Abstract:
The present invention addresses the problem of providing technology which increases the accuracy for estimating quality of a communication channel even in a case in which transmission time limit frames have been set between neighboring cells. The present application relates to quality estimation of a communication channel used by a base station for performing wireless communication with a terminal within a communication area, and is characterized in acquiring quality information for the communication channel between the base station and the terminal, acquiring reception error information related to reception errors for data communication using the communication channel, acquiring transmission time-limit frame information set by a neighboring base station of the base station, updating correction values in accordance with setting information for the transmission time-limit frame information and the reception error information, and estimating the quality of the communication channel using the correction values and the acquired quality information.

Description:
TECHNICAL FIELD 
     The present invention relates to a communication channel quality estimating method, a wireless communications system, a base station, and a program. 
     BACKGROUND ART 
     In wireless communications systems, such as LTE (Long Term Evolution) standardized in the 3GPP (3rd Generation Partnership Project), it is assumed that a plurality of wireless base stations are disposed, where each wireless base station communicates with wireless terminals (referred to as terminals hereinbelow) within its communication area. The communication area is referred to as a cell, which may be divided into a plurality of sub-regions by imparting directivity to an antenna. The sub-region is referred to as a sector cell. In the following description, the term cell refers to a sector cell. 
     In LTE downlink transmission, a terminal measures communication channel quality information such as an SINR (Signal to Interference plus Noise Ratio), converts it into a quantized CQI (Channel Quality Indicator) referring to a lookup table or the like, and reports the result to the base station. The lookup table is generally created by a link-level simulation in which a physical layer is simulated. 
     When transmitting data to the terminal, the base station uses the reported CQI to calculate an estimated SINR (SINR_Est), and selects an MCS (Modulation and Coding Schemes) Index referring to a lookup table. Again, the lookup table is generally created by a link-level simulation in which a physical layer is simulated. Then, a TBS (Transport Block Size) Index is determined referring to a lookup table (NPL 1) from the MCS Index, whereby data can be transmitted with optimum data size. 
     SINR_Est is calculated from EQ. (a) below. SINR_CQI represents an SINR corresponding to a CQI, and Offset represents an offset.
 
SINR_Est=SINR_CQI+Offset  EQ. (a)
 
Control for regulating Offset above is OLLA (Outer Loop Link Adaptation). In case that a notification of a reception error (NACK) is received from a terminal, Offset is updated to a smaller value, as given by EQ. (b) below; and in case that a notification of a successful reception (ACK) is received, Offset is updated to a greater value, as given by EQ. (c) below, whereby the SINR_Est can be corrected to achieve a target reception error rate. Delta_Down represents an arbitrary fixed value, and T_Bler represents a target reception error rate.
 
On reception of NACK: Offset=Offset−Delta_Down  EQ. (b)
 
On reception of ACK: Offset=Offset+ T _Bler/(1 −T _Bler)*Delta_Down  EQ. (c)
 
     On the other hand, as measures for addressing an increase of traffic in recent years, as shown in  FIG. 12 , attention is attracted to a heterogeneous network in which cells of various sizes are present together by introducing a base station with low transmission power (small cell base station) in addition to an ordinary macro base station; however, since the same wireless band is used between adjacent cells, inter-cell interference is perceived as a problem. It is an interference management technology that circumvents the problem. For an interference management technology according to 3GPP Release 10, an eICIC (enhanced Inter-Cell Interference Coordination) is standardized and an ABS (Almost Blank Subframe) is configured (NPL 2). Here, the eICIC is also referred to as a time domain ICIC. The ABS is also referred to as a Protected Subframe. A base station having the ABS configured stops transmission of a data channel (PDSCH: Physical Data Shared Channel) in a downlink. Thus, an SINR in a terminal in an adjacent cell is significantly improved, and enhancement of the throughput of that terminal can be expected. 
     With introduction of the ABS, a base station can define two measurement subframe sets differentiated between the ABS and a non-ABS from Release 10 (NPL 3). A terminal measures communication channel quality information for each measurement subframe set, and reports a CQI of each set. Thus, a base station can calculate the SINR_Est with high precision regardless whether the subframe is an ABS or a Non-ABS. In an example shown in  FIG. 13 , four subframes (# 1 , # 3 , # 5 , # 9 ) in a macro cell is defined as an ABS, and a pico terminal connected to a pico cell has Measurement Subframes  1  and  2  configured according to the ABS and the Non-ABS, respectively. 
     CITATION LIST 
     Non Patent Literature 
     NPL 1: 3GPP TS 36.213 V9.3.0 (2010-09), 3GPP TSG RAN E-UTRA Physical layer procedures (Release 9), p. 27. 
     NPL 2: 3GPP TS 36.300 V10.6.0 (2011-12), 3GPP TSG-RAN E-UTRA and E-UTRAN Overall description Stage 2 (Release 10), p. 116. 
     NPL 3: 3GPP TS 36.311 V10.4.0 (2011-12), 3GPP TSG-RAN E-UTRA RRC Protocol specification (Release 10), pp. 163-4. 
     SUMMARY OF INVENTION 
     Technical Problem 
     Even though the ABS is introduced as described above, however, there is a problem that the transmission rate is not improved much for a terminal not supporting Release 10 because precision of the estimated SINR (SINR_Est) is significantly degraded relative to an actual SINR (SINR_Real). 
     A terminal not supporting Release 10 cannot have a measurement subframe set configured. Accordingly, it reports a CQI calculated by averaging the measured interference power values for the ABS and the Non-ABS. Then, as shown in  FIG. 14 , the Non-ABS has a high SINR_CQI as compared with the SINR_Real, while the ABS has a low SINR_CQI as compared with the SINR_Real. Consequently, in an attempt to attain a target reception error rate, the SINR_Est is considerably small as compared with the SINR_Real for the ABS. Therefore, an MCS Index to be selected becomes significantly smaller for the ABS, thus lowering the transmission rate. 
     Therefore, a problem to be solved by the present invention is to solve the problem described above, and is to provide a technology for improving precision in SINR estimation. 
     Disclosure of the Invention 
     The invention in the present application for solving the problem described above is a quality estimating method for a communication channel used by a base station for wireless communicating with a terminal within a communication area, said method characterized in comprising: a step of acquiring quality information for a communication channel between said base station and said terminal; a step of acquiring reception error information relating to a reception error in a data communication using said communication channel; a step of acquiring information on a transmission limit time frame defined by a base station adjacent to said base station; and an estimating step of updating a corrective value according to the definition in said transmission limit time frame information and said reception error information, and estimating quality of said communication channel using said corrective value and said acquired quality information. 
     The invention in the present application for solving the problem described above is a wireless communications system in which a base station wireless communicates with a terminal within a communication area, said system characterized in comprising: means for acquiring quality information for a communication channel between said base station and said terminal; means for acquiring reception error information relating to a reception error in a data communication using said communication channel; means for acquiring information on a transmission limit time frame defined by a base station adjacent to said base station; and estimating means for updating a corrective value according to the definition in said transmission limit time frame information and said reception error information, and estimating quality of said communication channel using said corrective value and said acquired quality information. 
     The invention in the present application for solving the problem described above is a base station for wireless communicating with a terminal within its communication area, said base station characterized in comprising: means for acquiring quality information for a communication channel between said base station and said terminal; means for acquiring reception error information relating to a reception error in a data communication using said communication channel; means for acquiring information on a transmission limit time frame defined by a base station adjacent to said base station; and estimating means for updating a corrective value according to the definition in said transmission limit time frame information and said reception error information, and estimating quality of said communication channel using said corrective value and said acquired quality information. 
     The invention in the present application for solving the problem described above is a program for a base station for wireless communicating with a terminal within its communication area, said program characterized in causing said base station to function as: means for acquiring quality information for a communication channel between said base station and said terminal; means for acquiring reception error information relating to a reception error in a data communication using said communication channel; means for acquiring information on a transmission limit time frame defined by a base station adjacent to said base station; and estimating means for updating a corrective value according to the definition in said transmission limit time frame information and said reception error information, and estimating quality of said communication channel using said corrective value and said acquired quality information. 
     Advantageous Effects of Invention 
     According to the present invention, the throughput of a terminal and the system capacity of a base station can be increased. This is because precision of the estimated SINR relative to the actual SINR is enhanced, so that the selected MCS Index is increased and the transmission rate is improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  block diagram showing a configuration of a wireless communications system in a first embodiment. 
         FIG. 2  A flow chart showing processing of decision of an adjacent cell, prescription of a method of reporting a CQI for a terminal, and setting of an initial value of an OLLA offset in the first embodiment. 
         FIG. 3  A flow chart showing processing of updating the OLLA offset in the first embodiment. 
         FIG. 4  A flow chart showing processing of OLLA-based SINR estimation in the first embodiment. 
         FIG. 5  An exemplary graph of a result of SINR estimation in the first embodiment. 
         FIG. 6  A flow chart showing processing of decision of an adjacent cell, prescription of a method of reporting a CQI for a terminal, and setting of an initial value of an OLLA offset in a second embodiment. 
         FIG. 7  A flow chart showing processing of updating the OLLA offset in the second embodiment. 
         FIG. 8  A flow chart showing processing of OLLA-based SINR estimation in the second embodiment. 
         FIG. 9  A block diagram showing a configuration of a wireless communications system in a third embodiment. 
         FIG. 10  A flow chart showing processing of decision of an adjacent cell, and setting of an initial value of an OLLA offset in the third embodiment. 
         FIG. 11  A flow chart showing processing of OLLA-based SINR estimation in the third embodiment. 
         FIG. 12  An exemplary configuration of a heterogeneous network. 
         FIG. 13  An exemplary ABS configuration. 
         FIG. 14  An exemplary graph of a result of SINR estimation. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The invention in the present application relates to quality estimation for a communication channel used by a base station  100  for wireless communicating with a terminal  200  within a communication area, and is characterized in: acquiring quality information for a communication channel between the base station  100  and the terminal  200 ; acquiring reception error information relating to a reception error in a data communication using the communication channel; acquiring information on a transmission limit time frame defined by a base station adjacent to the base station; updating a corrective value according to the definition in the transmission limit time frame information and the reception error information; and estimating quality of the communication channel using the corrective value and the acquired quality information. 
     Specifically, the base station  100  in the present invention is characterized in comprising: a limit time frame control section  104  for acquiring, via a network, information on a pattern of an ABS (Almost Blank Subframe) defined by a base station surrounding the base station  100  and retaining the information; and a channel quality estimating section  105  for deciding whether the terminal  200  is a terminal capable of reporting CSI (Channel State Information) according to the ABS pattern, deciding an adjacent cell from RSRP (Reference Signal Received Power) information received from the terminal, and estimating an SINR (Signal Interference plus Noise Ratio) for the terminal  200  based on OLLA (Outer Loop Link Adaptation) from a CQI (Channel Quality Indicator) and reception decision information. 
     First Embodiment 
     [Configuration] 
       FIG. 1  is a block diagram showing a configuration of a wireless communications system in a first embodiment of the present invention. As shown in  FIG. 1 , the wireless communications system comprises a base station  100  and a terminal  200 . 
     The base station  100  is a wireless communication apparatus for wireless communicating with the terminal  200  lying in a communication area of the base station  100  via a wireless channel. The base station  100  is also connected to a network (not shown) and is capable of making data communications with surrounding base stations. Although not shown, the base station  100  is capable of connecting with a plurality of terminals. Moreover, a plurality of base stations may exist. A wireless band is divided into PRBs (Physical Resource Blocks), the PRB being a unit of allocation. This embodiment will be described for a wireless communications system with reference to an LTE downlink as an example. 
     The base station  100  comprises main functional sections including a base station operating section  101 , a reference signal generating section  102 , a transmission buffer  103 , a limit time frame control section  104 , a channel quality estimating section  105 , and a scheduler  106 . 
     The base station operating section  101  has similar functions to those of base stations commonly used in a wireless communications system, including a function of notifying the terminal  200  of information on surrounding cells such as a surrounding base station cell (referred to as a surrounding cell hereinbelow) number, and descriptions thereof will be omitted herein because the configuration and operation thereof are well known in the art. 
     The reference signal generating section  102  has a function of transmitting a reference signal serving as a reference of communication channel quality information at certain times from the base station operating section  101  to the terminal  200 . 
     The transmission buffer  103  has a function of accumulating data that has arrived from the network and is to be transmitted to the terminal  200 , along with management information such as a time of arrival and a destination terminal number. 
     The limit time frame control section  104  has a function of retaining information on an ABS pattern that has arrived from the network and is defined by a surrounding base station, and notifying the information to the channel quality estimating section  105  and scheduler  106 . Further, the limit time frame control section  104  is capable of defining an ABS pattern of its cell. When the pattern is defined, the limit time frame control section  104  notifies the ABS pattern via a wireless channel to a terminal capable of reporting CSI (Channel State Information) according to an ABS pattern. The CSI is a generic name of information on a status of a downlink reference signal, such as a CQI (Channel Quality Indicator). The limit time frame control section  104  is also capable of notifying the ABS pattern to surrounding base stations via the network. The notification of the ABS pattern may be made between base stations directly, or an operation and maintenance (OAM) server may manage the information and notify the ABS pattern. 
     The channel quality estimating section  105  has a function of deciding whether the terminal  200  is a terminal supporting Release 10 from UE Capability information for the terminal  200  and storing a result, and prescribing a method of reporting a CQI for the terminal  200 , a function of deciding a base station cell adjacent to the terminal  200  (referred to as an adjacent cell hereinbelow) from RSRP (Reference Signal Received Power) information received from the terminal  200 , a function of retaining CSI reported from the terminal  200 , a function of retaining reception decision information (ACK, NACK) reported from the terminal  200 , and a function of estimating an SINR for the terminal  200  based on OLLA from a CQI contained in CSI and the reception decision information. 
     The scheduler  106  has a function of determining a PRB and a TBS Index to be allocated to a terminal based on CSI and the estimated SINR, creating transmission data (Transport Block), and transmitting the data to the mobile station  200  via the base station operating section  101 . 
     Subsequently, the terminal  200  will be described. The terminal  200  comprises main functional sections including a terminal operating section  201 , a channel quality measuring section  202 , and a reception decision section  203 . In this embodiment, a terminal capable of reporting CSI according to an ABS pattern is referred to as “terminal supporting Release 10,” and a terminal except that as “terminal not supporting Release 10.” 
     The terminal operating section  201  has similar functions to those of terminals commonly used in a wireless communications system, including a function of transferring UE Capability to the base station  100 , and descriptions thereof will be omitted herein because the configuration and operation thereof are well known in the art. 
     The channel quality measuring section  202  has a function of measuring communication channel quality such as an SINR from a reference signal received from the base station  100 , quantizing a result as CSI, and reporting it to the base station  100  via the terminal operating section  201  at a time cued by the base station  100 , and a function of measuring RSRP (Reference Signal Received Power) for a reference signal of a currently connecting base station cell and for those of surrounding base station cells (referred to as surrounding cells hereinbelow) notified by the base station  100 , and reporting them to the base station  100  at certain times. 
     The reception decision section  203  has a function of making reception decision for transmission data received from the base station  100 , and notifying the reception decision information to the base station  100  via the terminal operating section  201 . 
     [Operation] 
     Next, an operation of the present embodiment will be described with reference to  FIGS. 2, 3, and 4 .  FIG. 2  shows a procedure of operations of the channel quality estimating section  105  for deciding an adjacent cell, prescribing a method of reporting a CQI for a terminal, and setting an OLLA initial value. These operations are conducted as appropriate, such as when a new terminal is connected the base station  100 , when RSRP information is received from a terminal, or when notification of an ABS pattern is received from a surrounding cell. 
     First, the channel quality estimating section  105  determines a cell adjacent to a terminal from RSRP information received from the terminal (S 1 ). In this embodiment, a surrounding cell having the highest RSRP is determined as adjacent cell. 
     Next, a decision is made as to whether the adjacent cell of the terminal has an ABS configured (S 2 ). An operation in a case wherein the ABS is configured (S 2 , Yes) will be described first. In case that the ABS is configured, and when the terminal does not support Release 10 (S 3 , No), a CQI without subframe-based differentiation is requested from the terminal (S 4 ), and a plurality of OLLA offsets are prepared for the current terminal (S 5 ); then, the processing is terminated. In this embodiment, two kinds of offsets (Offset_ABS, Offset_NonABS) are prepared for the ABS and a Non-ABS, and Offset initial values are set according to EQs. (1) and (2) below. In the equations, u represents a terminal number, and (u) represents a parameter of the terminal u. Moreover, Offset_Init_ABS [dB], Offset_Init_NonABS [dB] are default values prepared beforehand.
 
Offset_ABS( u )[dB]=Offset_Init_ABS  EQ. (1)
 
Offset_NonABS( u )[dB]=Offset_Init_NonABS  EQ. (2)
 
On the other hand, for a terminal supporting Release 10 (S 3 , Yes), a measurement subframe set is defined for the terminal based on the ABS pattern for the adjacent cell, CQI reporting is requested for each set (S 6 ), and one OLLA Offset is prepared for the current terminal (S 7 ); then, the processing is terminated. In this embodiment, one kind of an offset (Offset_Com) common to ABS and Non-ABS is prepared, and the Offset initial value is set according to EQ. (3) below. Offset_Init [dB] is a preset default value.
 
Offset_Com( u )[dB]=Offset_Init  EQ. (3)
 
     Next, an operation in a case wherein the adjacent cell for the terminal does not have an ABS configured (S 2 , No) will be described. In this case, CQI having no subframe-based differentiation is requested from the terminal (S 8 ), and one OLLA Offset is prepared for the current terminal (S 9 ); then, the processing is terminated. In this embodiment, as in S 7 , the Offset initial value is set according to EQ. (3). 
       FIG. 3  shows a procedure of an operation of the channel quality estimating section  105  for updating the OLLA offset for a terminal. This operation is conducted each time reception decision information (ACK, NACK) is received from the terminal. 
     First, the channel quality estimating section  105  decides whether an adjacent cell for the terminal that has transmitted reception decision information has an ABS configured (S 11 ). An operation in a case wherein no ABS is configured (S 11 , No) will be described first. In case that no ABS is configured, and when reception decision is ACK (S 12 , Yes), Offset_Com is decremented according to EQ. (4) (S 13 ); when NACK, Offset_Com is incremented according to EQ. (5) (S 14 ).
 
Offset_Com( u )[dB]=Offset_Com( u )−Delta_Down  EQ. (4)
 
Offset_Com( u )[dB]=Offset_Com( u )+Delta_Up  EQ. (5)
 
     Delta_Down and Delta_Up represent decrement and increment step sizes, respectively. Delta_Down is an input parameter. Delta_Up is calculated using Delta_Down according to EQ. (6) below. T_Bler designates a preset target reception error rate.
 
Delta_Up= T _Bler/(1 −T _Bler)*Delta_Down  EQ. (6)
 
     Next, an operation in a case wherein the adjacent cell for the terminal that has transmitted reception decision information has an ABS configured (S 11 , Yes) will be described. In case that the ABS is configured, a decision is made as to whether the terminal that has transmitted reception decision information is a terminal supporting Release 10 (S 15 ). 
     In case that the terminal is not a terminal supporting Release 10 (S 15 , No), and when reception decision is ACK (S 16 , Yes) and is of Transport Block transmitted with the ABS (S 17 , Yes), Offset_ABS is decremented according to EQ. (7) (S 18 ); when reception decision is not of Transport Block transmitted with the ABS (S 17 , No), Offset_NonABS is decremented according to EQ. (8) (S 19 ):
 
Offset_ABS( u )[dB]=Offset_ABS( u )−Delta_Down  EQ. (7)
 
Offset_NonABS( u )[dB]=Offset_NonABS( u )−Delta_Down  EQ. (8)
 
     When reception decision is NACK (S 16 , No) and is of Transport Block transmitted with the ABS (S 20 , Yes), Offset_ABS is incremented according to EQ. (9) (S 21 ); when reception decision is not of Transport Block transmitted with the ABS (S 20 , No), Offset_NonABS is incremented according to EQ. (10) (S 22 ).
 
Offset_ABS( u )[dB]=Offset_ABS( u )+Delta_Up  EQ. (9)
 
Offset_NonABS( u )[dB]=Offset_NonABS( u )+Delta_Up  EQ. (10)
 
     On the other hand, in case that the terminal that has transmitted reception decision information is a terminal supporting Release 10 (S 15 , Yes), and when reception decision is ACK (S 23 , Yes), Offset_Com is decremented according to EQ. (4) (S 24 ); when NACK (S 23 , No), Offset_Com is incremented according to EQ. (5) (S 25 ). 
       FIG. 4  shows a procedure of an operation of the channel quality estimating section  105  for estimating an SINR for a terminal. This operation is conducted for a subframe to which the scheduler applies PRB allocation processing. 
     First, the channel quality estimating section  105  decides whether an adjacent cell for a terminal of interest for which an SINR is estimated has an ABS configured (S 31 ). In case that the adjacent cell for the terminal of interest does not have an ABS configured (S 31 , No), an estimated SINR value (SINR_Est) is calculated according to EQ. (11) (S 32 ). SINR_CQI_Com [dB] is an SINR corresponding to a CQI.
 
SINR_Est( u )[dB]=SINR_CQI_Com( u )+Offset_Com( u )  EQ. (11)
 
     In case that the adjacent cell for the terminal of interest has an ABS configured (S 31 , Yes), a decision is made as to whether the terminal is a terminal supporting Release 10 (S 33 ). For a terminal not supporting Release 10 (S 33 , No), when the currently transmitted Subframe is the ABS (S 34 , Yes), Offset_ABS is used to calculate SINR_Est according to EQ. (12) (S 35 ); when not the ABS (S 34 , No), Offset_NonABS is used to calculate SINR_Est according to EQ. (13) (S 36 ).
 
SINR_Est( u )[dB]=SINR_CQI_Com( u )+Offset_ABS( u )  EQ. (12)
 
SINR_Est( u )[dB]=SINR_CQI_Com( u )+Offset_NonABS( u )  EQ. (13)
 
     On the other hand, for a terminal supporting Release 10 (S 33 , Yes), when the currently transmitted Subframe is an ABS (S 37 , Yes), an SINR corresponding to a CQI of a measurement subframe set with the ABS (SINR_CQI_ABS) is used to calculate an SINR according to EQ. (14) (S 38 ); when not the ABS (S 37 , No), an SINR corresponding to a CQI of a measurement subframe set with a Non-ABS (SINR_CQI_NonABS) is used to calculate the SINR according to EQ. (15) (S 39 ).
 
SINR_Est( u )[dB]=SINR_CQI_ABS( u )+Offset_Com( u )  EQ. (14)
 
SINR_Est( u )[dB]=SINR_CQI_NonABS( u )+Offset_Com( u )  EQ. (15)
 
     By practicing the present embodiment, as shown in  FIG. 5 , the throughput for a terminal not supporting Release 10 is improved because precision in SINR estimation for the terminal not supporting Release 10 is enhanced both for the ABS and the Non-ABS. Moreover, as it is improved, the system capacity of a base station is improved. 
     While in this embodiment, a preset default value is used for an OLLA Offset initial value in  FIG. 2 , the present invention is not limited thereto, and a statistical value for currently connecting terminals may be used, for example. In particular, an average value or a 50% value of Offsets of the currently connecting terminals or the like may be used. Then, reduction in the Offset convergence time can be expected. 
     Moreover, while in this embodiment, in  FIG. 3 , Offset is always incremented/decremented according to reception decision information (ACK, NACK) received from a terminal, the present invention is not limited thereto, and upper and lower limit values for Offset may be defined. Then, excessively small/large estimated SINR values due to a transient increase/decrease of the interference power may be suppressed. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described. While in the first embodiment, a plurality of OLLA Offsets are prepared only for a terminal not supporting Release 10, such a plurality of Offsets are prepared for all terminals including those supporting Release 10 in the present embodiment. 
     [Configuration] 
     A block diagram representing a configuration of a wireless communications system in the present embodiment is similar to that in the first embodiment. 
     [Operation] 
     Next, an operation of the present embodiment will be described with reference to  FIGS. 6, 7, and 8 .  FIG. 6  shows a procedure of operations of the channel quality estimating section  105  for deciding upon an adjacent cell, prescribing a method of reporting a CQI for a terminal, and setting an OLLA initial value. 
     Referring to  FIG. 6 , S 7  in  FIG. 2  of the first embodiment is replaced with S 41 . Specifically, in case that an adjacent cell for a terminal has an ABS configured (S 2 , Yes), and that the terminal is a terminal supporting Release 10 (S 3 , Yes), the channel quality estimating section  105  prepares a plurality of OLLA Offsets for the current terminal according to EQs. (1) and (2) (S 41 ), as in the processing at S 5  for a terminal not supporting Release 10. 
       FIG. 7  shows a procedure of an operation of the channel quality estimating section  105  for updating an OLLA offset for a terminal. Referring to  FIG. 7 , S 23 , S 24 , and S 25  in  FIG. 3  of the first embodiment are eliminated and S 15  and S 16  are replaced with S 51 . Specifically, when an adjacent cell for a terminal has an ABS configured (S 11 , Yes), a decision is made as to whether reception decision is ACK or NACK; when ACK (S 51 , Yes), the flow goes to the processing at S 17 , and when NACK (S 51 , No), goes to the processing at S 20 . 
       FIG. 8  shows a procedure of an operation of the channel quality estimating section  105  for estimating an SINR of a terminal Referring to  FIG. 8 , S 38  and S 39  in  FIG. 4  of the first embodiment are replaced with S 61 , S 62 , respectively. Specifically, for a terminal supporting Release 10 (S 33 , Yes), when the currently transmitted subframe is an ABS (S 37 , Yes), SINR_CQI_ABS and Offset_ABS are used to calculate the SINR according to EQ. (16) (S 61 ); when not the ABS (S 37 , No), SINR_CQI_NonABS and Offset_NonABS are used to calculate the SINR according to EQ. (17) (S 62 ).
 
SINR_Est( u )[dB]=SINR_CQI_ABS( u )+Offset_ABS( u )  EQ. (16)
 
SINR_Est( u )[dB]=SINR_CQI_NonABS( u )+Offset_NonABS( u )  EQ. (17)
 
     By practicing the present embodiment, when the amount of variation of an interference level is different between the ABS and a Non-ABS, the level of the variation can be corrected individually for the ABS and the Non-ABS by preparing a plurality of Offsets for a Release 10 terminal, and therefore, the throughput of a terminal supporting Release 10 can also be improved. Moreover, as it is improved, the system capacity of a base station can be further improved. 
     Moreover, while in this embodiment, a plurality of Offsets are prepared for all terminals, the present invention is not limited thereto, and such a plurality of Offsets may be applied only to terminals in which the level of variation of interference relative to a desired signal significantly varies when comparing the ABS and the Non-ABS, for example. Thus, reduction of the memory space and maintenance of the effect can be achieved together. In particular, such a plurality of Offsets may be applied to terminals having a difference between RSRP (RSRP_Own) of its cell and RSRP (RSRP_Adj) of an adjacent cell (RSRP_Own−RSRP_Adj) that is less than a prespecified threshold. Moreover, the CQI may be used. Furthermore, when it is possible to acquire the power levels of interference in the ABS and the Non-ABS, a difference between them may be used. Similar configurations and operations may be applied to the First Embodiment. 
     Third Embodiment 
     Next, a third embodiment of the present invention will be described. While in the first and second embodiments, an LTE downlink is exemplified, an uplink is taken up as an example in the present embodiment. 
     [Configuration] 
       FIG. 9  is a block diagram showing a configuration of a wireless communications system in the third embodiment of the present invention. Referring to  FIG. 9 , the wireless communications system comprises a base station  100  and a terminal  200 , as with  FIG. 1 . The base station  100  is a wireless communication apparatus for wireless communicating with the terminal  200  lying in a communication area of the base station  100  via a wireless channel, and is also connected with a network (not shown) and is capable of making data communications with surrounding base stations. 
     The base station  100  comprises main functional sections including a base station operating section  101 , a reference signal generating section  102 , a limit time frame control section  104 , a channel quality estimating section  111 , a scheduler  112 , a reference signal measuring section  113 , and a reception decision section  114 . 
     The base station operating section  101  has the same function as that of the first embodiment, description of which will be therefore omitted herein. 
     The reference signal generating section  102  has the same function as that of the first embodiment, description of which will be therefore omitted herein. 
     The limit time frame control section  104  has the same function as that of the first embodiment, description of which will be therefore omitted herein. 
     The channel quality estimating section  111  has a function of estimating an SINR for the terminal  200  based on OLLA from UE Capability information for the terminal  200  using the SINR retained in the reference signal measuring section  113 , and a function of deciding an adjacent base station cell (referred to as an adjacent cell hereinbelow) from RSRP information received from the terminal. 
     The scheduler  112  has a function of determining a PRB and a TBS Index to be allocated to a terminal based on the estimated SINR, and transmitting a result of the allocation to the terminal  200  as scheduling information. 
     The reference signal measuring section  113  has a function of measuring communication channel quality such as an SINR from a reference signal received from the terminal  200 . Although it also has a function of correcting any difference between the transmission powers of the reference signal and a signal transmitting data from the data generating section  211 , the present embodiment assumes that the transmission powers are not different. 
     The reception decision section  114  has a function of conducting reception decision (ACK, NACK) for transmission data received from the terminal  200 , and notifying the reception decision information to the channel quality estimating section  111  via the base station operating section  101 . 
     The terminal  200  comprises main functional sections including a terminal operating section  201 , a channel quality measuring section  202 , a data generating section  211 , and a reference signal generating section  212 . 
     The terminal operating section  201  has the same function as that of the first embodiment, description of which will be therefore omitted herein. It has functions equivalent to those of common terminals, including a function of transmitting data accumulated in the data generating section  211  based on scheduling information received from the base station. 
     The channel quality measuring section  202  has the same function as that of the first embodiment, description of which will be therefore omitted herein. 
     The data generating section  211  has a function of generating data to be transmitted by the terminal  200 , and accumulating it along with management information such as a time of generation. The data is transmitted to the base station  100  via the terminal operating section  201  based on the scheduling information received from the base station  100 . 
     The reference signal generating section  212  has a function of transmitting a reference signal for measuring communication channel quality at the base station  100  to the base station  100  via the terminal operating section  201  at certain times. 
     [Operation] 
     Next, an operation of the present embodiment will be described with reference to  FIGS. 10 and 11 .  FIG. 10  shows a procedure of operations of the channel quality estimating section  111  for deciding an adjacent cell and setting an OLLA initial value. 
     First, the channel quality estimating section  111  determines an adjacent cell for the terminal from RSRP received from the terminal (S 71 ). Since an uplink is assumed in this embodiment, a surrounding cell having the highest path loss is defined as an adjacent cell, where the path loss is a difference between the transmission and reception powers for the reference signal. 
     Next, a decision is made as to whether the adjacent cell for the terminal has an ABS configured (S 72 ). In case that the ABS is configured (S 72 , Yes), a plurality of OLLA Offsets are prepared for the current terminal (S 73 ), and the processing is terminated. As with the first embodiment, two kinds of Offsets are set for the ABS and a Non-ABS according to EQs. (1) and (2) in this embodiment. When no ABS is configured (S 72 , No), one kind of Offset is set according to EQ. (3) (S 74 ). 
     A procedure of an operation of updating the OLLA offset for a terminal is similar to that in the second embodiment shown in  FIG. 7 . While in the second embodiment, reception decision information transmitted by a terminal is used because a downlink is assumed, the present embodiment is different therefrom only in that reception decision information (ACK, NACK) in the reception decision section  114  is used because an uplink is assumed. 
       FIG. 11  shows a procedure of an operation of the channel quality estimating section  111  for estimating an SINR of a terminal. 
     First, the channel quality estimating section  111  decides whether an adjacent cell for the terminal of interest for which the SINR is estimated has the ABS configured (S 81 ). In case that the adjacent cell for the terminal of interest does not have the ABS configured (S 81 , No), an estimated SINR value (SINR_Est) is calculated according to EQ. (16) (S 82 ). SINR_Mes [dB] is an SINR measured from a transmission signal from the terminal.
 
SINR_Est( u )[dB]=SINR_Mes( u )+Offset_Com( u )  EQ. (16)
 
     On the other hand, in case that the adjacent cell for the terminal of interest has an ABS configured (S 81 , Yes), and when the currently transmitted subframe is the ABS (S 83 , Yes), Offset_ABS is used to calculate SINR_Est according to EQ. (17) (S 84 ); when not the ABS (S 83 , No), Offset_NonABS is used to calculate SINR_Est according to EQ. (18) (S 85 ). SINR_Mes_ABS and SINR_Mes_NonABS represent an SINR measured in the ABS and that measured in the Non-ABS, respectively.
 
SINR_Est( u )[dB]=SINR_Mes_ABS( u )+Offset_ABS( u )  EQ. (17)
 
SINR_Est( u )[dB]=SINR_Mes_NonABS( u )+Offset_NonABS( u )  EQ. (18)
 
     Other Embodiments 
     While several embodiments of the present invention have been described above, the present invention is not limited to these embodiments. 
     For example, while RSRP is used as a criterion of decision of an adjacent cell for a terminal, a ratio of the total reception power to the reception power of a reference signal (RSRQ: Reference Signal Received Quality) may be used. Moreover, a CQI or an SINR may be used. Further, in case that the current base station is in a pico cell, an adjacent cell may be a macro cell whose communication area overlaps, as shown in  FIG. 12 . Furthermore, there is a concern about interference that a femto cell, which is an indoor small base station, may have upon an outdoor large base station such as a macro cell, so that it is contemplated that an ABS is applied to the femto cell. In this case, an adjacent cell is a small cell such as a femto cell whose communication area overlaps. 
     Moreover, the present invention may be applied to a system comprised of a plurality of devices, or to a single apparatus. Furthermore, the present invention may be applied to a case in which programs implementing the functions described in the embodiments above are supplied from the system or from a remote system to execute processing of the operation procedures described in these embodiments. Therefore, programs installed in a base station and executed by a processor in the base station, media storing therein the programs, and servers for downloading the programs therefrom for implementing the functions of the present invention in the base station may fall within the scope of the present invention. 
     (Appendix 1) 
     A quality estimating method for a communication channel used by a base station for wireless communicating with a terminal within a communication area, characterized in comprising: 
     a step of acquiring quality information for a communication channel between said base station and said terminal; 
     a step of acquiring reception error information relating to a reception error in a data communication using said communication channel; 
     a step of acquiring information on a transmission limit time frame defined by a base station adjacent to said base station; and 
     an estimating step of updating a corrective value according to the definition in said transmission limit time frame information and said reception error information, and estimating quality of said communication channel using said corrective value and said acquired quality information. 
     (Appendix 2) 
     The communication channel quality estimating method as recited in appendix 1, characterized in that said estimating step comprises: 
     a step of updating a first corrective value according to said reception error by a communication in said limit time frame, and updating a second corrective value according to said reception error by a communication in a time frame that is not said limit time frame; and 
     a calculating step of calculating, in the communication in said limit time frame, quality of a communication channel using said acquired quality information for the communication channel and said first corrective value, and calculating, in the communication in a time frame that is not said limit time frame, quality of a communication channel using said acquired quality information for the communication channel and said second corrective value. 
     (Appendix 3) 
     The communication channel quality estimating method as recited in appendix 2, characterized in that, in said calculation of the quality of the communication channel, said calculating step uses, for said limit time frame, quality information for the communication channel information in said limit time frame, and uses, for the time frame that is not said limit time frame, quality of the communication channel in the time frame that is not said limit time frame. 
     (Appendix 4) 
     The communication channel quality estimating method as recited in appendix 2, characterized in that 
     said calculating step comprises: 
     a step of summing up said first and second corrective values for currently connecting terminals; and 
     a step of determining initial values of said first and second corrective values from said summed up first and second corrective values for said terminals. 
     (Appendix 5) 
     The communication channel quality estimating method as recited in appendix 2, characterized in that the initial values of said first and second corrective values are defined as respective prespecified initial values. 
     (Appendix 6) 
     The communication channel quality estimating method as recited in any one of appendices 1 to 5, characterized in that: said wireless communication is a downlink data communication. 
     (Appendix 7) 
     The communication channel quality estimating method as recited in any one of appendices 1 to 5, characterized in that said wireless communication is an uplink data communication. 
     (Appendix 8) 
     The communication channel quality estimating method as recited in any one of appendices 1 to 7, characterized in that said adjacent base station is a base station determined based on communication channel quality information for a communication area of said adjacent base station. 
     (Appendix 9) 
     The communication channel quality estimating method as recited in any one of appendices 1 to 7, characterized in that said adjacent base station is defined as a base station having a communication area that overlaps that of said base station and has an area greater than that of said base station. 
     (Appendix 10) 
     The communication channel quality estimating method as recited in any one of appendices 1 to 7, characterized in that said adjacent base station is defined as a base station having a communication area that overlaps that of said base station and has an area smaller than that of said base station. 
     (Appendix 11) 
     The communication channel quality estimating method as recited in any one of appendices 1 to 10, characterized in that said terminal is a terminal having a difference or a ratio between a level of interference received in said limit time frame and that received in a time frame that is not said limit time frame that is equal to or lower than a threshold. 
     (Appendix 12) 
     A wireless communications system in which a base station wireless communicates with a terminal within a communication area, said system characterized in comprising: 
     means for acquiring quality information for a communication channel between said base station and said terminal; 
     means for acquiring reception error information relating to a reception error in a data communication using said communication channel; 
     means for acquiring information on a transmission limit time frame defined by a base station adjacent to said base station; and 
     estimating means for updating a corrective value according to the definition in said transmission limit time frame information and said reception error information, and estimating quality of said communication channel using said corrective value and said acquired quality information. 
     (Appendix 13) 
     The wireless communications system as recited in appendix 12, characterized in that said estimating means comprises: 
     updating means for updating a first corrective value according to said reception error by a communication in said limit time frame, and updating a second corrective value according to said reception error by a communication in a time frame that is not said limit time frame; and 
     calculating means for calculating, in the communication in said limit time frame, quality of a communication channel using said acquired quality information for the communication channel and said first corrective value, and calculating, in the communication in a time frame that is not said limit time frame, quality of a communication channel using said acquired quality information for the communication channel and said second corrective value. 
     (Appendix 14) 
     The wireless communications system as recited in appendix 13, characterized in that, in said calculation of the quality of the communication channel, said calculating means uses, for said limit time frame, quality information for the communication channel information in said limit time frame, and uses, for the time frame that is not said limit time frame, quality of the communication channel in the time frame that is not said limit time frame. 
     (Appendix 15) 
     The wireless communications system as recited in appendix 13, characterized in that said calculating means comprises: 
     means for summing up said first and second corrective values for currently connecting terminals; and 
     means for determining initial values of said first and second corrective values from said summed up first and second corrective values for said terminals. 
     (Appendix 16) 
     The wireless communications system as recited in appendix 13, characterized in that the initial values of said first and second corrective values are defined as respective prespecified initial values. 
     (Appendix 17) 
     The wireless communications system as recited in any one of appendices 12 to 16, characterized in that said wireless communication is a downlink data communication. 
     (Appendix 18) 
     The wireless communications system as recited in any one of appendices 12 to 16, characterized in that said wireless communication is an uplink data communication. 
     (Appendix 19) 
     The wireless communications system as recited in any one of appendices 12 to 18, characterized in that said adjacent base station is a base station determined based on communication channel quality information for a communication area of said adjacent base station. 
     (Appendix 20) 
     The wireless communications system as recited in any one of appendices 12 to 18, characterized in that said adjacent base station is defined as a base station having a communication area that overlaps that of said base station and has an area greater than that of said base station. 
     (Appendix 21) 
     The wireless communications system as recited in any one of appendices 12 to 18, characterized in that said adjacent base station is defined as a base station having a communication area that overlaps that of said base station and has an area smaller than that of said base station. 
     (Appendix 22) 
     The wireless communications system as recited in any one of appendices 12 to 21, characterized in that said terminal is a terminal having a difference or a ratio between a level of interference received in said limit time frame and that received in a time frame that is not said limit time frame that is equal to or lower than a threshold. 
     (Appendix 23) 
     A base station for wireless communicating with a terminal within its communication area, said base station characterized in comprising: 
     means for acquiring quality information for a communication channel between said base station and said terminal; 
     means for acquiring reception error information relating to a reception error in a data communication using said communication channel; 
     means for acquiring information on a transmission limit time frame defined by a base station adjacent to said base station; and 
     estimating means for updating a corrective value according to the definition in said transmission limit time frame information and said reception error information, and estimating quality of said communication channel using said corrective value and said acquired quality information. 
     (Appendix 24) 
     The base station as recited in appendix 23, characterized in that said estimating means comprises: 
     updating means for updating a first corrective value according to said reception error by a communication in said limit time frame, and updating a second corrective value according to said reception error by a communication in a time frame that is not said limit time frame; and 
     calculating means for calculating, in the communication in said limit time frame, quality of a communication channel using said acquired quality information for the communication channel and said first corrective value, and calculating, in the communication in a time frame that is not said limit time frame, quality of a communication channel using said acquired quality information for the communication channel and said second corrective value. 
     (Appendix 25) 
     The base station as recited in appendix 24, characterized in that, in said calculation of the quality of the communication channel, said calculating means uses, for said limit time frame, quality information for the communication channel information in said limit time frame, and uses, for the time frame that is not said limit time frame, quality of the communication channel in the time frame that is not said limit time frame. 
     (Appendix 26) 
     The base station as recited in appendix 24, characterized in that said calculating means comprises: 
     said calculating means comprises: 
     means for summing up said first and second corrective values for currently connecting terminals; and 
     means for determining initial values of said first and second corrective values from said summed up first and second corrective values for said terminals. 
     (Appendix 27) 
     The base station as recited in appendix 24, characterized in that the initial values of said first and second corrective values are defined as respective prespecified initial values. 
     (Appendix 28) 
     The base station as recited in any one of appendices 23 to 27, characterized in that said wireless communication is a downlink data communication. 
     (Appendix 29) 
     The base station as recited in any one of appendices 23 to 27, characterized in that said wireless communication is an uplink data communication. 
     (Appendix 30) 
     The base station as recited in any one of appendices 23 to 29, characterized in that said adjacent base station is a base station determined based on communication channel quality information for a communication area of said adjacent base station. 
     (Appendix 31) 
     The base station as recited in any one of appendices 23 to 29, characterized in that said adjacent base station is defined as a base station having a communication area that overlaps that of said base station and has an area greater than that of said base station. 
     (Appendix 32) 
     The base station as recited in any one of appendices 23 to 29, characterized in that said adjacent base station is defined as a base station having a communication area that overlaps that of said base station and has an area smaller than that of said base station. 
     (Appendix 33) 
     The base station as recited in any one of appendices 23 to 32, characterized in that said terminal is a terminal having a difference or a ratio between a level of interference received in said limit time frame and that received in a time frame that is not said limit time frame that is equal to or lower than a threshold. 
     (Appendix 34) 
     A program for a base station for wireless communicating with a terminal within its communication area, said program characterized in causing said base station to function as: 
     means for acquiring quality information for a communication channel between said base station and said terminal; 
     means for acquiring reception error information relating to a reception error in a data communication using said communication channel; 
     means for acquiring information on a transmission limit time frame defined by a base station adjacent to said base station; and 
     estimating means for updating a corrective value according to the definition in said transmission limit time frame information and said reception error information, and estimating quality of said communication channel using said corrective value and said acquired quality information. 
     The present application claims priority based on Japanese Patent Application No. 2012-073287 filed on Mar. 28, 2012, disclosure of which is incorporated herein in its entirety. 
     REFERENCE SIGNS LIST 
     
         
           100  Base station 
           101  Base station operating section 
           102  Reference signal generating section 
           103  Transmission buffer 
           104  Limit time frame control section 
           105  Channel quality estimating section 
           106  Scheduler 
           111  Channel quality estimating section 
           112  Scheduler 
           113  Reference signal measuring section 
           114  Reception decision section 
           200  Terminal 
           201  Terminal operating section 
           202  Channel quality measuring section 
           203  Reception decision section 
           211  Data generating section 
           212  Reference signal generating section