A method is provided for a base station to transmit downlink control information to a relay through a Relay-Physical Downlink Control Channel (R-PDCCH). The base station transmits one or more candidate positions for the R-PDCCH. The base station further determines, based on the one or more candidate positions, a Virtual Resource Block (VRB) set for the R-PDCCH. Moreover, the base station transmits the downlink control information to the relay through the R-PDCCH. The one or more candidate positions are within the VRB set including at least one VRB, and a candidate position for the R-PDCCH of a higher aggregation level includes a combination of 2 adjacent candidate positions among candidate positions for the R-PDCCH of a lower aggregation level.