Massive MIMO for next generation wireless systems

The article gives an overview of massive MIMO, also called large-scale antenna systems, for next-generation wireless. It begins from multi-user MIMO, which offers advantages over point-to-point MIMO by working with cheap single-antenna terminals, not requiring a rich scattering environment, and simplifying resource allocation, yet which does not scale in its original form with roughly equal antennas and terminals and frequency-division duplex. Massive MIMO makes a clean break by using a large excess of service antennas over active terminals together with time-division duplex operation.

The surplus of antennas focuses energy into ever smaller regions of space, bringing large gains in throughput and radiated energy efficiency, along with extensive use of inexpensive low-power components, reduced latency, a simplified MAC layer, and robustness against intentional jamming. The authors note the anticipated throughput depends on the propagation environment providing near-orthogonal channels, which experiments so far have not contradicted, and they highlight new problems such as coordinating many low-cost low-precision components, synchronizing newly joined terminals, and reducing internal power consumption.