Relay station, base station and communication system

1. A relay station for relaying data from a base station to a mobile station, the relay station comprising: a transmitter configured to transmit data in a timing indicated in downlink control information that is transmitted from the base station; and a receiver configured to receive specific data and first downlink control information indicating a first timing for a transmission of the received specific data from the relay station to the mobile station, the specific data and the received first downlink control information being transmitted from the base station to the relay station, the specific data being intended for the mobile station; wherein the transmitter is configured to transmit the specific data to the mobile station in the first timing indicated in the received first downlink control information, when it is determined that the receiver successfully receives the specific data from the base station; wherein the receiver is configured to receive a second downlink control information indicating a second timing for a retransmission of the specific data from the relay station to the mobile station when it is determined that the mobile station unsuccessfully receives the specific data from the relay station that was transmitted in said first timing, the second downlink control information being transmitted from the base station to the relay station without a retransmission of the specific data from the base station to the relay station when it is determined that the receiver has already successfully received the specific data from the base station; and wherein the transmitter is configured to retransmit the specific data to the mobile station in the second timing indicated in the received second downlink control information.

2. The relay station according to claim 1 , wherein the transmitter is configured to transmit a uplink control information to the base station when it is determined that the mobile station receives the specific data from the relay station unsuccessfully, the uplink control information indicating that the specific data is received unsuccessfully by the mobile station in said first timing, the receiver is configured to receive the second downlink control information being generated by the base station based on the uplink control information, the second downlink control information indicating the second timing, as determined by the base station.

3. A base station for transmitting data to a mobile station via a relay station, the base station comprising: a receiver; a transmitter configured to transmit, to the relay station, specific data and first downlink control information indicating a first timing for a transmission of the specific data from the relay station to the mobile station, the specific data and the first downlink control information being intended for delivery to the mobile station, wherein the specific data is transmitted from the relay station to the mobile station in accordance with the first timing when it is determined that the relay station successfully receives the specific data from the base station; and wherein the transmitter is further configured to transmit a second downlink control information indicating to the relay station a second timing for a retransmission of the specific data, which was already transmitted by the base station to the relay station, said retransmission being from the relay station to the mobile station when the base station is notified that the mobile station unsuccessfully receives the specific data transmitted previously from the relay station in the first timing, the second downlink control information being transmitted from the base station to the relay station without a retransmission of the transmitted specific data from the base station to the relay station when it is determined that the receiver has already successfully received the specific data from the base station.

4. The base station according to claim 3 , wherein the receiver is configured to receive a uplink control information from the relay station when it is determined that the mobile station unsuccessfully receives the transmitted data from the relay station, the uplink control information indicating that the data is received unsuccessfully by the mobile station; and wherein the transmitter is configured to transmit a second downlink control information being generated in response to the uplink control information, the second downlink control information indicating a second timing, as determined by the base station, for the retransmission of the specific data from the relay station to the mobile station, the transmission timing being determined by the base station.

5. A mobile station for receiving data from a base station via a relay station, the mobile station comprising: a transmitter; and a receiver configured to: receive, in a first timing indicated in a first downlink control information that is received by the relay station from the base station, specific data transmitted from the relay station when the relay station has successfully received the specific data from the base station, the specific data having been intended for delivery from the base station to the mobile station via the relay station, and receive, in a second timing indicated in a second downlink control information that is received by the relay station from the base station, the specific data retransmitted from the relay station when it is determined that the mobile station unsuccessfully receives the specific data from the relay station that was transmitted in said first timing, wherein the retransmission of the specific data, which was previously transmitted to the mobile station in the first timing, from the relay station to the mobile station is performed without a retransmission of the specific data from the base station to the relay station after it is determined that the relay station successfully receives the specific data from the base station.

6. The mobile station according to claim 5 , wherein the transmitter is configured to transmit a response signal to the relay station when it is determined that the mobile station unsuccessfully receives the data from the relay station in said first timing, and the receiver is configured to receive the retransmitted specific data from the relay station during the second timing, the second downlink control information generated by the base station in response to reception of an uplink control information from the relay station, wherein uplink control information is generated by the relay station in response to reception of the response signal, the second downlink control information scheduling the second timing for the retransmission of the transmitted data from the relay station to the mobile station, the second timing being determined by the base station.