Patent Publication Number: US-2009219914-A1

Title: Base station, mobile station, and method of communicating

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to base stations, mobile stations, and method of communicating. 
     2. Description of the Related Art 
     In HSDPA (High speed downlink packet access), HS-PDSCH, which carries data traffic is determined on a fixed basis with 3 slots (2 ms) as the unit of measure. (See TS25.211 Section 7.8 and TS25.214 Section 6A.1.1, for example.) In HSDPA, data is transferred from layer 2 to layer 1 with three slots as the unit of measure. 
     Allocation of transmission opportunities in HSDPA is described with reference to  FIG. 1 . 
     Each UE receives an HS-SCCH, and, for allocation of transmission opportunities for an own UE, a subsequent HS-PDSCH is received, and an HS-DSCH is decoded. In HSDPA, if one UE fails in receiving the HS-SCCH, as a base station cannot receive a reception acknowledgment for the HS-DSCH, a DTX is detected, and the HS-DSCH is retransmitted. 
     On the other hand, in standardizing evolved UTRA, supporting a variable-length TTI (transmission time interval) is being proposed. (See Non-patent documents: Motorola, R2-060122, “Layer 1 Data Transfer Formats and Definitions”, 3GPP TSG RAN WG2 #50 Sophia Antipolis, France, 9-13 Jan. 2006; Ericsson, R2-060868, “Increased TTI Length”, 3GPP TSG-RAN Joint WG1/WG2 Athens, Greece, 27-31 Mar. 2006; and Motorola, R2-060944, “HARQ Considerations”, 3GPP TSG RAN WG2 #52 Athens, Greece, 27-31 Mar. 2006, for example.) 
     SUMMARY OF THE INVENTION 
     Problem(s) to be Solved by the Invention 
     However, the related art as described above has the following problem. 
     In the variable-length TTI, even for making the length of the TTI, which includes multiple subframes, variable for transmitting, downlink-scheduling information (DL-SI) for reporting transmission allocation opportunities that correspond to HS-SCCH in HSDPA is transmitted from a base station to a mobile station. 
     In the mobile station, where the downlink scheduling information is decoded, when a control method similar to HSDPA is performed, a downlink shared channel (DL-SCH) is transmitted even when a decoding error of the downlink scheduling information occurs at the mobile station. In this case, the downlink shared channel is transmitted without allowing the mobile station to receive information about any transmission allocation to the own mobile station, making it not possible to receive the downlink shared channel at the mobile station. Thus, in the base station, allocated transmission opportunities are wasted. 
     In the evolved UTRA standardization, allocating a maximum of approximately 20 MHz as a transmission band is envisaged, which, when compared to HSDPA of approximately 5 MHz as a transmission band, causes the transmit data capacity to vary by a factor of approximately 4. Thus, loss in a case such that the downlink shared channel cannot be received may become large. 
     Thus, the present invention aims to solve at least one of the problems described above, and to provide a base station, a mobile station, and a method of communicating that make it possible to prevent a case such that a downlink shared channel cannot be received due to a decoding error of the downlink scheduling information. 
     Means for Solving the Problem 
     In order to solve the problem as described above, a base station of the present invention includes a transmitting unit which variably controls a TTI length including multiple subframes, each of which is to be allocated to a mobile station, and transmits to the mobile station scheduling information which indicates allocation of wireless resources to each user; a receive-acknowledgment determining unit which determines whether a receive acknowledgment for the scheduling information is reported from the mobile station; and a shared-channel transmitting unit which transmits a shared channel if it is determined that the receive acknowledgment is received. 
     Such arrangement as described above makes it possible at the mobile station to prevent not receiving a downlink shared channel due to an error in decoding downlink scheduling information, and at the base station to eliminate waste in allocated transmission opportunities. 
     The mobile station of the present invention includes a scheduling-information decoding unit which decodes scheduling information indicating allocation of wireless resources to each user that is reported by a base station; and a receive-acknowledgment generating unit which generates a receive acknowledgment for the scheduling information according to the decoded result of the scheduling information. 
     The features as described above make to possible to eliminate a case such that a downlink shared channel is not received due to a decoding error of downlink scheduling information. 
     The method of communicating according to the present invention includes the steps of: transmitting, by a base station to a mobile station, scheduling information indicating allocation of wireless resources to each user; decoding, by the mobile station, scheduling information indicating allocation of wireless resources to each user that is reported by the base station; generating, by the mobile station, a receive acknowledgment for the scheduling information according to the decoded result of the scheduling information; determining, by the base station, whether the receive acknowledgment for the scheduling information is reported from the mobile station; and transmitting, by the base station, a shared channel if it is determined that the receive acknowledgment is received. 
     Such an arrangement as described above makes it possible at the mobile station to prevent not receiving a downlink shared channel due to an error in decoding downlink scheduling information, and at the base station to eliminate waste in allocated transmission opportunities. 
     Advantage of the Invention 
     The embodiment of the present invention makes it possible to realize a base station, a mobile station, and a method of communicating that prevent a downlink shared channel not being received due to a decoding error of downlink scheduling information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a diagram explaining allocation of transmission opportunities in HSDPA; 
         FIG. 2  is a diagram explaining allocation of transmission opportunities in a wireless communications system according to an embodiment of the present invention; 
         FIG. 3  is a diagram explaining transmit timings in the wireless communications system according to an embodiment of the present invention; 
         FIG. 4  is a partial block diagram illustrating a base station according to an embodiment of the present invention; 
         FIG. 5  is an explanatory diagram illustrating an example of scheduling information according to an embodiment of the present invention; 
         FIG. 6  is a partial block diagram illustrating a mobile station according to an embodiment of the present invention; 
         FIG. 7  is an explanatory diagram illustrating an operation of a base station according to an embodiment of the present invention; 
         FIG. 8  is an explanatory diagram illustrating an operation of a mobile station according to an embodiment of the present invention; 
         FIG. 9  is a partial block diagram illustrating a base station according to an embodiment of the present invention; 
         FIG. 10  is a partial block diagram illustrating a mobile station according to an embodiment of the present invention; 
         FIG. 11  is an explanatory diagram illustrating an operation of a base station according to an embodiment of the present invention; 
         FIG. 12  is an explanatory diagram illustrating an operation of a mobile station according to an embodiment of the present invention; 
         FIG. 13  is a partial block diagram illustrating a base station according to an embodiment of the present invention; and 
         FIG. 14  is a partial block diagram illustrating a mobile station according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     [Description of Notations] 
       100  Base station;  200  Mobile station 
     BEST MODE OF CARRYING OUT THE INVENTION 
     A description is given below with regard to preferred embodiments of the present invention. 
     Throughout the drawings for explaining the embodiments, the same letters are used for those having the same functions, so that repetitive explanations are omitted. 
     A wireless communications system according to an embodiment of the present invention is explained. 
     The wireless communications system according to the present embodiment includes a base station  100  and a mobile station  200 . 
     In the mobile communications system according to the present embodiment, as shown in  FIG. 2 , when downlink scheduling information (DL-SI) is received, the mobile station  200  transmits a receive acknowledgment (DL-SI-Ack) for the DL-SI. When the receive acknowledgment is received from the mobile station  200 , the base station  100  transmits a downlink shared channel (DL-SCH). 
     More specifically, as shown in  FIG. 3 , the base station  100  reports the downlink scheduling information to the mobile station  200 . Moreover, when the receive acknowledgment (DL-SI-Ack) for the scheduling information is received from the mobile station  200 , the base station  100  transmits data in multiple subframes corresponding to TTIs allocated to the mobile station. For example, the base station  100  transmits data in two subframes when allocating a TTI including two subframes to the mobile station  200 , in four subframes when allocating a TTI including four subframes to the mobile station  200 , and in eight subframes when allocating a TTI including eight subframes to the mobile station  200 . The base station  100  variably controls the number of subframes making up a TTI allocated to the mobile station  200 . 
     As shown in  FIG. 4 , the base station  100  includes a transmitter  102 , a scheduling information generator  104 , a shared channel generator  106  as a unit which transmits a shared channel, a scheduler  108  as a scheduling unit, a data buffer  110 , a receiver  112 , a scheduling-information reception determining section  114  as a unit which determines a receive acknowledgment, and a shared-channel reception determining section  116 . 
     Scheduling which allocates wireless resources to each user is performed at the scheduler  108  in order to transmit data stored in the data buffer  110 , and information indicating the result of the scheduling is input to the scheduling information generator  104 . 
     The scheduling information generator  104  generates, based on information indicating the scheduling result input, scheduling information including information indicating users to which wireless resources are allocated, and reports the generated information to the mobile station  200  via the transmitter  102 . For example, the scheduling information generator  104  generates scheduling information including at least part of information as shown in  FIG. 5 . 
     More specifically, the scheduling information generator  104  generates a user ID (UE or group specific) which is specific for a UE or group of UEs, resource assignment information (resource assignment) and the number of subframes (duration assignment) that are included in Category 1; multi-antenna related information, a modulation scheme, and a payload size that are included in Category 2; and a process number (Hybrid ARQ process number), information indicating the type of redundant bits (RV (redundancy version)), a new data indicator when asynchronous hybrid ARQ (HARQ) is adopted and a retransmission sequence number when synchronous HARQ is adopted, that are included in Category 3. In the present embodiment, a case such that the scheduling information generator  104  generates all of the information items recited above is described. The scheduling information generator  104  reports the information items generated to the mobile station  200  via the transmitter  102 . 
     The transmitter  102  reports, to the scheduling-information reception determining section  114 , scheduling-information transmission information indicating that the scheduling information items have been transmitted. 
     The receiver  112  receives from the mobile station  200  a receive acknowledgment for the scheduling information items, and inputs the receive acknowledgment to the scheduling-information reception determining section  114 . 
     Based on the receive acknowledgment input by the receiver  112 , the scheduling-information reception determining section  114  determines whether scheduling information is received, e.g., whether decoding of the scheduling information has been successful, at the mobile station  200 . If it is determined that scheduling information is received at the mobile station  200 , the scheduling-information reception determining section  114  reports, to the scheduler  108 , scheduling-information reception information indicating that scheduling information has been received at the mobile station  200 . 
     The scheduler  108  instructs the shared channel generator  106  to transmit a shared channel in response to reporting of the scheduling-information reception information from the scheduling-information reception determining section  114 . As a result, a shared channel is transmitted from the transmitter  102 . 
     The receive acknowledgement for the shared channel is input to the shared-channel reception determining section  116  via the receiver  112 . Based on the receive acknowledgement for the shared channel that is transmitted from the mobile station  200 , the shared-channel reception determining section  116  determines whether the shared channel is received at the mobile station  200  based on the receive acknowledgment for the shared channel that has been transmitted from the mobile station  200 , and reports the result to the scheduler  108 . The scheduler  108  schedules to allocate wireless resources to the respective users in response to the reporting from the shared-channel reception determining section  116  in order to retransmit the shared channel or in order to transmit data stored in the data buffer  110 . 
     On the other hand, based on the time elapsed from the time the scheduling-information transmission information had been input from the transmitter  102 , if the receive acknowledgment is not input even after a predetermined time elapses, the scheduling-information reception determining section  114  determines that scheduling information has not been received at the mobile station  200 . The scheduling-information reception determining section  114  instructs the scheduler  108  to reschedule in order to transmit data in subframes making up a TTI due to be allocated that corresponds to the scheduling information transmitted to the mobile station  200 . 
     The scheduler  108  reschedules in response to an instruction from the scheduling-information reception determining section to reschedule. For example, the scheduler  108  divides multiple RLC-PDUs within transport blocks (TBs), and reorganizes (remultiplexes) the TBs. 
     For example, when a user continues to use wireless resources allocated, but only subframes less than subframes to be allocated can be allocated, subframes less than the subframes to be allocated are redivided and allocated to the user by the scheduler  108 . 
     Moreover, the scheduler  108  may allocate, to the subframes less than subframes to be allocated, part of the data multiplexed to the subframes. Furthermore, the scheduler  108  may allocate, to another user, subframes less than subframes to be allocated. In this case, scheduling is performed at a different timing for a user to be allocated to. 
     Now, a mobile station  200  according to the embodiment of the present invention is described with reference to  FIG. 6 . 
     The mobile station  200  includes a receiver  202 , a shared-channel decoder  204 , a scheduling-information decoder  206 , a shared-channel receive acknowledgment generator  208 , a scheduling-information receive acknowledgment generator  210  as a unit which generates a receive acknowledgment, and a transmitter  212 . 
     Scheduling information transmitted by the base station  100  is received at the receiver  202  and the received information is input to the scheduling-information decoder  206 . 
     The scheduling-information decoder  206  decodes the scheduling information input, determines whether wireless resources are allocated to the own mobile station  200 , and, if yes, reports to the scheduling-information receive acknowledge generator  210  that the scheduling information has been received. 
     In response to a report of receiving scheduling information input from the scheduling-information decoder  206 , the scheduling-information receive acknowledgment generator  210  generates a scheduling-information receive acknowledgment, and transmits the generated acknowledgment to the base station  100  via the transmitter  212 . 
     Moreover, the scheduling-information decoder  206  inputs the decoded result of the scheduling information to the shared-channel decoder  204 . 
     Furthermore, after transmitting the scheduling-information receive acknowledgment, the shared channel is received and the received channel is input to the shared-channel decoder  204  by the receiver  202 . 
     The shared-channel decoder  204  decodes the shared channel input, and reports to the upper layer. Moreover, when the decoding of the shared channel is completed, the shared-channel decoder  204  inputs, to the shared-channel receive acknowledgement generator  208 , a shared-channel decoding completion report indicating that the decoding of the shared channel is completed. 
     In response to the shared-channel decoding completion report input by the shared-channel decoder  204 , the shared-channel receive acknowledgment generator  208  generates a shared-channel receive acknowledgment and reports the generated acknowledgment to the base station  100  via the transmitter  212 . 
     Now, an operation of the wireless communications system according to the present embodiment is described. 
     An operation of the base station  100  is explained with reference to  FIG. 7 . 
     The scheduler  108  newly allocates shared-channel transmission opportunities (step S 702 ). For example, the scheduler  108  variably controls a TTI length including multiple subframes to be allocated to a mobile station, and allocates shared-channel transmission opportunities. 
     Then, the scheduling information generator  104  generates a scheduling-information message (step S 704 ). 
     Then, the transmitter  102  transmits the scheduling information (step S 706 ). 
     Then, the scheduling-information reception determining section  114  determines whether a receive acknowledgment for the scheduling information is received (step S 708 ). 
     If it is determined that the receive acknowledgment for the scheduling information is received (step S  708 : YES) the transmitter  102  transmits the shared channel generated at the shared channel generator  106  (step S 710 ). The receive acknowledgment for the transmitted shared channel is transmitted from the mobile station  200 , and based on whether the receive acknowledgment has been received, the shared-channel reception determining section  116  determines whether the shared channel is received at the mobile station  200 . If it is determined that the shared channel is not received at the mobile station  200 , the shared-channel reception determining section  116  instructs the transmitter  102  to retransmit. 
     If it is determined that the shared channel is received at the mobile station  200 , the shared-channel reception determining section  116  reports to the scheduler  108  that the shared channel has been received at the mobile station  200 . 
     Then, the scheduler  108  determines whether the shared-channel transmission is completed (step S 714 ). 
     If it is determined that the shared-channel transmission is completed (step S 714 : YES) the process returns to step S 702 . 
     On the other hand, if it is not determined that the shared-channel transmission is completed (step S 714 : NO) the process returns to step S 704 . 
     In step S 708 , if it is determined that the scheduling-information receive acknowledgment is not received (step S 708 : NO) for example, if a predetermined time elapses from the time the scheduling information is transmitted, the scheduling-information receive determining section  114  instructs the scheduler  108  to reallocate the downlink shared channel. The scheduler  108  reallocates the downlink shared channel according to the instruction by the scheduling-information reception determining section  114  (step S 712 ). Then the process returns to step S 704 . 
     An operation of the mobile station  200  is explained with reference to  FIG. 8 . Scheduling information transmitted by the base station  100  is received at the receiver  202  and the received information is input to the scheduling-information decoder  206  (step S 802 ). 
     Then, the scheduling-information decoder  206  decodes the scheduling information, and determines whether the scheduling information is successfully received, e.g., whether the scheduling information is successfully decoded (step S 804 ). 
     If it is determined that the scheduling information is successfully received (step S  804 : YES) the scheduling-information decoder  206  instructs the scheduling-information receive acknowledgment generator  210  to generate a scheduling-information receive acknowledgment. According to the instruction by the scheduling-information decoder  206 , the scheduling-information receive acknowledgment generator  210  generates the scheduling-information receive acknowledgment, and transmits the generated acknowledgment via the transmitter  212  (step S 806 ). 
     On the other hand, if it is not determined that the scheduling information is successfully received (step S 804 : NO) the process returns to step S 802 . 
     Now, a mobile communications system according to another embodiment of the present invention is described. 
     The wireless communications system according to the present embodiment includes a base station  100  and a mobile station  200 , as described in the above. 
     In the wireless communications system according to the present embodiment, the base station  100  determines whether to request the mobile station  200  to send a receive acknowledgment for scheduling information. 
     An operation of the base station  100  is explained with reference to  FIG. 9 . 
     The base station  100  differs from the base station described with reference to  FIG. 4  in that it includes a scheduling-information receive acknowledgment request determining section  118 . 
     The scheduling-information receive acknowledgment request determining section  118  determines whether to request a receive acknowledgment for scheduling information. For example, based on the number of subframes to be allocated to the mobile station  200 , the scheduling-information receive acknowledgment request determining section  118  determines to request the receive acknowledgment if the number is not less than a predetermined number of subframes. 
     Moreover, the scheduling-information receive acknowledgment request determining section  118  may determine whether to request the mobile station  200  to send a scheduling-information receive acknowledgment based on receive quality information such as a CQI (Channel Quality Indicator) which is reported from the mobile station  200 . In this case, receive quality information transmitted from the mobile station  200  is input to the scheduling-information receive acknowledgment request determining section  118 . For example, if the input receive quality information indicates a receive quality which is worse than a predetermined receive quality, the scheduling-information receive acknowledgment request determining section  118  determines that there may be a case such that scheduling information is not received at the mobile station  200 , and determines to request the receive acknowledgment. 
     Moreover, the scheduling-information receive acknowledgment request determining section  118  may determine whether to request the mobile station  200  to send a scheduling-information receive acknowledgment based on the quality of a signal received from the mobile station  200 . For example, if the quality is worse than a predetermined quality, the scheduling-information receive acknowledgment determining section  118  determines that there may be a case such that scheduling information is not received at the mobile station  200 , and determines to request the receive acknowledgment. 
     If it is determined that a request to the mobile station  200  is to be made for the scheduling-information receive acknowledgment, the scheduling-information receive acknowledgment request determining section  118  reports to the scheduling information generator  104  that the request is to be made for the scheduling-information receive acknowledgment. If it is reported by the scheduling-information receive acknowledgment request determining section  118  that the receive acknowledgment request is to be made, scheduling information is generated including information indicating that the receive acknowledgment request is to be made. For example, the scheduling information generator  104  generates scheduling information including a flag indicating whether to request the receive acknowledgment. 
     An operation of the mobile station  200  is explained with reference to  FIG. 10 . 
     The mobile station  200  differs from the mobile station described with reference to  FIG. 6  in that it includes a receive-quality information generator  214 . 
     Based on a signal received from the base station  100 , the receive-quality information generator  214  generates receive-quality information such as a CQI (Channel Quality Indicator) and reports the generated information to the base station  100  via the transmitter  212 . 
     The scheduling-information decoder  206  decodes the scheduling information transmitted from the base station  100 , and determines whether a receive acknowledgment is requested. If it is determined that the receive acknowledgment is requested, the scheduling-information decoder  206  instructs the scheduling-information receive acknowledgment generator  210  to generate the receive acknowledgment. Here, when some of the scheduling information is decoded, the scheduling-information decoder  206  may instruct the scheduling-information receive acknowledgment generator  210  to generate the receive acknowledgment. It is envisaged that decoding some of the scheduling information makes it possible also to decode other information. In this way, a delay in transmitting a receive acknowledgment may be reduced. For example, when information indicating allocation of wireless resources, out of scheduling information, is decoded, the scheduling-information decoder  206  instructs the scheduling-information receive acknowledgment generator  210  to generate the receive acknowledgment. 
     Moreover, the transmitter  212  may transmit the receive acknowledgment as Layer 1 control information. 
     Now, an operation of the wireless communications system according to the present embodiment is described. 
     An operation of the base station  100  is explained with reference to  FIG. 11 . 
     The scheduler  108  newly allocates shared-channel transmission opportunities (step S 1102 ). 
     Then, based on the number of subframes to be allocated to the mobile station  200 , the scheduling-information receive acknowledgment request determining section  118  determines whether to request the receive acknowledgment. For example, when the number of subframes to be allocated to the mobile station  200  is less than a predetermined value, it is determined that a loss due to receive error at the mobile station or a delay that would be caused by not requesting a receive acknowledgment should be small, and that the receive acknowledgment is not requested. 
     On the other hand, if the number of subframes to be allocated to the mobile station  200  is greater than a predetermined value, when the scheduling-information receive acknowledgment request determining section  118  does not request a receive acknowledgment, a receive error of the scheduling information occurs at the mobile station  200 , and a shared channel is transmitted, the resulting loss due to the receive error at the mobile station or a delay caused by the retransmission thereof may be large, so that a receive acknowledgment is requested. 
     If it is determined to request a receive acknowledgment (step S 1104 : YES) the scheduling information generator  104  generates a scheduling information message including information on the receive acknowledgment (step S 1106 ). 
     Then, the transmitter  102  transmits the scheduling information (step S 1108 ). 
     Then, the scheduling-information reception determining section  114  determines whether a receive acknowledgment for the scheduling information is received (step S 1110 ). 
     If it is determined that the receive acknowledgment for the scheduling information is received (step S 1110 : YES) the transmitter  102  transmits the shared channel generated at the shared channel generator  106  (step S 1112 ). The receive acknowledgment for the transmitted shared channel is transmitted from the mobile station  200 , and based on the receive acknowledgment received, the shared-channel reception determining section  116  determines whether the shared channel is received at the mobile station  200 . If it is determined that the shared channel is not received at the mobile station  200 , the shared-channel reception determining section  116  instructs the transmitter  102  to retransmit. 
     If it is determined that the shared channel is received at the mobile station  200 , the shared-channel reception determining section  116  reports to the scheduler  108  that the shared channel has been received at the mobile station  200 . 
     Then, the scheduler  108  determines whether the shared-channel transmission is completed (step S 1114 ). 
     If it is determined that the shared-channel transmission is completed (step S 1114 : YES) the process goes back to step S 1102 . 
     On the other hand, if it is not determined that the shared-channel transmission is completed (step S 1114 : NO) the process returns to step S 1106 . 
     In step S 1110 , if it is determined that the downlink scheduling-information receive acknowledgment is not received (step S 1110 : NO) for example, if a predetermined time elapses from the time the scheduling information is transmitted, the scheduling-information receive determining section  114  instructs the scheduler  108  to reallocate the downlink channel. The scheduler  108  reallocates a downlink shared channel according to the instruction by the scheduling-information reception determining section  114  (step S 1116 ). Then the process returns to step S 1106 . 
     If it is determined in step S 1104  that the receive acknowledgment is not requested (step S 1104 : NO) the scheduling information generator  104  generates a scheduling information message (step S 1118 ). 
     Then, the transmitter  102  transmits the scheduling information (step S 1120 ). Then the process transitions to step S 1112 . 
     An operation of the mobile station  200  is explained with reference to  FIG. 12 . 
     Based on a signal received from the base station  100 , mobile station  200 , at the receive-quality information generator  214 , generates receive-quality information such as a CQI (Channel Quality Indicator) and reports the generated information to the base station  100 . 
     Scheduling information transmitted by the base station  100  is received at the receiver  202  and the received information is input to the scheduling-information decoder  206  (step S 1202 ). 
     Then, the scheduling-information decoder  206  decodes the scheduling information, and determines whether the scheduling information is successfully received, e.g., whether the scheduling information is successfully decoded (step S 1204 ). 
     If it is determined that the scheduling information is successfully received (step S 1204 : YES) the scheduling-information decoder  206  determines whether information on the receive acknowledgment request is included in the scheduling information (step S 1206 ). 
     If it is determined that the scheduling information includes the information on the receive acknowledgment request (step S 1206 : YES) the scheduling-information decoder  206  instructs the scheduling-information receive acknowledgment generator  210  to generate a scheduling-information receive acknowledgment. According to the instruction by the scheduling-information decoder  206 , the scheduling-information receive acknowledgment generator  210  generates the scheduling-information receive acknowledgment, and transmits the generated acknowledgment via the transmitter  212  (step S 1208 ). 
     On the other hand, if it is not determined that the scheduling information is successfully received (step S  1204 : NO) or that the scheduling information does not include information for which a receive acknowledgment is requested (step S  1206 : NO) the process returns to step S 1202 . 
     In the present embodiment, while a case is described for a base station  100  determining whether to request a receive acknowledgment for scheduling information based on receive-quality information reported from the mobile station  200 , the base station  100  may determine based on the quality of a receive signal such as an uplink data channel, transmitted from the mobile station  200 . 
     Moreover, in the present embodiment, while a case is described for a base station  100  reporting to a mobile station  200  scheduling information including a request for a receive acknowledgment for scheduling information, reporting may be done by RRC to the mobile station  200 . In this case, in the base station  100 , as shown in  FIG. 13 , information indicating whether to request scheduling-information receive acknowledgment is input from a RRC  120  to the scheduling-information receive acknowledgment request determining section  118 . Moreover, in the mobile station  200 , as shown in  FIG. 14 , information indicating whether to send a scheduling-information receive acknowledgment is input from a RRC  216  to the scheduling-information receive acknowledgment request generator  210 . 
     The base station, mobile station, and method of communicating according to the present invention may be applied to wireless communications systems. 
     The present application claims priority based on Japanese Patent Application No. 2006-127998 filed on May 1, 2006 with the Japanese Patent Office, the entire contents of which are hereby incorporated herein by reference.