Index Modulation for 5G: Striving to Do More with Less

5G wireless communications expect to bring both high spectrum efficiency and high energy efficiency. To meet the requirements, various new techniques have been proposed. Among these, the recently emerging index modulation has attracted significant interest. By judiciously activating a subset of certain communication building blocks, such as antenna, subcarrier, and time slot, index modulation is claimed to have the potential to meet the challenging 5G needs. In this article, we discuss index modulation and its general and specific representations, enhancements, and potential applications in various 5G scenarios. The objective is to reveal whether, and how, index modulation may strive for more performance gains with less medium resource occupation.

Introduction

The explosive increase of mobile data services and the use of smartphones require the fifth generation (5G) network to support higher spectrum efficiency (SE), higher energy efficiency (EE), and higher mobility. The currently employed modulation techniques based on multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM), unfortunately, are not sufficient to satisfy such 5G requirements. Conventional MIMO may achieve high SE with massive antennas, but has compromised EE due to the scaled power consumption of a large number of RF chains. The OFDM modulation is prone to Doppler-induced intercarrier interference (ICI). Its inherent high peak-to-average power ratio (PAPR) also necessitates expensive power amplifiers. Novel advanced modulation techniques are therefore very much needed. To this end, the recently emerging index modulation (IM) techniques arise as a promising candidate with the potential to meet the 5G requirements [1].