Multiple Doppler shifts compensation and ICI elimination by beamforming in high-mobility OFDM systems

Abstract

Although OFDM is an effective way to mitigate the multipath spread of the wireless channels by a simple equalization, it is very sensitive to Doppler effect. Doppler spreading due to the mobility of communication terminals destroys the orthogonality among the subcarriers, and results in intercarrier interference, which degrades the system performance. In this paper, we employ array beamforming and interference suppression to compensate multiple Doppler shifts in high-speed OFDM systems. The proposed method uses uniform circular array to separate different paths with unique Doppler shift, and then correct Doppler offsets in different paths respectively. This scheme not only eases channel estimation and equalization but also utilizes the multipath characteristics of wireless channel and provides Doppler diversity gains. Simulation results show that when sufficient elements were used, the proposed scheme can effectively combat the BER error floor in high-mobility scenario and have great performance enhancement over traditional methods.Index Terms-OFDM, Doppler spreading, antenna array, beamforming, intercarrier interference.