Abstract:
A radio base station for performing communication through three or more frequency bands based on orthogonal frequency division multiplexing includes a transmission unit configured to transmit a first channel through at least one of the three or more frequency bands and to transmit a second channel having smaller power than the first channel through at least another one of the three or more frequency bands, the first channel and the second channel being transmittable concurrently in time, a reception condition detecting unit configured to detect a reception condition of one or more mobile stations residing within a local cell, and a scheduling unit configured to select one of the first channel and the second channel, a modulation scheme, and a transmission power to be used for at least a downlink to one of the mobile stations based on the detected reception condition.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-007835 filed on Jan. 17, 2008, with the Japanese Patent Office, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The disclosures herein relate to a scheduling method and a radio base station. The disclosures herein relate to a radio communication system using orthogonal frequency division multiplexing in which radio frequency resources are divided into three or more communication channels. 
         [0004]    2. Description of the Related Art 
         [0005]    In mobile communication systems utilizing OFDM (orthogonal frequency division multiplexing), the simultaneous use of overlapping radio frequency resources by adjacent cells causes mutual interference. Frequency allocation thus needs to ensure that different frequency resources are allocated to adjacent cells. 
         [0006]    It is practically impossible, however, to divide frequency resources into a large number of resource portions that are fixedly allocated to respective cells in such a manner thus all the cells use different frequency resources. It is thus common to allow nonadjacent cells to repeatedly use overlapping frequency resources, thereby making recycling use of frequency resources. 
         [0007]    In such frequency allocation system, FFR (fractional frequency reuse) has been attracting attention as a means to achieve further improvement in frequency utilization. FFR allows a frequency reuse distance to vary in response to the distance between a mobile station and a radio base station. As the mobile station moves farther away from the base station (thus suffering increased interference), the frequency reuse distance is increased to prevent interference between adjacent cells. As the mobile station moves closer to the base station (thus suffering less interference), the frequency reuse distance is decreased to improve frequency utilization. This arrangement is aimed at improving frequency utilization for the system as a whole. 
         [0008]    Non-patent Document 1 discloses using FFR together with transmission power control for the purpose of further improving frequency utilization. 
         [0009]    In this system, when a mobile station is situated far away from a radio base station (thus suffering large interference), a frequency band (priority channel) that is different from those of the adjacent cells is used. When the mobile station is situated close to the radio base station (thus suffering small interference), transmission power is reduced so as not to interfere with the adjacent cells, and a frequency band (non-priority channel) that is used by an adjacent cell is allocated. In this manner, transmission power is reduced to suppress interference with adjacent cells, thereby making it possible to use a frequency band that would not be used in a conventional system. With this arrangement, frequency utilization can be improved. 
         [0010]    Further, Patent Document 1 discloses changing a frequency reuse distance in response to the distance between a mobile station and a radio base station in the FFR in which a default frequency reuse distance is 3. The frequency band is divided into four communication channels. Among these, three communication channels are used in a region where a frequency reuse distance is set equal to 3 for mobile stations situated near the edge of the cell, and the one remaining communication channel is used in a region where a frequency reuse distance is set equal to 1 for mobile stations situated near the center of the cell. With such provision, frequency utilization is improved while avoiding quality degradation caused by interference. 
         [0011]    Patent Document 2 discloses dividing a cell into a center area and a surrounding area in a concentric fashion and suppressing transmission power to such a degree that the center area does not interfere with the adjacent cells when the same frequency is used in the cell of interest and the adjacent cells. 
         [0012]    With regard to the allocation of a non-priority channel, Non-patent Document 1 only describes setting the transmission power to a level that does not affect the adjacent cells. No disclosure is given with respect to a method of controlling interference between the priority channel and the non-priority channel. Because of this, it is not possible to determine an optimum modulation and coding scheme (MCS), resulting in a drop of throughput. 
         [0013]    There is thus a need for a scheduling method and a radio base station in which a suitable modulation and coding scheme can be selected for each mobile station to improve throughput. 
         [0014]    [Patent Document 1] Japanese Patent Application Publication No. 2004-159345 
         [0015]    [Patent Document 2] Japanese Patent Application Publication No. 2007-235201 
         [0016]    [Non-patent Document 1] Samsung, “Flexible Fractional Frequency Reuse Appro,” 3rd Generation Partnership Project TSG-RAN WG1, R1-051341, 8.2, November 2005 
       SUMMARY OF THE INVENTION 
       [0017]    According to one embodiment, a radio base station for performing communication through three or more frequency bands based on orthogonal frequency division multiplexing includes a transmission unit configured to transmit a first channel through at least one of the three or more frequency bands and to transmit a second channel having smaller power than the first channel through at least another one of the three or more frequency bands, the first channel and the second channel being transmittable concurrently in time, a reception condition detecting unit configured to detect a reception condition of one or more mobile stations residing within a local cell, and a scheduling unit configured to select one of the first channel and the second channel, a modulation scheme, and a transmission power to be used for at least a downlink to one of the mobile stations based on the detected reception condition. 
         [0018]    A scheduling method used in a radio communication system for performing communication through three or more frequency bands based on orthogonal frequency division multiplexing includes transmitting a first channel through at least one of the three or more frequency bands and a second channel having smaller power than the first channel through at least another one of the three or more frequency bands, the first channel and the second channel being transmittable concurrently in time, detecting a reception condition of one or more mobile stations residing within a local cell, and selecting one of the first channel and the second channel, a modulation scheme, and a transmission power to be used for at least a downlink to one of the mobile stations based on the detected reception condition. 
         [0019]    According to the radio mobile station as described above, a modulation and coding scheme suitable for each mobile station can be selected to improve throughput. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
           [0021]      FIG. 1  is a drawing showing an example of frequency allocation when the frequency reuse distance is 3; 
           [0022]      FIG. 2  is a drawing showing an example of a downlink subframe of an OFDMA radio frame when FFR is applied; 
           [0023]      FIG. 3  is a drawing showing an example of the configuration of an OFDMA radio frame; 
           [0024]      FIG. 4  is a block diagram showing an embodiment of a radio base station; 
           [0025]      FIG. 5  is a block diagram showing an embodiment of a mobile station; 
           [0026]      FIG. 6  is a drawing showing an example of a format of the MS profile list. 
           [0027]      FIG. 7  is a drawing for explaining CINR 1R  and CINR 3R ; 
           [0028]      FIG. 8  is a flowchart of selection of communication channel and initial scheduling for downlink performed at a radio base station; 
           [0029]      FIG. 9  is a drawing showing an example of a scheduling table; 
           [0030]      FIG. 10  is a flowchart of scheduling for downlink after selection of communication channels performed at a radio base station; 
           [0031]      FIG. 11  is a flowchart of scheduling for uplink performed at a radio base station; 
           [0032]      FIG. 12  is a drawing showing the frequency/power characteristics of downlinks of BS 1  through BS 3 ; and 
           [0033]      FIG. 13  is a flowchart showing a procedure of correcting an interference power correction value. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    In the following, embodiments of the present invention will be described with reference to the accompanying drawings. 
         [0035]    The disclosed embodiments are directed to an FFR method using a frequency reuse distance that is equal to 3. The frequency reuse distance may be any value that is 3 or more such as 4, 5, 6, and so on. Either CINR (Carrier to Interference and Noise Ratio) or CQI (Channel Quality Indicator) may be used as an indicator of reception condition. In the following embodiments, procedures will be described with reference to an example in which CINR is employed. 
         [0036]    &lt;Frequency Allocation&gt; 
         [0037]    The frequency bands (F 1 +F 2 +F 3 ) of OFDM is divided into three communication channels (F 1 , F 2 , F 3 ) at the time of cell designing. As shown in  FIG. 1 , a priority channel serving as a first channel is allocated to each cell such that the allocated channel does not overlap the communication channels used by the adjacent cells. A cell  1   a  has a priority channel (F 1 ) allocated thereto as shown by hatching, and also has non-priority channels (F 2 +F 3 ) serving as second channels allocated thereto as shown in gray. A cell  1   b  has a priority channel (F 2 ) allocated thereto as shown by a dotted area, and also has non-priority channels (F 3 +F 1 ) allocated thereto as shown in gray. A cell  1   c  has a priority channel (F 3 ) allocated thereto as shown as a mesh, and also has non-priority channels (F 1 +F 2 ) allocated thereto as shown in gray. 
         [0038]      FIG. 2  is a drawing showing an example of a downlink subframe of an OFDMA (OFDM Access) radio frame when FFR is applied. Although control information areas such as FCH (Frame Control Header), DL-MAP, UL-MAP, and so on are provided in the case of IEEE802.16d/e, these control information areas are omitted in  FIG. 2 . In TDD (Time Division Duplexing), there are a subframe for downlink (i.e., link in a downward direction from a radio base station to a mobile station) and a subframe for uplink (i.e., link in an upward direction from a mobile station to a base station). For the sake of simplicity of illustration, however, only one subframe is shown in  FIG. 2  as a representative example illustrating a common configuration. The horizontal axis represents a time dimension in units of symbols, and the vertical axis represents a frequency dimension in units of sub-channels. 
         [0039]    As shown in  FIG. 2 , a radio base station BS 1  of the cell  1   a  transmits with great power a DL-MAP and a downlink (DL) by use of a priority channel (F 1 ) shown by hatching, and transmits with small power other downlinks by use of non-priority channels (F 2 +F 3 ) shown in gray. A radio base station BS 2  of the cell  1   b  transmits with great power a DL-MAP and a downlink (DL) by use of a priority channel (F 2 ) shown as a dotted area, and transmits with small power other downlinks by use of non-priority channels (F 3 +F 1 ) shown in gray. A radio base station BS 3  of the cell  1   c  transmits with great power a DL-MAP and a downlink (DL) by use of a priority channel (F 3 ) shown as a mesh, and transmits with small power other downlinks by use of non-priority channels (F 1 +F 2 ) shown in gray. The frequency/power characteristics of BS 1  through BS 3  shown on the right-hand side of  FIG. 2  illustrate the frequency/power characteristics of the portion corresponding to time T 2  in the mappings for BS 1  through BS 3  shown at the center. 
         [0040]      FIG. 3  is a drawing showing an example of the configuration of an OFDMA radio frame used in WiMAX (Worldwide Interoperability for Microwave Access). In  FIG. 3 , the horizontal axis represents the OFDMA symbol number, which corresponds to a time dimension. The vertical axis represents the subchannel logical number. 
         [0041]    The OFDMA frame includes a downlink subframe, an uplink subframe, a TTG (Transmit/Receive Transition Gap), and a RTG (Receive/Transmit Transition Gap). 
         [0042]    The DL subframe includes a preamble, an FCH (Frame Control Header), a DL-MAP, a UL-MAP, and a plurality of DL bursts. The preamble includes a preamble pattern required by a mobile station to establish frame synchronization. The FCH includes information about subchannels used and the DL-MAP that is provided at the immediately following position. The DL-MAP includes mapping information regarding the DL bursts in the DL subframe. By receiving and analyzing this information, a mobile station can identify a UL-MAP (transmitted on a DL burst # 1 ) and DL bursts # 2  through # 6 . 
         [0043]    The UL-MAP includes mapping information regarding the ranging regions and UL bursts in the UL subframe. By reading this information, a mobile station can identify the ranging regions and UL bursts # 1  through # 4 . 
         [0044]    The term “burst” refers to the allocation and arrangement of slots in the downlink subframe and uplink subframe of a radio frame with respect to downlink user data and control messages transmitted to MS and uplink user data and control messages transmitted from MS. A burst is an area in which the same modulation-scheme and FEC (forward error correction) combination is used. DL-MAP/UL-MAP specifies a particular combination of a modulation scheme and an FEC for each burst. Results of scheduling performed by the radio base station are broadcast to all mobile stations by use of DL-MAP and UL-MAP attached at the beginning of a DL subframe in each frame. 
         [0045]    DL-MAP (excluding FCH) having OFDMA symbol numbers k+ 1  and k+ 2  in  FIG. 3  correspond to time T 1  in the mapping shown in  FIG. 2 . Further, DL bursts having OFDMA symbol numbers k+ 3  through k+ 16  in  FIG. 3  correspond to time T 2  in the mapping shown in  FIG. 2 . 
         [0046]    &lt;Configuration of Radio Base Station&gt; 
         [0047]      FIG. 4  is a block diagram showing an embodiment of a radio base station. In  FIG. 4 , a preamble generating unit  10  generates a preamble signal responsive to a local cell ID and segment number for provision to a mapping unit  11 . The segment number is a number that identifies each of the cells  1   a,    1   b,  and  1   c  shown in  FIG. 1 , for example. 
         [0048]    A pilot generating unit  12  generates a pilot signal for provision to a power control unit  14 . A modulation unit  13  performs modulation with respect to downlink data and broadcast information. The modulation and coding scheme (MCS) used for this modulation process is specified by a scheduler  20 . The modulation unit  13  supplies a modulated signal obtained through modulation to the power control unit  14 . The power control unit  14  amplifies the pilot signal and the modulated signal such that the transmission power becomes equal to a power specified by the scheduler  20 , and supplies the amplified signals to the mapping unit  11 . 
         [0049]    The mapping unit  11  maps the preamble signal, the pilot signal, and the modulated signal according to mapping information specified by the scheduler  20 . Output signals of the mapping unit  11  are IFFT transformed by an IFFT (Inverse FFT) unit  15  into time-domain signals, which are then subjected to digital-to-analog conversion by a DAC  16 . A transmission-side amplifier  17  amplifies and changes the converted analog signals into high-frequency signals, which are then transmitted from an antenna  19  through a shared radio unit  18 . 
         [0050]    High frequency signals received from a mobile station (MS) by the antenna  19  are supplied through the shared radio unit  18  to a reception-side amplifier  21  for amplification and conversion into base-band signals. An ADC  22  performs analog-to-digital conversion with respect to the base-band signals. The converted signals are then FFT transformed by an FFT unit  23  into frequency-domain signals, which are then supplied to a demapping unit  24 . 
         [0051]    The demapping unit  24  extracts a preamble signal, a pilot signal, and a modulated signal inclusive of uplink data and control information from the frequency-domain signals. The demapping unit  24  supplies the pilot signal to a pilot-power measuring unit  25 , and supplies the modulated signal inclusive of uplink data and control information to a demodulation unit  27 . Demapping information is specified by the scheduler  20 . 
         [0052]    The pilot-power measuring unit  25  measures an electric power of the pilot signal to obtain CINR (or CQI) data regarding the uplink, and adds the data to an MS profile list stored in a memory unit  26  on a mobile-station-specific basis. CINR for uplink may be CINR pilot . 
         [0053]    The demodulation unit  27  demodulates the modulated signal inclusive of uplink data and control information. The demodulation unit  27  supplies the demodulated uplink data to a subsequent circuit (not illustrated), and also supplies the demodulated control information to a control information reading unit  28 . 
         [0054]    The control information reading unit  28  supplies the demodulated control information to a subsequent circuit (not illustrated). The control information reading unit  28  also extracts CINR (or CQI) data regarding the downlink contained in the control information, and adds the extracted data to the MS profile list stored in the memory unit  26  on a mobile-station-specific basis. CINR for downlink may be CINR 1R , CINR 3R , and CINR pilot . 
         [0055]    The scheduler  20  receives, from an upper-level circuit, downlink scheduling information such as an ID of each mobile station having radio connection with the local radio base station. The scheduler  20  determines a communication channel, a modulation and coding scheme (MCS), and a transmission power for use by each mobile station by referring to the MS profile list and a scheduling table stored in the memory unit  26 , thereby controlling the modulation unit  13 , the power control unit  14 , the mapping unit  11 , and the demapping unit  24  accordingly. 
         [0056]    &lt;Configuration of Mobile Station&gt; 
         [0057]      FIG. 5  is a block diagram showing an embodiment of a mobile station. In  FIG. 5 , high frequency signals received from a radio base station by an antenna  31  are supplied through a shared radio unit  32  to a reception-side amplifier  33  for amplification and conversion into base-band signals. An ADC  34  performs analog-to-digital conversion with respect to the base-band signals. The converted signals are then FFT transformed by an FFT unit  35  into frequency-domain signals, which are then supplied to a demapping unit  36 . 
         [0058]    The demapping unit  36  extracts a preamble signal, a pilot signal, and a modulated signal inclusive of downlink data and broadcast information from the frequency-domain signals. The demapping unit  36  supplies the preamble signal and the pilot signal to a preamble/pilot-power measuring unit  38 , and supplies the modulated signal inclusive of downlink data and broadcast information to a demodulation unit  37 . Demapping information is specified by a control unit (not shown) based on the received DL-MAP. 
         [0059]    The demodulation unit  37  demodulates the modulated signal inclusive of downlink data and broadcast information, and supplies the demodulated downlink data and broadcast information to a subsequent circuit (not illustrated). 
         [0060]    The preamble/pilot-power measuring unit  38  measures the electric powers of the preamble signal and pilot signal to obtain CINR (or CQI) data regarding the downlink for provision to a control information generating unit  39 . The control information generating unit  39  generates control information based on CINR (or CQI) data regarding the downlink and information such as Ack/NAck specified by an upper-level circuit. The generated control information is supplied to a modulation unit  41 . 
         [0061]    A pilot generating unit  42  generates a pilot signal for provision to a power control unit  43 . 
         [0062]    The modulation unit  41  performs modulation with respect to uplink data and the control information. The modulation and coding scheme (MCS) used for the modulation is specified by a control unit (not shown) based on the received UL-MAP. The modulation unit  41  supplies a modulated signal obtained through modulation to the power control unit  43 . 
         [0063]    The power control unit  43  amplifies the pilot signal and the modulated signal such that the transmission power becomes equal to a specified power, and supplies the amplified signals to a mapping unit  44 . The mapping unit  44  maps the preamble signal, the pilot signal, and the modulated signal according to specified mapping information. A transmission power and demapping information are specified by a control unit (not shown) based on the received UL-MAP. 
         [0064]    Output signals of the mapping unit  44  are IFFT-transformed by an IFFT unit  45  into time-domain signals, which are then subjected to digital-to-analog conversion by a DAC  46 . A transmission-side amplifier  47  amplifies and changes the converted analog signals into high-frequency signals, which are then transmitted from the antenna  31  through the shared radio unit  32 . 
         [0065]    &lt;Frequency Allocation and Preparation for Interference Prevention&gt; 
         [0066]    The transmission power of a priority channel is set to a fixed value. The transmission power of a non-priority channel is determined as follows. In order to compensate for interference between a priority channel (or non-priority channel) of a local cell and a non-priority channel (or priority channel) of another cell, a tolerable interference power value P limit  [dBm] of the interference with a non-priority channel is set to a fixed value, and a transmission power threshold Tr [dBm] of the non-priority channel is determined such that the interference electric power at the edge of each cell does not exceed the tolerable interference power value. In the following, BW is a bandwidth of the non-priority channel, c being an attenuation constant, d being a radius of the area covered by the cell, and α being an attenuation index. 
         [0000]        Tr=P   limit /[Γ( r   edge )  BW]   
         [0000]      Γ( d )= c/d   α   (1) 
         [0067]    &lt;Selection of Communication Channel and Initial Scheduling at Radio Base Station&gt; 
         [0068]    A radio base station obtains, on a mobile-station-specific basis, the CINR value (CINR 3R ) of a priority channel (reuse frequency=3) and the CINR value (CINR 1R ) of a non-priority channel (reuse frequency=1) derived from a preamble signal by each mobile station. The radio base station also obtains, on a mobile-station-specific basis, the CINR values (CINR pilot ) of the downlink and uplink derived from pilot signals. The radio base station stores these obtained values in the MS profile list stored in the memory unit  26 . Further, the radio base station stores an average of the numbers of Ack and NAck returned from each mobile station in the MS profile list. 
         [0069]      FIG. 6  is a drawing showing an example of a format of the MS profile list. The MS profile list includes the CINR value (CINR 1R ) of the downlink, the CINR value (CINR 3R ) of the downlink, the CINR value (CINR pilot ) of the downlink, the CINR value (CINR pilot ) of the uplink, an indication of either a priority channel or a non-priority channel (i.e., an indication of an FFR zone), an indication of either Ack or NAck returned from a mobile station, MCS, and an NAck rate, separately for each mobile station (MS# 1  through MS#n). 
         [0070]    The difference between CINR 1R  and CINR 3R  derived from a preamble signal relates to whether interference with other cells is involved. As shown in  FIG. 7 , these values are obtained as a ratio of the desired signal power of the local cell to the interference power from other cell(s). Namely, CINR 1R  is derived by use of formula (2), and CINR 3R  is derived by use of formula (3) as follows. 
         [0000]      CINR 1R   =C /( I   1   +I   2   +I   3   +N )   (2) 
         [0000]      CINR 3R   =C /( I   1   +N )   (3) 
         [0071]    C: Signal Level of Local Cell (Segment # 0  ID_Cell=0) 
         [0072]    I 1 : Level of Interference with Closest Cell (Segment # 0  ID_Cell≠0) 
         [0073]    I 2 : Level of Interference with Adjacent Cell (Segment # 1 ) 
         [0074]    I 3 : Level of Interference with Adjacent Cell (Segment # 2 ) 
         [0075]    N: Noise Level 
         [0076]    &lt;Selection of Communication Channel and Initial Scheduling for Downlink at Radio Base Station &gt; 
         [0077]      FIG. 8  is a flowchart of selection of communication channel and initial scheduling for downlink performed at a radio base station. In step S 1 , the scheduler  20  obtains CINR data (CINR 3R , CINR 1R ) of the preamble of the downlink for each mobile station from the MS profile list. 
         [0078]    In step S 2 , mobile stations are grouped into a mobile station group A consisting of mobile stations having CINR values (CINR 1R ) smaller than a channel threshold Tch and a mobile station group B consisting of mobile stations having CINR values (CINR 1R ) equal to or larger than the channel threshold Tch. Data of the groups (mobile station group A or B) are then stored in the FFR zone field of the MS profile list. The purpose of this grouping is to assign mobile stations having poor reception conditions to a priority channel having little interference with adjacent cells because such mobile stations are likely to suffer interference with other cells. Further, mobile stations having satisfactory reception conditions are assigned to a non-priority channel because such mobile stations are not likely to suffer interference with other cells, and, also, the transmission power of these mobile stations is set to a level that does not interfere with adjacent cells. 
         [0079]    The channel threshold Tch [dB] is determined as follows, such that mobile stations having sufficiently high robustness (i.e., robustness against disturbance) can be selected despite the fact that the transmission power is set lower than the transmission power threshold Tr [dBm]. 
         [0000]      Tch &gt;CINR(MCS min )−( Tr−P   PRE ) 
         [0080]    CINR (MCS min ): CINR [dB] required for MCS having the lowest encoding ratio 
         [0081]    P PRE : Transmission Power Value [dBm] for Preamble Signal 
         [0082]    In step S 3 , one mobile station belonging to the mobile station group A is selected from the MS profile list, and is assigned to the frequency band of the priority channel. In step S 4 , CINR 3R  of the priority channel is corrected as shown in formula (4) by taking into account an interference power correction value β serving as a margin in order to take into account interference with the non-priority channels of adjacent cells. Further, transmission power P is set to P prior . 
         [0000]      CINR adjust   =P   Prior   −P   PRE +CINR 3R −β [dB]  (4) 
         [0000]      P=P prior    
         [0000]    Here, P PRE  is a transmission power (fixed value) of the preamble, and P prior  is a transmission power of the priority channel (which is set to a fixed value such that all mobile stations residing in the local cell can receive signals). CINR 3 R is corrected for an error between the transmission power of the preamble and the transmission power of the priority channel. 
         [0083]    In step S 5 , a row corresponding to required CINR corresponding to CINR adjust  is selected from the scheduling table shown in  FIG. 9 . MCS corresponding to the selected row corresponding to the required CINR is chosen as MCS to be used for the downlink with respect to the mobile station of interest. When CINR 3  is selected from the scheduling table, for example, MCS to be used is QPSK, CTC (Convolutional Turbo Coding), R (encoding ratio)=1/2, Repetition (i.e. number of repetitions)=1. 
         [0084]    As shown in  FIG. 9 , the scheduling table includes CINR required for each MCS, i.e., CINR 0  through CINR 5  which are arranged in an ascending order of satisfactory reception conditions. With respect to each CINR, a corresponding modulation and coding scheme is registered in advance by specifying either 16 QAM or QPSK, CTC, R, and Repetition. 
         [0085]    According to step S 6 , steps S 5  through S 5  are repeated until a frequency band is allocated to all the mobile stations in the mobile station set A or until all the priority channels are allocated. 
         [0086]    In step S 7 , one of the mobile stations belonging to the mobile station group B is selected, and is assigned either to the frequency band of a priority channel that has not yet been allocated in step S 3  or to the frequency band of a non-priority channel. Here, the frequency band of a remaining priority channel is preferentially allocated. 
         [0087]    In step S 8 , a check is made as to whether the frequency band to be allocated is that of a priority channel. If the frequency band to be allocated is that of a priority channel, CINR 3R  of the priority channel is corrected in step S 9  by use of formula (8) for the interference power correction value β in order to take into account interference with the non-priority channels of adjacent cells. Further, transmission power P is set to P prior . 
         [0000]      CINR adjust   =P   Prior   −P   PRE +CINR 3R −β [dB]  (4) 
         [0000]      P=P prior    
         [0000]    In step S 10 , a row corresponding to required CINR corresponding to CINR adjust  is selected from the scheduling table shown in  FIG. 9 . MCS corresponding to the selected row corresponding to the required CINR is chosen as MCS to be used for the downlink with respect to the mobile station of interest. 
         [0088]    If the check in step S 8  finds that a non-priority channel is to be allocated, the procedure proceeds to step S 11 . In step S 11 , MCS having a sufficiently low encoding ratio such as MCS (QPSK, CTC, R=1/2, Repetition=1) corresponding CINR 3  shown in the scheduling table of  FIG. 9  is selected as an initial setting. 
         [0089]    CINR required for MCS selected in step S 11  is referred to as CINR MCS . CINR MCS  is corrected for the interference power correction value β, and a difference ΔP from the CINR value (CINR 1R ) of a non-priority channel is calculated. Then, transmission power P PRE  is weakened by an amount equal to the difference ΔP to derive optimum transmission power P (see formula (5)). 
         [0000]        P=P   PRE −(CINR 1R −CINR MCS +β) [dB]  (5) 
         [0090]    For a non-priority channel, the transmission power needs to be set lower than the transmission power threshold Tr. If the check in step S 13  finds that transmission power P is equal to or larger than the transmission power threshold Tr, MCS having a lower encoding ratio is selected in step S 14 , followed by performing step S 11  and step S 12  to recalculate transmission power P. 
         [0091]    Steps S 7  through S 14  are repeated until a check in step S 15  finds that all the frequency bands are allocated, or finds that frequency band allocation is performed for all the mobile stations belonging to the mobile station group B. The scheduling then comes to an end. When step S 9  and S 10  are performed, the FFR zone field of the MS profile list is changed from “B” to “A” for the mobile stations that initially belonged to the mobile station group B but are assigned to priority channels. 
         [0092]    After the scheduling for downlink is completed according to the above-described procedure, the modulation unit  13  performs various modulation processes on transmission data according to MCS obtained by the scheduler  20 . The power control unit  14  sets the transmission power of the downlink data and pilot signal for non-priority channels equal to the transmission power obtained by the scheduler  20 . The mapping unit  11  allocates frequency bands. 
         [0093]    &lt;Scheduling for Downlink after Selection of Communication Channel at Radio Base Station&gt; 
         [0094]      FIG. 10  is a flowchart of scheduling for downlink after selection of communication channels performed at a radio base station. In step S 21 , the scheduler  20  obtains CINR data (CINR Pilot ) of the pilot signal of the downlink for each mobile station from the MS profile list. 
         [0095]    The transmission condition of a mobile station using a non-priority channel may deteriorate, such that a transmission power lower than the transmission power threshold is not sufficient for proper transmission. In consideration of this, Step S 22  detects a mobile station belonging to the mobile station group B for which CINR Pilot  is lower than the channel threshold Tch. In step S 23 , this mobile station is moved to the mobile station group A. When a communication channel being used is changed, the CINR value of the preamble is used instead of the CINR value of the pilot signal. 
         [0096]    In step S 24 , one mobile station belonging to the mobile station group A is selected from the MS profile list, and is assigned to the frequency band of the priority channel. In step S 25 , CINR and transmission power P are selected. 
         [0000]      CINR adjust =CINR Pilot    
         [0000]      P=P Prior    
         [0097]    In step S 26 , a row corresponding to required CINR corresponding to CINR adjust  is selected from the scheduling table shown in  FIG. 9 . MCS corresponding to the selected row corresponding to the required CINR is chosen as MCS to be used for the downlink with respect to the mobile station of interest. 
         [0098]    According to step S 27 , steps S 24  through S 26  are repeated until a frequency band is allocated to all the mobile stations in the mobile station set A or until all the priority channels are allocated. 
         [0099]    In step S 28 , one of the mobile stations belonging to the mobile station group B is selected, and is assigned either to the frequency band of a priority channel that has not yet been allocated in step S 24  or to the frequency band of a non-priority channel. 
         [0100]    In step S 29 , a check is made as to whether the frequency band to be allocated is that of a priority channel. If the frequency band to be allocated is that of a priority channel, CINR and transmission power P are selected in step S 30 . 
         [0000]      CINR adjust =CINR Pilot    
         [0000]      P=P Prior    
         [0000]    In step S 31 , a row corresponding to required CINR corresponding to CINR adjust  is selected from the scheduling table shown in  FIG. 9 . MCS corresponding to the selected row corresponding to the required CINR is chosen as MCS to be used for the downlink with respect to the mobile station of interest. 
         [0101]    If the check in step S 29  finds that a non-priority channel is to be allocated, the procedure proceeds to step S 32 . In step S 32 , MCS having a sufficiently low encoding ratio such as MCS (QPSK, CTC, R=1/2, Repetition=1) corresponding CINR 3  shown in the scheduling table of  FIG. 9  is selected as an initial setting. 
         [0102]    CINR required for MCS selected in step S 32  is referred to as CINR MCS . A difference ΔP between CINR MCS  and the CINR value (CINR Pilot ) of the pilot signal is calculated. Then, transmission power threshold Tr is weakened by an amount equal to the difference ΔP to derive optimum transmission power P (see formula (6)). 
         [0000]        P=Tr −(CINR Pilot −CINR MCS ) [dB]  (6) 
         [0103]    For a non-priority channel, the transmission power needs to be set lower than the transmission power threshold Tr. If the check in step S 34  finds that transmission power P is equal to or larger than the transmission power threshold Tr, MCS having a lower encoding ratio is selected in step S 35 , followed by performing step S 32  and step S 33  to recalculate transmission power P. 
         [0104]    Steps S 28  through S 35  are repeated until a check in step S 36  finds that all the frequency bands are allocated, or finds that frequency band allocation is performed for all the mobile stations belonging to the mobile station group B. The scheduling for downlink then comes to an end. 
         [0105]    &lt;Scheduling for Uplink at Radio Base Station&gt; 
         [0106]      FIG. 11  is a flowchart of scheduling for uplink performed at a radio base station. In step S 41 , the scheduler  20  obtains CINR data (CINR pilot ) of the pilot signal of the uplink for each mobile station from the MS profile list. 
         [0107]    In step S 43 , one mobile station belonging to the mobile station group A is selected from the MS profile list, and is assigned to the frequency band of the priority channel. In step S 44 , CINR and transmission power P are selected. 
         [0000]      CINR adjust =CINR Pilot    
         [0000]      P=P Prior    
         [0108]    In step S 45 , a row corresponding to required CINR corresponding to CINR adjust  is selected from the scheduling table shown in  FIG. 9 . MCS corresponding to the selected row corresponding to the required CINR is chosen as MCS to be used for the downlink with respect to the mobile station of interest. 
         [0109]    According to step S 46 , steps S 43  through S 45  are repeated until a frequency band is allocated to all the mobile stations in the mobile station set A or until all the priority channels are allocated. 
         [0110]    In step S 47 , one of the mobile stations belonging to the mobile station group B is selected, and is assigned either to the frequency band of a priority channel that has not yet been allocated in step S 43  or to the frequency band of a non-priority channel. 
         [0111]    In step S 48 , a check is made as to whether the frequency band to be allocated is that of a priority channel. If the frequency band to be allocated is that of a priority channel, CINR and transmission power P are selected in step S 49 . 
         [0000]      CINR adjust =CINR Pilot    
         [0000]      P=P Prior    
         [0000]    In step S 50 , a row corresponding to required CINR corresponding to CINR adjust  is selected from the scheduling table shown in  FIG. 9 . MCS corresponding to the selected row corresponding to the required CINR is chosen as MCS to be used for the uplink with respect to the mobile station of interest. 
         [0112]    If the check in step S 48  finds that a non-priority channel is to be allocated, the procedure proceeds to step S 51 . In step S 51 , MCS having a sufficiently low encoding ratio such as MCS (QPSK, CTC, R=1/2, Repetition=1) corresponding CINR 3  shown in the scheduling table of  FIG. 9  is selected as an initial setting. 
         [0113]    CINR required for MCS selected in step S 51  is referred to as CINR MCS . A difference ΔP between CINR MCS  and the CINR value (CINR Pilot ) of the pilot signal is calculated. Then, transmission power threshold Tr is weakened by an amount equal to the difference ΔP to derive optimum transmission power P (see formula (6)). 
         [0000]        P=Tr −(CINR pilot −CINR MCS ) [dB]  (6) 
         [0114]    For a non-priority channel, the transmission power needs to be set lower than the transmission power threshold Tr. If the check in step S 53  finds that transmission power P is equal to or larger than the transmission power threshold Tr, MCS having a lower encoding ratio is selected in step S 54 , followed by performing step S 51  and step S 52  to recalculate transmission power P. 
         [0115]    Steps S 47  through S 54  are repeated until a check in step S 55  finds that all the frequency bands are allocated, or finds that frequency band allocation is performed for all the mobile stations belonging to the mobile station group B. The scheduling then comes to an end. 
         [0116]    After the scheduling for uplink and downlink is completed according to the procedures shown in  FIG. 8 ,  FIG. 10 , and  FIG. 11 , the modulation unit  13  performs various modulation processes on transmission data according to the downlink MCS selected by the scheduler  20 . The power control unit  14  sets the transmission power of the downlink data and pilot signal for non-priority channels equal to the downlink transmission power obtained by the scheduler  20 . The mapping unit  11  allocates frequency bands. The schedule information regarding uplink is required by the modulation unit  41  and the power control unit  43  at the mobile station side. BS (base station) thus includes the uplink schedule information in UL-MAP as control information for transmission to each mobile station. 
         [0117]      FIG. 12  is a drawing showing the frequency/power characteristics of downlinks of BS 1  through BS 3  scheduled according to  FIG. 8  or  FIG. 10 . As shown in  FIG. 12 , the priority channels have a fixed power while the non-priority channels have powers that are lower than the transmission power threshold Tr. 
         [0118]    &lt;Correction of Interference Power Correction Value β and Transmission Power Threshold Tr&gt; 
         [0119]    The scheduler  20  makes correction to the interference power correction value at constant intervals as shown in  FIG. 13 . In step S 61 , the scheduler  20  reads the numbers of Ack and Nack from the MS profile list stored in the memory unit  26  on a mobile-station-specific basis, and obtains a PER (Packet Error Rate) as a Nack rate for recording in the MS profile list. In step S 62 , an average NAVE of the Nack rates for mobile stations (MS 1  through MSn) is obtained. 
         [0120]    In steps S 63  and S 64 , average NAVE is compared with communication quality thresholds TRMAX and TRMIN. Communication quality thresholds TRMAX and TRMIN are fixed values selected in advance such that TRMAX&gt;TRMIN. 
         [0121]    If N AVE  is larger than or equal to TRMAX, i.e., if average N AVE  has deteriorated due to a large number of Nack occurrences, the interference power correction value β is increased by a correction amount equal to Δβ (which is a small fixed value), and the transmission power threshold Tr is decreased by a correction amount equal to ΔTr (which is a small fixed value). If N AVE  is smaller than TRMIN, i.e., if average N AVE  has improved due to a small number of Nack occurrences, the interference power correction value β is decreased by a correction amount equal to ΔTr (which is a small fixed value), and the transmission power threshold Tr is increased by a correction amount equal to ΔTr (which is a small fixed value). 
         [0122]    With this arrangement, the interference power correction value β and the transmission power threshold Tr can be optimized. 
         [0123]    Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention.