Abstract:
A base station including: a memory, and a processor coupled to the memory and configured to: wirelessly communicate with one or more terminals via a plurality of component carriers of carrier aggregation, and allocate each of the plurality of component carriers to each of the one or more terminals based on both of each number of terminals allocated to each component carrier and each wireless quality of each component carrier for each terminal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-099179, filed on May 14, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments disclosed herein are related to a base station and a processing method by a base station. 
       BACKGROUND 
       [0003]    A base station that carries out radio communications with plural pieces of radio equipment is known (for example, refer to Japanese Laid-open Patent Publications No. 2014-150558 and No. 2014-049932, and 3GPP TS 36.300 V10.11.0, “Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 10),” [online], September 2013, [retrieved on Feb. 2, 2015], Internet &lt;URL:http://www.3gpp.org/ftp/Specs/archive/36_series/36.300/36300-ab0.zip&gt;). For example, the base station carries out communications in accordance with the LTE-Advanced system. LTE is an abbreviation of Long Term Evolution. 
         [0004]    The LTE-Advanced system uses a carrier aggregation (CA) technique. In the CA technique, communications are carried out by using plural component carriers (CCs). 
         [0005]    For example, the LTE-Advanced system uses up to five CCs. The frequency bandwidth possessed by one CC is at most 20 MHz. Therefore, in the LTE-Advanced system, communications are carried out by using a frequency bandwidth of up to 100 MHz. This can increase the amount of data transmitted per unit time (in other words, communication throughput). 
       SUMMARY 
       [0006]    According to an aspect of the embodiment, a base station includes a memory, and a processor coupled to the memory and configured to: wirelessly communicate with one or more terminals via a plurality of component carriers of carrier aggregation, and allocate each of the plurality of component carriers to each of the one or more terminals based on both of each number of terminals allocated to each component carrier and each wireless quality of each component carrier for each terminal. 
         [0007]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0008]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is an explanatory diagram representing one example of CCs used by pieces of radio equipment; 
           [0010]      FIG. 2  is a table representing one example of RSRP measured in pieces of radio equipment; 
           [0011]      FIG. 3  is a table representing one example of CCs allocated to pieces of radio equipment; 
           [0012]      FIG. 4  is a table representing one example of CCs allocated to pieces of radio equipment; 
           [0013]      FIG. 5  is a block diagram representing one example of configuration of a radio communication system according to a first embodiment; 
           [0014]      FIG. 6  is a block diagram representing one example of configuration of a base station in  FIG. 5 ; 
           [0015]      FIG. 7  is a block diagram representing one example of functions of the base station in  FIG. 5 ; 
           [0016]      FIG. 8  is a flowchart representing one example of processing executed by the base station in  FIG. 5 ; 
           [0017]      FIG. 9  is a flowchart representing one example of processing executed by the base station in  FIG. 5 ; 
           [0018]      FIG. 10  is a table representing one example of RSRP measured in pieces of radio equipment; 
           [0019]      FIG. 11  is a table representing one example of CCs allocated to pieces of radio equipment; 
           [0020]      FIG. 12  is a flowchart representing one example of processing executed by a base station of a first modification example of the first embodiment; 
           [0021]      FIG. 13  is a flowchart representing one example of processing executed by a base station of a second embodiment; 
           [0022]      FIG. 14  is a table representing one example of SINR measured in pieces of radio equipment; 
           [0023]      FIG. 15  is a table representing one example of CCs allocated to pieces of radio equipment; 
           [0024]      FIG. 16  is a flowchart representing one example of processing executed by a base station of a first modification example of the second embodiment; 
           [0025]      FIG. 17  is a block diagram representing one example of functions of a base station of a third embodiment; and 
           [0026]      FIG. 18  is a flowchart representing one example of processing executed by the base station of  FIG. 17 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    For each piece of radio equipment, the above-described base station allocates, with higher priority, the CC with higher RSRP to communications with the radio equipment. RSRP is an abbreviation of Reference Signal Received Power. Therefore, the numbers of pieces of radio equipment that use the respective CCs often involve a bias. As a result, the communication throughput often decreases. 
         [0028]    As one aspect, one of objects of the embodiments disclosed herein is to enhance the communication throughput. 
         [0029]    Embodiments will be described below with reference to the drawings. However, the embodiments described below are exemplification. Therefore, it is not excluded that various modifications and techniques that are not clearly specified below are applied to the embodiments. In the drawings used in the following embodiments, a part given the same symbol represents the same or similar part unless a change or modification is clearly specified. 
         [0030]    As represented in  FIG. 1 , for example, three pieces of radio equipment  901  to  903  carry out communications by using three CCs  911  to  913 . The radio equipment may be represented as user equipment (UE). The UE  901  carries out communications by using the CC  911 . The UE  902  carries out communications by using the CC  911  and the CC  912 . The UE  903  carries out communications by using the CC  911 , the CC  912 , and the CC  913 . 
         [0031]    In the present example, the CC  911  is a primary component carrier (PCC) for each of the UE  901  and the UE  902 . Furthermore, in the present example, the CC  912  is a PCC for the UE  903 . Moreover, in the present example, the CC  912  is a secondary component carrier (SCC) for the UE  902 . In addition, in the present example, each of the CC  911  and the CC  913  is an SCC for the UE  903 . 
         [0032]    The UE  902  and the UE  903  use two or more CCs and thus can carry out communications with higher communication throughput than the UE  901 , which carries out communications by using one CC. 
         [0033]    For example, the CCs used for communications between the respective pieces of radio equipment and a base station are allocated by the base station. Incidentally, the state of communications by the CC (for example, the quality of communications, the load of communications, and so forth) differs on each CC basis. Therefore, if the CCs are not properly selected, the communication throughput often decreases. 
         [0034]    For example, the base station selects the CCs in accordance with a round-robin method in some cases. Furthermore, in other cases, on the basis of a parameter indicating the quality of communications (for example, RSRP, RSRQ, CQI, SINR, or other parameters indicating wireless quality), the base station allocates the CC with higher quality to radio equipment with higher priority. RSRQ is an abbreviation of Reference Signal Received Quality. CQI is an abbreviation of Channel Quality Indicator. SINR is an abbreviation of Signal to Interference plus Noise Ratio. 
         [0035]    A description will be made about one example of operation in which, as represented in  FIG. 2  and  FIG. 3 , a base station allocates one CC of two CCs to each of five pieces of radio equipment. In the present example, the k-th radio equipment is identified by equipment #k as an equipment identifier (in other words, equipment identification (ID)). k represents an integer of 1 to 5. The i-th CC is identified by CC #i as a CC identifier (in other words, CC ID). i represents an integer of 1 or 2. 
         [0036]      FIG. 2  represents the RSRP of each CC about each piece of radio equipment. In the present example, regarding each piece of radio equipment, the RSRP about the first CC is higher than the RSRP about the second CC. Therefore, as represented in  FIG. 3 , the base station allocates the first CC to all pieces of radio equipment if the base station allocates, with higher priority, the CC with higher RSRP to each piece of radio equipment as the CC used for communications with the radio equipment. Circles in  FIG. 3  represent that the CC is allocated to communications between the base station and the radio equipment. Circles in diagrams that represent tables similar to  FIG. 3  and will be described later also represent that the CC is used for communications between the base station and the radio equipment similarly to  FIG. 3 . 
         [0037]    In this case, the number of pieces of radio equipment that use the first CC is excessively large. As a result, the amount of radio resources that can be allocated to each piece of radio equipment becomes small in the first CC. Therefore, the communication throughput is not sufficiently enhanced in some cases. 
         [0038]    Furthermore, it will be possible that the base station allocates the CC to each piece of radio equipment on the basis of the quality of communications and thereafter changes the CC allocated to part of the plural pieces of radio equipment so that the bias in the numbers of pieces of radio equipment that use the respective CCs may be suppressed. The case in which the RSRP of each CC about each piece of radio equipment is measured as represented in  FIG. 2  will be assumed. 
         [0039]    For example, first, for each piece of radio equipment, the base station allocates the CC with higher RSRP to communications with the radio equipment with higher priority. Therefore, as represented in  FIG. 3 , the base station allocates the first CC to each piece of radio equipment. 
         [0040]    Thereafter, for example, the base station extracts the radio equipment regarding which the magnitude of the difference between the RSRP about the first CC and the RSRP about the second CC is relatively small. In the present example, the case in which the base station extracts the second and fifth pieces of radio equipment is assumed. In this case, as represented in  FIG. 4 , the base station changes the CC allocated to the extracted pieces of radio equipment from the first CC to the second CC. 
         [0041]    This can suppress the bias in the numbers of pieces of radio equipment that use the respective CCs. As a result, the communication throughput can be enhanced. 
         [0042]    Incidentally, the change (in other words, switching) of the CC is carried out in accordance with a procedure similar to a procedure of handover (HO) between cells. 
         [0043]    Therefore, in the case of changing the CC, first, the quality of communications about the CC of the change destination is measured for each piece of radio equipment. For example, the measurement of the quality is carried out by a function of the radio equipment (for example, function called UE Measurement). In this case, transmission and reception of user data are stopped in the period during which the quality of communications is measured in some cases. Furthermore, a given time (for example, time of several minutes to several tens of minutes) is taken from issuance of an instruction of measurement to the completion of the measurement in some cases. 
         [0044]    Moreover, in this case, a control signal to carry out the handover is transmitted and received and therefore the radio resources that can be allocated to transmission and reception of user data decrease in some cases. In addition, in this case, the communications between the radio equipment whose CC is changed and the base station stop in the period until the completion of the change of the CC in some cases. 
         [0045]    Because of the above, the communication throughput decreases more readily as the frequency of the change of the CC increases. 
         [0046]    Incidentally, in order to distribute the load of a macro base station, a large number of small base stations that form relatively-small cells (for example, picocells, femtocells, or the like) are disposed in some cases. Therefore, the cost of the radio communication system becomes high more readily as the cost of the small base stations becomes higher. 
         [0047]    Furthermore, the processing load of the base station in association with the change of the CC is comparatively large. Therefore, as the frequency of the change of the CC increases, the cost of the base station becomes higher because it is preferable for the base station to have higher processing capability. In other words, the cost of the radio communication system becomes higher as the frequency of the change of the CC increases. 
       First Embodiment 
     Configuration 
       [0048]    As represented in  FIG. 5 , a radio communication system  1  according to a first embodiment illustratively includes M base stations  10 - 1 ,  10 - 2 , . . . , and  10 -M, N pieces of radio equipment  20 - 1 ,  20 - 2 , . . . , and  20 -N, and a control device  30 . 
         [0049]    In the present example, M represents an integer equal to or larger than 2. Furthermore, hereinafter, the base station  10 - m  will be represented also as the base station  10  if there is no need for differentiation. m represents each integer from 1 to M. In the present example, N represents an integer equal to or larger than 2. Furthermore, hereinafter, the radio equipment  20 - n  will be represented also as the radio equipment  20  if there is no need for differentiation. n represents each integer from 1 to N. 
         [0050]    In the radio communication system  1 , radio communications in accordance with a given communication method are carried out between the base stations  10 - m  and the pieces of radio equipment  20 - n . For example, the communication method is the LTE-Advanced system. The communication method may be a method different from the LTE-Advanced system. 
         [0051]    The base station  10 - m  forms a radio area. The base station  10 - m  may form plural radio areas. The radio area may be represented as a coverage area or a communication area. Furthermore, the radio area may be represented as a cell. For example, the cell is a macrocell, microcell, nanocell, picocell, femtocell, home cell, small cell, sector cell, or the like. 
         [0052]    The base station  10 - m  communicates, by radio, with the radio equipment  20 - n  located in the cell formed by this base station  10 - m.    
         [0053]    In the present example, the base station  10 - m  provides radio resources in the cell formed by this base station  10 - m . In the present example, the radio resources are identified by the time and the frequency. The base station  10 - m  communicates with the radio equipment  20 - n  located in the cell formed by this base station  10 - m  by using the radio resources provided in this cell. 
         [0054]    The base station  10 - m  may be represented as a radio communication device, evolved Node B (eNB), or Node B (NB). 
         [0055]    In the present example, as represented in  FIG. 5 , the base stations  10 - m  are coupled to a communication network NW (for example, core network) with which the base stations  10 - m  can communicate in a wired or wireless manner. The interface between the base station  10 - m  and the communication network NW may be represented as an S1 interface. Furthermore, the interface between the base stations  10  may be represented as an X2 interface. 
         [0056]    The part on the side of the communication network NW at a higher level than the base stations  10  in the radio communication system  1  may be represented as EPC. EPC is an abbreviation of Evolved Packet Core. The part formed by the base stations  10  in the radio communication system  1  may be represented as E-UTRAN. E-UTRAN is an abbreviation of Evolved Universal Terrestrial Radio Access Network. 
         [0057]    The radio equipment  20 - n  communicates, by radio, with the base station  10 - m  that forms the cell in which this radio equipment  20 - n  is located by using the radio resources provided in this cell. 
         [0058]    The radio equipment  20 - n  may be represented as a radio terminal, a radio device, or UE. The radio equipment  20 - n  may be carried by a user or be mounted on a moving body such as a vehicle or be fixed. 
         [0059]    In the present example, the radio communication system  1  carries out CA by using plural CCs and thereby the base stations  10 - m  and the pieces of radio equipment  20 - n  communicate by radio. 
         [0060]    The CC is a radio resource identified by a frequency band having a given frequency bandwidth. In the present example, the base station  10 - m  provides plural CCs different from each other in the frequency band. The number of CCs provided by the base station  10 - m  may be 1. 
         [0061]    The plural CCs used for the CA include one PCC and at least one SCC. The plural CCs used for the CA are different from each other in the frequency band. For example, the frequency band of the PCC is the 800-MHz band and the frequency band of the SCC is the 2-GHz band. In the present example, the plural CCs used for the CA are provided by one base station  10 - m . The plural CCs used for the CA may be provided by the plural base stations  10 . 
         [0062]    In the present example, the base station  10 - m  allocates the CCs provided by this base station  10 - m  to the radio equipment  20 - n  located in the cell formed by this base station  10 - m . The allocation of the CCs may be carried out by a base station  10 - p  different from the base station  10 - m  that provides these CCs or the control device  30 . p represents each integer from 1 to M different from m. 
         [0063]    The radio equipment  20 - n  carries out the CA by using plural CCs allocated to this radio equipment  20 - n  to thereby communicate with the base station  10  that provides the respective CCs. 
         [0064]    The control device  30  is coupled to the communication network NW in such a manner as to be capable of communicating with the communication network NW in a wired or wireless manner. In the present example, the control device  30  is communicably coupled to each base station  10  via the communication network NW. The control device  30  may be represented as a control station, a management device, a control server, or a management server. Furthermore, the control device  30  may include plural devices. 
         [0065]    (Configuration; Base Station  10 - m ) 
         [0066]    Next, the configuration of the base station  10 - m  will be described. 
         [0067]    In the present example, as represented in  FIG. 6 , the base station  10 - m  includes a processing device  11 , a storing device  12 , a radio communication unit  13 , a baseband signal processing unit  14 , and a network (NW) communication unit  15  that are coupled to each other via a bus BU 1 . 
         [0068]    The processing device  11  controls each unit in the base station  10 - m  in order to implement functions to be described later. In the present example, the processing device  11  is a central processing unit (CPU). In the present example, the processing device  11  implements the functions to be described later by executing a program stored in the storing device  12 . 
         [0069]    The functions of the processing device  11  may be implemented by large scale integration (LSI) or a programmable logic device (PLD). 
         [0070]    The storing device  12  includes at least one of RAM, ROM, HDD, SSD, semiconductor memory, and organic memory for example. RAM is an abbreviation of Random Access Memory. ROM is an abbreviation of Read Only Memory. HDD is an abbreviation of Hard Disk Drive. SSD is an abbreviation of Solid State Drive. The storing device  12  may include a recording medium such as flexible disk, optical disk, magneto-optical disk, and semiconductor memory and a reading device that can read information from the recording medium. 
         [0071]    The radio communication unit  13  has an antenna  16  and carries out communications in accordance with the above-described communication method with the radio equipment  20  located in a cell formed via the antenna  16 . The radio communication unit  13  transmits a radio signal corresponding to an electrical signal input from the baseband signal processing unit  14  via the antenna  16 . The radio communication unit  13  outputs an electrical signal corresponding to a radio signal received via the antenna  16  to the baseband signal processing unit  14 . In the present example, functions of the radio communication unit  13  are implemented by LSI. 
         [0072]    The baseband signal processing unit  14  executes given signal processing on the electrical signal generated by this baseband signal processing unit  14  and the electrical signal input from the radio communication unit  13 . For example, the signal processing includes termination of a transmission signal, termination of a received signal, conversion of the communication protocol, and so forth. 
         [0073]    In the present example, the baseband signal processing unit  14  implements functions to be described later by executing a program held by a digital signal processor (DSP) in advance. The functions of the baseband signal processing unit  14  may be implemented by LSI. 
         [0074]    The NW communication unit  15  communicates with another device coupled to the communication network NW (for example, control device  30 ). For example, the NW communication unit  15  carries out communications in accordance with a wired local area network (LAN) system. For example, the wired LAN system is an IEEE 802.3 series or Ethernet (registered trademark) system. In the present example, functions of the NW communication unit  15  are implemented by LSI. 
         [0075]    (Functions; Base Station  10 - m ) 
         [0076]    Next, the functions of the base station  10 - m  will be described. In the present example, the functions of the base station  10 - m  include a coupling control unit  101 , a CC allocating unit  102 , and a scheduler unit  103  as represented in  FIG. 7 . In the present example, functions of the coupling control unit  101 , the CC allocating unit  102 , and the scheduler unit  103  are implemented by the processing device  11 , the storing device  12 , and the baseband signal processing unit  14 . 
         [0077]    The coupling control unit  101  executes processing of terminating a message in accordance with a given communication protocol used for communications between the base station  10 - m  and the radio equipment  20 - n . The communication protocol is a radio resource control (RRC) protocol for example. 
         [0078]    The coupling control unit  101  acquires the quality of communications by the CC about each CC, included in a measurement report received from each piece of radio equipment  20  located in the cell formed by the base station  10 - m . In the present example, the coupling control unit  101  uses the RSRP as the parameter representing the quality of communications. The coupling control unit  101  may use a parameter different from the RSRP (for example, RSRQ, CQI, SINR, or the like) as the parameter representing the quality of communications. 
         [0079]    The CC allocating unit  102  allocates the CC to each piece of radio equipment  20  located in the cell provided by the base station  10 - m . Details of the functions of the CC allocating unit  102  will be described later. 
         [0080]    The scheduler unit  103  executes scheduling processing on each piece of radio equipment  20  located in the cell provided by the base station  10 - m . The scheduling processing includes processing of allocating, to each piece of radio equipment  20 , the radio resource included in the CC allocated to the radio equipment  20 . 
         [0081]    The base station  10 - m  communicates with the radio equipment  20  located in the cell provided by the base station  10 - m  by using the radio resource allocated to this radio equipment  20  by the scheduler unit  103 . 
         [0082]    A description will be added about the functions of the CC allocating unit  102 . In the present example, the CC allocating unit  102  includes a CC allocation limitation processing unit  1021  as represented in  FIG. 7 . 
         [0083]    In the present example, on the basis of the load of communications by each of plural CCs provided by the base station  10 - m , the CC allocation limitation processing unit  1021  limits the CC permitted to be allocated to the radio equipment  20  among the plural CCs. The “limitation of the CC” is one example of allocation control of the CC. The “allocation control of the CC” may be referred to as “scheduling of the CC.” The CC allocating unit  102  and the scheduler unit  103  may form one functional unit. 
         [0084]    In the present example, if a given limitation condition about the load of communications by the CC is satisfied, the CC allocation limitation processing unit  1021  does not permit allocation of this CC to the radio equipment  20 . 
         [0085]    In the present example, the CC allocation limitation processing unit  1021  uses the number of pieces of radio equipment  20  to which the CC is allocated as the parameter representing the load of communications by the CC. The number of pieces of radio equipment  20  to which the CC is allocated may be represented as the number of pieces of equipment. 
         [0086]    In the present example, the limitation condition about the load of communications by CC #i is a condition that such CC #j exists that a value obtained by subtracting the number N UEj  of pieces of equipment about CC #j different from CC #i from the number N UEi  of pieces of equipment about CC #i is larger than a given threshold α. CC #i represents the i-th CC. i represents each integer from 1 to N cc . N cc  represents the number of CCs provided by the base station  10 - m . In the present example, N cc  represents an integer equal to or larger than 2. j represents each integer from 1 to N cc  different from i. In the present example, the threshold α is equal to or larger than 0. The value N UEi −N UEj  obtained by subtracting the number N UEj  of pieces of equipment about CC #j different from CC #i from the number N UEi  of pieces of equipment about CC #i may be represented as the equipment-number difference N UEi −N UEj . 
         [0087]    The CC allocating unit  102  allocates, with higher priority, the CC whose quality of communications is higher among the CCs permitted to be allocated to the radio equipment  20  by the CC allocation limitation processing unit  1021  to the radio equipment  20 . 
         [0088]    As described above, in the present example, the quality of communications by the CC is acquired by the coupling control unit  101 . In the present example, the CC allocating unit  102  uses the RSRP of communications by the CC as the parameter representing the quality of communications by this CC. 
         [0089]    In the present example, the CC allocating unit  102  allocates, to the radio equipment  20 , the CC whose RSRP for this radio equipment  20  is the highest among the CCs permitted to be allocated to this radio equipment  20 . 
         [0090]    The CC allocating unit  102  is one example of a control unit. 
         [0091]    (Operation) 
         [0092]    One example of the operation of the radio communication system  1  will be described with reference to  FIG. 8  to  FIG. 11 . 
         [0093]    In the present example, the base station  10 - m  executes processing represented by a flowchart of  FIG. 8  every time a given cycle elapses. 
         [0094]    In the present example, the base station  10 - m  allocates the CC provided by this base station  10 - m  to each piece of radio equipment  20  located in a cell formed by this base station  10 - m  (step S 101  in  FIG. 8 ). In the present example, in the step S 101  in  FIG. 8 , the base station  10 - m  executes processing represented by a flowchart in  FIG. 9 . 
         [0095]    A description will be added below about the processing represented in  FIG. 9 . 
         [0096]    The base station  10 - m  sets the number of pieces of equipment about each of N cc  CCs to 0 (step S 201  in  FIG. 9 ). In other words, the base station  10 - m  sets the number N UEi  of pieces of equipment about each CC #i to 0. 
         [0097]    Next, the base station  10 - m  sequentially executes N u  rounds of loop processing each associated with a respective one of N u  pieces of radio equipment  20  located in the cell formed by this base station  10 - m . Each of the N u  rounds of loop processing may be represented as loop processing for each equipment #k. 
         [0098]    N u  represents the number of pieces of radio equipment  20  located in the cell formed by the base station  10 - m . k represents each integer from 1 to N u . In the present example, equipment #k represents the k-th radio equipment  20 . In the present example, the start point of the loop processing for each equipment #k is a step S 202  and the end point of the loop processing for each equipment #k is a step S 212 . 
         [0099]    A description will be added about the loop processing for each equipment #k. 
         [0100]    The base station  10 - m  sets a flag about each of the N cc  CCs (in other words, flag F i  about each CC #i) to 0 (step S 203  in  FIG. 9 ). When being set to 0, the flag F i  represents that allocation of CC #i to the radio equipment  20  is permitted. When being set to 1, the flag F i  represents that allocation of CC #i to the radio equipment  20  is not permitted. 
         [0101]    Subsequently, the base station  10 - m  sequentially executes N c  rounds of loop processing each associated with a respective one of combinations of two CCs selected from the N cc  CCs provided by this base station  10 - m . The two CCs forming the combination may be represented as CC #i and CC #j. Each of the N c  rounds of loop processing may be represented as loop processing for each of the combinations of CC #i and CC #j. 
         [0102]    N c  represents the number of combinations of the two CCs selected from the N cc  CCs provided by the base station  10 - m . In the present example, N c  represents an integer equal to N cc !/{2!(N cc −2)!}. In the present example, the start point of the loop processing for each of the combinations of CC #i and CC #j is a step S 204  and the end point of the loop processing for each of the combinations of CC #i and CC #j is a step S 209 . 
         [0103]    A description will be added about the loop processing for each of the combinations of CC #i and CC #j. 
         [0104]    The base station  10 - m  determines whether or not a value obtained by subtracting the number N UEj  of pieces of equipment about CC #j different from CC #i from the number N UEi  of pieces of equipment about CC #i (in other words, equipment-number difference N UEi −N UEj ) is larger than a given threshold α 1  (step S 205  in  FIG. 9 ). 
         [0105]    If the equipment-number difference N UEi −N UEj  is larger than the threshold α 1 , the base station  10 - m  makes a determination result of “Yes,” and sets the flag F i  about CC #i to 1 (step S 206  in  FIG. 9 ) to proceed to the step S 209 . 
         [0106]    On the other hand, if the equipment-number difference N UEi −N UEj  is equal to or smaller than the threshold α 1 , the base station  10 - m  makes a determination result of “No,” and proceeds to a step S 207  in  FIG. 9 . Then, the base station  10 - m  determines whether or not the equipment-number difference N UEj −N UEi  is larger than a given threshold α 2  (step S 207  in  FIG. 9 ). The threshold α 2  may have the same value as the threshold α 1 . The threshold α 2  may have a different value from the threshold α 1 . 
         [0107]    If the equipment-number difference N UEj −N UEi  is larger than the threshold α 2 , the base station  10 - m  makes a determination result of “Yes.” Then, the base station  10 - m  sets the flag F j  about CC #j to 1 (step S 208  in  FIG. 9 ) and proceeds to the step S 209 . 
         [0108]    On the other hand, if the equipment-number difference N UEj −N UEi  is equal to or smaller than the threshold α 2 , the base station  10 - m  makes a determination result of “No.” Then, the base station  10 - m  proceeds to the step S 209  without updating the flags F i  and F j . 
         [0109]    In this manner, the base station  10 - m  executes the loop processing for each of the combinations of CC #i and CC #j. 
         [0110]    Then, after executing the loop processing for the combinations of the two CCs selected from the N cc  CCs provided by the base station  10 - m , this base station  10 - m  proceeds to a step S 210  in  FIG. 9 . 
         [0111]    Subsequently, if CC #i whose flag F 1  is set to 0 exists, the base station  10 - m  allocates CC #s with the highest RSRP in the collection of CC #i whose flag F, is set to 0 to equipment #k. s represents an integer from 1 to N cc . On the other hand, if CC #i whose flag F i  is set to 0 does not exist, the base station  10 - m  allocates CC #s with the highest RSRP in the N cc  CCs to equipment #k (step S 210  in  FIG. 9 ). 
         [0112]    Subsequently, the base station  10 - m  adds 1 to the number N UEs  of pieces of equipment about CC #s allocated to equipment #k (step S 211  in  FIG. 9 ) and proceeds to the step S 212 . 
         [0113]    In this manner, the base station  10 - m  executes the loop processing for each equipment #k. 
         [0114]    Then, after executing the N u  rounds of loop processing, the base station  10 - m  ends the processing represented in  FIG. 9 . 
         [0115]    Substantially, the base station  10 - m  determines whether or not a CC switching condition is satisfied (step S 102  in  FIG. 8 ). In the present example, the CC switching condition is a condition that such a CC exists that the number of pieces of radio equipment  20  to which the CC is allocated is equal to or larger than a given threshold. 
         [0116]    If the CC switching condition is satisfied, the base station  10 - m  makes a determination result of “Yes,” and instructs each piece of radio equipment  20  located in the cell formed by the base station  10 - m  to measure the quality of communications by the CC on each CC basis (step S 103  in  FIG. 8 ). 
         [0117]    Thereafter, the base station  10 - m  receives a measurement report from each piece of radio equipment  20  in response to the instruction and decides CC-switched equipment on the basis of the received measurement reports (step S 104  in  FIG. 8 ). The measurement report represents the quality of communications by the CC measured in the radio equipment  20 - n  about each CC. The CC-switched equipment is the radio equipment  20 - n  whose allocated CC is to be changed. 
         [0118]    Then, the base station  10 - m  carries out CC switching for the decided CC-switched equipment (step S 105  in  FIG. 8 ). The CC switching is processing of changing the allocated CC. In the present example, the CC switching includes procedure similar to HO between cells. 
         [0119]    Thereafter, the base station  10 - m  ends the processing represented in  FIG. 8 . 
         [0120]    If the CC switching condition is not satisfied, the base station  10 - m  makes a determination result of “No” in the step S 102  in  FIG. 8 , and ends the processing represented in  FIG. 8 . 
         [0121]    A description will be added below about a concrete example of the operation of the base station  10 - m.    
         [0122]    The case will be assumed in which the number of CCs provided by the base station  10 - m  is 3 and the number of pieces of radio equipment  20  located in a cell formed by the base station  10 - m  is 6 and the threshold α 1  and the threshold α 2  are 0. 
         [0123]    Moreover, the case will be assumed in which the RSRP of each CC is measured in each piece of radio equipment  20  as represented in  FIG. 10 . 
         [0124]    In this case, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 1  (step S 202  in  FIG. 9 ), the numbers N UEi  of pieces of equipment about respective CC #i are all set to 0. Therefore, as represented in  FIG. 11 , the equipment-number difference N UE1 −N UE2  is 0. Similarly, the equipment-number difference N UE2 −N UE3  and the equipment-number difference N UE3 −N UE1  are also 0. 
         [0125]    Therefore, in the loop processing for equipment # 1 , the base station  10 - m  sets the flag F i  to 1 for none of CC #i. In other words, the base station  10 - m  permits allocation of three CCs of CC # 1  to CC # 3  to equipment # 1 . 
         [0126]    As represented in  FIG. 10 , the RSRP about CC # 1  measured in equipment # 1  is the highest in the RSRP about respective CC #i measured in equipment # 1 . Therefore, in the loop processing for equipment # 1 , the base station  10 - m  allocates CC # 1  to equipment # 1  (step S 210  in  FIG. 9 ) and adds 1 to the number N UE1  of pieces of equipment about CC # 1  (step S 211  in  FIG. 9 ). 
         [0127]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 2  (step S 202  in  FIG. 9 ), the number N UE1  of pieces of equipment about CC # 1  is set to 1 and the numbers N UE2  and N UE3  of pieces of equipment about CC # 2  and CC # 3  are set to 0. Therefore, as represented in  FIG. 11 , the equipment-number difference N UE1 −N UE2  is 1, the equipment-number difference N UE2 −N UE3  is 0, and the equipment-number difference N UE3 −N UE  is −1. 
         [0128]    Therefore, in the loop processing for equipment # 2 , the base station  10 - m  sets the flag F 1  about CC # 1  to 1. In other words, the base station  10 - m  permits CC # 2  and CC # 3  among the three CCs of CC # 1  to CC # 3  to be allocated to equipment # 2 . 
         [0129]    As represented in  FIG. 10 , the RSRP about CC # 3  measured in equipment # 2  is higher than the RSRP about CC # 2  measured in equipment # 2 . Therefore, in the loop processing for equipment # 2 , the base station  10 - m  allocates CC # 3  to equipment # 2  (step S 210  in  FIG. 9 ) and adds 1 to the number N UE3  of pieces of equipment about CC # 3  (step S 211  in  FIG. 9 ). 
         [0130]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 3  (step S 202  in  FIG. 9 ), the number N UE2  of pieces of equipment about CC # 2  is set to 0 and the numbers N UE1  and N UE3  of pieces of equipment about CC # 1  and CC # 3  are set to 1. Therefore, as represented in  FIG. 11 , the equipment-number difference N UE1 −N UE2  is 1, the equipment-number difference N UE2 −N UE3  is −1, and the equipment-number difference N UE3 −N UE1  is 0. 
         [0131]    Therefore, in the loop processing for equipment # 3 , the base station  10 - m  sets the flags F 1  and F 3  about CC # 1  and CC # 3  to 1. In other words, the base station  10 - m  permits CC # 2  among the three CCs of CC # 1  to CC # 3  to be allocated to equipment # 3 . 
         [0132]    Therefore, in the loop processing for equipment # 3 , the base station  10 - m  allocates CC # 2  to equipment # 3  (step S 210  in  FIG. 9 ) and adds 1 to the number N UE2  of pieces of equipment about CC # 2  (step S 211  in  FIG. 9 ). 
         [0133]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 4  (step S 202  in  FIG. 9 ), the numbers N UEi  of pieces of equipment about respective CC #i are all set to 1. Therefore, as represented in  FIG. 11 , the equipment-number difference N UE1 −N UE2 , the equipment-number difference N UE2 −N UE3 , and the equipment-number difference N UE3 −N UE1  are all 0. 
         [0134]    Therefore, in the loop processing for equipment # 4 , the base station  10 - m  sets the flag F i  to 1 for none of CC #i. In other words, the base station  10 - m  permits allocation of the three CCs of CC # 1  to CC # 3  to equipment # 4 . 
         [0135]    As represented in  FIG. 10 , the RSRP about CC # 1  measured in equipment # 4  is the highest in the RSRP about respective CC #i measured in equipment # 4 . Therefore, in the loop processing for equipment # 4 , the base station  10 - m  allocates CC # 1  to equipment # 4  (step S 210  in  FIG. 9 ) and adds 1 to the number N UE1  of pieces of equipment about CC # 1  (step S 211  in  FIG. 9 ). 
         [0136]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 5  (step S 202  in  FIG. 9 ), the number N UE1  of pieces of equipment about CC # 1  is set to 2 and the numbers N UE2  and N UE3  of pieces of equipment about CC # 2  and CC # 3  are set to 1. Therefore, as represented in  FIG. 11 , the equipment-number difference N UE1 −N UE2  is 1, the equipment-number difference N UE2 −N UE3  is 0, and the equipment-number difference N UE3 −N UE1  is −1. 
         [0137]    Therefore, in the loop processing for equipment # 5 , the base station  10 - m  sets the flag F 1  about CC # 1  to 1. In other words, the base station  10 - m  permits CC # 2  and CC # 3  among the three CCs of CC # 1  to CC # 3  to be allocated to equipment # 5 . 
         [0138]    As represented in  FIG. 10 , the RSRP about CC # 2  measured in equipment # 5  is higher than the RSRP about CC # 3  measured in equipment # 5 . Therefore, in the loop processing for equipment # 5 , the base station  10 - m  allocates CC # 2  to equipment # 5  (step S 210  in  FIG. 9 ) and adds 1 to the number N UE2  of pieces of equipment about CC # 2  (step S 211  in  FIG. 9 ). 
         [0139]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 6  (step S 202  in  FIG. 9 ), the number N UE3  of pieces of equipment about CC # 3  is set to 1 and the numbers N UE1  and N UE2  of pieces of equipment about CC # 1  and CC # 2  are set to 2. Therefore, as represented in  FIG. 11 , the equipment-number difference N UE1  N UE2  is 0, the equipment-number difference N UE2 −N UE3  is 1, and the equipment-number difference N UE3 −N UE1  is −1. 
         [0140]    Therefore, in the loop processing for equipment # 6 , the base station  10 - m  sets the flags F 1  and F 2  about CC # 1  and CC # 2  to 1. In other words, the base station  10 - m  permits CC # 3  among the three CCs of CC # 1  to CC # 3  to be allocated to equipment # 6 . 
         [0141]    Therefore, in the loop processing for equipment # 6 , the base station  10 - m  allocates CC # 3  to equipment # 6  (step S 210  in  FIG. 9 ) and adds 1 to the number N UE3  of pieces of equipment about CC # 3  (step S 211  in  FIG. 9 ). 
         [0142]    Incidentally, as some posit, the case will be assumed in which a base station does not limit the CC permitted to be allocated to the radio equipment  20  and allocates, with higher priority, the CC with higher RSRP to the radio equipment  20 . Moreover, the case will be assumed in which the RSRP of each CC is measured in each piece of radio equipment  20  as represented in  FIG. 10 . In this case, the base station allocates CC # 1  to each piece of radio equipment  20 . 
         [0143]    In contrast, according to the base station  10 - m  of the first embodiment, the bias in the numbers of pieces of radio equipment  20  to which the respective CCs are allocated can be suppressed. Therefore, according to the base station  10 - m  of the first embodiment, the number of pieces of radio equipment  20  whose allocated CC is changed can be reduced compared with the case in which the base station does not limit the CC permitted to be allocated to the radio equipment  20 . 
         [0144]    As described above, the base station  10 - m  of the first embodiment limits the CC permitted to be allocated to the radio equipment  20 - n  in plural CCs on the basis of the state of communications by each of the plural CCs used for CA. 
         [0145]    This can properly select the CC allocated to the radio equipment  20 - n . As a result, the situation in which the number of pieces of radio equipment  20  that use a specific CC becomes excessively large can be suppressed for example. Therefore, the communication throughput can be enhanced. 
         [0146]    Furthermore, the processing load of the base station  10 - m  can be reduced compared with the case in which the allocated CC is changed after the CC is allocated. As a result, the cost of the base station  10 - m  can be reduced. 
         [0147]    Moreover, in the base station  10 - m  of the first embodiment, the state of communications by the CC includes the load of the communications. 
         [0148]    According to this, the CC whose load of communications is relatively low can be allocated to the radio equipment  20 - n . This can properly select the CC allocated to the radio equipment  20 - n . As a result, the situation in which the number of pieces of radio equipment  20  that use a specific CC becomes excessively large can be suppressed for example. Therefore, the communication throughput can be enhanced. 
         [0149]    Moreover, the base station  10 - m  of the first embodiment allocates, to the radio equipment  20 - n , the CC whose quality of communications is highest in the CCs permitted to be allocated with higher priority. 
         [0150]    According to this, the CC whose quality of communications is relatively high can be allocated to the radio equipment  20 - n . This can properly select the CC allocated to the radio equipment  20 - n . As a result, the lowering of the quality of communications can be suppressed for example. Therefore, the communication throughput can be enhanced. 
         [0151]    As described above, the base station  10 - m  of the first embodiment uses the number of pieces of equipment as the parameter representing the load of communications by the CC. The base station  10 - m  may use the amount of communication traffic or the transmission delay time as the parameter representing the load of communications by the CC. For example, the amount of communication traffic is the amount of data communicated by using the CC. For example, the transmission delay time is the time for which data to be communicated by using the CC is made to wait until the actual communications. 
         [0152]    The load of communications by the CC may be represented as the degree of congestion of communications in the CC. 
         [0153]    Furthermore, the limitation of the CC permitted to be allocated to the radio equipment  20  may be represented as exclusion of the CC from candidates of allocation to the radio equipment  20 . In addition, the limitation of the CC permitted to be allocated to the radio equipment  20  may be represented as setting of the CC prohibited from being allocated to the radio equipment  20 . 
         [0154]    Moreover, limiting the CC permitted to be allocated to the radio equipment  20  in plural CCs may be represented as limiting the CC permitted to be allocated to the radio equipment  20  to the CC as part of the plural CCs. 
       First Modification Example of First Embodiment 
       [0155]    Next, a radio communication system according to a first modification example of the first embodiment will be described. The radio communication system according to the first modification example of the first embodiment is different from the radio communication system according to the first embodiment in that thresholds used for limitation conditions are adjusted. A description will be made below mainly about this difference. In the description of the first modification example of the first embodiment, an object given the same symbol as the symbol used in the first embodiment is the same or substantially similar object. 
         [0156]    In the present example, the CC allocation limitation processing unit  1021  holds a threshold α ij  and a threshold α ji  regarding each of combinations of CC #i and CC #j. In the present example, the limitation condition about the load of communications by CC #i is a condition that such CC #j exists that the equipment-number difference N UEi −N UEj  is larger than the threshold α ij . Similarly, in the present example, the limitation condition about the load of communications by CC #j is a condition that such CC #i exists that the equipment-number difference N UEj −N UEi  is larger than the threshold α ji . 
         [0157]    Moreover, in the present example, if the limitation condition about the load of communications by CC #i is satisfied, the CC allocation limitation processing unit  1021  adds a given change amount Δα to the threshold α ij  regarding CC #i and CC #j with which the equipment-number difference N UEi −N UEj  is larger than the threshold α ij . Similarly, in the present example, if the limitation condition about the load of communications by CC #j is satisfied, the CC allocation limitation processing unit  1021  adds the change amount Δα to the threshold α ji  regarding CC #j and CC #i with which the equipment-number difference N UEj −N UEi  is larger than the threshold α ji . In the present example, the change amount Δα is larger than 0. 
         [0158]    In the present example, the base station  10 - m  executes processing represented in  FIG. 12  instead of the processing represented in  FIG. 9 . The processing represented in  FIG. 12  is processing obtained by replacing the processing from the step S 205  to the step S 208  in the processing represented in  FIG. 9  by processing from a step S 221  to a step S 226 . 
         [0159]    In loop processing for each of the combinations of CC #i and CC #j, the base station  10 - m  determines whether or not the equipment-number difference N UEi −N UEj  is larger than the threshold α ij  (step S 221  in  FIG. 12 ). 
         [0160]    If the equipment-number difference N UEi −N UEj  is larger than the threshold α ij , the base station  10 - m  makes a determination result of “Yes,” and sets the flag F i  about CC #i to 1 (step S 222  in  FIG. 12 ). Subsequently, the base station  10 - m  adds the change amount Δα to the threshold α ij  (step S 223  in  FIG. 12 ) and proceeds to the step S 209 . 
         [0161]    On the other hand, if the equipment-number difference N UEi −N UEj  is equal to or smaller than the threshold α ij , the base station  10 - m  makes a determination result of “No,” and proceeds to the step S 224  in  FIG. 12 . Then, the base station  10 - m  determines whether or not the equipment-number difference N UEj −N UEi  is larger than the threshold α ji  (step S 224  in  FIG. 12 ). 
         [0162]    If the equipment-number difference N UEj −N UEi  is larger than the threshold α ji , the base station  10 - m  makes a determination result of “Yes.” Then, the base station  10 - m  sets the flag F j  about CC #j to 1 (step S 225  in  FIG. 12 ). Subsequently, the base station  10 - m  adds the change amount Δα to the threshold α ji  (step S 226  in  FIG. 12 ) and proceeds to the step S 209 . 
         [0163]    On the other hand, if the equipment-number difference N UEj −N UEi  is equal to or smaller than the threshold α ji , the base station  10 - m  makes a determination result of “No” in the step S 224 . Then, the base station  10 - m  proceeds to the step S 209  without updating the flags F i  and F j . 
         [0164]    According to this, if allocation of CC #i to the radio equipment  20 - n  is not permitted by CC #j, the probability of that allocation of CC #i to the radio equipment  20 - n  is not permitted by CC #j in the next processing can be reduced. Similarly, if allocation of CC #j to the radio equipment  20 - n  is not permitted by CC #i, the probability of that allocation of CC #j to the radio equipment  20 - n  is not permitted by CC #i in the next processing can be reduced. 
         [0165]    In other words, according to the base station  10 - m , ease of permission of allocation of the relevant CC to the radio equipment  20 - n  can be adjusted according to the frequency of limitation of the CC permitted to be allocated to the radio equipment  20 - n.    
         [0166]    As described above, according to the base station  10 - m  of the first modification example of the first embodiment, the same operation and effects as the base station  10 - m  of the first embodiment can be achieved. 
         [0167]    Moreover, the base station  10 - m  of the first modification example of the first embodiment adjusts the threshold α ij  and the threshold α ji  so that allocation of the CC to the radio equipment  20 - n  may be permitted more readily as the frequency at which allocation of this CC to the radio equipment  20 - n  is permitted decreases. 
         [0168]    According to this, the bias in the CCs allocated to the pieces of radio equipment  20 - n  can be suppressed. This can properly select the CC allocated to the radio equipment  20 - n . As a result, the communication throughput can be enhanced. 
       Second Embodiment 
       [0169]    Next, a radio communication system according to a second embodiment will be described. The radio communication system according to the second embodiment is different from the radio communication system according to the first embodiment in the CC allocation method. A description will be made below mainly about the difference. In the description of the second embodiment, an object given the same symbol as the symbol used in the first embodiment is the same or substantially similar object. 
         [0170]    (Functions) 
         [0171]    The CC allocation limitation processing unit  1021  of the second embodiment is different from the CC allocation limitation processing unit  1021  of the first embodiment in that the quality of communications by the CC is used instead of the load of communications by the CC for limitation of the CC permitted to be allocated to the radio equipment  20 . 
         [0172]    Therefore, the CC allocation limitation processing unit  1021  of the second embodiment limits the CC permitted to be allocated to the radio equipment  20  in plural CCs provided by the base station  10 - m  on the basis of the quality of communications by each of the plural CCs. 
         [0173]    In the present example, if a given limitation condition about the quality of communications by the CC is satisfied, the CC allocation limitation processing unit  1021  does not permit allocation of this CC to the radio equipment  20 . 
         [0174]    In the present example, the CC allocation limitation processing unit  1021  uses the SINR about the CC as the parameter representing the quality of communications by this CC. 
         [0175]    In the present example, the limitation condition about the quality of communications by CC #i is a condition that such CC #j exists that a value obtained by subtracting an SINR R k, i  about CC #i and equipment #k from an SINR R k, j  about CC #j different from CC #i and equipment #k is larger than a given threshold β. In the present example, the threshold β is equal to or larger than 0. The value obtained by subtracting the SINR R k, i  about CC #i and equipment #k from the SINR R k, j  about CC #j different from CC #i and equipment #k may be represented as the SINR difference R k, j −R k, i . 
         [0176]    The CC allocating unit  102  of the second embodiment is different from the CC allocating unit  102  of the first embodiment in that a round-robin method is used for allocation of the CC instead of the method in accordance with the quality of communications by the CC. 
         [0177]    Therefore, the CC allocating unit  102  of the second embodiment allocates, to the radio equipment  20 , the CCs permitted to be allocated to the radio equipment  20  by the CC allocation limitation processing unit  1021  in accordance with the round-robin method. 
         [0178]    (Operation) 
         [0179]    One example of the operation of the radio communication system  1  will be described with reference to  FIG. 8  and  FIG. 13  to  FIG. 15 . 
         [0180]    The base station  10 - m  of the second embodiment is different from the base station  10 - m  of the first embodiment in that processing represented in  FIG. 13  is executed in the step S 101  in  FIG. 8  instead of the processing represented in  FIG. 9 , and is different in the CC switching condition in the step S 102  in  FIG. 8 . 
         [0181]    In the present example, the CC switching condition used by the base station  10 - m  of the second embodiment is a condition that such a CC exists that the SINR about the CC and the radio equipment  20  to which this CC is allocated is equal to or lower than a given threshold. 
         [0182]    In the present example, in the step S 101  in  FIG. 8 , the base station  10 - m  executes the processing represented by a flowchart in  FIG. 13 . 
         [0183]    A description will be added below about the processing represented in  FIG. 13 . 
         [0184]    The base station  10 - m  sets a counter c to 0 (step S 301  in  FIG. 13 ). 
         [0185]    Subsequently, the base station  10 - m  sequentially executes N u  rounds of loop processing each associated with a respective one of N u  pieces of radio equipment  20  located in a cell formed by this base station  10 - m . In the present example, the start point of the loop processing for each equipment #k is a step S 302  and the end point of the loop processing for each equipment #k is a step S 316 . 
         [0186]    A description will be added about the loop processing for each equipment #k. 
         [0187]    The base station  10 - m  sets a flag about each of N cc  CCs (in other words, flag F i  about each CC #i) to 0 (S 303  in  FIG. 13 ). 
         [0188]    Subsequently, the base station  10 - m  sequentially executes N c  rounds of loop processing each associated with a respective one of combinations of two CCs selected from the N cc  CCs provided by this base station  10 - m.    
         [0189]    In the present example, the start point of the loop processing for each of the combinations of CC #i and CC #j is a step S 304  and the end point of the loop processing for each of the combinations of CC #i and CC #j is a step S 309 . 
         [0190]    A description will be added about the loop processing for each of the combinations of CC #i and CC #j. 
         [0191]    The base station  10 - m  determines whether or not the SINR difference R k, j −R k, i  is larger than a given threshold β 1  (step S 305  in  FIG. 13 ). 
         [0192]    If the SINR difference R k, j −R k, i  is larger than the threshold β 1 , the base station  10 - m  makes a determination result of “Yes,” and sets the flag F i  about CC #i to 1 (step S 306  in  FIG. 13 ) to proceed to the step S 309 . 
         [0193]    On the other hand, if the SINR difference R k, j −R k, i  is equal to or smaller than the threshold β 1 , the base station  10 - m  makes a determination result of “No,” and proceeds to a step S 307  in  FIG. 13 . Then, the base station  10 - m  determines whether or not the SINR difference R k, i −R k, j  is larger than a given threshold α 2  (step S 307  in  FIG. 13 ). The threshold β 2  may have the same value as the threshold β 1 . The threshold β 2  may have a different value from the threshold β 1 . 
         [0194]    If the SINR difference R k, i −R k, j  is larger than the threshold β 2 , the base station  10 - m  makes a determination result of “Yes.” Then, the base station  10 - m  sets the flag F j  about CC #j to 1 (step S 308  in  FIG. 13 ) and proceeds to the step S 309 . 
         [0195]    On the other hand, if the SINR difference R k, i −R k, j  is equal to or smaller than the threshold β 2 , the base station  10 - m  makes a determination result of “No.” Then, the base station  10 - m  proceeds to the step S 309  without updating the flags F i  and F j . 
         [0196]    In this manner, the base station  10 - m  executes the loop processing for each of the combinations of CC #i and CC #j. 
         [0197]    Then, after executing the loop processing for the combinations of the two CCs selected from the N cc  CCs provided by the base station  10 - m , this base station  10 - m  proceeds to a step S 310  in  FIG. 13 . 
         [0198]    Subsequently, the base station  10 - m  determines whether or not CC #i whose flag F i  is set to 0 exists (step S 310  in  FIG. 13 ). 
         [0199]    If CC #i whose flag F i  is set to 0 exists, the base station  10 - m  makes a determination result of “Yes,” and calculates a value s obtained by adding 1 to the remainder mod(c, N cc ) of division in which the counter c is divided by the number N cc  of CCs provided by the base station  10 - m  (step S 311  in  FIG. 13 ). 
         [0200]    Then, the base station  10 - m  determines whether or not the flag F s  corresponding to the value s calculated in the step S 311  is set to 1 (step S 312  in  FIG. 13 ). 
         [0201]    If the flag F s  is set to 1, the base station  10 - m  makes a determination result of “Yes,” and adds 1 to the counter c (step S 313  in  FIG. 13 ) to return to the step S 311  in  FIG. 13 . Then, the base station  10 - m  repeats the processing from the step S 311  to the step S 313  until a determination result of “No” is made in the step S 312 . 
         [0202]    If the flag F s  is set to 0, the base station  10 - m  makes a determination result of “No” in the step S 312  in  FIG. 13 , and allocates CC #s corresponding to the value s calculated in the step S 311  to equipment #k (step S 314  in  FIG. 13 ). Subsequently, the base station  10 - m  adds 1 to the counter c (step S 315  in  FIG. 13 ) and proceeds to the step S 316 . 
         [0203]    On the other hand, if CC #i whose flag F 1  is set to 0 does not exist, the base station  10 - m  makes a determination result of “No” in the step S 310  in  FIG. 13 , and calculates the value s obtained by adding 1 to the remainder mod(c, N cc ) of division in which the counter c is divided by the number N cc  of CCs provided by the base station  10 - m  (step S 317  in  FIG. 13 ). 
         [0204]    Subsequently, the base station  10 - m  allocates CC #s corresponding to the value s calculated in the step S 317  to equipment #k (step S 314  in  FIG. 13 ). Then, the base station  10 - m  adds 1 to the counter c (step S 315  in  FIG. 13 ) and proceeds to the step S 316 . 
         [0205]    In this manner, the base station  10 - m  executes the loop processing for each equipment #k. 
         [0206]    Then, after executing the N u  rounds of loop processing, the base station  10 - m  ends the processing represented in  FIG. 13 . 
         [0207]    A description will be added below about a concrete example of the operation of the base station  10 - m.    
         [0208]    The case will be assumed in which the number of CCs provided by the base station  10 - m  is 3 and the number of pieces of radio equipment  20  located in a cell formed by the base station  10 - m  is 6 and the threshold β 1  and the threshold β 2  are 3. 
         [0209]    Moreover, the case will be assumed in which the SINR of each CC is measured in each piece of radio equipment  20  as represented in  FIG. 14 . 
         [0210]    In this case, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 1  (step S 302  in  FIG. 13 ), the counter c is set to 0. Furthermore, as represented in  FIG. 15 , the SINR difference R 1, 1 −R 1, 2  is −9. In addition, the SINR difference R 1, 2 −R 1, 3  is 2 and the SINR difference R 1, 3 −R 1, 1  is 7. 
         [0211]    Therefore, in the loop processing for equipment # 1 , the base station  10 - m  sets the flag F 1  about CC # 1  to 1. In other words, the base station  10 - m  permits CC # 2  and CC # 3  among the three CCs of CC # 1  to CC # 3  to be allocated to equipment # 1 . 
         [0212]    Then, the base station  10 - m  calculates 1 as the value s (step S 311  in  FIG. 13 ). Because the flag F 1  about CC # 1  is set to 1, the base station  10 - m  adds 1 to the counter c (step S 313  in  FIG. 13 ) and thereafter calculates 2 as the value s (step S 311  in  FIG. 13 ). 
         [0213]    Because the flag F 2  about CC # 2  is set to 0, the base station  10 - m  allocates CC # 2  to equipment # 1  (step S 314  in  FIG. 13 ) and adds 1 to the counter c (step S 315  in  FIG. 13 ) in the loop processing for equipment # 1 . 
         [0214]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 2  (step S 302  in  FIG. 13 ), the counter c is set to 2. Furthermore, as represented in  FIG. 15 , the SINR difference R 2, 1 −R 2, 2  is −7, the SINR difference R 2, 2 −R 2, 3  is 3, and the SINR difference R 2, 3 −R 2, 1  is 4. 
         [0215]    Therefore, in the loop processing for equipment # 2 , the base station  10 - m  sets the flag F 1  about CC # 1  to 1. In other words, the base station  10 - m  permits CC # 2  and CC # 3  among the three CCs of CC # 1  to CC # 3  to be allocated to equipment # 2 . 
         [0216]    Then, the base station  10 - m  calculates 3 as the value s (step S 311  in  FIG. 13 ). Because the flag F 3  about CC # 3  is set to 0, the base station  10 - m  allocates CC # 3  to equipment # 2  (step S 314  in  FIG. 13 ) and adds 1 to the counter c (step S 315  in  FIG. 13 ) in the loop processing for equipment # 2 . 
         [0217]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 3  (step S 302  in  FIG. 13 ), the counter c is set to 3. Furthermore, as represented in  FIG. 15 , the SINR difference R 3, 1 −R 3, 2  is −4, the SINR difference R 3, 2 −R 3, 3  is 2, and the SINR difference R 3, 3 −R 3, 1  is 2. 
         [0218]    Therefore, in the loop processing for equipment # 3 , the base station  10 - m  sets the flag F 1  about CC # 1  to 1. In other words, the base station  10 - m  permits CC # 2  and CC # 3  among the three CCs of CC # 1  to CC # 3  to be allocated to equipment # 3 . 
         [0219]    Then, the base station  10 - m  calculates 1 as the value s (step S 311  in  FIG. 13 ). Because the flag F 1  about CC # 1  is set to 1, the base station  10 - m  adds 1 to the counter c (step S 313  in  FIG. 13 ) and thereafter calculates 2 as the value s (step S 311  in  FIG. 13 ). 
         [0220]    Because the flag F 2  about CC # 2  is set to 0, the base station  10 - m  allocates CC # 2  to equipment # 3  (step S 314  in  FIG. 13 ) and adds 1 to the counter c (step S 315  in  FIG. 13 ) in the loop processing for equipment # 3 . 
         [0221]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 4  (step S 302  in  FIG. 13 ), the counter c is set to 5. Furthermore, as represented in  FIG. 15 , the SINR difference R 4, 1 −R 4, 2  is 1, the SINR difference R 4, 2 −R 4, 3  is −1, and the SINR difference R 4, 3 −R 4, 1  is 0. 
         [0222]    Therefore, in the loop processing for equipment # 4 , the base station  10 - m  sets the flag F i  to 1 for none of CC #i. In other words, the base station  10 - m  permits allocation of the three CCs of CC # 1  to CC # 3  to equipment # 4 . 
         [0223]    Then, the base station  10 - m  calculates 3 as the value s (step S 311  in  FIG. 13 ). Because the flag F 3  about CC # 3  is set to 0, the base station  10 - m  allocates CC # 3  to equipment # 4  (step S 314  in  FIG. 13 ) and adds 1 to the counter c (step S 315  in  FIG. 13 ) in the loop processing for equipment # 4 . 
         [0224]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 5  (step S 302  in  FIG. 13 ), the counter c is set to 6. Furthermore, as represented in  FIG. 15 , the SINR difference R 5, 1 −R 5, 2  is −1, the SINR difference R 5, 2 −R 5, 3  is 1, and the SINR difference R 5, 3 −R 5, 1  is 0. 
         [0225]    Therefore, in the loop processing for equipment # 5 , the base station  10 - m  sets the flag F i  to 1 for none of CC #i. In other words, the base station  10 - m  permits allocation of the three CCs of CC # 1  to CC # 3  to equipment # 5 . 
         [0226]    Then, the base station  10 - m  calculates 1 as the value s (step S 311  in  FIG. 13 ). Because the flag F 1  about CC # 1  is set to 0, the base station  10 - m  allocates CC # 1  to equipment # 5  (step S 314  in  FIG. 13 ) and adds 1 to the counter c (step S 315  in  FIG. 13 ) in the loop processing for equipment # 5 . 
         [0227]    Next, when the base station  10 - m  advances the processing to the start point of loop processing for equipment # 6  (step S 302  in  FIG. 13 ), the counter c is set to 7. Furthermore, as represented in  FIG. 15 , the SINR difference R 6, 1 −R 6, 2  is 0, the SINR difference R 6, 2 −R 6, 3  is 0, and the SINR difference R 6, 3 −R 6, 1  is 0. 
         [0228]    Therefore, in the loop processing for equipment # 6 , the base station  10 - m  sets the flag F i  to 1 for none of CC #i. In other words, the base station  10 - m  permits allocation of the three CCs of CC # 1  to CC # 3  to equipment # 6 . 
         [0229]    Then, the base station  10 - m  calculates 2 as the value s (step S 311  in  FIG. 13 ). Because the flag F 2  about CC # 2  is set to 0, the base station  10 - m  allocates CC # 2  to equipment # 6  (step S 314  in  FIG. 13 ) and adds 1 to the counter c (step S 315  in  FIG. 13 ) in the loop processing for equipment # 6 . 
         [0230]    Incidentally, as some posit, the case will be assumed in which a base station does not limit the CC permitted to be allocated to the radio equipment  20  and allocates the CC to the radio equipment  20  in accordance with a round-robin method. Moreover, the case will be assumed in which the SINR of each CC is measured in each piece of radio equipment  20  as represented in  FIG. 14 . In this case, the base station allocates CC # 1  to CC # 3  to equipment # 1  to equipment # 3 , respectively, and allocates CC # 1  to CC # 3  to equipment # 4  to equipment # 6 , respectively. 
         [0231]    Therefore, in this case, for example, the SINR about CC # 1  allocated to equipment # 1  is considerably lower than the SINRs about CC # 2  and CC # 3  among the SINRs measured in equipment # 1 . 
         [0232]    In contrast, according to the base station  10 - m  of the second embodiment, the situation in which the CC whose quality of communications by the CC is excessively low is allocated to the radio equipment  20  can be suppressed. Therefore, according to the base station  10 - m  of the second embodiment, the number of pieces of radio equipment  20  whose allocated CC is changed can be reduced compared with the case in which the base station does not limit the CC permitted to be allocated to the radio equipment  20 . 
         [0233]    As described above, the base station  10 - m  of the second embodiment limits the CC permitted to be allocated to the radio equipment  20 - n  in plural CCs on the basis of the state of communications by each of the plural CCs used for CA. 
         [0234]    This can properly select the CC allocated to the radio equipment  20 - n . As a result, the lowering of the quality of communications can be suppressed for example. Therefore, the communication throughput can be enhanced. 
         [0235]    Furthermore, the processing load of the base station  10 - m  can be reduced compared with the case in which the allocated CC is changed after the CC is allocated. As a result, the cost of the base station  10 - m  can be reduced. 
         [0236]    Moreover, in the base station  10 - m  of the second embodiment, the state of communications by the CC includes the quality of the communications. 
         [0237]    According to this, the CC whose quality of communications is relatively high can be allocated to the radio equipment  20 - n . This can properly select the CC allocated to the radio equipment  20 - n . As a result, the lowering of the quality of communications can be suppressed for example. Therefore, the communication throughput can be enhanced. 
         [0238]    Moreover, the base station  10 - m  of the second embodiment allocates the CC for which allocation is permitted to the radio equipment  20 - n  in accordance with a round-robin method. 
         [0239]    According to this, the bias in the CCs allocated to the pieces of radio equipment  20 - n  can be suppressed. As a result, the situation in which the number of pieces of radio equipment  20  that use a specific CC becomes excessively large can be suppressed. Therefore, the communication throughput can be enhanced. 
         [0240]    As described above, the base station  10 - m  of the second embodiment uses the SINR as the parameter representing the quality of communications by the CC. The base station  10 - m  may use RSRP, RSRQ, CQI, or throughput estimate as the parameter representing the quality of communications by the CC. 
         [0241]    For example, the throughput estimate is the amount of information normally transmitted per unit time in communications by the CC. The throughput estimate may be estimated on the basis of a signal representing whether or not information is normally transmitted (for example, signal representing acknowledgement (ACK) or not ACK or negative ACK (NACK)). 
       First Modification Example of Second Embodiment 
       [0242]    Next, a radio communication system according to a first modification example of the second embodiment will be described. The radio communication system according to the first modification example of the second embodiment is different from the radio communication system according to the second embodiment in that thresholds used for limitation conditions are adjusted. A description will be made below mainly about this difference. In the description of the first modification example of the second embodiment, an object given the same symbol as the symbol used in the second embodiment is the same or substantially similar object. 
         [0243]    In the present example, the CC allocation limitation processing unit  1021  decides a threshold β ij  a threshold β ji  regarding each of combinations of CC #i and CC #j. In the present example, the limitation condition about the quality of communications by CC #i is a condition that such CC #j exists that the SINR difference R k, j −R k, i  is larger than the threshold β ij . Similarly, in the present example, the limitation condition about the quality of communications by CC #j is a condition that such CC #i exists that the SINR difference R k, i −R k, j  is larger than the threshold β ji . 
         [0244]    In the present example, the base station  10 - m  executes processing represented in  FIG. 16  instead of the processing represented in  FIG. 13 . The processing of  FIG. 16  is processing obtained by replacing the processing of the step S 305  and the step S 307  in the processing of  FIG. 13  by processing of a step S 322  and a step S 323 , respectively, and adding processing of a step S 321  between the step S 304  and the step S 322 . 
         [0245]    In loop processing for each of the combinations of CC #i and CC #j, the base station  10 - m  decides the threshold β ij  and the threshold β ji  regarding the combination of CC #i and CC #j (step S 321  in  FIG. 16 ). In the present example, the threshold β ij  is a value obtained by averaging the SINR difference R q, j −R q, i  with respect to N u  pieces of radio equipment  20  located in a cell formed by the base station  10 - m . Similarly, in the present example, the threshold β ji  is a value obtained by averaging the SINR difference R q, i −R q, j  with respect to the N u  pieces of radio equipment  20  located in the cell formed by the base station  10 - m . q represents each integer from 1 to N. 
         [0246]    Then, the base station  10 - m  determines whether or not the SINR difference R k, j −R k, i  is larger than the decided threshold β ij  (step S 322  in  FIG. 16 ). 
         [0247]    If the SINR difference R k, j −R k, i  is larger than the decided threshold β ij , the base station  10 - m  makes a determination result of “Yes,” and sets the flag F i  about CC #i to 1 (step S 306  in  FIG. 16 ) to proceed to the step S 309 . 
         [0248]    On the other hand, if the SINR difference R k, j −R k, i  is equal to or smaller than the decided threshold β ij , the base station  10 - m  makes a determination result of “No,” and proceeds to the step S 323  in  FIG. 16 . Then, the base station  10 - m  determines whether or not the SINR difference R k, i −R k, j  is larger than the decided threshold β ji  (step S 323  in  FIG. 16 ). 
         [0249]    If the SINR difference R k, i −R k, j  is larger than the decided threshold β ji , the base station  10 - m  makes a determination result of “Yes.” Then, the base station  10 - m  sets the flag F j  about CC #j to 1 (step S 308  in  FIG. 16 ) and proceeds to the step S 309 . 
         [0250]    On the other hand, if the SINR difference R k, i −R k, j  is equal to or smaller than the decided threshold β ji , the base station  10 - m  makes a determination result of “No.” Then, the base station  10 - m  proceeds to the step S 309  without updating the flags F i  and F j . 
         [0251]    As described above, according to the base station  10 - m  of the first modification example of the second embodiment, the same operation and effects as the base station  10 - m  of the second embodiment can be achieved. 
         [0252]    Furthermore, the base station  10 - m  of the first modification example of the second embodiment decides, regarding each CC, the threshold β ij  and the threshold β ij  on the basis of the values obtained by averaging the parameter representing the state of communications by the CC with respect to plural pieces of radio equipment  20 . Moreover, regarding each piece of radio equipment  20 , the base station  10 - m  carries out the limitation of the CC permitted to be allocated to the radio equipment  20  on the basis of the decided threshold β ij  and threshold β ji  and the parameter of each CC about the piece of radio equipment  20 . 
         [0253]    According to this, when the parameter representing the state of communications by the CC is biased among CCs, the bias in the CCs allocated to the pieces of radio equipment  20 - n  can be suppressed. This can properly select the CC allocated to the radio equipment  20 - n . As a result, the communication throughput can be enhanced. 
         [0254]    The cycle at which the threshold β ij  and the threshold β ji  are decided may be a different cycle from the cycle in the processing represented in  FIG. 16 . For example, the cycle at which the threshold β ij  and the threshold β ji  are decided may be the cycle at which the base station  10 - m  receives a measurement report. Furthermore, the cycle at which the threshold β ij  and the threshold β ji  are decided may be longer than the cycle at which the base station  10 - m  receives the measurement report. 
       Third Embodiment 
       [0255]    Next, a radio communication system according to a third embodiment will be described. The radio communication system according to the third embodiment is different from the radio communication system according to the first embodiment in that the allocation system of the CC is selected from plural different methods. A description will be made below mainly about the difference. In the description of the third embodiment, an object given the same symbol as the symbol used in the first embodiment is the same or substantially similar object. 
         [0256]    (Functions) 
         [0257]    In the present example, as represented in  FIG. 17 , a CC allocating unit  102  of the third embodiment includes a CC allocation method selecting unit  1022  in addition to the functions of the CC allocating unit  102  of the first embodiment. 
         [0258]    In the present example, the CC allocation method selecting unit  1022  selects one CC allocation method from plural different CC allocation methods. The CC allocation method selecting unit  1022  may select one CC allocation method from three or more CC allocation methods. 
         [0259]    In the present example, the plural different CC allocation methods include a first CC allocation method and a second CC allocation method. 
         [0260]    The first CC allocation method is a method used for allocation of the CCs by the CC allocating unit  102  of the first embodiment. 
         [0261]    The second CC allocation method is a method used for allocation of the CCs by the CC allocating unit  102  of the second embodiment. 
         [0262]    The CC allocation limitation processing unit  1021  of the third embodiment functions similarly to the CC allocation limitation processing unit  1021  of the first embodiment if the first CC allocation method is selected by the CC allocation method selecting unit  1022 . In other words, in this case, the CC allocation limitation processing unit  1021  of the third embodiment limits the CC permitted to be allocated to the radio equipment  20  in plural CCs provided by the base station  10 - m  on the basis of the parameter representing the load of communications by each of the plural CCs. 
         [0263]    Moreover, the CC allocation limitation processing unit  1021  of the third embodiment functions similarly to the CC allocation limitation processing unit  1021  of the second embodiment if the second CC allocation method is selected by the CC allocation method selecting unit  1022 . In other words, in this case, the CC allocation limitation processing unit  1021  of the third embodiment limits the CC permitted to be allocated to the radio equipment  20  in plural CCs provided by the base station  10 - m  on the basis of the parameter representing the quality of communications by each of the plural CCs. 
         [0264]    In this manner, the CC allocation limitation processing unit  1021  of the third embodiment uses the parameter selected according to the selected CC allocation method as the parameter representing the state of communications by the CC, used for the limitation of the CC permitted to be allocated to the radio equipment  20 . 
         [0265]    The parameter (in the present example, the number of pieces of equipment) representing the load of communications by the CC is one example of the parameter according to the first CC allocation method. 
         [0266]    The parameter (in the present example, SINR) representing the quality of communications by the CC is one example of the parameter according to the second CC allocation method. 
         [0267]    (Operation) 
         [0268]    One example of the operation of the radio communication system  1  will be described with reference to  FIG. 18 . 
         [0269]    The base station  10 - m  of the third embodiment is different from the base station  10 - m  of the first embodiment in that the base station  10 - m  executes processing represented in  FIG. 18  instead of the processing represented in  FIG. 8 . 
         [0270]    The processing represented in  FIG. 18  is processing obtained by replacing the step S 101  in the processing represented in  FIG. 8  by a step S 401  and a step S 402 . 
         [0271]    In the present example, the base station  10 - m  selects one CC allocation method from plural different CC allocation methods (step S 401  in  FIG. 18 ). Subsequently, in accordance with the selected CC allocation method, the base station  10 - m  allocates CCs provided by this base station  10 - m  to the respective pieces of radio equipment  20  located in a cell formed by this base station  10 - m  (step S 402  in  FIG. 18 ). 
         [0272]    In the present example, when selecting the first CC allocation method, the base station  10 - m  executes the processing represented by the flowchart in  FIG. 9  in the step S 402  in  FIG. 18 . 
         [0273]    Furthermore, in the present example, when selecting the second CC allocation method, the base station  10 - m  executes the processing represented by the flowchart in  FIG. 13  in the step S 402  in  FIG. 18 . 
         [0274]    Thereafter, the base station  10 - m  executes processing from a step S 102  to a step S 105  in  FIG. 18  similarly to the processing from the step S 102  to the step S 105  in  FIG. 8 . 
         [0275]    As described above, according to the base station  10 - m  of the third embodiment, the same operation and effects as the base stations  10 - m  of the first embodiment and the second embodiment can be achieved. 
         [0276]    Furthermore, in the base station  10 - m  of the third embodiment, the CC allocation method is selected from plural different methods. Moreover, the parameter representing the state of communications by the CC is selected according to the selected method from plural different parameters according to the plural different methods. 
         [0277]    According to this, the CC permitted to be allocated to the radio equipment  20 - n  is limited on the basis of the parameter selected according to the CC allocation method. This can properly select the CC allocated to the radio equipment  20 - n . As a result, the communication throughput can be enhanced. 
         [0278]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.