An Enhanced Detection Algorithm for MIMO-OFDM Beamforming System With Feedback Delay

The traditional beamforming in MIMO-OFDM systems uses the subcarriers characterized by the largest eigenvalues to transmit the OFDM block symbols. In contrast to the previous one, the optimal beamforming in MIMO-OFDM systems use the N best subchannels in all optional orthogonal subchannels. But when feedback from receiver delays, the optimal beamforming in MIMO-OFDM will appear self- interference in the subcarriers that have more than one subchannels. The self-interference will impact the performance severely especially when the normalized Doppler frequency is large. In this paper, we proposed two novel detection algorithms to reduce the self-interference. Both of them use the instantaneous and last OFDM symbol's channel coefficients to compute the self-interference and depress it before demodulation. Simulation results reveal that when feedback delays, the optimal beamforming will be impacted severely and sometimes even degrade worse than the traditional beamforming. After adopting the proposed detection algorithms, the performance will be improved.