Spatial Modulation for 2 Generalized MIMO : Challenges , 3 Opportunities , and 4 Implementation 5 By Marco

8 ABSTRACT | A key challenge of future mobile communication 9 research is to strike an attractive compromise between 10 wireless network’s area spectral efficiency and energy effi11 ciency. This necessitates a clean-slate approach to wireless 12 system design, embracing the rich body of existing knowledge, 13 especially on multiple-input–multiple-ouput (MIMO) technolo14 gies. This motivates the proposal of an emerging wireless 15 communications concept conceived for single-radio-frequency 16 (RF) large-scale MIMO communications, which is termed as SM. 17 The concept of SM has established itself as a beneficial 18 transmission paradigm, subsuming numerous members of the 19 MIMO system family. The research of SM has reached sufficient 20 maturity to motivate its comparison to state-of-the-art MIMO 21 communications, as well as to inspire its application to other 22 emerging wireless systems such as relay-aided, cooperative, 23 small-cell, optical wireless, and power-efficient communica24 tions. Furthermore, it has received sufficient research attention 25 to be implemented in testbeds, and it holds the promise of 26 stimulating further vigorous interdisciplinary research in the 27 years to come. This tutorial paper is intended to offer a 28 comprehensive state-of-the-art survey on SM–MIMO research, 29 to provide a critical appraisal of its potential advantages, and to 30 promote the discussion of its beneficial application areas and 31 their research challenges leading to the analysis of the 32 technological issues associated with the implementation of 33 SM–MIMO. The paper is concluded with the description of the 34 world’s first experimental activities in this vibrant research 35 field.