Adaptive Quadrature Spatial Modulation

Abstract

ABSTRACT In this paper, we investigate an enhanced form of spatial modulation, in the form of quadrature spatial modulation (QSM). The existing analytical error performance of QSM does not agree well with Monte Carlo simulation results in the low signal-to-noise ratio (SNR) region. Hence, the first contribution of the paper is to formulate a new analytical bound on error performance, which improves on the validation of simulation results at low SNRs. Secondly, a link adaptation technique for QSM is investigated in order to further improve its error performance. The proposed scheme is based on a selection technique between candidate transmission modes chosen to satisfy a target spectral efficiency, which employs optimal transmit antenna selection and modulation order selection, such as to minimize the average bit error probability (BEP). Euclidean distance-based antenna selection is employed to select the enumeration of transmit antennas for each transmission candidate, while the instantaneous BEP (IBEP) is employed to select the transmission candidate mode. Significant SNR gain over QSM is demonstrated. In order to reduce the computational complexity (CC) overhead of optimal transmit antenna selection, the third contribution is to investigate suboptimal low-complexity transmit antenna selection for the proposed scheme. Monte Carlo simulation results demonstrate a trade-off between the error performance and CC.