Simultaneous channel estimation and decoding for diagonal space-time codes

Multiple input, multiple output (MIMO) wireless communications links have been shown to have the potential for significant increases in capacity, provided they are deployed in an environment with rich multipath scattering. To realize these gains, a number of space-time coding strategies have previously been proposed. Most of these algorithms assume that, via training data, the channel is known at least on one end of the link. However if the channel is time-varying or even just quasi-stationary, the training overhead can offset much of the throughput gain. In this paper a space-time coding scheme is presented that allows for simultaneous blind or semi-blind channel estimation and decoding of the symbols transmitted by multiple users. The method relies on the use of "diagonal" space-time codes in which the same symbol is successively transmitted from each antenna in turn. This structure leads to a simple subspace-based algorithm that produces closed-form estimates of both the channel and the transmitted symbols. The algorithm is shown to be applicable to cases involving fewer receive than transmit antennas, rank-deficient channels, flat or frequency selective fading, and multiple users.