Standardization works of international mobile telecommunication (IMT)-advanced which is a next generation (i.e., post 3rd generation) mobile communication system are carried out in the international telecommunication union radio communication sector (ITU-R).  The IMT-advanced aims at support of an Internet protocol (IP)-based multimedia service with a data transfer rate of 1 Gbps in a stationary or slowly moving state or 100 Mbps in a fast moving state. 
3rd generation partnership project (3GPP) prepares a system standard satisfying requirements of the IMT-advanced, long term evolution (LTE)-advanced, which is an improved version of LTE based on orthogonal frequency division multiple access (OFDMA)/single carrier-frequency division multiple access (SC-FDMA) transmission.  The LTE-advanced is one of promising candidates for the IMT-advanced.  Technology related to a relay station is one of main technologies for the LTE-advanced. 
A relay station (RS) is a device for relaying a signal between a base station (BS) and a user equipment (UE), and is used for cell coverage extension and throughput enhancement of a wireless communication system. 
The RS can transmit a control signal to the BS.  Examples of the transmitted signal may include a hybrid automatic repeat request (HARQ) acknowledgement/negative acknowledgement (ACK/NACK), a channel quality indicator (CQI), a scheduling request (SR), etc.  A mechanism of allocating a radio resource needs to be considered when the RS transmits the control signal to the BS. 
In addition, the UE can also transmit the control signal to the BS in the wireless communication system including the RS.  Therefore, it is not preferable if a method of transmitting the control signal by the RS to the BS has an effect on a procedure of transmitting the control signal by the UE to the BS.  That is, it is preferable to maintain backward compatibility with the legacy UE. 
Accordingly, there is a need for a method and apparatus for transmitting a control signal of an RS by considering the aforementioned aspects.