Low complexity iterative method of equalization for OFDM in doubly selective channels

In a multi-path channel an orthogonal frequency division multiplexing (OFDM) system is very robust to frequency selective fading, but it is sensitive to the time selective fading of the mobile channel. Time selectivity of the channel causes inter-carrier-interference (ICI) in OFDM, thereby degrading the performance significantly and increasing the computational complexity of the receiver. On the other hand, it introduces temporal and frequency diversity. In this work, a low complexity iterative method is addressed to compensate for the adverse effects of time and frequency selectivity of the channel while achieving the diversity benefits. The method splits the equalization into two stages. The first stage exploits the sparsity present in the channel convolution matrix (CCM) to estimate the time domain transmitted samples and the second stage performs the maximum a posteriori (MAP) detection of the frequency domain symbols. Simulation results show the performance of the proposed algorithm is close to the match filter bound (MFB) with lower computational complexity.