Multiple Doppler frequency offsets compensation technique for high-mobility OFDM uplink

A new scheme is proposed to compensate the multiple Doppler frequency offsets (DFOs) for high-mobility OFDM uplink transmissions in this paper. According to the characteristics of uplink transmission, we find it is a good choice to solve the multiple DFOs problem in the spatial-domain. The proposed scheme consists of a mobile relay station (MRS) between the base station (BS) and the mobile terminal (MT). The MRS is immobile respect to the MT, and hence the DFOs are only generated between the MRS and the BS. The MRS uses an antenna array to transmit signals through different paths. The DFOs are estimated during the downlink, and the DFO for each path is separately compensated before the particular transmit beamforming for this path. Therefore, all the signals in different paths are superimposed at the BS without DFO, and the BS does not have to be changed in this case of high-mobility scenarios. The effectiveness of the proposed scheme is verified by simulations.