MIMO is an effective approach to increase throughput and energy efficiency through the collaboration of individual antennas working together as a virtual multi-antenna system. Several CMIMO strategies have been propounded as major candidates for achieving green communications in wireless sensor networks. Compared to conventional MIMO, CMIMO provides significant gains in terms of flexibility. Recently, more advanced cooperation strategies have been proposed to improve the performance of CMIMO by using emerging techniques such as spatial modulation and coding. Although some breakthroughs have been made in this area, the problem of how to accurately adopt these emerging techniques to model CMIMO is far from being fully understood. This article surveys several state-of-the-art CMIMO models for different scenarios, including data aggregated, multihop-based, and clustered schemes. Moreover, it discusses the implementation of CMIMO techniques, which are expected to be candidate techniques for green communications in modern applications. In the implementation, the trade-offs between energy efficiency and spectral efficiency, quality of service, fairness, and security are discussed. Several simulation results are given to show how emerging techniques in CMIMO design can lead to energy efficiency enhancement. Finally, some challenges and open issues that present future research directions are discussed.
Energy efficiency; MIMO; Wireless sensor networks; Modulation; Quality of service; Energy consumption; Antenna arrays