I. Introduction
Spatial modulation (SM) is a recent technique in multiple-antenna communications, where, along with the classic modulated symbol transmitted from the antenna, additional implicit information is conveyed by the specific index of the transmit antennas (TAs). For a system with TAs, bits are conveyed by the index of the TA to be activated, and a symbol selected from a constellation of size is transmitted through the selected TA, giving a total rate of bits per channel use. Excellent recent tutorial surveys on SM include [1]– [3]. In the early work on SM, e.g., [4]– [11], basic signaling schemes and optimal detectors were proposed, and their corresponding symbol error probability (SEP) performance was analyzed. For example, in [12], the authors derive expressions for the average bit error probability of an SM system in terms of the Marcum- and hypergeometric functions. However, these expressions cannot be readily extended to the case where partial channel state information (CSI) is available at the transmitter (CSIT) via a finite-rate feedback link.