A bandwidth-efficient scheme for non-coherent transmit diversity

Differential transmit diversity which can be detected noncoherently is an attractive alternative to coherent space-time block codes since channel estimation is more difficult in multi-antenna systems than in single antenna systems. We focus on differential space-time block codes from orthogonal designs which derive the transmit symbols from an M-PSK constellation in order to fulfill the requirement that the transmit vectors have unit length. Since PSK is only advantageous for M ≤ 8, we propose to extend the transmit symbol constellation for bandwidth-efficient transmission such that multiple levels are allowed for the length of the transmit vector. Furthermore, we derive a simple soft-output detector which does not require channel estimation. The new scheme outperforms the existing unit-length approach at high bandwidth-efficiency, particularly in time-varying channels. Furthermore, it is more flexible in terms of data rate adaptation and has lower detection complexity.