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Precoding for Spatial Modulation Against Correlated Fading Channels

We present a precoding approach for spatial modulation to provide robustness against both the Rayleigh/ Rician fading effects and also spatial correlations among transmit antennas. This approach, based on phase-rotation and/or amplitude scaling of the transmitted symbols according to the active transmit antenna, can be implemented while preserving the average power budget and without any explicit knowledge of the channel coefficients at the transmitter. The optimum values of the precoding coefficients are determined so as to minimize the asymptotic average bit-error rate. Both theoretical analysis and simulation results indicate significant performance improvements even in the case of heavily correlated transmit antennas. Moreover, it is also shown that optimal precoding significantly compensates for the vulnerability of the antenna index bits against direct line-of-sight channel components and/or heavy inter-antenna correlations at the transmitter.