MIMO vs. Beamforming

MIMO is based on multiple antennas similar to antenna array however each antenna is working independently of other antennas.  The overall data is decomposed to lower data rate and each antenna is transmitting portion of that data, independently.  In essence MIMO is using spatial diversity and multiplexing for very high data rate transmission.  The spacing between each antenna is a wavelength to create adequate isolation while uncorrelated signals are picked up by each antenna.

Beamforming is achieved via Phased Array Antennas.  The Phased Array Antennas are based on array technologies which have been used extensively in military applications in the past 4 decades.  The antenna arrays electronically steers the beam to illuminate the intended target.  The beam steering occurs via changing the relative phase of each antenna element, such that the overall beam is formed of construction of Electromagnetic Waves at desired direction in the far field and produce higher SNR compare to single antenna at the receiver end.  The Phased Array Antennas are working together to achieve high gain/directional antenna, hence higher SNR at the receiver. The spacing between each antenna element is typically half wavelength to avoid grating lobe.

5G Technology will be utilizing massive MIMO as well as Beamforming, BF.  Massive MIMO is intended for below 6GHz, whereas BF will be used for mmW bands (i.e. where wavelength is in order of mm, e.g. 30GHz).