Intercarrier Interference Alleviation Beamforming for Ofdm with Space Diversity

Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from performance deterioration when the length of Cyclic Prefix (CP) is shorter than the Channel Impulse Response (CIR). The fundamental reason of this impairment is the InterCarrier Interference (ICI) and InterSymbol Interference (ISI) introduced by the excessive multipath delay. Specifically, Multiple Input Multiple Output (MIMO) beamforming is helpful in cancelling such interference since it can spatially suppress some of the multipath. In this paper, we propose an ICI eliminating beamforming scheme employing a per-tone processing approach, thus with moderate computational complexity. The ISI is removed by using a simple decision feedback equalizer, while the optimal steering and combining vectors are then derived to maximize the Signal to Interference plus Noise Ratio (SINR). This method not only achieves the beamforming benefit, but also significantly alleviates the ICI. Simulation results show that the proposed algorithm can effectively reduce the system Symbol Error Rate (SER), permitting good performance for multipath delay profiles that would break conventional links.