beam sweeping patterns. 
         [0131]    The beam sweeping pattern indicates a mapping relation between a beam and a resource used for signal transmission. According to an embodiment, the resource includes at least one of a time, frequency, and orthogonal code. 
         [0132]    Referring to  FIG. 12B , the base station  100  includes the controller  1000 , the transmitter  1100 , the receiver  1200 , and the antenna unit  1300 . The controller  1000  controls the general operation of the base station  100 . The transmitter  1100  processes a transmission signal. The receiver  1200  processes a reception signal. The antenna unit  1300  transmits a transmission signal processed by the transmitter  1100  to the outside, receives a signal from the outside, and provides the received signal to the receiver  1200 . The transmitter  1100 , the receiver  1200 , and the antenna unit  1300  may include elements which are the same as those described in  FIG. 12A . 
         [0133]    The controller  1000  includes the beam sweeping pattern adjustment necessity determiner  1010  and the beam collision detector  1020 . The beam sweeping pattern adjustment necessity determiner  1010  determine whether the adjustment of the beam sweeping pattern is necessary. When it is determined that the adjustment of the beam sweeping pattern is necessary, the beam collision detector  1020  detect whether the beam collision occurs in the terminal based on the beam collision information received from at least one terminal. 
         [0134]    The above elements perform the centralized beam sweeping pattern adjusting operation according to an embodiment of the present invention. 
         [0135]    The receiver  1200  receives, from at least one terminal, beam collision information indicating the collision of beams received from the serving base station and at least one neighboring base station adjacent to the serving base station. According to an embodiment, the beam collision information includes information determined based on a signal quality of a beam having the best signal quality among the beams transmitted to at least one terminal from the serving base station and a signal quality of a beam having the best signal quality among the beams transmitted to at least one terminal from the neighboring base station. 
         [0136]    The receiver  1200  receives a result of the adjustment of the beam sweeping pattern from the central control station in response to the request for adjusting the beam sweeping pattern. 
         [0137]    The transmitter  1100  transmits a result of the adjustment of the beam sweeping pattern to at least one terminal. According to an embodiment, the result of the adjustment of the beam sweeping pattern includes at least one of whether the beam sweeping pattern of the serving base station is changed, information on the changed beam sweeping pattern of the serving base station, and a time point when the change in the beam sweeping pattern of the serving base station is applied. 
         [0138]    When it is determined that the adjustment of the beam sweeping pattern is necessary, the transmitter  1100  transmits a start notification message indicating the start of the adjustment of the beam sweeping pattern to the neighboring base station and the central control station. 
         [0139]    The transmitter  1100  transmits an end notification message indicating that the adjustment of the beam sweeping pattern ends to the neighboring base station and the central control station. According to an embodiment, the end notification message includes at least one of whether the adjustment of the beam sweeping pattern of the serving base station ends, whether the beam sweeping pattern of the serving base station is changed, and information on the changed beam sweeping pattern. According to an embodiment, the changed beam sweeping pattern information of the serving base station includes information on at least one of a beam sweeping pattern randomly selected from a plurality of beam sweeping patterns, a beam sweeping pattern which makes the number of changed beams minimal among the plurality of beam sweeping patterns, and a beam sweeping pattern which makes a total sum or a maximum value of an amount of interference which the serving base station receives minimal among the plurality of beam sweeping patterns. 
         [0140]    The controller  1000  detects the beam collision based on the received beam collision information and, when the beam collision is detected, transmits a request for adjusting the beam sweeping pattern to the central control station. According to an embodiment, the request for adjusting the beam sweeping pattern includes at least one of a beam index of the serving base station from which the beam collision is detected, a beam index of the neighboring base station from which the beam collision with the serving base station is detected, and metric indicating a degree of the beam collision. 
         [0141]    The controller  1000  determines whether the adjustment of the beam sweeping pattern is necessary through the beam sweeping pattern adjustment necessity determiner  1010 . When it is determined that the adjustment of the beam sweeping pattern is necessary, the controller  1000  transmits a request for beam collision information to at least one terminal. 
         [0142]    According to an embodiment, when the serving base station receives a report on a possibility of the collision between the beam transmitted from the serving base station and the beam transmitted from the neighboring base station by a predetermined number of times or more, the beam sweeping pattern adjustment necessity determiner  1010  of the controller  1000  determines that the adjustment of the beam sweeping pattern is necessary. 
         [0143]    According to another embodiment, when the serving base station is installed, when the serving base station is turned off from a turned on state, when the neighboring base station is turned off, when the neighboring base station is turned on, when the neighboring base station changes the beam sweeping pattern, when a predefined time elapses after the beam sweeping pattern is adjusted, or when a request for adjusting the beam sweeping pattern is received, the beam sweeping pattern adjustment necessity determiner  1010  of the controller  1000  determines that the adjustment of the beam sweeping pattern is necessary. 
         [0144]    The beam sweeping pattern indicates a mapping relation between a beam and a resource used for signal transmission. According to an embodiment, the resource includes at least one of a time, frequency, and orthogonal code. 
         [0145]      FIG. 13  illustrates an example of a block diagram of the terminal for the beam sweeping pattern adjusting procedure according to embodiments of the present invention. For example, terminal 1   200  illustrated in  FIGS. 6A, 6B, 9A, and 9B  may be configured in such a form. The configuration illustrated in  FIG. 13  merely corresponds to an example for describing the present invention and can be variously changed, and thus should not be interpreted to limit the scope of the present invention. 
         [0146]    Referring to  FIG. 13 , the terminal  200  includes a controller  2000 , a transmitter  2100 , a receiver  2200 , and an antenna unit  2300 . The controller  2000  controls the general operation of the terminal  200 . The transmitter  2100  processes a transmission signal. The receiver  2200  processes a reception signal. The antenna unit  2300  transmits a transmission signal processed by the transmitter  2100  to the outside, receives a signal from the outside, and provides the received signal to the receiver  2200 . The transmitter  2100 , the receiver  22000 , and the antenna unit  2300  may be configured in a similar form as the elements corresponding to the base station illustrated in  FIGS. 12A and 12B . 
         [0147]    The elements perform the operation for beam sweeping pattern adjusting procedure according to embodiments of the present invention. 
         [0148]    A beam collision information generator  2010  of the controller  2000  generates beam collision information indicating the collision of beams received from the serving base station and at least one neighboring base station adjacent to the serving base station. 
         [0149]    When it is determined that the adjustment of the beam sweeping pattern is necessary by the serving base station, the controller  2000  generates the beam collision information in response to a request for the beam collision information. 
         [0150]    According to an embodiment, the request for the beam collision information is generated by the serving base station when a possibility of the collision between the beam transmitted by the serving base station and the beam transmitted by the neighboring base station is reported from at least one terminal by a predetermined number of times or more. 
         [0151]    According to another embodiment, in at least one of the cases where the serving base station is installed, the serving base station is turned off from a turned on state, the neighboring base station is turned off, the neighboring base station is turned on, the neighboring base station changes the beam sweeping pattern, a predefined time elapses after the beam sweeping pattern is adjusted, and a request for adjusting the beam sweeping pattern is received, the request for the beam collision information is generated by the serving base station. 
         [0152]    According to an embodiment, the beam collision information includes information determined based on a signal quality of a beam having the best signal quality among the beams transmitted to at least one terminal from the serving base station and a signal quality of a beam having the best signal quality among the beams transmitted to at least one terminal from the neighboring base station. 
         [0153]    The transmitter  2100  transmits the generated beam collision information to the serving base station. 
         [0154]    The receiver  2200  receives a result of the adjustment of the beam sweeping pattern transmitted from the serving base station in response to the generated beam collision information. According to an embodiment, the result of the adjustment of the beam sweeping pattern includes at least one of whether the beam sweeping pattern of the serving base station is changed, information on the changed beam sweeping pattern of the serving base station, and a time point when the change in the beam sweeping pattern of the serving base station is applied. 
         [0155]    The beam sweeping pattern indicates a mapping relation between a beam and a resource used for signal transmission. According to an embodiment, the resource includes at least one of a time, frequency, and orthogonal code. 
         [0156]      FIG. 14  illustrates an example of a block diagram of the central control station for the beam sweeping pattern adjusting procedure according to embodiments of the present invention. For example, the central control station  300  illustrated in  FIGS. 9A and 9B  may be configured in such a form. Here, the configuration corresponds to a case where the central controls station  300  is one of a plurality of base stations. If the central control station  300  is a control station independent from the base stations, the central control station  300  may include a network interface corresponding to an element that substitutes for a transmitter  3100 , a receiver  3200 , and an antenna unit  3300 . The configuration illustrated in  FIG. 14  merely corresponds to an example for describing the present invention and can be variously changed, and thus should not be interpreted to limit the scope of the present invention. 
         [0157]    Referring to  FIG. 14 , the central control station  300  includes a controller  3000 , the transmitter  3100 , the receiver  3200 , and the antenna unit  3300 . The controller  3000  controls the general operation of the central control station  300 . The transmitter  3100  processes a transmission signal. The receiver  3200  processes a reception signal. The antenna unit  3300  transmits a transmission signal processed by the transmitter  3100  to the outside, receives a signal from the outside, and provides the received signal to the receiver  3200 . The transmitter  3100 , the receiver  3200 , and the antenna unit  3300  may be configured in a similar form as the elements corresponding to the base station illustrated in  FIGS. 12A and 12B . 
         [0158]    The receiver  3200  receives, from the serving base station, a beam sweeping pattern adjusting request indicating that the collision between beams transmitted from the serving base station and at least one neighboring base station adjacent to the serving base station among a plurality of base stations is detected in at least one terminal. According to an embodiment, the request for adjusting the beam sweeping pattern includes at least one of a beam index of the serving base station from which the beam collision is detected, a beam index of the neighboring base station from which the beam collision with the serving base station is detected, and metric indicating a degree of the beam collision 
         [0159]    A beam sweeping pattern adjustor  3010  of the controller  3000  adjusts the beam sweeping pattern of the beam transmitted to at least one terminal in response to the beam sweeping pattern adjusting request. 
         [0160]    The transmitter  3100  transmits a result of the adjustment of the beam sweeping pattern to the serving base station and the neighboring base station. According to an embodiment, the result of the adjustment of the beam sweeping pattern includes at least one of whether the beam sweeping pattern of the serving base station is changed, information on the changed beam sweeping pattern of the serving base station, and a time point when the change in the beam sweeping pattern of the serving base station is applied. 
         [0161]    The beam sweeping pattern adjustor  3010  of the controller  3000  adjusts the beam sweeping pattern through at least one of a process of randomly selecting one of a plurality of beam sweeping patterns, a process of selecting a beam sweeping pattern which makes the number of changed beams minimal among the plurality of beam sweeping patterns, and a process of selecting a beam sweeping pattern which makes a total sum or a maximum value of an amount of interference which the serving base station receives minimal among the plurality of beam sweeping patterns. 
         [0162]    The beam sweeping pattern indicates a mapping relation between a beam and a resource used for signal transmission. According to an embodiment, the resource includes at least one of a time, frequency, and orthogonal code. 
         [0163]    As described above, according to the embodiments of the present invention, when the collision between base stations occurs in the beamforming-based wireless communication system, the beam sweeping pattern is adaptively determined. According to the embodiments of the present invention, it is possible to improve accuracy of channel state estimation and increase a success rate of reception of the synchronization channel or the broadcast channel. 
         [0164]    Although the present invention has been described by the restricted embodiments and the drawings as described above, the present invention is not limited to the aforementioned embodiments, and various modifications and alterations can be made from the descriptions by those skilled in the art to which the present invention pertains. The case where the beams are divided by time resources has been described as an example in the embodiments of the present invention, but the present invention can be applied to a case where the beams are divided by frequency or orthogonal code resources. That is, the beam sweeping pattern may be changed to avoid the beam collision or minimize an interference amount by changing a frequency location or an orthogonal code of the beam after the beam collision is detected. 
         [0165]    The case where the beam sweeping pattern is changed through the change in used resources without the change in the beam has been described as another example, but the beam itself may be changed without the change in the time, frequency, orthogonal code, and the like. That is, a direction, power, width, and the like of the beam having the collision may be changed. 
         [0166]    In another example, the number of beams operated by the base station or a beam transmission period may be changed through another method of changing the beam sweeping pattern. When the number of beams or the beam transmission period is changed, a relation with beam sweeping patterns used by neighboring base stations is changed and thus an interference amount is also changed. At this time, the beam sweeping pattern may be changed to minimize the interference amount. 
         [0167]    Further, although it has been described that the operations according to embodiments of the present invention are performed by the elements of the base station, the terminal, and the central control station illustrated in  FIGS. 12A, 12B, 13, and 14 , the operations according to embodiments of the present invention may be implemented by other forms of elements. When the operations according to embodiments of the present invention are implemented by a single controller (or processor), program instructions for performing various computer-implemented operations may be stored in a computer-readable medium. The computer readable medium may include a program command, a data file, a data structure, and the like independently or in combination. The program command may be things specially designed and configured for the present invention, or things that are well known to and can be used by those skilled in the related art. For example, the computer readable recoding medium includes magnetic media such as a hard disk, a floppy disk, and a magnetic tape, optical media such as a CD-ROM and a DVD, magneto-optical media such as a floptical disk, and hardware devices such as a ROM, RAM, and a flash memory, which are specially constructed in such a manner that they can store and execute a program command. Examples of the program command include a machine language code generated by a compiler and a high-level language code executable by a computer through an interpreter and the like. When all or some of the base stations or relays as described in the present invention are implemented by a computer program, a computer-readable recording medium in which the computer program is stored also falls within the scope of the present invention. Therefore, the scope of the present invention should not be defined as being limited to the embodiments, but should be defined by the appended claims and equivalents thereof.