A method of transmitting signals by a transmitting side device having multiple antennas (hereinafter ‘N antennas’) is disclosed. In this method, the transmitting side device transmits reference signals (RSs) via M antenna among the N antennas, where M≦N, where one or more of M and a sequence of antenna numbers used for transmitting RSs informs a receiving side device of first information for data transmission, and where the RSs are used by the receiving side device for identifying second information for channel estimation. Transmitting side device transmits data to the receiving side device according to the first information.