A method is provided for demodulating a signal. A relay node receives control information, from an evolved-NodeB (eNB), through a relay-physical downlink control channel (R-PDCCH), and receives a data, from the eNB, through a physical downlink shared channel (PDSCH). When a number of transmission layers of the PDSCH is 2 or more than 2 and a plurality of reference signals for a demodulation of the data are transmitted on antenna ports by the eNB, a reference signal transmitted on a minimum antenna port among the antenna ports is used for a demodulation of the control information.