Two-Stage Blind Detection of Alamouti Based Minimum-Shift Keying

In a recent study [7], the authors successfully incorporated minimum-shift keying (MSK) into an Alamouti-type space-time (ST) transmission system, operating in a fading channel environment. This work extends the investigation to include an enhanced receiver and a more realistic channel model that does not limit the fading to be constant over each ST block. The proposed receiver first detects an underlying differential ST ¿ / 2 -shifted BPSK code present in the ST-MSK signal, by performing low-complexity non-coherent multiple-symbol differential detection with decision feedback. The relatively reliable initial data estimates are then used to obtain high-quality channel estimates, at a rate notably higher than the MSK symbol rate. The availability of these channel estimates enables a second-stage coherent sequence detector to significantly refine the initial data decisions. In fast fading, results show that the proposed receiver performance is within 2 dB of the coherent detection lower bound, at a bit-error-rate of 10-5. When compared to a linearly modulated ST ¿ / 2 -shifted BPSK code, the proposed ST-MSK scheme achieves a greater order of diversity and hence better performance in a fast fading environment. We attribute this to the additional time-diversity effect associated with the phase coding evident in MSK.