Abstract:
Provided is a small base station apparatus (HeNB), wherein interference between the HeNB and an MeNB can be inhibited, without any exchange of information between the HeNB and the MeNB. In the HeNB ( 100 ), which forms a cell smaller than a cell formed by the MeNB, a pattern generation unit ( 101 ) generates an assigning pattern of subbands to be assigned to the HeNB ( 100 ), from among a plurality of subbands that can be used by the HeNB ( 100 ), wherein combinations of subbands are different for each of the frames. An assignment unit ( 102 ) assigns subbands to communication terminal apparatuses connected to the HeNB ( 100 ), on the basis of the assigning pattern.

Description:
TECHNICAL FIELD 
     The present invention relates to a micro base station apparatus and a method of assigning subbands. 
     BACKGROUND ART 
     Recently, micro base station apparatuses (home base station: Home eNB, hereinafter HeNB) to form small cells have been developed for complementing dead zones of mobile phone networks. The small cell is referred to as a femto cell, covering a smaller communication area than one conventional cell. Conventional large base station apparatuses to form cells having large communication areas (Macro base station: Macro eNB, hereinafter referred to as an MeNB) are set beforehand through an appropriate design of placement of stations by operators. Interference between cells does not make a significant problem owing to an ICIC (Inter Cell Interference Coordination) control function between the MeNBs. In contrast with this, end users can set HeNBs in any place and there is no ICIC control function between the HeNB and the MeNB. Interference between the HeNB and the MeNB therefore makes a significant problem in HeNB. Especially, the placement of the HeNB should not interfere with the communications of any existing MeNB. This is because the MeNB is used for forming an existing communication area, for example, for mobile phone networks, and it is necessary to avoid inconvenience such as sudden disconnection of the mobile phones caused by a newly placed HeNB. 
     With LTE (Long Term Evolution) which has been standardized by international standards organization 3GPP (3rd Generation Partnership Project), subbands allocated to the HeNB are scheduled in a frequency band (including a plurality of subbands) available for the HeNB (see, for example, Non-patent Literature 1). The HeNB assigns subbands based on the resulting schedule and communicates with a communication terminal apparatus (hereinafter, referred to as HUE: Home UE) connected to the HeNB. 
     With LTE, MeNBs (surrounding MeNBs) are connected to each other by an X2 interface. Each eNB (an MeNB and an HeMB), and an MME (Mobility Management Entity)/S-GW (Serving Gateway) or an HeNB GW are connected by an S1 interface (see, for example, Non-Patent Literature 2). By contrast with this, LTE has no interface directly connecting the MeNB and the HeNB. 
     CITATION LIST 
     Non-Patent Literature 
     NPL 1 
     
         
         R4-093651 “Intercell interference management for HeNBs”(ETRI)
 
NPL 2
 
         3GPP TS 36.300 v9.2.0, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2” 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the above conventional technique, subbands assigned to the HeNB through scheduling are fixed (the same subband) over a plurality of frames. When the MeNB and the HeNB exchange no control information at this time, the MeNB may assign the same subband as the subband allocated to the HeNB, to a communication terminal apparatus connected to the MeNB (hereinafter referred to as an MUE: Macro UE). That is to say, subbands used in the MeNB and the HeNB may overlap. 
     In this case, when the MUE receives downlink signals (desired signals) from the MeNB, the MUE may receive interference due to signals transmitted from the HeNB to the HUE in downlink. Also, when the MeNB receives uplink signals (desired signals) from the MUE, the MeNB may receive interference due to signals transmitted from an HUE located in the vicinity of the MeNB to the HeNB in uplink. In view of the above, the communications of the HeNB may interfere with the existing communications of the MeNB. 
     When the HeNB receives uplink signals (desired signals) from the HUE, the HeNB may receive interference due to signals transmitted from an MUE located in the vicinity of the HeNB to the MeNB in uplink. When the HUE receives downlink signals (desired signals) from the HeNB, the HUE may receive interference due to signals transmitted from the MeNB to the MUE in downlink. That is to say, the communications of the MeNB may interfere with the communications of the HeNB. 
     Here, the exchange of control information (for example, information indicating used MeNB subbands) between the MeNB and the HeNB prevents subbands used between the MeNB and the HeNB from overlapping. However, there is no interface that directly connects the MeNB with the HeNB, as described above. Furthermore, when the MeNB and the HeNB exchange information using an Si interface, the information need to be transmitted through other devices (for example, MME/S-GW), so that the delay of a process occurs. 
     It is an object of the present invention to provide a micro base station apparatus and a subband assigning method that can suppress interference between an HeNB and an MeNB without exchanging information between the MeNB and the HeNB. 
     Solution to Problem 
     A micro base station apparatus according to the first aspect of the present invention is a micro base station apparatus forming a smaller cell than a cell formed by a macro base station apparatus, and employs a configuration including: a generation section that generates an assigning pattern of subbands assigned to the micro base station apparatus among a plurality of subbands available for the micro base station apparatus, the assigning pattern having a subband combination which varies every predetermined time interval; and an assignment section that assigns the subbands to a communication terminal apparatus connected to the micro base station apparatus, based on the assigning pattern. 
     A method for assigning subbands according to the second aspect of the present invention is a method for assigning subbands in a micro base station apparatus forming a smaller cell than a cell formed by a macro base station apparatus, and employs a configuration including the steps of: generating an assigning pattern of subbands assigned to the micro base station apparatus among a plurality of subbands available for the micro base station apparatus, the assigning pattern having a subband combination which varies every predetermined time interval; and assigning the subbands to a communication terminal apparatus connected to the micro base station apparatus based on the assigning pattern. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to suppress interference between an HeNB and an MeNB without exchanging information between the MeNB and the HeNB. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of an HeNB according to Embodiment 1 of the present invention; 
         FIG. 2  is a drawing showing an assigning pattern according to Embodiment 1 of the present invention; 
         FIG. 3  is a drawing showing an assigning pattern according to Embodiment 1 of the present invention; 
         FIG. 4  is a drawing showing an assigning pattern according to Embodiment 1 of the present invention; 
         FIG. 5  is a block diagram showing a configuration of an HeNB according to Embodiment 2 of the present invention; 
         FIG. 6  is a drawing showing an assigning pattern according to Embodiment 2 of the present invention; 
         FIG. 7  is a drawing showing an assigning pattern according to Embodiment 2 of the present invention; 
         FIG. 8  is a block diagram showing a configuration of an HeNB according to Embodiment 3 of the present invention; 
         FIG. 9  is a drawing showing an assigning pattern according to Embodiment 3 of the present invention; 
         FIG. 10  is a drawing showing an assigning pattern according to Embodiment 3 of the present invention; 
         FIG. 11  is a drawing showing an assigning pattern according to Embodiment 4 of the present invention; 
         FIG. 12  is a drawing showing an assigning pattern according to Embodiment 4 of the present invention; 
         FIG. 13  is a block diagram showing an HeNB according to Embodiment 5 of the present invention; 
         FIG. 14  is a drawing showing an assigning pattern in discontinuous subbands; and 
         FIG. 15  is a drawing showing an assigning pattern in discontinuous subbands. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments according to the present invention will be described below in detail with reference to the drawings. In the following explanation, embodiments will be described using an LTE as an example, 
     (Embodiment 1) 
       FIG. 1  is a block diagram showing a configuration of an HeNB forming a smaller cell than one formed by an MeNB. In HeNB  100  shown in  FIG. 1 , pattern generating section  101  receives as input information showing the number of subbands used by HeNB  100  (the number of used subbands) and a total number of subbands available for HeNB  100 . Pattern generating section  101  then generates an assigning pattern of subbands assigned to HeNB  100  (and an HUE), based on the number of used subbands and the total number of subbands. Specifically, pattern generating section  101  selects subbands assigned to HeNB  100  (an HUE) (the number of used subbands) from among a plurality of subbands available for HeNB  100  (the total number of subbands), and generates an assigning pattern including the selected subbands. Pattern generating section  101  generates an assigning pattern having a subband combination which varies every predetermined time interval (one frame in the present embodiment). The predetermined time interval is not limited to one frame, and may be a plurality of frames (this is the same as in the following embodiments). 
     Assignment section  102  assigns subbands to an HUE based on the assigning pattern inputted from pattern generating section  101 . 
     Notification section  103  notifies an HUE connected to HeNB  100  of notification information showing subband assignment result in assignment section  102 . 
     Details of a process in HeNB  100  will be then described. 
     In the following description, subbands available for HeNB  100  are defined to be subbands  1  to  12  (subband total number: 12) as shown in  FIG. 2 . Subbands used for HeNB  100  in each frame are assumed to be four (the number of used subbands: 4). As shown in  FIG. 2 , MUEs are assigned to three subbands  6  to  8  over a plurality of frames. 
     Pattern generating section  101  generates an assigning pattern of subbands assigned to HeNB  100  (Here, four subbands) among twelve subbands  1  to  12  shown in  FIG. 2 , every frame. At this time, pattern generating section  101  generates an assigning pattern having a subband combination which varies every frame. Pattern generating section  101  randomly selects four subbands from subbands  1  to  12  shown in  FIG. 2  every frame, thereby generating an assigning pattern having a subband combination which varies every frame, for example. 
     In frame  1  shown in  FIG. 2 , pattern generating section  101 , for example, generates an assigning pattern including a combination of subbands  2 ,  6 ,  7 , and  11 . As shown in  FIG. 2 , pattern generating section  101  also generates an assigning pattern including a combination of subbands  2 ,  4 ,  10 , and  12  in frame  2 , an assigning pattern including subbands  1 ,  3 ,  5 , and  9  in frame  3 , an assigning pattern including subbands  2 ,  3 ,  8 , and  11  in frame  4 . 
     Here, it is assumed that HUE  1  and HUE  2  are connected to HeNB  100 . As shown in  FIG. 3 , assignment section  102  assigns subbands to each of HUE  1  and HUE  2  based on the assigning pattern shown in  FIG. 2 . In frame  1  shown in  FIG. 3 , assignment section  102  assigns subbands  6  and  11  to HUE  1 , and assigns subbands  2  and  7  to HUE  2  among subbands  2 ,  6 ,  7 , and  11  shown in the assigning pattern, for example. In frame  2  shown in  FIG. 3 , assignment section  102  similarly assigns subbands  4  and  12  to HUE  1 , and assigns subbands  2  and  10  to HUE  2  among subbands  2 ,  4 ,  10 , and  12  shown in the assigning pattern. In frame  3  and frame  4  shown in  FIG. 3 , assignment section  102  assigns subbands in the same manner as the above. 
     Pattern generating section  101  and assignment section  102  perform the same process as the above on frames other than frames  1  to  4  (frame  5  and thereafter, not shown). 
     Then, notification section  103  notifies HUE  1  and HUE  2  of notification information showing a subband assignment result shown in  FIG. 3 . 
     In view of the above, even if the same subband is assigned to the HUE and the MUE in a frame (for example, frame  1  shown in  FIG. 3 ), varying a subband combination included in a subband assigning pattern every frame reduces the probability that the same subband is assigned to the HUE and the MUE in the next frame (for example, frame  2  shown in  FIG. 3 ). That is to say, each subband (subbands  1  to  12  shown in  FIG. 3 ) is equally assigned to HeNB  100 , so that the probability that subbands used for HeNB  100  and the MeNB overlap over a plurality of frames is reduced. 
     Accordingly, the above process reduces the probability that signals transmitted from an HeNB to the HUE in downlink interfere with the MUE when the MUE receives downlink signals (desired signals) from the MeNB, for example. Moreover, the above process reduces the probability that signals transmitted from the MeNB to the MUE in downlink interfere with the HUE when the HUE receives downlink signals (desired signals) from the HeNB. 
     Next, as shown in  FIG. 4 , a case will be described where an MeNB is assigned to three subbands  6  to  8  over a plurality of frames as with  FIG. 3 . In  FIG. 4 , pattern generating section  101  of HeNB  100  generates the assigning pattern shown in  FIG. 2  and assignment section  102  assigns subbands to UEs based on the assigning pattern shown in  FIG. 2 . 
     In  FIG. 4  as well, the above process reduces the probability that signals transmitted from an HUE located in the vicinity of the MeNB to the HeNB in uplink interfere with the MeNB over a plurality of frames when the MeNB receives uplink signals (desired signals) from the MUE, for example. The above process reduces the probability that signals transmitted from an MUE located in the vicinity of the HeNB to the MeNB in uplink interfere with the HeNB over a plurality of frames when the HeNB receives uplink signals (desired signals) from the HUE. 
     That is to say, varying a subband combination included in a subband assigning pattern, every frame can randomize (average) interference between the MeNB (MUE) and the HeNB (HUE) as shown in  FIG. 3  and  FIG. 4 . This makes it possible to reduce the probability that the communications of HeNB  100  interfere with the communications of an existing MeNB and to reduce the probability that the communications of the MeNB interfere with the communications of HeNB  100 . 
     HeNB  100  also generates a subband assigning pattern based on only a total number of subbands available for HeNB  100  and the number of used subbands for HeNB  100 . That is to say, HeNB  100  can generate a subband assigning pattern without exchanging information (for example, information showing the used MeNB subbands) with the MeNB. 
     According to the present embodiment, it is possible to suppress interference between an HeNB and an MeNB without exchanging information between the MeNB and the HeNB. 
     (Embodiment 2) 
       FIG. 5  is a block diagram showing a configuration of an HeNB according to the present embodiment. Here, in  FIG. 5 , the same components as in  FIG. 1  will be assigned the same reference numerals, and overlapping descriptions will be omitted. 
     In HeNB  200  according to the present embodiment shown in  FIG. 5 , detection section  201  detects signals from an MUE (uplink signals transmitted from the MUE to an MeNB) from signals received in the reception section of HeNB  200  (not shown). 
     Specification section  202  specifies subbands (positions and the number of subbands) to which signals from the MUE are assigned among a plurality of subbands, using the signals detected in detection section  201 . Specification section  202 , for example, specifies subbands to which signals having lager power than a preset threshold are assigned among the signals detected in detection section  201 . In other words, specification section  202  specifies the subbands (interference bands) which may interfere with HeNB  200  (or the HUE). Specification section  202  then outputs subband information showing the specified subbands to pattern generating section  203 . 
     Pattern generating section  203  generates an assigning pattern of subbands assigned to HeNB  200  (and the HUE) based on the number of used subbands of HeNB  200  and the subband information inputted from specification section  202 . Specifically, pattern generating section  203  selects subbands assigned by HeNB  200  to the HUE, in subbands other than subbands to which signals from the MUE are assigned (interference bands), from among a plurality of subbands available for HeNB  200 , and generates an assigning pattern including the selected subbands (subbands assigned to the HUE). 
     Next, a process in HeNB  200  according to the present embodiment will be described in detail. 
     In the following description, subbands available for HeNB  200  are assumed to be subbands  1  to  12  (subband total number: 12) as shown in  FIG. 6  as with Embodiment 1. Subbands used for HeNB  200  in each frame are assumed to be four (the number of used subbands: 4) as with Embodiment 1. 
     In  FIG. 6 , specification section  202  specifies three subbands  6  to  8  as subbands (interference bands) to which signals having lager power than a preset threshold are assigned, among the signals from the MUE detected in detection section  201 . 
     Pattern generating section  203  generates an assigning pattern of subbands (four subbands) assigned to HeNB  100  in subbands (subbands  1  to  5  and subbands  9  to  12 ) other than subbands  6  to  8  (interference bands) specified in specification section  202 , among twelve subbands  1  to  12  shown in  FIG. 6 . 
     Pattern generating section  203 , for example, generates an assigning pattern including a combination of subbands  2 ,  4 ,  9 , and  11  among subbands  1  to  5  and subbands  9  to  12  (subbands other than subbands  6  to  8 ) as shown in  FIG. 6 . 
     Here, HUE  1  and HUE  2  are assumed to be connected to HeNB  200  as with Embodiment 1 ( FIG. 3 ). Assignment section  102  assigns subbands  4  and  11  to HUE  1 , and assigns subbands  2  and  9  to HUE  2  among subbands  2 ,  4 ,  9 , and  11  shown in the assigning pattern, as shown in  FIG. 6 . 
     In view of the above, HeNB  200  generates a subband assigning pattern to the HUE in subbands other than subbands to which signals which may interfere with HeNB  200  (HUE) (signals from an MUE) are assigned. That is to say, HeNB  200  does not assign subbands to which signals having a possibility of interfering with HeNB  200  (HUE) are assigned, to the HUE. 
     By this means, HeNB  200  (HUE) and the MUE which may interfere with HeNB  200  are not assigned to the same subband over all frames. Accordingly, in  FIG. 6 , signals transmitted from the HeNB to the HUE in downlink do not interfere with the MUE when the MUE receives downlink signals (desired signals) from the MeNB, for example. Moreover, signals transmitted from the MeNB to the MUE in downlink do not interfere with the HUE when the HUE receives downlink signals (desired signals) from the HeNB. 
     Similarly, even when the MeNB is assigned to three subbands  6  to  8  over a plurality of frames instead of the MUE shown in  FIG. 4  (not shown), for example, signals transmitted from the HUE located in the vicinity of an MeNB to the HeNB in uplink do not interfere with the MeNB when the MeNB receives uplink signals (desired signals) from the MUE. Moreover, signals transmitted from an MUE located in the vicinity of the HeNB to the MeNB in uplink do not interfere with the HeNB when the HeNB receives signals (desired signals) from the HUE. 
     HeNB  200  also generates a subband assigning pattern based on only the signals from an MUE, which are detected in detection section  201 , a total number of subbands available for HeNB  200 , and the number of used subbands of HeNB  200 . That is to say, HeNB  200  can generate a subband assigning pattern without exchanging information (for example, information showing the used MeNB subbands) with the MeNB, as with Embodiment 1. 
     In view of the above, according to the present embodiment, it is possible to suppress interference between an HeNB and an MeNB without exchanging information between the MeNB and the HeNB as with Embodiment 1. 
     In the present embodiment, a case has been described where pattern generating section  203  in HeNB  200  employs the same subband combination included in the subband assigning pattern every frame. Pattern generating section  203  may vary a subband combination included in the assigning pattern every frame by combining the present embodiment with Embodiment 1. For example, pattern generating section  203  randomly selects four subbands every frame in subbands (subbands  1  to  5  and subbands  9  to  12 ) other than subbands  6  to  8  (interference bands) specified in specification section  202  from among twelve subbands  1  to  12 , as shown in  FIG. 7 , thereby generating an assigning pattern having a subband combination which varies every frame. 
     This makes it possible to avoid assigning a subband to HeNB  200  (HUE) in interference bands (subbands  6  to  8  in  FIG. 7 ) and prevent HeNB  200  (HUE) from receiving interference from the MUE (an MUE for which signals are assigned to subbands having higher received signal power than a threshold). Furthermore, employing the assigning pattern having a subband combination which varies every frame as with Embodiment 1 in subbands other than the interference bands can randomize (average) interference between other MUEs (MUEs for which signals are assigned to subbands having received signal power equal to or less than a threshold) and HeNB  200 , and suppress interference between the MeNB and HeNB  200 . 
     (Embodiment 3) 
       FIG. 8  is a block diagram showing a configuration of an HeNB according to the present embodiment. Here, in  FIG. 8 , the same components as in  FIG. 5  will be assigned the same reference numerals, and overlapping descriptions will be omitted. 
     In HeNB  300  according to the present embodiment, specification section  301  specifies subbands (positions and the number of subbands) to which signals from an MUE are assigned among a plurality of subbands, using the signals detected in detection section  201 , as with specification section  202  in Embodiment 2. Furthermore, specification section  301  specifies received signal power (that is to say, interference power) in subbands to which signals from the MUE are assigned. 
     Subband number determination section  302  first classifies a plurality of subbands available for HeNB  300  into a plurality of subband groups according to the level of the specified received signal power in specification section  301 . That is to say, subband number determination section  302  groups the plurality of subbands available for HeNB  300  into subband groups including subbands having the same degree of received signal power. Subband number determination section  302  then determines the number of subbands used for an assigning pattern every subband group such that HeNB  300  is assigned to subband groups having lower received signal power. Here, a total number of subbands determined in each subband group is the number of used subbands of HeNB  300 . 
     Pattern generating section  303  generates an assigning pattern of subbands assigned to HeNB  300  (and an HUE) based on the number of subbands determined in subband number determination section  302 . Specifically, pattern generating section  303  generates the assigning pattern of subbands by extracting the number of subbands determined in each subband group in subband number determination section  302  from subbands in each subband group. That is to say, pattern generating section  303  generates the subband assigning pattern such that a larger number of subbands forming a subband group having lower received signal power are assigned to HeNB  300 , among the plurality of subband groups resulting from the classification according to the level of received signal power. 
     Next, a process in HeNB  300  according to the present embodiment will be described in detail. 
     In the following description, subbands available for HeNB  300  are assumed to be subbands  1  to  12  (subband total number: 12) as shown in  FIG. 9  as with Embodiment 1. Subbands used for HeNB  300  in each frame are assumed to be six (the number of used subbands: 6). 
     In  FIG. 9 , specification section  301  specifies subbands (subbands  3  to  11 ) to which signals from the MUEs are assigned, using the signals detected in detection section  201 . Furthermore, specification section  301  specifies received signal power in subbands to which signals from the MUEs are assigned. In HeNB  300 , subbands  6  to  8  (subbands to which signals from MUE  2  are assigned) have the highest received signal power, subbands  3  to  5  (subbands to which signals from MUE  3  are assigned) have the second highest received signal power, and subbands  9  to  11  (subbands to which signals from MUE  1  are assigned) have the third highest received signal power as shown in  FIG. 9 . Meanwhile, HeNB  300  does not detect any signals from the MUEs in subbands  1 ,  2 , and  12 , and received signal power in subbands  1 ,  2 , and  12  is lowest. 
     Subband number determination section  302  then classifies subbands  1  to  12  shown in  FIG. 9  into a plurality of subband groups according to the level of the specified received signal power in specification section  301 . Specifically, subband number determination section  302  classifies subbands into a subband group including subbands  1 ,  2 , and  12  having the lowest received signal power, a subband group including subbands  9  to  11  having the second lowest received signal power, a subband group including subbands  3  to  5  having the third lowest received signal power, and a subband group including subbands  6  to  8  having the highest received signal power. 
     Next, subband number determination section  302  determines the number of subbands used for the assigning pattern every subband group such that HeNB  300  is assigned to a subband group having lower received signal power. Since the number of subbands used for HeNB  300  is six, subband number determination section  302  determines the number of subbands used for an assigning pattern in a subband group including subbands  1 ,  2 , and  12  as three, determines the number of subbands used for the assigning pattern in a subband group including subbands  9  to  11  as two, determines the number of subbands used for the assigning pattern in a subband group including subbands  3  to  5  as one, and determines the number of subbands used for the assigning pattern in a subband group including subbands  6  to  8  as zero, for example. 
     Pattern generating section  303  then generates a subband assigning pattern based on the number of subbands in each subband group determined in subband number determination section  302 . That is to say, pattern generating section  303  generates the subband assigning pattern such that a larger number of subbands forming a subband group having lower received signal power are assigned to HeNB  300 . As shown in  FIG. 9 , pattern generating section  303  extracts all subbands  1 ,  2 , and  12  since subband number determination section  302  has determined the number of subbands as three in the subband group including subbands  1 ,  2 , and  12 , for example. As shown in  FIG. 9 , pattern generating section  303  also extracts two subbands of subbands  9  and  11  from subbands  9  to  11  since subband number determination section  302  has determined the number of subbands as two in the subband group including subbands  9  to  11 . The same applies to subband group including subbands  3  to  5  shown in  FIG. 9 . On the other hand, pattern generating section  303  extracts no subband in the subband group including subbands  6  to  8  shown in  FIG. 9 . 
     That is to say, pattern generating section  303  generates the assigning pattern including the combination of subbands  1 ,  2 ,  4 ,  9 ,  11 , and  12  among subbands  1  to  12  as shown in  FIG. 9 . 
     In view of the above, a subband group having lower received signal power (that is to say, the power of interference signals to HeNB  300  (or the HUE)) has a larger number of subbands used for the assigning pattern. Here, subbands forming a subband group having the highest received signal power (subbands  6  to  8 ) are not used for the assigning pattern as with Embodiment 2. 
     Here, HUE  1 , HUE  2 , and HUE  3  are assumed to be connected to HeNB  300 . As shown in  FIG. 9 , assignment section  102  assigns subbands  4  and  12  to HUE  1 , assigns subbands  2  and  9  to HUE  2 , assigns subbands  1  and  11  to HUE  3  among subbands  1 ,  2 ,  4 ,  9 ,  11 , and  12  shown in the assigning pattern. 
     As the power of signals from the MUE (received signal power), that is, the power of interference signals is high, the effect on the communications of HeNB  300  increases. Meanwhile, subbands having lower power (the power of interference signals) of signals from the MUE are likely to be assigned to HeNB  300 . In other words, subbands having higher power (the power of interference signals) of signals from the MUE are not likely to be assigned to HeNB  300 . Especially, HeNB  300  does not assign subbands (subbands  6  to  8  in  FIG. 9 ) forming a subband group having the highest power of signals (the power of interference signals) from the MUE among a plurality of subbands to HeNB  300 . 
     The present embodiment avoids assigning subbands to HeNB  300  (HUE) in a subband which is likely to receive interference from an MUE and therefore can suppress interference from the MUE. 
     HeNB  300  also generates a subband assigning pattern based on only signals from the MUE, which are detected in detection section  201 , a total number of subbands available for HeNB  300 , and the number of subbands used for HeNB  300  as with Embodiment 2. That is to say, HeNB  300  can generate the subband assigning pattern without exchanging information (for example, information showing the used MeNB subbands) with the MeNB as with Embodiment 2. 
     In view of the above, the present embodiment can suppress interference between an HeNB and an MeNB without exchanging information between the MeNB and the HeNB as with Embodiment 1. The present embodiment also avoids assigning subbands to the HeNB in subbands receiving interference from the MUE (interference bands) as with Embodiment 2. Furthermore, HeNB is likely to be assigned to subbands which are not likely to receive interference from the MUE in the present embodiment. This makes it possible to further suppress interference between the MeNB and the HeNB. 
     In the present embodiment, a case has been described where pattern generating section  303  in HeNB  300  employs the same subband combination included in a subband assigning pattern every frame. However, pattern generating section  303  may vary a subband combination included in the assigning pattern every frame by combining the present embodiment with Embodiment 1. As shown in  FIG. 10 , subband number determination section  302 , for example, classifies twelve subbands  1  to  12  into a plurality of subband groups according to received signal power, and determines the number of subbands used for the assigning pattern every subband group such that HeNB  300  is assigned to subbands forming a subband group having lower received signal power as with  FIG. 9 . Pattern generating section  303  then extracts subbands used for the assigning pattern based on the number of subbands in each subband group, which is determined in subband number determination section  302 . At this time, pattern generating section  303  varies a combination of subbands used for an assigning pattern every frame as shown in  FIG. 10 . 
     This avoid assigning subbands to HeNB  300  in a subband which is likely to receive interference, and can thereby suppress interference between the MeNB and HeNB  300  as with the present embodiment. Furthermore, Embodiment 3 can randomize (average) interference between the MeNB and HeNB  300  using an assigning pattern having a subband combination which varies every frame and therefore suppress interference between the MeNB and HeNB  300  as with Embodiment 1. 
     (Embodiment 4) 
     In HeNB  300  ( FIG. 8 ) according to the present embodiment, subband number determination section  302  first classifies a plurality of subbands available for HeNB  300  into a plurality of subband groups according to the level of the received signal power specified in specification section  301  as with Embodiment 3. Subband number determination section  302  then determines the number of subbands used for an assigning pattern every subband group such that subbands are assigned to HeNB  300  in sequence from subbands forming a subband group having lower received signal power. Here, a total number of subbands determined in each subband group is the number of subbands used for HeNB  300 . 
     Pattern generating section  303  generates an assigning pattern of subbands assigned to HeNB  300  (and an HUE) based on the number of subbands determined in subband number determination section  302 . Specifically, pattern generating section  303  generates a subband assigning pattern such that subbands are assigned to HeNB  300  in sequence from subbands forming a subband group having lower received signal power among a plurality of subband groups classified according to the level of received signal power. 
     Next, a process in HeNB  300  according to the present embodiment will be described in detail. 
     In the following description, subbands available for HeNB  300  are assumed to be subbands  1  to  12  (subband total number: 12) as shown in  FIG. 11  as with Embodiment 3 ( FIG. 9 ). Subbands used for HeNB  300  in each frame are assumed to be four (the number of used subbands: 4). 
     In HeNB  300 , subbands  6  to  8  (subbands to which signals from MUE  2  are assigned) have the highest received signal power, subbands  3  to  5  (subbands to which signals from MUE  3  are assigned) have the second highest received signal power, and subbands  9  to  11  (subbands to which signals from MUE  1  are assigned) have the third highest received signal power as shown in  FIG. 11  as with Embodiment 3 ( FIG. 9 ). On the other hand, HeNB  300  does not detect any signals from the MUEs in subbands  1 ,  2 , and  12 , and the received signal power is the lowest level. 
     Accordingly, subband number determination section  302  classifies subbands  1  to  12  shown in  FIG. 11  into a subband group including subbands  1 ,  2 , and  12  having the lowest received signal power, a subband group including subbands  9  to  11  having the second lowest received signal power, a subband group including subbands  3  to  5  having the third lowest received signal power, and a subband group including subbands  6  to  8  having the highest received signal power as with Embodiment 3 ( FIG. 9 ). 
     Next, subband number determination section  302  determines the number of subbands used for the assigning pattern every subband group such that subbands are assigned to HeNB  300  in sequence from subbands forming a subband group having lower received signal power. Since the number of subbands used for HeNB  300  is four, for example, subband number determination section  302  first determines the number of subbands used for the assigning pattern in a subband group including subbands  1 ,  2 , and  12  having the lowest received signal power as three. Here, while the number of subbands used for HeNB  300  is four, the number of determined subbands is three. Subband number determination section  302  therefore needs to further determine another subband. Subband number determination section  302  further determines the number of subbands used for the assigning pattern as one (=4−3) in a subband group including subbands  9  to  11  having the second lowest received signal power. A total number of subbands determined in each subband group is the number of used subbands for HeNB  300  (that is to say, four). Accordingly, subband number determination section  302  determines the number of subbands used for the assigning pattern as zero in a subband group including subbands  3  to  5  and a subband group including subbands  6  to  8 . 
     Pattern generating section  303  then generates the subband assigning pattern such that subbands are assigned to HeNB  300  in sequence from subbands forming a subband group having lower received signal power. As shown in  FIG. 11 , pattern generating section  303 , for example, extracts all subbands  1 ,  2 , and  12  since subband number determination section  302  has determined the number of subbands as three in the subband group including subbands  1 ,  2 , and  12 . As shown in  FIG. 11 , pattern generating section  303  also extracts, one subband, for example, subband  10 , from subbands  9  to  11  since subband number determination section  302  has determined the number of subbands as one in the subband group including subbands  9  to  11 . On the other hand, pattern generating section  303  extracts no subband in the subband group including subbands  3  to  5  and the subband group including subbands  6  to  8  shown in  FIG. 11 . 
     That is to say, pattern generating section  303  generates an assigning pattern including a combination of subbands  1 ,  2 ,  10 , and  12  among subbands  1  to  12  as shown in  FIG. 11 . 
     Here, HUE  1  and HUE  2  are assumed to be connected to HeNB  300 . Assignment section  102  assigns subbands  1  and  12  to HUE  1 , and assigns subbands  2  and  10  to HUE  2  among subbands  1 ,  2 ,  10 , and  12  shown in the assigning pattern as shown in  FIG. 11 . 
     In view of the above, HeNB  300  assigns subbands to HeNB  300  in sequence from subbands (subbands having lower interference from signals of an MUE) having lower received signal power (that is to say, power of interference signals to HeNB  300  (or an HUE)). The subbands assigned to HeNB  300  (subbands included in the assigning pattern) are a combination of subbands having lower interference from signals of the MUEs among a plurality of subbands available for HeNB  300  (subbands  1  to  12  in  FIG. 11 ). This makes it possible to suppress interference between HeNB  300  (HUE) and an MeNB (MUE) to the lowest level. 
     HeNB  300  also generates the subband assigning pattern based on only signals from the MUEs, which are detected in detection section  201 , a total number of subbands available for HeNB  300 , and the number of subband used for HeNB  300  as with Embodiment 3. That is to say, HeNB  300  can generate the subband assigning pattern without exchanging information (for example, information showing the used MeNB subbands) with the MeNB as with Embodiment 3. 
     In view of the above, the present embodiment can suppress interference between an HeNB and an MeNB without exchanging information between the MeNB and the HeNB as with Embodiment 1. The present embodiment preferentially assigns subbands to the HeNB in sequence from subbands having a lower effect from signals of the MUEs, and therefore can suppress interference between the MeNB and the HeNB to the lowest level. 
     In the present embodiment, a case has been described where pattern generating section  303  in HeNB  300  employs the same subband combination included in a subband assigning pattern every frame. However, pattern generating section  303  may vary a subband combination included in the assigning pattern every frame by combining the present embodiment with Embodiment 1, As shown in  FIG. 12 , subband number determination section  302 , for example, classifies twelve subbands  1  to  12  into a plurality of subband groups according to received signal power, and determines the number of subbands used for the assigning pattern every subband group in such that subbands are assigned to HeNB  300  in sequence from subbands forming a subband group having lower received signal power as with  FIG. 11 . Pattern generating section  303  then extracts subbands used for the assigning pattern based on the number of subbands in each subband group determined in subband number determination section  302 . At this time, pattern generating section  303  varies a combination of subbands used for an assigning pattern every frame as shown in  FIG. 12 . Furthermore, pattern generating section  303  varies subbands assigned to different HUEs (HUE  1  and HUE  2  in  FIG. 12 ) in subbands used for the assigning pattern, every frame. 
     This makes it possible to preferentially assign subbands to HeNB  300  in sequence from subbands having a lower effect from signals of the MUEs, and to suppress interference between the MeNB and the HeNB to the lowest level as with the present embodiment. Furthermore, Embodiment 4 can randomize (average) interference between the MeNB and HeNB  300  using an assigning pattern having a subband combination which varies every frame and therefore suppress interference between the MeNB and HeNB  300  as with Embodiment 1. 
     (Embodiment 5) 
     In the present embodiment, a plurality of HeNBs which are adjacent to each other will be described. In the following description, a case where three HeNBs  1  to  3  are adjacent to each other will be described as shown in  FIG. 13 . HeNBs  1  to  3  shown in  FIG. 13  include the configuration of HeNB  100  ( FIG. 1 ) according to Embodiment 1, for example. 
     That is to say, pattern generating section  101  in each of HeNBs  1  to  3  shown in  FIG. 13  generates an assigning pattern having a combination of subbands assigned to the HeNB varies every frame in subbands available for the HeNB as shown in  FIG. 3 . It is noted that HeNBs  1  to  3  shown in  FIG. 13  independently set assigning patterns used in the HeNBs. 
     In view of the above, HeNBs  1  to  3  shown in  FIG. 13  which are adjacent to each other independently generate assigning patterns. HeNBs  1  to  3  are therefore likely to use different assigning patterns in each frame. Specifically, although there is a possibility that a plurality of adjacent HeNBs generate the identical assigning patterns in a certain frame (the probability of using the same subband), the probability of generating the identical assigning patterns in a plurality of continuous frames is reduced. This makes it possible to randomize (average) interference which may be given between HeNBs  1  to  3  adjacent to each other shown in  FIG. 13 . 
     Accordingly, the present embodiment, for example, can reduce the probability that signals transmitted from a certain HeNB to an HUE connected to the HeNB in downlink interfere with an HUE connected to another HeNB adjacent thereto over a plurality of frames. The present embodiment can reduce the probability that signals transmitted from an HUE connected to a certain HeNB to the HeNB in uplink interfere with another adjacent HeNB over a plurality of frames. 
     HeNBs  1  to  3  shown in  FIG. 13  can randomize (average) interference between HeNBs and an MeNB (not shown) as with Embodiment 1 and can suppress interference between the HeNBs and the MeNB. 
     HeNBs  1  to  3  shown in  FIG. 13  each generate a subband assigning pattern based on only a total number of subbands available for HeNB  100 , and the number of subbands used for HeNB  100  as with Embodiment 1. That is to say, HeNBs  1  to  3  shown in  FIG. 13  can each generate the subband assigning pattern without exchanging information (for example, information showing the used subbands in each apparatus) with the MeNB, and with adjacent HeNBs. 
     In view of the above, the present embodiment can suppress interference between an HeNB and an MeNB without exchanging information between the MeNB and the HeNB as with Embodiment 1. Furthermore, the present embodiment can suppress interference between HeNBs without exchanging information between a plurality of adjacent HeNBs. 
     In the present embodiment, a case has been described where HeNBs  1  to  3  shown in  FIG. 13  include the configuration of HeNB  100  ( FIG. 1 ) according to Embodiment 1. However, HeNBs  1  to  3  shown in  FIG. 13  may include the configuration of the HeNB according to Embodiments 2 to 4 (HeNB  200  ( FIG. 5 ), HeNB  300  ( FIG. 8 )). In this case, the HeNB can obtain the same effect as that of each embodiment and suppress interference with HeNBs as with the present embodiment, 
     Embodiments of the present invention have been described above. 
     The embodiments have been described using an LTE system as example, but the present invention is not limited to this, and can also be applied to all radio communication standards which allow a mixture of the MeNB and the HeNB. 
     In the above embodiments, an example in which continuous subbands are used has been described. The present invention is not limited to the case of using continuous subbands, but can be applied to a case of using discontinuous subbands, for example, as shown in  FIGS. 14 and 15  and can obtain the same effect as that of the above embodiments. In  FIG. 14  and  FIG. 15 , the groups of subbands  1  to  4 , subbands  5  to  7 , and subbands  8  to  10  are discontinuous.  FIG. 14  shows a case of employing the same subband combination included in a subband assigning pattern every frame,  FIG. 15  shows a case of using different subband combination included in a subband assigning pattern every frame. 
     The disclosure of Japanese Patent Application No. 2010-047985, filed on Mar. 4, 2010, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
     Industrial Applicability 
     The present invention is suitable for a mobile communication system including an MeNB, an MUE, an HeNB, and an HUE. 
     Reference Signs List 
     
         
           100 ,  200 ,  300  HeNB 
           101 ,  203 ,  303  Pattern generating section 
           102  Assignment section 
           103  Notification section 
           201  Detection section 
           202 ,  301  Specification section 
           302  Subband number determination section