Patent ID: 8885742

Claim:
A method for transmitting a demodulation reference signal (DM RS) at a base station (BS) in a wireless communication system, the method comprising: determining whether a downlink subframe is a normal subframe or a backhaul subframe; mapping the DM RS on resource elements (REs) of the backhaul subframe if the downlink subframe is the backhaul subframe, the REs excluding orthogonal frequency division multiplexing (OFDM) symbols corresponding to a physical downlink control channel (PDCCH) and a guard time, the guard time for a mode transition of a relay node (RN) between a reception mode and a transmission mode; and transmitting the DM RS for to the RN through the backhaul subframe, wherein subcarrier frequency indexes of the REs are 2 , 5 , 8 and 11 in a frequency axis within a second slot of the backhaul subframe if an extended cyclic prefix (CP) is applied to the backhaul subframe.