A Space-Time MSK Code and its Detection

Motivated by the desirable attributes of both Alamouti-type space-time (ST) codes and constant envelope modulations, we introduce in this paper an ST minimum-shift keying (MSK) transmission scheme and the companion receiver. Taking advantage of the block-wise differential encoding on which the MSK transmission is based, the receiver performs noncoherent sequence detection on a down-sampled subset of the received statistics. As a result of the sequence detection, the fast-fading error floor associated with symbol-by-symbol differential detection is essentially eliminated. Furthermore, using the original received sequence and performing iterative channel estimation and sequence detection, the decisions are refined and further performance gains are observed. In fast fading, results show that the proposed receiver performance is within 3 dB of the coherent detection lower bound, at a bit-error-rate of 10^-3. It attains not only space diversity, but also time-diversity from the implicit coding in MSK. Further results also demonstrate that the receiver experiences only small performance degradation when the fading samples are not constant within each ST interval