Patent Publication Number: US-2010113059-A1

Title: Radio access network apparatus and the method

Description:
TECHNICAL FIELD 
     The present invention generally relates to a technical field of mobile communication. More particularly, the present invention relates to a radio access network apparatus and the method. 
     BACKGROUND ART 
     In a conventional mobile communication system of a time division multiple access (TDMA) scheme, frequencies that are different with each other are used in adjacent cells. A group of frequencies are used for a set of cells, and the same group of frequencies are used in another set of cells that is geographically apart from the set of cells. Although such a method is preferable in view of decreasing other cell interference, frequency use efficiency is not high. 
     On the other hand, in the W-CDMA scheme such as IMT-2000, users are distinguished by using spread codes so that a same frequency is used for all cells and “one cell frequency reuse” is realized. Accordingly, the frequency use efficiency and the system capacity largely increase. However, since the same frequency is used among adjacent cells, a problem that interference level at a cell edge tends to become large is a concern. As to this problem, a technique called interference coordination is proposed. In this technique, in addition to that a frequency common to all cells is used, different frequencies are used for each cell at the cell edge. 
       FIG. 1  shows a frequency use situation when the interference coordination is performed. The frequency band b is a band common to all cells, and frequency bands a 1 , a 2  and a 3  are used separately by each cell. For the sake of convenience of representation, the frequencies a 1 , a 2 , a 3  and b are depicted such that they have similar bands. But, it should be noted that, in actuality, the frequency band b is very wide, and the frequency bands a 1 , a 2  and a 3  are relatively narrow. The frequency bands a 1 , a 2  and a 3  are frequencies to be assigned to users at cell edges, and the frequency band b is a frequency to be assigned to a user (a user located near a base station, for example) in a region other than the cell edge. The frequency al is used for a user belonging to the cell edge of the cell  1 , so that the frequency a 1  is not used in adjacent cells. Similarly, the frequency a 2  is used for a user belonging to the cell edge of the cell  2 , so that the frequency a 2  is not used in adjacent cells. The frequency a 3  is used for a user belonging to the cell edge of the cell  3 , so that the frequency a 3  is not used in adjacent cells. Therefore, each user at the cell edge of the cell  1 , cell  2  and cell  3  can perform communication under a small interference state. The interference coordination is described in the non-patent document 1, for example. [Non-patent document 1] 3GPP R1-060670, Siemens, “Interference Mitigation by Partial Frequency Reuse” 
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     In the interference coordination, the frequencies a 1 , a 2  and a 3  for users at the cell edge are exclusively used in the cells  1 ,  2  and  3  respectively. Therefore, there is a problem in that use efficiency of frequencies to be assigned to users at the cell edge is not good. In addition, there may be a situation in which it is difficult to clearly set frequency bands a 1 , a 2  and a 3  for each cell. Also, there is a problem that interference is not sufficiently suppressed in a communication environment in which cell boundary is not clear according to circumstances and it is difficult to clearly determine a frequency beforehand to be used at the cell edge. 
     An object of the present invention is to provide a radio access network apparatus and a method for improving frequency use efficiency at the cell edge and sufficiently suppressing other cell interference. 
     Means for Solving the Problem 
     In the present invention, a radio access network apparatus is used, wherein the radio access network apparatus includes: means configured to determine whether a mobile station belongs to a region at a cell edge; and means configured to assign a cell edge frequency to a mobile station at the cell edge, and assign a non-cell edge frequency that is different from the cell edge frequency to a mobile station in a region other than the cell edge. The cell edge frequency includes a first band that is different for each cell. The non-cell edge frequency includes a second band common to a plurality of cells including the own cell and a third band equal to a cell edge frequency of an adjacent cell. 
     Effect of the Invention 
     According to the present invention, frequency use efficiency at the cell edge can be improved and other cell interference can be sufficiently suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a frequency assignment example in conventional frequency coordination; 
         FIG. 2  is a diagram showing a mobile station and a base station according to an embodiment of the present invention; 
         FIG. 3  is a diagram showing a situation for grouping mobile stations according to interference power; 
         FIG. 4A  is a diagram showing correspondence relationship (1) between resource blocks and transmission power; 
         FIG. 4B  is a diagram showing correspondence relationship (2) between resource blocks and transmission power; 
         FIG. 5  is a diagram showing a mobile station and a base station according to an embodiment of the present invention; 
         FIG. 6  is a diagram showing correspondence relationship among mobile stations, resource blocks and transmission power; 
         FIG. 7  is a diagram showing a mobile station, a base station and an upper station according to an embodiment of the present invention; 
         FIG. 8  is a diagram showing a frequency assignment example according to an embodiment of the present invention; 
         FIG. 9  is a diagram showing a frequency assignment example according to an embodiment of the present invention; 
         FIG. 10  is a diagram showing a mobile station, a base station and an upper station according to an embodiment of the present invention; 
         FIG. 11  is a diagram for explaining operation according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF REFERENCE SIGNS 
     
         
           21  reception quality measurement unit 
           22 ,  23  reception quality reporting unit 
           24  base station includes a grouping control unit of each UE 
           25  determination unit for determining transmission power for each group and a number of resource blocks (RB number) to be assigned 
           26  transmission power determination unit for RB 
           27  frequency scheduling unit 
           28  transmission power correction unit 
       
    
     PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     According to an embodiment of the present invention, a cell edge frequency is assigned to a mobile station at the cell edge, and a non-cell edge frequency that is different from the cell edge frequency is assigned to a mobile station in a region other than the cell edge. The cell edge frequency includes a first band that is different for each cell. The non-cell edge frequency includes a second band common to a plurality of cells including the own cell and a third band equal to a cell edge frequency of an adjacent cell. Transmission power of a signal transmitted using the second band may be set to be smaller than transmission power of a signal transmitted by the first band. Transmission power of a signal transmitted using the first band or the second band may be set to be and greater than transmission power of a signal transmitted by the third band. Accordingly, other cell interference can be suppressed while improving frequency use efficiency in the cell edge. 
     The radio access network apparatus may or may not include an apparatus (upper station) in an upper side of the base station. From the viewpoint for suppressing other cell interference with reliability, it is desirable that the upper station controls assignment of frequency and transmission power. 
     From the viewpoint of easily determining whether the mobile station resides in the cell edge, whether the mobile station belongs to the cell edge may be determined based on interference power of downlink reported from the mobile station. 
     In addition, total transmission power of each cell may be arranged to be a given level. 
     From the viewpoint of suppressing other cell interference at the cell edge with reliability, it is desirable that control is performed such that signal transmission using the first band in a cell and signal transmission using the third band in an adjacent cell are performed at different times. 
     Embodiment 1 
       FIG. 2  shows a mobile station UE and a base station or a Node B according to an embodiment of the present invention. The mobile station includes a reception quality measurement unit  21  and a reception quality reporting unit  22 . The reception quality measurement unit  21  measures quality of a signal (downlink pilot channel, for example) received from the base station. The quality may be represented as various amounts, and it may be represented as interference power, geometry, and other proper channel state information CQI (Channel quality indicator). The reception quality reporting unit  22  transmits the measurement value to the base station. 
     The base station includes a grouping control unit  24  of each UE, a determination unit  25  for determining transmission power for each group and a number of resource blocks (RB number) to be assigned, a transmission power determination unit  26  for each RB, a frequency scheduling unit  27  and a transmission power correction unit  28 . 
     The grouping control unit  24  for each UE divides UEs to one or more groups based on reception quality reported from each UE. For example, as shown in  FIG. 3 , UE 1 - 8  are divided into three groups based on interference power reported from each of the UE 1 - 8 . The grouping may be determined based on whether the interference power exceeds a threshold. In the example shown in the figure, two thresholds are prepared so that three groups are formed, but, the number of prepared thresholds and the number of the groups may be any numbers. In  FIG. 3 , interference power of UE 1 , UE 6  and UE 5  exceeds a first threshold value and they belong to a first group. Typically, each mobile station belonging to the first group is located at a cell edge. Interference power of UE 2  and UE 8  are below the first threshold, but exceeds the second threshold, and they belong to a second group. Interference power of other mobile stations is below the second threshold, and the mobile stations belong to the third group. Typically, the mobile stations belonging to the third group are located near the base station or located at a place where visibility is good. 
     The determination unit  25  for determining transmission power for each group and the number of RBs determines transmission power for each group according to a group determination result in the grouping control unit  24 . Generally, large transmission power is required for UEs belonging to a group of large interference power, and only small transmission power is necessary for UEs belonging to a group of small interference power. The determination unit  25  determines the number of resource blocks (number of RBs) to be assigned to UE 1 - 8 . In the present embodiment, a frequency block of a narrow bandwidth is used as a unit of radio resources for assignment, so that the mobile station performs communication using one or more resource blocks depending on the channel state and data amount. 
     The RB transmission power determination unit  26  associates each value of determined transmission power with a resource block. However, it is not determined which mobile station UE corresponds to which transmission power value at this stage. Each base station individually determines which resource block corresponds to which transmission power value, and it may be variously determined as shown in  FIGS. 4A and 4B . In the example shown in the figure, although eight resource blocks corresponding to the total number (8) of mobile stations are shown for the sake of simplicity, resource blocks more than those shown in the figure may be used since a mobile station can use one or more resource blocks as mentioned above. Correspondence relationship (or assignment pattern) between resource blocks and transmission power values may be changed in each base station as necessary. 
     The frequency scheduling unit  27  determines which resource block is assigned to each mobile station in consideration of not only quality of the channel state of each resource block reported. from each mobile station but also the transmission power value determined for each resource block. The point that the scheduling is performed in consideration of the transmission power value is largely different from conventional frequency scheduling. More particularly, since interference power of UE 1 , UE 6  and UE 5  belonging to the first group is large as a result of group determination, it is desirable to assign resource blocks of large transmission power for the first group. Since interference power of UE 3 , UE 4  and UE 7  belonging to the third group is small, resource blocks of small transmission power can be assigned. It is desirable to assign, to UE 2  and UE 8  belonging to the second group, resource blocks of power smaller than the transmission power of the first group and larger than the transmission power of the third group. 
     More particularly, when the transmission power assignment pattern shown in  FIG. 4A  is used, it is desirable that RB 1 , RB 2  and RB 4  are assigned to UE 1 , UE 6  and UE 5 , RB 3  and RB 5  are assigned to UE 2  and UE 8 , and that RB 6 , RB 7  and RB 8  are assigned to UE 3 , UE 4  and UE 7 . Similarly, when the transmission power assignment pattern shown in  FIG. 4B  is used, it is desirable that RB 3 , RB 5  and RB 6  are assigned to UE 1 , UE 6  and UE 5 , RB 1  and RB 8  are assigned to UE 2  and UE 8  respectively, and that RB 2 , RB 4  and RB 7  are assigned to UE 3 , UE 4  and UE 7 . More detailed correspondence relationship between mobile stations and resource blocks is determined according to channel states. For example, when RB 1 , RB 2  and RB 4  are assigned to UE 1 , UE 6  and UE 5  in the pattern of  FIG. 4A , any of RB 1 , RB 2  and RB 4  is assigned according to channel state of each resource block in UE 1 . In the above-mentioned example, for example, although UE 1 , UE 6  and UE 5  are basically assigned to RB 1 , RB 2  and RB 4 , there is a case in which it is desirable that they are assigned to other resources according to instantaneous channel state since actual resource assignment is performed by frequency scheduling (this holds true also in the after-mentioned third embodiment). 
     When transmitting a signal to each mobile station using the determined transmission power (strictly speaking, power ratio), the transmission power correction unit  28  performs adjustment as necessary according to total transmission power. For example, when an arrangement has been made such that total transmission power becomes the same among cells, the power value is corrected such that the transmission power pattern is realized within a range of the total transmission power. 
     According to the present embodiment, an assignment pattern ( FIGS. 4A and 4B ) of transmission power used for each resource block is determined in each cell individually. Therefore, as long as assignment patterns are different among cells, interference to be received by mobile stations located at the cell edge is suppressed small. For example, assuming that the pattern of  FIG. 4A  is used in the first cell and that the pattern of  FIG. 4B  is used in the adjacent second cell. In this case, a signal is transmitted to mobile stations located at the cell edge of the first cell with large transmission power using the frequency of RB 1 , RB 2 , RB 4 . On the other hand, a signal is transmitted to mobile stations located at the cell edge of the second cell with large transmission power using the frequency of RB 3 , RB 5 , RB 6 . Therefore, the mobile stations at the cell edge do not receive large interference from an adjacent cell. Mobile stations located at the edge of the first cell uses frequencies of RB 1 , RB 2  and RB 4 . Although the frequencies are also used in the second cell, since the second cell uses the frequencies by suppressing transmission power to be small, it can be considered that the frequencies do not exert large interference on the edge of the first cell. Similarly, mobile stations located at the edge of the second cell use frequencies of RB 3 , RB 5  and RB 6 . Although the frequencies are also used in the first cell, since the first cell uses the frequencies by suppressing transmission power to b small, it can be considered that the frequencies do not exert large interference on the edge of the second cell. According to the present embodiment, frequency use efficiency can be improved while effectively suppressing interference also at the cell edge. 
     Embodiment 2 
       FIG. 5  shows a mobile station UE and a base station (node B) according to an embodiment of the present invention. Similar to the example shown in  FIG. 2 , the mobile station includes the reception quality measurement unit  21  and the reception quality reporting unit  22 , and repeated explanations are not given. In addition, similar to the example shown in  FIG. 2 , the base station includes the grouping control unit  24  of each UE, a transmission power determination unit  25 ′ for determining transmission power for each group, the frequency scheduling unit  27  and the transmission power correction unit  28 . 
     The grouping control unit  24  for each UE divides UEs to one or more groups based on reception quality reported from each UE. 
     The transmission power determination unit  25 ′ for each group determines transmission power for each group according to a group determination result in the grouping control unit  24 . Generally, large transmission power is required for UEs belonging to a group of large interference power, and only small transmission power is necessary for UEs belonging to a group of small interference power. Assuming that grouping is performed as shown in  FIG. 3 , determination is performed such that large transmission power P 1  is used for UE 1 , UE 6  and UE 5  of the first group, intermediate transmission power P 2  is used for UE 2  and UE 8  for the second group, and small transmission power P 3  is used for UE 3 , UE 4  and UE 7  of the third group. However, which resource block is associated with which mobile station UE is not determined by the transmission power determination unit  25 ′, and it is determined by the frequency scheduling unit  27 . 
     The frequency scheduling unit  27  determines which resource block is assigned to each mobile station in consideration of quality of the channel state of each resource block reported from each mobile station. 
     Although the figure is depicted such that processing of the frequency scheduling unit  27  is performed after the processing of the transmission power determination unit  25 ′ for the sake of convenience of explanation, the order may be one as shown in the figure, may be reversal, or the whole or a part of the processing may be performed simultaneously since the processes can be performed independently. In all cases, performing transmission using which resource block with what degree of transmission power to which mobile station is determined based on both process results. 
     When transmitting a signal to each mobile station using the determined transmission power (strictly speaking, power ratio), the transmission power correction unit  28  performs adjustment as necessary according to total transmission power. For example, when an arrangement has been made such that total transmission power becomes the same among cells, the power value is corrected such that the transmission power pattern is realized within a range of the total transmission power. 
     Also, according to the present embodiment, an assignment pattern of transmission power used for each resource block is determined in each cell individually. Therefore, in the same way as the first embodiment, as long as assignment patterns are different among cells, interference to be received by mobile stations located at a cell edge is suppressed to be small. 
     However, assignment procedure for transmission power and resource blocks are slightly different from the case of the first embodiment. In the present embodiment, relationship between respective mobile station and transmission power is determined as one-to-one correspondence relationship according to the result of grouping irrespective of the frequency scheduling. This point is different from the method of the first embodiment in which frequency scheduling is performed while transmission power is taken into consideration. Then, separately from the transmission power, the frequency scheduling unit (scheduler) determines resource blocks to be assigned to each mobile station according to quality of channel state of each resource block reported from each mobile station. 
     As shown in the upper side of  FIG. 6 , transmission power P 1 , P 2  and P 3  for each UE is determined according to the result of grouping. Resource blocks used for each UE are separately determined according to channel state of each UE. These results are combined so that transmission power and assignment of resource blocks are determined for each mobile station as shown in the lower side of  FIG. 6B . Since the assignment pattern is determined independently in each cell, frequency use efficiency can be improved while effectively suppressing interference at the cell edge unless assignment patterns incidentally become the same among cells. 
     Embodiment 3 
       FIG. 7  shows a mobile station UE and a base station (node B) according to an embodiment of the present invention. Similar to the example shown in  FIG. 2 , the mobile station includes the reception quality measurement unit  21  and the reception quality reporting unit  22 , and repeated explanations are not given. In the present embodiment, different from the first and the second embodiments, assignment of radio resources and transmission power is performed by an upper station of the base station such as a radio network controller (RNC), for example. The base station transfers, to the upper station, reception quality reported from the mobile station and measurement values measured in the own cell and the like using the reception quality reporting unit  23 . 
     By the way, although assignment of radio resources and transmission power is performed in a radio access network apparatus (RAN) in all embodiments, the base station performs main processes in the first and second embodiments, and the upper station such as RNC performs main processes in the third embodiment and later embodiments. 
     The upper station includes the grouping control unit  24  of each UE, the determination unit  25  for determining transmission power for each group and a number of resource blocks (RB number) to be assigned, the transmission power determination unit  26  for each RB, the frequency scheduling unit  27  and the transmission power correction unit  28 . The upper station includes configurations and functions similar to those of the base station of the first embodiment shown in  FIG. 2 , but the upper station is different from the already described schemes in that assignment of transmission power and resource blocks is performed in consideration of not only the inside of the same cell but also a plurality of cells. 
     The grouping control unit  24  for each UE divides UEs to one or more groups based on reception quality reported from each UE. Grouping is performed for each cell. 
     The determination unit  25  for determining transmission power for each group and the number of assigning RBs determines transmission power for each group according to a group determination result in the grouping control unit  24 . Generally, large transmission power is required for UEs belonging to a group of large interference power, and only small transmission power is necessary for UEs belonging to a group of small interference power. The determination unit also determines the number of resource blocks (number of RBs) to be assigned to the mobile station. 
     RB transmission power determination unit  26  associates each value of determined transmission power with each resource block individually. However, which mobile station UE corresponds to which transmission power value is not determined at this stage. It is determined by the frequency scheduling unit  27 . 
     The frequency scheduling unit  27  determines which resource block is assigned to which mobile station in consideration of quality of the channel state of each resource block reported from each mobile station and the determined transmission power value. 
     When transmitting a signal to each mobile station using the determined transmission power (strictly speaking, power ratio), the transmission power correction unit  28  performs adjustment as necessary according to total transmission power. 
     In the present embodiment, the assignment patterns of the transmission power used for each resource block are determined such that assignments are different among cells. This point is different from the scheme of the first and the second embodiments in which the pattern is determined in each cell individually. Therefore, it can be maintained with reliability that the assignment patterns are different among cells, so that frequency use efficiency can be improved while effectively suppressing interference also at the cell edge. 
       FIG. 8  shows a frequency use state in which the present embodiment is used. The frequency band b is a band common to all cells, and frequency bands a 1 , a 2  and a 3  are bands to be used by uses at a cell edge of each cell. In the present embodiment, in addition to that, frequency bands a 1 , a 2  and a 3  are set so as to be also assigned to users other than users at the cell edge. The frequency a 1  is used for users belonging to the cell edge of cell  1 . Although the frequency a 1  is also used in adjacent cells  2  and  3 , the frequency a 1  is used only for users near a base station of the cell  2  and users near the base station of cell  3 . As shown in the figure, in the cell  1 , transmission power p 1  of the frequency a 1  is the largest, and the transmission power p 2  of the frequency b is the second largest, and the transmission power p 3  of the frequencies a 2  and a 3  are set to be the smallest. Therefore, the frequency a 1  used in the cell  2  and cell  3  is considered not to exert large interference to users at the cell edge of cell  1 . In the same way, since the frequency a 2  used in the cell  1  and the cell  3  is used only by users near base stations, it can be considered that the frequency a 2  used by the cell  1  and the cell  3  does not exert large interference to users at cell edge of the cell  2  using the frequency a 2 . Since the frequency a 3  used in the cell  1  and the cell  2  is used only by users near base stations, it can be considered that the frequency a 3  used by the cell  1  and the cell  3  does not exert large interference on users at cell edge of the cell  3  using the frequency a 3 . The frequency bandwidth may be changed as necessary according to necessary traffic amount and channel status. According to the present embodiment, by collectively managing the use pattern of frequencies and the transmission power in each cell, interference can be suppressed at the cell edge and frequency use efficiency can be improved. In addition, even in a situation in which it is difficult to properly set frequency bands a 1 , a 2  and a 3  in individual cells, since the frequencies are determined by the upper station controlling each cell, interference at the cell edge can be decreased more effectively. 
     Embodiment 4 
     In the fourth embodiment of the present invention, the base station measures interference power from the adjacent cell, and reports the measurement result to the upper station in addition to reported values from mobile stations. The upper station includes configurations and functions the same as those of the third embodiment, and groups mobile stations for each cell, specifies necessary transmission power values and resource blocks, and determines correspondence relationship between transmission power and resource blocks. In this case, an assignment pattern is determined such that, as to a resource block for which large transmission power is set in a cell, small transmission power is set in other cell. 
       FIG. 9  shows a situation in which an assignment pattern is determined and shows other cell interference amount in the cell  1 . First, assuming that correspondence relationship between resource blocks RB and transmission power is determined in the cell  1 . Since the cell  2  gives large interference to the cell  2 , consideration is given such that large transmission power is not used for a same resource block between the cell  1  and the cell  2 . In the cell  1 , large transmission power is used for RB 1 , RB 3  and RB 8 , and consideration is given such that large transmission power is not used for these resource blocks in the cell  2 . As a result, large transmission power is used for RB 2  and RB 7  in the cell  2 . In the same way, also as to cell  4  that exerts large interference effect to cell  1 , consideration is given such that large transmission power is not used in the same resource blocks. Since large transmission power is used for RB 1 , RB 3 , RB 8  and RB 2 , RB 7  in cells  1  and  2  respectively, consideration is given such that large transmission power is not used for these resource blocks in cell  4 . As a result, large transmission power is used for RB 4  and RB 6  in cell  4 . As mentioned above, by giving consideration to cells having large interference effect in order, interference amount can be effectively decreased in the whole system. 
     Embodiment 5 
       FIG. 10  shows a mobile station UE and a base station (node B) according to an embodiment of the present invention. Similar to the example shown in  FIG. 2 , the mobile station includes the reception quality measurement unit  21  and the reception quality reporting unit  22 , and repeated descriptions are not given. Also in this embodiment, assignment of radio resources and transmission power is performed in the upper station of the base station. The base station transfers reception quality reported from the mobile station and measurement values and the like measured in the own cell to the upper cell using the reception quality reporting unit  23 . 
     The upper station includes the frequency scheduling unit  27  and the transmission power correcting unit  28 . 
     The frequency scheduling unit  27  determines which resource block is to be assigned to each mobile station according to quality of the channel state of each resource block reported from each mobile station and the determined transmission power value. 
     Since the frequency scheduling unit  27  is provided in the upper station of the base station, frequency scheduling for one or more cells under the upper station is performed collectively. 
     When transmitting a signal to each mobile station using the determined transmission power (strictly speaking, power ratio), the transmission power correction unit  28  performs adjustment as necessary according to total transmission power. 
     In the present embodiment, an active set is defined as to mobile stations at the cell edge. Similar to the active set when performing handover, this active set includes a connected cell of the mobile station at the cell edge and a cell adjacent to the connected cell. 
       FIG. 11  is a figure for explaining operation according to the present embodiment. As an example, assuming that users A and B belong to the cell  1 , users C and D belong to the cell  2 , and users E and F belong to the cell  3 , and user B and user F are located at cell edge. In addition, the active set number is  2  respectively. That is, the active set for the user B is cell  1  and cell  2 , and the active set for user F is cell  3  and cell  2 . 
     When resource assignment in the cell  1  is determined as shown in  FIG. 11 , resource assignment in the cell  2  is determined next. The resource block RB 2  is assigned to the user B at the cell edge in the cell  1 . In this case, a cell included in the active set is configured not to transmit a signal using the resource block RB 2 . In the example shown in the figure, the cell  2  prohibits signal transmission using RB 2  (to be also referred to as muting). Similarly, in the example shown in the figure, the resource block RB 5  is used by a user F at the cell edge in the cell  3 . Therefore, signal transmission using the RB 5  is prohibited in the cell  2  that is included in an active set. As mentioned above, among cells included in an active set, consideration is given such that the frequency used for a user at the cell edge is not used at the same time. Accordingly, although improvement effect of frequency use efficiency falls compared with that of the above-mentioned embodiment, interference can be suppressed with reliability by just that much. Although higher priority is given to assignment for users at the cell edge in the above example, higher priority may be given to assignment for users near the cell inversely. 
     For the sake of explanation, although the present invention is described by being divided to some embodiments, the division to each embodiment is not essential for the present invention, and equal to or greater than one embodiment may be used as necessary. As mentioned above, although preferred embodiments of the present invention are described, the present invention is not limited to those, and various variations and modifications may be made without departing from the scope of the present invention. For the sake of explanation, although the present invention is described by being divided to some embodiments, the division to each embodiment is not essential for the present invention, and equal to or greater than two embodiment may be used as necessary. 
     The present international application claims priority based on Japanese patent application No. 2006-077823, filed in the JPO on Mar. 20, 2006 and the entire contents of the Japanese patent application No. 2006-077823 is incorporated herein by reference.