Semi-blind channel estimation for block precoded space-time OFDM transmissions

We develop in this paper a (semi-) blind channel estimation algorithm for space time (ST) block precoded OFDM transmissions over frequency-selective channels. We establish that multi-channel identifiability is guaranteed up to one or two scalar ambiguities, when distinct or identical precoders are employed for even and odd indexed symbol blocks. With known pilots inserted before precoding, we resolve the residual scalar ambiguities and show that distinct precoders require less pilots than identical precoders to achieve the same channel estimation accuracy. Simulation results confirm our theoretical analysis and illustrate that the proposed semiblind algorithm is capable of tracking slow channel variations and improving the overall system performance relative to competing differential ST alternatives.