Massive MIMO systems: Signal processing challenges and future trends

This article presents a tutorial on multi-user multiple-antenna wireless systems with a very large number of antennas, known as massive multi-input multi-output (MIMO) systems. Signal-processing challenges and future trends in the area of massive MIMO systems are presented, and key application scenarios are detailed. A linear-algebra approach is considered for the description of the system and data models of massive MIMO architectures. The operational requirements of massive MIMO systems are discussed, along with their operation in time-division duplexing mode, resource allocation, and calibration requirements. In particular, transmitter and receiver processing algorithms are examined in light of the specific needs of massive MIMO systems. Simulation results illustrate the performance of transmitter and receiver processing algorithms under scenarios of interest. Key problems are discussed, and future trends in the area of massive MIMO systems are pointed out.