A method and a base station are described for transmitting a signal. The base station transmits control information to a relay node through a relay-physical downlink control channel (R-PDCCH), and transmits a data to the relay node through a relay-physical downlink shared channel (R-PDSCH). When a number of transmission layers of the R-PDSCH is 2 or more than 2, reference signals, among a plurality of reference signals, transmitted by a specific one of a plurality of antenna ports are used, in the relay node, for a demodulation of the control information.