Differential spatial multiplexing from orthogonal designs

We propose a differential spatial multiplexing (SM) scheme based on complex square orthogonal designs, referred to as differential orthogonal spatial multiplexing (DOSM). The receiver of DOSM does not require estimation of channel fading coefficients, channel power, signal power, or noise power to decode the data symbols and the decision is based on the two consecutively received codewords. A constellation rotation strategy is introduced to enhance the transmission rate. An upper bound of the pair-wise error probability (PEP) for DOSM in Rayleigh fading channels is derived. Based on this bound we propose design criteria for the constellation rotation angel and use them to search for the optimal rotation angle for PSK constellations. Simulation results show that the proposed DOSM outperforms the existing differential spatial multiplexing schemes in terms of error-rate performance over quasi-static and time-selective Rayleigh fading channels. Furthermore, it is estimated from the bound that DOSM is only 0.4 dB poorer than coherent SM in a two-input two-output system at high SNR. The computational complexity of DOSM is moderate among the differential SM systems.