Constellation Designs for the Spatial Modulation MIMO Systems

Abstract

This paper shows that the information transmitted over the spatial dimension in the Multiple Input Multiple Output systems with Spatial Modulation (MIMO-SM) is sensitive to the transmission of the conventional amplitude and phase modulated (APM) symbols with small magnitude (e.g. from the inner ring of the constellation). This sensitivity is a limiting factor in the performance of the quadrature amplitude modulated (QAM) SM. We propose three novel MIMO-SM constellation designs to mitigate the performance limitation: (i) a hybrid PSK-QAM MIMO-SM that leverages the constant modulus phase shift keying (PSK) in conjunction with the QAM to minimize the sum of the antenna errors and the APM symbol errors. This is achieved by increasing the number of transmit antennas, which need not be an integer power of two; (ii) MIMO-SM with a novel APM QAM constellation, with optimized radius of the inner constellation ring; and (iii) a MIMO-SM that transmits the QAM symbols from the inner ring on different orthogonal resources (e.g., subcarriers) to reduce their impact on the antenna errors. The simulation results demonstrate the performance benefit of the proposed approaches compared to the conventional SM.