Low Complexity Beamforming Methods for MIMO-OFDM Systems

Multiple-input multiple-output (MIMO) systems can significantly improve the network capacity and the quality of service (QoS). We propose a novel beamforming method for MIMO orthogonal frequency division multiplexing (OFDM) systems in this work. The presented method is based on the Rayleigh Quotient (RQ) of the Fourier transform of the channel matrix. Two RQ analysis algorithms, simple steepest descent and Luo´s algorithms, are used to obtain the new beamforming method. It is demonstrated that the proposed method can considerably reduce the complexity and needs only (2K+1)L complex multiplications and 2KL-1 complex additions for a single run, where K and L are the number of antennas at the transmitter and the receiver, respectively. We evaluate the performance of the presented method in AWGN and Rayleigh fading channels. Simulation results show that the new method reduces the bit error rate (BER) significantly while having low computational complexity. It is also shown that the presented method has a very fast convergence rate.