Joint Design of the Spatial and of the Classic Symbol Alphabet Improves Single-RF Spatial Modulation

A new joint spatial and classic symbol alphabet is designed for spatial modulation (SM)-based multiple-input multiple-output systems. The employment of multiple active antennas instead of a single active antenna is proposed for increasing the achievable throughput and the joint design of the antenna selection and classic transmit symbol is explored, while maintaining the compelling advantages of SM. This framework combines the bit-to-antenna mapping and classic bit-to-constellation mapping into a single function, which defines the joint-alphabet and the joint optimization of the amplitude-phase modulation and its constellation for transmission over multiple active antennas. The conventional SM system is also interpreted within our framework. An example design is proposed, which aims for a high spectral efficiency of 11 b per channel use, achieving a gain of up to 5 dB over generalized SM (GSM).