Generalized-Spatial-Modulation-Based Reduced-RF-Chain Millimeter-Wave Communications

A generalized spatial modulation (GSM)-based millimeter-wave communications system is proposed. The GSM transmitter is characterized by a lower number of radio frequency (RF) chains than the number of transmit antennas; hence, it is capable of reducing both the transmitter cost and the energy consumption. The antenna array alignment is optimized so as to maximize the rank of the channel matrix encountered. Furthermore, we employ an array of analog beamformers, which allows us to benefit both from the beamforming gain and from the GSM scheme's high rate. It is demonstrated that the constrained capacity of the GSM transmitter equipped with as few as two RF chains is capable of approaching the performance of the full-RF spatial multiplexing having eight RF chains.

I. Introduction

Spatial modulation (SM)-aided multiple-input multiple-output (MIMO) schemes are capable of increasing the attainable data rate with the aid of a single radio frequency (RF) transmitter [1]. In the SM transmitter, the information bits are mapped to transmitted symbols by activating a single transmit antenna (TA) element out of multiple TA elements, and only a single symbol is transmitted from the activated TA. This allows us to avoid the interchannel interference at the receiver; hence, low-complexity single-stream decoding [2], [3] is applicable. Furthermore, the single-RF transmitter structure specific to the SM scheme reduces static power consumption [4]. In [5] and [6], the SM scheme was extended to a more flexible framework referred to as the generalized SM (GSM), where multiple antenna elements are simultaneously activated in each symbol duration. More specifically, the GSM scheme subsumes several classic MIMO schemes, such as the SM and Bell Laboratories Layered Space-Time (BLAST) schemes [7].