Space-Time Mapping for Equiprobable Antenna Activation in Spatial Modulation

Abstract

Spatial modulation (SM) conveys additional information bits via the index of an activated transmit antenna. When the number of antennas is not an integer power of two, the antenna activation becomes challenging. In such a case, only a subset of the available transmit antennas whose cardinality is an integer power of two is used. This leads to antenna activation with unequal probability, which causes high error rates and losses in the spectral efficiency. The same limitations and performance losses equally exist in quadrature spatial modulation (QSM) and generalized spatial modulation (GSM), the two prominent variants of SM. In this contribution, in contrast to the conventional approach of antenna activation within each symbol period, a space-time bit-mapping method in which the antenna selection procedure is extended to multiple symbol periods is proposed. Use of the proposed method in SM, QSM, and GSM techniques, is shown to achieve performances close to their full potential for any given number of transmit antennas, with only a marginal increment in detection complexity.