  In this paper, we consider the Spatial Modulation (SM) system in a frequency
selective channel under single carrier (SC) communication scenario and propose
zero-padding instead of cyclic prefix considered in the existing literature. We
show that the zero-padded single carrier (ZP-SC) SM system offers full
multipath diversity under maximum-likelihood (ML) detection, unlike the cyclic
prefixed SM system. Further, we show that the order of ML decoding complexity
in the proposed ZP-SC SM system is independent of the frame length and depends
only on the number of multipath links between the transmitter and the receiver.
Thus, we show that the zero-padding in the SC SM system has two fold advantage
over cyclic prefixing: 1) gives full multipath diversity, and 2) offers
relatively low ML decoding complexity. Furthermore, we extend the partial
interference cancellation receiver (PIC-R) proposed by Guo and Xia for the
decoding of STBCs in order to convert the ZP-SC system into a set of
flat-fading subsystems. We show that the transmission of any full rank STBC
over these subsystems achieves full transmit, receive as well as multipath
diversity under PIC-R. With the aid of this extended PIC-R, we show that the
ZP-SC SM system achieves receive and multipath diversity with a decoding
complexity same as that of the SM system in flat-fading scenario.
