  In this paper, a downlink macro-diversity precodingaided spatial modulation
(MD-PSM) scheme is proposed, in which two base stations (BSs) communicate
simultaneously with a single mobile station (MS). As such, the proposed scheme
achieved twice the spectral efficiency of the conventional PSM scheme. To
render the demodulation possible, the two signal constellation sets used at the
two BSs should be disjoint. Also, since the two BSs use the same spatial
dimension, i.e., indices of receive antennas, the Minkowski sum of the two
constellation sets should include unrepeated symbols. This is achieved through
rotating the constellation set used by the second BS, where the error rate is
also minimized. After obtaining the optimal rotation angles for several
scenarios, a reduced complexity maximum-likelihood receiver is introduced. For
an equal number of transmit and receive antennas of 4 and at a target BER of
10^{-4}, the simulation results show that the proposed MD-PSM scheme
outperforms the conventional PSM by about 17.3 dB and 12.4 dB, while achieving
the same and double the spectral efficiency, respectively. Also, due to the
distributed nature of MDPSM, it is shown that the diversity order of the novel
MD-PSM scheme is twice that of the conventional PSM.
