Energy-Versus-Bandwidth-Efficiency Tradeoff in Spatially Modulated Massive MIMO Downlink

In this letter, we investigate the effects of pulse shaping on the bandwidth-versus-energy-efficiency tradeoff of band-limited spatial modulation (SM) massive multiple-input multiple-output (MIMO) systems. Although single-RF SM schemes have the merit of achieving high energy and bandwidth efficiencies, owing to the benefits of its antenna-activation principle, most of the previous studies assumed the use of a time-orthogonal shaping filter, which is unrealistic for a single-RF SM transmitter. To this end, we consider the use of time-limited shaping filters, such as a truncated root-raised cosine filter and a truncated Gaussian filter, for the single-RF SM transmitter. Our information-theoretic results demonstrate that, unlike in the previous studies, single-RF SM schemes do not exhibit any substantial advantages over the conventional full-RF MIMO schemes for a low number of transmit antennas, while for a large-scale antenna array, single-RF SM schemes outperform the conventional full-RF MIMO schemes.