Massive MIMO for 5G: Overview and the road ahead

摘要

Massive MIMO is the currently most compelling sub-6 GHz wireless access technology for 5G. Since its inception about a decade ago, it has evolved from a wild “academic” idea to one of the most vibrant research topics in the wireless communications community, as well as a main work item in 5G standardization. The concept is to equip base stations with arrays of many antennas that serve many terminals simultaneously, in the same time-frequency resource. The arrays have attractive form factors: in the 2 GHz band, a halfwave-length-spaced rectangular array with 200 dual-polarized elements is about 1.5 × 0.75 meters large. Massive MIMO operates in TDD mode and the downlink beamforming exploits the uplink-downlink reciprocity of radio propagation. Specifically, the base station array uses channel estimates obtained from uplink pilots transmitted by the terminals to learn the channel in both directions. This makes Massive MIMO entirely scalable with respect to the number of base station antennas. Base stations operate autonomously, with no sharing of payload data or channel state information with other cells. In this talk I will discuss the development of Massive MIMO over the last five years, and outline the most important research problems ahead.