Channel Code Aided Decision-Directed Channel Estimation for MIMO OFDM/SDMA Systems Based on the "Expectation-Conditional Maximization Either" Algorithm

In this paper, a Forward Error Coded (FEC) Decision-Directed (FEC-DD) channel estimation scheme is proposed for Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing/Space Division Multiple Access (OFDM/SDMA) systems which is based on the Expectation-Conditional Maximization Either (ECME) algorithm. The proposed DD technique is combined with the Optimised Hierarchy Reduced Search Algorithm (OHRSA) based Multi-User Detector (MUD) and directly calculates the Maximization-Step (M-Step) by conditionally maximizing the logarithmic likelihood function of the ``incomplete'' data. We avoid the employment of matrix inversion, since only a single subcarrier's Frequency-Domain CHannel Transfer Function (FD-CHTF) is calculated at a time, since we assume that the other subcarriers' FD-CHTFs are the most recent estimates from the previous iteration of the proposed scheme. Our simulation results have demonstrated that the proposed scheme is capable of reducing the received power requirement by $4 dB$ upon exploiting the error correction capability of a FEC decoder within the ECME loop.