Semi-Blind Data Detection for Unitary Space-Time Modulation in MIMO Communications Systems

We propose an iterative algorithm based on expectation maximization (EM) to jointly estimate the system parameters and decode the data in a MIMO system using unitary space-time block codes. It is assumed that the receiver is unaware of the channel coefficients and their distribution, the average energy of the received signal, the prior probability of each signal in the constellation, and the noise power. The algorithm works for arbitrary modulation schemes and any channel model including Rayleigh and Rician fading. The complexity of the proposed receiver is computed and it is shown to be significantly lower than previously published methods, as it does not require any matrix inversion or trellis search. The performance of the proposed receiver is evaluated by simulations in terms of symbol error rate (SER) vs. signal-to-noise ratio (SNR) and it is shown that with only a few iterations of the algorithm it achieves a performance close to that of the receiver which knows all the parameters.