Patent Publication Number: US-2012039306-A1

Title: Radio communication system, radio base station, and radio communication method

Description:
TECHNICAL FIELD 
     The present invention relates to a radio communication system, a radio base station, and a radio communication method for providing a first call type to which radio resources are allocated in a time division manner. 
     BACKGROUND ART 
     There has heretofore been known a technique for controlling allocation of radio resources based on a priority class (for example, “priority class”) set for each call. Generally, the priority class of the call is fixedly set depending on a contract type or the like. 
     For example, for a call type to which the radio resources are allocated in a time division manner (hereinafter, a first call type), the control of allocating the radio resources is to control the order (scheduling priorities) of allocating the radio resources (such as time slots or frequencies) to the calls. The first call type includes calls for HSDPA (High Speed Downlink Packet Access) and a HSUPA (High Speed Uplink Packet Access), for example. 
     In the meantime, for a call type to which the radio resources are allocated depending on a transmission rate (hereinafter, a second call type), the control of allocating the radio resources is to control the transmission rate (an allocated transmission rate) which varies depending on the allocation of the radio resources. The second call type is a call for R99 (Release 99), for example. 
     Here, an upper node such as a radio network controller or an exchange notifies a radio base station of the priority class of a call. 
     Specifically, in a W-CDMA/UTMS system standardized by the 3GPP (3rd Generation Partnership Project), the priority class of a call can be notified by using “Allocation/Retention Priority Level” as a signal format for notification sent from the exchange to the radio network controller (see Non-Patent Document 1, for example). Meanwhile, the priority class of the call can be notified by using “MAC-hs Scheduling Priority Indicator” as a signal format sent from the radio network controller to the radio base station (see Non-Patent Document 2, for example). 
     PRIOR ART DOCUMENTS 
     Non-Patent Documents 
     
         
         Non-Patent Document 1: TS25.413 V7.9.0 “UTRAN Iu interface RANAP signalling” 
         Non-Patent Document 2: TS25.433 V8.1.0 “UTRAN Iub interface Node B Application Part (NBAP) signalling” 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     As described above, the allocation of the radio resources is controlled based on the priority class of each call. In this way, QoS (Quality of Service) is differentiated depending on a user or service. 
     In general, however, the priority class of each call is set fixedly by the contract type or the like. For this reason, when a call having a high priority class involves a large amount of communication, a transmission rate of a call having a low priority class is lowered even when the call having the low priority class involves a small amount of communication, for example. In this way, fair services have not been provided to users. 
     The present invention has been made to solve the above-mentioned problem, and an objective thereof is to provide a radio communication system, a radio base station, and a radio communication method capable of providing fair services. 
     Means for Solving the Problem 
     A radio communication system according to a first feature provides a first call type to which radio resources are allocated in a time division manner. The radio communication system includes: a measurement unit configured to measure an actual usage record of the first call type during execution of the first call type after starting the first call type; and a setting unit configured to set a scheduling order of the first call type based on the actual usage record of the first call type, during execution of the first call type. 
     In the first feature, the setting unit sets the scheduling order of the first call type based on communication quality of the first call type during execution of the first call type. 
     In the first feature, the setting unit sets the scheduling order of the first call type based on an average transmission rate of the first call type during execution of the first call type. 
     In the first feature, the setting unit sets the scheduling order of the first call type based on a difference between a target transmission rate of the first call type and the average transmission rate of the first call type. 
     A radio base station according to a second feature is provided in a radio communication system providing a first call type to which radio resources are allocated in a time division manner. The radio base station includes: a measurement unit configured to measure an actual usage record of the first call type during execution of the first call type after starting the first call type; and a setting unit configured to set a scheduling order of the first call type based on the actual usage record of the first call type during execution of the first call type. 
     A radio communication method according to a third feature provides a first call type to which radio resources are allocated in a time division manner. The radio communication method includes: a step A of measuring an actual usage record of the first call type during execution of the first call type after starting the first call type; and a step B of setting a scheduling order of the first call type based on the actual usage record of the first call type during execution of the first call type. 
     Effects of the Invention 
     According to the present invention, it is possible to provide a radio communication system, a radio base station, and a radio communication method capable of providing fair services. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing a radio communication system according to an embodiment. 
         FIG. 2  is a block diagram showing a radio base station  20  according to the embodiment. 
         FIG. 3  is a block diagram showing a baseband signal processing unit  220  according to the embodiment. 
         FIG. 4  is a block diagram showing a MAC processing unit  222  according to the embodiment. 
         FIG. 5  is a view showing a table for specifying a priority according to the embodiment. 
         FIG. 6  is a flowchart showing an operation of the radio base station  20  according to the embodiment. 
         FIG. 7  is a view showing a table for specifying a target transmission rate according to a modified example 1. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     A radio communication system according to an embodiment of the present invention will be described below with reference to the drawings. Note that, in the following description of the drawings, same or similar reference numerals denote same or similar elements and portions. 
     In addition, it should be noted that the drawings are schematic and ratios of dimensions and the like are different from actual ones. Therefore, specific dimensions and the like should be determined in consideration of the following description. Moreover, the drawings also include portions having different dimensional relationships and ratios from each other. 
     Summary of the Embodiment 
     The embodiment relates to a radio communication system providing a first call type to which radio resources are allocated in a time division manner. Here, the radio communication system may also provide a second call type to which the radio resources are allocated based on a transmission rate. 
     In the W-CDMA, the first call type is a call for a bearer of the HSDPA (High Speed Downlink Packet Access) or for a packet bearer of the LTE (Long Term Evolution) mode, for example. In the first call type, control of allocation of the radio resources is to control the order (scheduling priorities) of allocating the radio resources (such as time slots or frequencies) to the calls. 
     Here, the scheduling order is controlled by a radio base station (eNodeB). Note that, the radio base station controls the allocation of the radio resources by applying the priority class of the first call type regardless of the congestion situation of a radio section. 
     Here, a first call type having a high priority class has more opportunities to receive allocation of the radio resources while a first call type having a low priority class has less opportunity to receive allocation of the radio resources. 
     A core network  40  (such as MME: Mobility Management Entity) sets the priority class of the first call type and notifies a radio base station  20  of the priority class. 
     A second call type is a call for R99 (Release 99), for example. In the second call type, control of allocation of the radio resources is control of a transmission rate (an allocated transmission rate) which varies depending on the allocation of the radio resources. 
     Here, the allocated transmission rate is controlled by a radio network controller (RNC). It should be noted that the radio network controller employs a priority class of the second call type in the control of allocation of the radio resources depending on the congestion situation of the radio section. 
     Here, the radio resources sufficient for a high allocated transmission rate (such as 64 kbps) are allocated to a second call type having a high priority class while the radio resources sufficient for a low allocated transmission rate (such as 32 kbps) are allocated to a second call type having a low priority class. 
     The priority class of the second call type is set by the core network  40  (such as an exchange) and is notified from the core network  40  to the radio network controller. 
     Here, the radio communication system includes a measurement unit configured to measure an actual usage record of the first call type during execution of the first call type after starting the first call type, and a setting unit configured to set the scheduling order of the first call type based on the actual usage record of the first call type. 
     In the embodiment, the setting unit sets the scheduling order of the first call type based on the actual usage record of the first call type during execution of the first call type. For example, the scheduling order is raised as the actual usage record of the first call type becomes larger, whereas the scheduling order is lowered as the actual usage record of the first call type becomes smaller. Accordingly, it is possible to provide fair services. 
     EMBODIMENT 
     (Radio Communication System) 
     The radio communication system according to the embodiment will be described below with reference to the accompanying drawing.  FIG. 1  is a view showing the radio communication system according to the embodiment. The radio communication system is a system employing the Evolved UTRA and UTRAN (LTE: Long Term Evolution or Super 3G). Therefore, it should be noted that a configuration used in R99 (such as a radio network controller) is omitted therein. 
     For example, in the radio communication system, the OFDMA (Orthogonal Frequency Division Multiple Access) is used as a radio access mode for a downlink. Meanwhile, the SC-FDMA (Single Carrier—Frequency Division Multiple Access) is used for an uplink. 
     In the OFDMA, a frequency band is divided into multiple narrow frequency bands (subcarriers) and data are transmitted by use of the multiple subcarriers. In the SC-FDMA, the frequency band is divided and the data are transmitted among multiple radio terminals by using different frequency bands. In this way, interferences among the multiple radio terminals are reduced in the SC-FDMA. 
     As shown in  FIG. 1 , the radio communication system provides services to a radio terminal  10 . For example, the radio communication system provides the first call type to which the radio resources are allocated in a time division manner and the second call type to which the radio resources are allocated depending on the transmission rate. In the embodiment, the first call type is the call for the HSDPA or the HSUPA while the second call type is the call for R99. Moreover, the embodiment mainly explains a case in which the first call type and the second call type are packet switch calls. 
     Specifically, the radio communication system includes radio base stations  20 , an access gateway  30 , and the core network  40 . 
     The radio terminal  10  is a terminal such as a mobile telephone, a PDA or a notebook PC. The radio terminal  10  performs communication with the radio base station  20  through a radio channel. The radio terminal  10  may also be referred to as UE (User Equipment). 
     Each of the radio base stations  20  manages a corresponding one of cells  80 . Specifically, the radio base station  20  performs communication with the radio terminal  10  located in the cell  80  through the radio channel. The radio base station  20  may also be referred to as eNB (eNode B). 
     In the embodiment, radio base stations  20   a  to  20   d  are provided as the radio base station  20 . Similarly, cells  80   a  to  80   d  are provided as the cell  80 . The multiple cells  80  (the cells  80   a  to  80   d ) constitute service areas. 
     Here, note that, the radio base station  20  performs communication with multiple radio terminals  10 . The radio base station  20  controls allocation of the radio resources for the first call type. Specifically, the radio base station  20  controls the order (scheduling priorities) of allocating the radio resources (such as the time slots or the frequencies) to the calls. 
     Details of the radio base station  20  will be described later (see  FIG. 2 ). 
     The access gateway  30  is a device configured to manage the multiple radio base stations  20 . That is, the access gateway  30  is an upper node of the radio base station  20 . 
     The core network  40  includes the MME (Mobility Management Entity), for example. The core network  40  may also be referred to as EPC (Evolved Packet Core). 
     (Channel Configuration) 
     A channel configuration of the first call type according to the embodiment will be described below. Here, a channel configuration for the second call type will be omitted herein. 
     A downlink may be a physical downlink shared channel (PDSCH: Physical Downlink Shared Channel), a downlink control channel for the first call type, and the like. An uplink may be a physical uplink shared channel (PUSCH: Physical Uplink Shared Channel), an uplink control channel for the first call type, and the like. 
     In the downlink, information on a user or information on a transport format to be mapped on the physical downlink shared channel, information on a user or information on a transport format to be mapped on the physical uplink shared channel, transmission acknowledgment information on the physical uplink shared channel, and the like is transmitted to the radio terminal  10  through the downlink control channel for the first call type. 
     Meanwhile, in the downlink, the user data are transmitted through the physical downlink shared channel. For example, the user data includes IP packets for Web browsing, file transfer (FTP), voice packets (VoIP), and the like, control signals used for radio resource control (RRC: Radio Resource Control), and so forth. The user data are mapped on the physical downlink shared channel as a physical channel, and are mapped on a downlink shared channel (DL-SCH) as a transport channel. 
     In the uplink, quality information (CQI: Channel Quality Indicator) on the downlink, transmission acknowledgment information on the physical downlink shared channel, and the like is notified to the radio terminal  10  through the uplink control channel for the first call type. Here, the quality information (CQI) on the downlink is used for scheduling of the physical downlink shared channel and adaptive modulation and coding scheme (AMCS: Adaptive Modulation and Coding Scheme). The uplink control channel for the first call type includes a channel to be time-multiplexed with the physical uplink shared channel, and a channel to be frequency-multiplexed with the physical uplink shared channel. 
     Meanwhile, in the uplink, the user data are transmitted through the physical uplink shared channel. For example, the user data includes IP packets for Web browsing, file transfer (FTP), voice packets (VoIP), and the like, control signals used for radio resource control (RRC: Radio Resource Control), and so forth. The user data are mapped on the physical uplink shared channel as a physical channel, and are mapped on an uplink shared channel (UL-SCH) as a transport channel. 
     (Radio Base Station) 
     The radio base station according to the embodiment will be described below with reference to the accompanying drawing.  FIG. 2  is a block diagram showing the radio base station  20  according to the embodiment. 
     As shown in  FIG. 2 , the radio base station  20  includes a radio communication unit  210 , a baseband signal processing unit  220 , a transmission channel IF  230 , and a call processing unit  240 . 
     For the downlink, the radio communication unit  210  transmits a radio frequency signal to the radio terminal  10 . Here, the radio communication unit  210  converts a baseband signal to be transmitted to the radio terminal  10  into the radio frequency signal, and then amplifies the radio frequency signal. 
     For the uplink, the radio communication unit  210  receives the radio frequency signal from the radio terminal  10 . Here, the radio communication unit  210  amplifies the radio frequency signal received from the radio terminal  10 , and then converts the radio frequency signal into the baseband signal. 
     The baseband signal processing unit  220  performs processing for a L1 (Layer 1), processing for a PDCP layer (Packet Data Convergence Protocol Layer), processing for an RLC layer (Radio Link Control Layer), and processing for a MAC layer (Media Access Control Layer). 
     For example, in the downlink, retransmission control processing (such as HARQ: Hybrid Automatic Repeat reQuest), scheduling processing, transmission format selection processing, channel coding processing, IFFT processing, and the like are performed as the processing for the layers described above. 
     For example, in the uplink, FFT processing, IDFT processing, channel decoding processing, error correction decoding processing, retransmission control processing (such as HQRQ), and the like are performed as the processing for the layers described above. 
     Note that, details of the baseband signal processing unit  220  will be described later (see  FIG. 3 ). 
     The transmission channel IF  230  is an interface for performing communication with the access gateway  30 . For example, the transmission channel IF  230  acquires a priority class of the first call type, which is set by the core network  40 , from the core network  40  through the access gateway  30 . 
     The call processing unit  240  performs call processing such as establishment or release of the communication channel, state management of the radio base stations  20 , management of the radio resources for the radio base stations  20 , and the like. 
     (Baseband Signal Processing Unit) 
     The baseband signal processing unit according to the embodiment will be described below with reference to the accompanying drawing.  FIG. 3  is a block diagram showing the baseband signal processing unit  220  according to the embodiment. 
     As shown in  FIG. 3 , the baseband signal processing unit  220  includes an L1 processing unit  221 , a MAC processing unit  222 , an RLC/PDCP processing unit  223 , and a data amount measurement unit  224 . 
     The L1 processing unit  221  performs the processing for the layer  1 . Specifically, the L1 processing unit  221  performs the channel coding processing, the IFFT processing, and the like for downlink data. The L1 processing unit  221  performs the FFT processing, the IDFT processing, the channel decoding processing, and the like for uplink data. 
     The L1 processing unit  221  transmits control information on the downlink shared channel (such as Downlink Scheduling Information) and control information on the uplink shared channel (such as Uplink Scheduling Information) to the radio terminal  10 . Meanwhile, the L1 processing unit  221  transmits uplink transmission acknowledgment information to the radio terminal  10 . 
     The L1 processing unit  221  receives the quality information (CQI) on the downlink and downlink transmission acknowledgment information from the radio terminal  10 . The quality information (CQI) on the downlink is notified to the MAC processing unit  222 . 
     The L1 processing unit  221  judges a state of synchronization of the uplink based on an uplink reference signal and the quality information on the downlink received from the radio terminal  10 . The state of synchronization of the uplink is notified to the MAC processing unit  222 . 
     The L1 processing unit  221  may estimate uplink reception timing based on the uplink reference signal and the quality information on the downlink received from the radio terminal  10 . 
     The L1 processing unit  221  may be configured to notify the data amount measurement unit  224  of an amount of the radio resources used for downlink data transmission during execution of the first call type. The L1 processing unit  221  may be configured to notify the data amount measurement unit  224  of an amount of the radio resources used for uplink data transmission during execution of the first call type. 
     Here, the radio resources may be frequency resources, time resources, code resources or power resources, for example. The frequency resources may also be defined as the number of resource blocks. 
     The MAC processing unit  222  performs the processing for the MAC layer. Specifically, the MAC processing unit  222  performs retransmission control (such as the HARQ) processing, the scheduling processing, and the transmission format selection processing in the MAC layer. Note that, details of the MAC processing unit  222  will be described later (see  FIG. 4 ). 
     The RLC/PDCP processing unit  223  performs the processing for the RLC layer and the processing for the PDCP layer. Specifically, the RLC/PDCP processing unit  223  performs transmission processing for the downlink data. For example, the RLC/PDCP processing unit  223  performs division and integration of packets in the PDCP layer as well as the retransmission control processing in the RLC layer for the downlink data. The RLC/PDCP processing unit  223  performs reception processing for the uplink data. For example, the RLC/PDCP processing unit  223  performs division and integration of packets in the PDCP layer as well as the retransmission control processing in the RLC layer for the uplink data. 
     The RLC/PDCP processing unit  223  may be configured to notify the data amount measurement unit  224  of an amount of downlink transmission data in the RLC layer during execution of the first call type. The RLC/PDCP processing unit  223  may be configured to notify the data amount measurement unit  224  of an amount of uplink reception data in the RLC layer during execution of the first call type. 
     Alternatively, the RLC/PDCP processing unit  223  may be configured to notify the data amount measurement unit  224  of an amount of downlink transmission data in the PDCP layer during execution of the first call type. The RLC/PDCP processing unit  223  may be configured to notify the data amount measurement unit  224  of an amount of uplink reception data in the PDCP layer during execution of the first call type. 
     Here, the RLC/PDCP processing unit  223  may be configured to notify the data amount measurement unit  224  of the amounts of the transmission data (or the reception data) in both of the RLC layer and the PDCP layer. 
     The data amount measurement unit  224  measures an actual usage record of the first call type during execution of the first call type after starting the first call type. 
     For example, any of the following actual usage records may be used as the actual usage record of the first call type. 
     (1) An accumulated value of the amount of the transmission data in the downlink during execution of the first call type. 
     (2) An accumulated value of the amount of the reception data in the uplink during execution of the first call type. 
     (3) An accumulated value of the amounts of the transmission data in the downlink and the uplink during execution of the first call type. 
     (4) An accumulated value of the amount of the radio resources used for data transmission in the downlink during execution of the first call type. 
     (5) An accumulated value of the amount of the radio resources used for data reception in the uplink during execution of the first call type. 
     (6) An accumulated value of the amount of radio resources used for the data transmission and data reception in the uplink during execution of the first call type. 
     The actual usage records shown in (1) to (6) may be measured depending on each radio terminal  10 . The actual usage records shown in (1) to (6) may be measured depending on each service type. The actual usage records shown in (1) to (6) may be measured depending on each contract type or each priority class. The actual usage records shown in (1) to (6) may be measured depending on each type of a logical channel (Logical Channel) or on each type of a radio bearer (Radio Bearer) established between the radio terminal  10  and the radio base station  20 . 
     The amount of the transmission data and the amount of the reception data may be amounts of data on the RLC layer. The amount of the transmission data and the amount of the reception data may be amounts of data on the PDCP layer. 
     The amount of the radio resources may be the frequency resources, the time resources, the code resources or the power resources. The amount of the radio resources may be a combination of two or more of the frequency resources, the time resources, the code resources, and the power resources. Here, the frequency resources may be defined as the number of resource blocks. 
     The service type may be the type such as VoIP (Voice over Internet Protocol), a voice service, a streaming service or FTP (File Transfer Protocol), for example. 
     The contract type is the type of a contract subscribed by the user of the radio terminal  10 . The contract type may be the type such as a low class contract, a high class contract, a flat-rate contract or a pay-as-you-go contract, for example. 
     The priority class is the class for categorizing transmission priorities in the downlink and the uplink. The priority class may be set based on the contract type, for example. Here, a call having a high priority class is transmitted in preference to a call having a low priority class. The priority class is linked with the logical channel and may also be referred to as a logical channel priority (Logical Channel Priority). Meanwhile, the priority class may also be referred to as Priority Class. 
     The logical channel type is the type such as a DCCH (Dedicated Control Channel) or a DTCH (Dedicated Traffic Channel). The DCCH and the DTCH may also be defined by using more detailed multiple logical channels. 
     The radio bearer type is the type of the radio bearer for transmitting the data. The radio bearer is linked one-to-one with the logical channel. Therefore, the radio bearer can be considered as the same as the logical channel. 
     (MAC Processing Unit) 
     The MAC processing unit according to the embodiment will be described below with reference to the accompanying drawing.  FIG. 4  is a block diagram showing the MAC processing unit  222  according to the embodiment. 
     As shown in  FIG. 4 , the MAC processing unit  222  includes a HARQ control unit  310 , a state management unit  320 , a priority setting unit  330 , a scheduling coefficient calculation unit  340 , a UE selection unit  350 , a frequency resource management unit  360 , and a TRF selection unit  370 . 
     The HARQ control unit  310  performs retransmission control in the MAC layer. Specifically, the HARQ control unit  310  combines a block initially transmitted from the radio terminal  10  (hereinafter a transmitted block) with a block retransmitted from the radio terminal  10  (hereinafter a retransmitted block). 
     Here, the HARQ control unit  310  may be provided for each radio terminal  10  (UE) or for each logical channel. The HARQ control unit  310  may also be provided in common to multiple radio terminals  10  (UE). 
     The state management unit  320  manages a state of each radio terminal  10  (UE). The state management unit  320  manages a state of a HARQ entity, a state of mobility of the UE, a DRX state (an intermittent reception cycle), a state of uplink synchronization, whether or not to employ persistent scheduling, presence or absence of transmission of a MAC control block, a state of downlink transmission, a buffer state, and the like depending on each UE. 
     The priority setting unit  330  sets the priority based on the actual usage record of the first call type measured by the data amount measurement unit  224 . For example, the priority setting unit  330  makes reference to a table shown in  FIG. 5  and sets a priority (A priority#n (Amount data )). On the table shown in  FIG. 5 , the priority (A priority#n (Amount data )) and the actual usage record (Amount data ) are linked with each priority class (A priority#n ). As shown in  FIG. 5 , the priority class (A priority#n (Amount data )) becomes higher as the actual usage record (Amount data ) becomes smaller. In the meantime, the priority (A priority#n (Amount data )) becomes higher as the priority class (A priority#n ) becomes higher. 
     The scheduling coefficient calculation unit  340  sets the scheduling order of the first call type based on the actual usage record of the first call type. Specifically, the scheduling coefficient calculation unit  340  calculates a scheduling coefficient C n  of a radio terminal  10   n  (UEn) in accordance with the following formula. 
     
       
         
           
             
               
                 
                   
                     C 
                     n 
                   
                   = 
                   
                     
                       
                         A 
                         
                           priority 
                            
                           # 
                            
                           n 
                         
                       
                        
                       
                         ( 
                         
                           Amount 
                           data 
                         
                         ) 
                       
                     
                     × 
                     
                       
                         Q 
                         n 
                       
                       
                         
                           R 
                           n 
                         
                         _ 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     A priority#n (Amount data ): the priority of the radio terminal  10   n  (UEn) 
     A priority#n : the priority class of the radio terminal  10   n  (UEn) 
     Amount data : the actual usage record of the radio terminal  10   n  (UEn) 
     Q n : the communication quality of the radio terminal  10   n  (UEn) 
       R n   : an average transmission rate of the radio terminal  10   n  (UEn) 
     As described above, the priority of the radio terminal  10   n  (UEn) is specified by the priority class and the actual usage record of use of the table shown in  FIG. 5 . 
     The communication quality of the radio terminal  10   n  (UEn) is obtained as described below. The communication quality of the downlink is calculated based on the CQI (Channel Quality Indicator) to be notified from the radio terminal  10   n  to the radio base station  20 , for example. The communication quality of the uplink is calculated based on a SIR (Signal to Interference Ratio) of the uplink reference signal to be received from the radio terminal  10   n  (UEn), for example. 
     Here, the communication quality of the uplink may be calculated based on a power offset value between the uplink reference signal and the uplink shared channel. In this case, the communication quality of the uplink shared channel is estimated based on the communication quality of the reference signal and on the power offset value. 
     The average transmission rate of the radio terminal  10   n  (UEn) is either an average value of a downlink transmission rate to be transmitted to the radio terminal  10   n  or an average value of an uplink transmission rate to be received from the radio terminal  10   n . In calculation of the average transmission rate, a time period for which the transmission data are present on a transmission buffer may be used as a denominator, for example. Alternatively, in calculation of the average transmission rate, a total time period of the time period for which the transmission data are present on the transmission buffer and the time period for which the transmission data are present on the transmission buffer, i.e., a time period for which the first call type is established may be used as the denominator. 
     Here, the scheduling coefficient C n  may be calculated based on each radio terminal  10 . In this case, the actual usage record measured based on each radio terminal  10  is used as the actual usage record. 
     The scheduling coefficient C n  may be calculated based on each service type. In this case, the actual usage record measured based on each service type is used as the actual usage record. 
     The scheduling coefficient C n  may be calculated based on each contract type or each priority class. In this case, the actual usage record measured based on each contract type or each priority class is used as the actual usage record. 
     The scheduling coefficient C n  may be calculated based on each logical channel or each radio bearer. In this case, the actual usage record measured based on each logical channel or each radio bearer is used as the actual usage record. 
     The UE selection unit  350  selects some of the radio terminals  10  (UE) to which the radio resources are to be allocated for the first call types under dynamic scheduling. Specifically, the UE selection unit  350  selects some of the radio terminals  10  (UE) to which the radio resources are to be allocated based on the scheduling coefficients C n  of the first call types. The UE selection unit  350  notifies the TRF selection unit  370  of the number of the radio terminals  10  (UE) to which the radio resources are to be allocated. 
     In this way, the UE selection unit  350  controls the order of allocating the radio resources (scheduling order) to the first call types for the radio terminals  10  (UE) based on the scheduling coefficients C n  of the first call types. 
     Here, a first call type having a larger scheduling coefficient C n  has more opportunities to receive allocation of the radio resources (such as the time slots and the frequencies) while a first call type having a smaller scheduling coefficient C n  has less opportunities to receive allocation of the radio resources (such as the time slots or the frequencies). That is, the first call type having the large scheduling coefficient C n  receives a higher scheduling order whereas the first call type having the small scheduling coefficient C n  receives a lower scheduling order. 
     Here, regarding the downlink, the UE selection unit  350  may select the radio terminals  10  (UE) based on the amount of data to be transmitted to the radio terminals  10  (UE) in addition to the scheduling coefficient C n . Regarding the uplink, the UE selection unit  350  may select the radio terminals  10  (UE) based on the amount of data to be received from the radio terminals  10  (UE) in addition to the scheduling coefficient C n . 
     The amount of data to be transmitted to the radio terminals  10  (UE) is acquired based on buffer amounts of buffers provided on the radio base stations  20 . The amount of data to be received from the radio terminals  10  (UE) is estimated based on buffer amounts (Buffer Status Report) to be reported from the radio terminals  10 . 
     The frequency resource management unit  360  manages the frequency resources. Specifically, the frequency resource management unit  360  monitors the remaining frequency resources available for the downlink shared channel which employs the dynamic scheduling. The frequency resource management unit  360  notifies the TRF selection unit  370  of the remaining frequency resources. 
     The TRF selection unit  370  determines the transmission formation of the downlink shared channel (DL-SCH) for the first call type under the dynamic scheduling. Meanwhile, the TRF selection unit  370  allocates the radio resources (such as the time slots or the frequencies) based on the transmission formation of the downlink shared channel (DL-SCH). Specifically, the TRF selection unit  370  allocates the radio resources based on the number of the ratio terminals  10  (UE) notified from the UE selection unit  350  and on the remaining frequency resources notified from the frequency resource management unit  360 . 
     (Operation of Radio Base Station) 
     An operation of the radio base station according to the embodiment will be described below with reference to the accompanying drawing.  FIG. 6  is a flowchart showing the operation of the radio base station  20  according to the embodiment. 
     As shown in  FIG. 6 , the radio base station  20  acquires the communication quality in step  10 . The downlink communication quality is calculated based on the CQI, for example. The uplink communication quality is calculated based on the SIR of the reference signal, for example. 
     In step  20 , the radio base station  20  acquires the average transmission rate of the radio terminals  10  (UE). The average transmission rate is the average value of the downlink transmission rate to be transmitted to the radio terminals  10  or the average value of the uplink transmission rate to be received from the radio terminals  10 . 
     In step  30 , the radio base station  20  acquires the actual usage record of the first call type. For example, any of the following actual usage records may be used as the actual usage record of the first call type. 
     (1) An accumulated value of the amount of the transmission data in the downlink during execution of the first call type. 
     (2) An accumulated value of the amount of the reception data in the uplink during execution of the first call type. 
     (3) An accumulated value of the amounts of the transmission data in the downlink and the uplink during execution of the first call type. 
     (4) An accumulated value of the amount of the radio resources used for data transmission in the downlink during execution of the first call type. 
     (5) An accumulated value of the amount of the radio resources used for data reception in the uplink during execution of the first call type. 
     (6) An accumulated value of the amount of radio resources used for the data transmission and data reception in the uplink during execution of the first call type. 
     In step  40 , the radio base station  20  acquires the priority. For example, the radio base station  20  makes reference to the table shown in  FIG. 5  and specifies the priority (A priority#n (Amount data )) based on the actual usage record (Amount data ) and the priority class (A priority#n ). 
     In step  50 , the radio base station  20  acquires the scheduling coefficient C n  of the radio terminal  10   n  (UEn). For example, the radio base station  20  calculates a scheduling coefficient C n  of a radio terminal  10   n  (UEn) in accordance with the following formula. 
     
       
         
           
             
               
                 
                   
                     C 
                     n 
                   
                   = 
                   
                     
                       
                         A 
                         
                           priority 
                            
                           # 
                            
                           n 
                         
                       
                        
                       
                         ( 
                         
                           Amount 
                           data 
                         
                         ) 
                       
                     
                     × 
                     
                       
                         Q 
                         n 
                       
                       
                         
                           R 
                           n 
                         
                         _ 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     A priority#n (Amount data ) the priority of the radio terminal  10   n  (UEn) 
     A priority#n : the priority class of the radio terminal  10   n  (UEn) 
     Amount data : the actual usage record of the radio terminal  10   n  (UEn) 
     Q n : the communication quality of the radio terminal  10   n  (UEn) 
       R n   : an average transmission rate of the radio terminal  10   n  (UEn) 
     Advantageous Effect 
     According to the embodiment, the scheduling coefficient calculation unit  340  calculates the scheduling coefficient C n  of the first call type based on the actual usage record of the first call type during execution of the first call type. The UE selection unit  350  controls the order of allocating the radio resources (scheduling order) to the first call type for the radio terminals  10  (UE) based on the scheduling coefficient C n  of the first call type. 
     Here, in the embodiment, the scheduling order is raised as the actual usage record of the first call type becomes larger, whereas the scheduling order is lowered as the actual usage record of the first call type becomes smaller. Accordingly, it is possible to provide fair services. 
     In the embodiment, the scheduling coefficient C n  is calculated based on the priority (A priority#n (Amount data )), and the priority (A priority#n (Amount data )) is specified based on the actual usage record (Amount data ). Accordingly, it should be noted that the scheduling coefficient C n  is calculated based on the actual usage record (Amount data ). 
     In the embodiment, the priority (A priority#n (Amount data )) is specified based on the priority class (A priority#n ). Therefore, it should be noted that the priority class (A priority#n ) is also considered in calculating the scheduling coefficient C n . 
     Modified Example 1 
     A modified example 1 of the embodiment will be described below with reference to the accompanying drawing. A difference from the first embodiment will be mainly described below. 
     Specifically, in the modified example 1, the scheduling coefficient C n  is calculated based on a target transmission rate of the radio terminal  10   n  (UEn) instead of the priority of the radio terminal  10   n  (UEn). To be specific, the radio base station  20  (scheduling coefficient calculation unit  340 ) calculates a scheduling coefficient C n  of a radio terminal  10   n  (UEn) in accordance with the following formula. 
     
       
         
           
             
               
                 
                   
                     C 
                     n 
                   
                   = 
                   
                     
                       Q 
                       n 
                     
                     
                       
                         
                           R 
                           n 
                         
                         _ 
                       
                       - 
                       
                         
                           R 
                           
                             target 
                             , 
                             
                               Priority 
                                
                               # 
                                
                               n 
                             
                           
                         
                          
                         
                           ( 
                           
                             Amount 
                             data 
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     Amount data : the actual usage record of the radio terminal  10   n  (UEn) 
     Q n : the communication quality of the radio terminal  10   n  (UEn) 
       R n   : an average transmission rate of the radio terminal  10   n  (UEn) 
     R target,Priority#n : the target transmission rate of the radio terminal  10   n  (UEn) 
     The target transmission rate of the radio terminal  10   n  (UEn) is specified by the priority class and the actual usage record of use of the table shown in  FIG. 7 , for example. On the table shown in  FIG. 7 , the target transmission rate (R target,Priority#n (Amount data )) and the actual usage record (Amount data ) are linked with each priority class (A priority#n ). As shown in  FIG. 7 , the target transmission rate (R target,Priority#n (Amount data )) becomes higher as the actual usage record (Amount data ) becomes smaller. In the meantime, the target transmission rate (R target,Priority#n (Amount data )) becomes higher as the priority class (A priority#n ) becomes higher. 
     Advantageous Effect 
     According to the modified example 1, the scheduling coefficient calculation unit  340  calculates the scheduling coefficient C n  of the first call type based on the actual usage record of the first call type during execution of the first call type, in the same manner as the embodiment. The UE selection unit  350  controls the order (scheduling priorities) of allocating the radio resources to the first call types for the radio terminals  10  (UE) based on the scheduling coefficients C n  of the first call types. 
     Here, in the modified example 1, the scheduling order is raised as the actual usage record of the first call type becomes larger, whereas the scheduling order is lowered as the actual usage record of the first call type becomes smaller, in the same manner as the embodiment. Accordingly, it is possible to provide fair services. 
     In the embodiment, the scheduling coefficient C n  is calculated based on the target transmission rate (R target,Prionty#n (Amount data )), and the target transmission rate (R target,Priority#n (Amount data )) is specified based on the actual usage record (Amount data ). Accordingly, it should be noted that the scheduling coefficient C n  is calculated based on the actual usage record (Amount data ). 
     In the embodiment, the target transmission rate (R target,Priority#n (Amount data )) is specified based on the priority class (A priority#n ). Therefore, it should be noted that the priority class (A priority#n ) is also considered in calculating the scheduling coefficient C n . 
     Modified Example 2 
     A modified example 2 of the embodiment will be described below with reference to the accompanying drawing. A difference from the first embodiment will be mainly described below. 
     Specifically, in the modified example 2, the scheduling coefficient C n  is calculated based on a target transmission rate of the radio terminal  10   n  (UEn) in addition to the priority of the radio terminal  10   n  (UEn). To be specific, the radio base station  20  (scheduling coefficient calculation unit  340 ) calculates a scheduling coefficient C n  of a radio terminal  10   n  (UEn) in accordance with the following formula. 
     
       
         
           
             
               
                 
                   
                     C 
                     n 
                   
                   = 
                   
                     
                       
                         A 
                         
                           priority 
                            
                           # 
                            
                           n 
                         
                       
                        
                       
                         ( 
                         
                           Amount 
                           data 
                         
                         ) 
                       
                     
                     × 
                     
                       
                         Q 
                         n 
                       
                       
                         
                           
                             R 
                             n 
                           
                           _ 
                         
                         - 
                         
                           
                             R 
                             
                               target 
                               , 
                               
                                 Priority 
                                  
                                 # 
                                  
                                 n 
                               
                             
                           
                            
                           
                             ( 
                             
                               Amount 
                               data 
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     A priority#n (Amount data ): the priority of the radio terminal  10   n  (UEn) 
     A priority#n : the priority class of the radio terminal  10   n  (UEn) 
     Amount data : the actual usage record of the radio terminal  10   n  (UEn) 
     Q n : the communication quality of the radio terminal  10   n  (UEn) 
       R n   : an average transmission rate of the radio terminal  10   n  (UEn) 
     R target,Priority#n : the target transmission rate of the radio terminal  10   n  (UEn) 
     Advantageous Effect 
     According to the modified example 2, the scheduling coefficient calculation unit  340  calculates the scheduling coefficient C n  of the first call type based on the actual usage record of the first call type during execution of the first call type, in the same manner as the embodiment and the modified example 1. Therefore, it is obvious that the modified example 2 produces similar effects to those of the embodiment and the modified example 1. 
     Other Embodiments 
     As described above, the details of the present invention have been disclosed by using the embodiment of the present invention. However, it should not be understood that the description and drawings which constitute part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples, and operation techniques will be easily found by those skilled in the art. 
     The system employing the LTE has been described as the example of the radio communication system in the embodiment. However, the embodiment is not limited only to this configuration. For example, the radio communication system may be a system employing the R99. 
     In the embodiment, the scheduling order of the first call type is controlled based on the actual usage record of the first call type. However, the embodiment is not limited only to this configuration. Specifically, the scheduling order of the second call type may be controlled based on the actual usage record of the second call type. 
     Although it is not particularly stated in the modified example 1 and the modified example 2, the scheduling coefficient C n  may be configured to be set to a maximum for the first call type having the average transmission rate which is lower than the target transmission rate. In other words, the first call type having the average transmission rate lower than the target transmission rate may be given the top priority. 
     Note that the entire content of Japanese Patent Application No. 2009-034217 (filed on Feb. 17, 2009) is incorporated herein by reference. 
     INDUSTRIAL APPLICABILITY 
     As described above, a radio communication system, a radio base station, and a radio communication method according to the present invention are capable of providing fair services and are therefore useful.