System and method for performing weighted processing on down link signal

A method, device, and communications system for performing weighted processing on a downlink signal are provided. The method includes: acquiring a first CIR from a BS to a relay station and a second CIR from the relay station to a MS; determining a pre-coding weight and a relay weight according to the first CIR and the second CIR; and respectively sending the pre-coding weight and the relay weight to the BS and the relay station, so that the BS is enabled to perform weighted processing on a downlink signal according to the pre-coding weight to obtain a downlink pre-coding weighted signal and send the downlink pre-coding weighted signal to the relay station, and the relay station is enabled to perform weighted processing on the downlink pre-coding weighted signal received by the relay station according to the relay weight to obtain a downlink relay weighted signal and send the downlink relay weighted signal to the MS. Thereby, the downlink signal is optimized at the BS and the relay station respectively, thus optimizing the network capacity and improving the communication quality.