Beam Steering
Beam steering is changing the direction of an antenna array's beam electronically, by adjusting the phase of the signal on each element, so that it follows a user.
What is Beam Steering?
The base station recalculates the direction as the user moves, effectively tracking them. Beam switching is the related approach of handing a user from one pre-formed beam to another when the current beam can no longer follow them. Beam steering works with fairly few elements (benefits start at around 8), needs no detailed knowledge of the radio channel, works with both FDD and TDD, and is most effective in open, line-of-sight conditions.
Example
One comparison in the source reports around 5 times capacity gain from beam steering with 64 antennas in live networks, compared with about 50 times for massive MIMO beamforming in laboratory conditions only.