An iterative beamforming technique for OFDM-based wireless networks with uncoordinated channel access

We first consider the problem of decoding a signal from a memoryless SIMO (single-input/multiple-output) channel subject to block-wise stationary cochannel interference (CCI). We employ an iterative expectation-maximization method, arriving at an algorithm which alternately performs a beamforming via a sample matrix inversion and a maximum-likelihood decoding. An analytical analysis of the sample errors after the beamforming provides insight into the procedure. A numerical study shows that with the number of iteration cycles increasing, the sample error squares decrease towards an analytical lower bound, and the error rates at the decoder output improve. Second, the iterative algorithm is employed for the reception of coded OFDM (orthogonal frequency-division multiplexing) signals subject to non-stationary CCI in both the time and frequency dimensions, as typically encountered in decentralized broad-band wireless networks with uncoordinated channel access. Results from computer simulations indicate that the proposed algorithm successfully mitigates the CCI, achieving gains of several decibels over conventional receiver techniques.