A simple antenna combining framework for Doppler compensation in mobile OFDM systems

In OFDM systems, Doppler spreading due to the mobility of the receiver distorts the orthogonality among the subcarriers, and results in intercarrier interference that degrades the performance. In this paper, we investigate how Doppler spreading can be mitigated by using multiple antennas. In this context, we propose a novel antenna combining framework exploiting the correlation among the time varying channels seen by the multiple antennas. Depending on the computational complexity requirements, the scheme can take the form of beamforming, beamforming with frequency offset correction and simple time-varying combining schemes. We derive the optimum combining scheme in each context, and show that by using the proposed combining schemes, the performance of the mobile OFDM systems can be greatly enhanced.