  Spatial modulation (SM) is a transmission scheme that uses multiple transmit
antennas but only one transmit RF chain. At each time instant, only one among
the transmit antennas will be active and the others remain silent. The index of
the active transmit antenna will also convey information bits in addition to
the information bits conveyed through modulation symbols (e.g.,QAM).
Pseudo-random phase precoding (PRPP) is a technique that can achieve high
diversity orders even in single antenna systems without the need for channel
state information at the transmitter (CSIT) and transmit power control (TPC).
In this paper, we exploit the advantages of both SM and PRPP simultaneously. We
propose a pseudo-random phase precoded SM (PRPP-SM) scheme, where both the
modulation bits and the antenna index bits are precoded by pseudo-random
phases. The proposed PRPP-SM system gives significant performance gains over SM
system without PRPP and PRPP system without SM. Since maximum likelihood (ML)
detection becomes exponentially complex in large dimensions, we propose low
complexity local search based detection (LSD) algorithm suited for PRPP-SM
systems with large precoder sizes. Our simulation results show that with 4
transmit antennas, 1 receive antenna, $5\times 20$ pseudo-random phase precoder
matrix and BPSK modulation, the performance of PRPP-SM using ML detection is
better than SM without PRPP with ML detection by about 9 dB at $10^{-2}$ BER.
This performance advantage gets even better for large precoding sizes.
