Differential Spatial Multiplexing for Two and Three Transmit Antennas

In this paper, we construct a differential spatial multiplexing method that can trade-off spatial diversity for increased transmission rate in differential multi-input multi-output (MIMO) systems. To achieve a desired multiplexing gain while providing simple encoding and decoding, Gram-Schmidt algorithm is used at the transmitter to construct the unitary transmission matrix. In addition, by applying optimum scaling factors to generate transmission matrix, the symbol error rates can be minimized. Because the transmission matrix itself is not the information we are interested in, the equivalent channel parameters for each transmitted information symbols are calculated and the linear signal model for the information symbols is derived. Since that model is exactly the same as that of the coherent spatial multiplexing, all kinds of coherent detection schemes can be directly applied. The advantage of the proposed scheme over the differential space-time block codes (STBC) and the effects of scaling factor are investigated by computer simulation. In high transmission rate regimes, the proposed differential spatial multiplexing method can outperform the differential STBC having the same transmit rate in the signal to noise ratios (SNRs) we are interested in.