Analytical evaluation of MIMO systems with unequal power transmission in a Rayleigh fading environment

We investigate the performance, in terms of symbol error probability (SEP), of multiple-input-multiple-output (MIMO) systems in a flat Rayleigh fading environment with coherent detection of M-PSK signals. The reception is based on linear minimum mean square error (MMSE) combining, followed by successive interference cancellation. Compared to conventional vertical-Bell Laboratories layered space-time (V-BLAST) MIMO systems, we assume a low complexity strategy that does not include the ordering phase. To reduce the difference in terms of SEP on the sub-streams, we consider a MIMO scheme where the symbols transmitted by the different antennas have different energy. Our methodology is completely analytical, is valid for an arbitrary number of receive and transmit antennas (provided that N_R≥N_T) and provides a very fast evaluation of MIMO performance. Results show that the unequal power transmission scheme gains about 3-4 dB over the conventional equal-power transmission case.