Directivity of an antenna array increases rapidly with the increase in its size. In massive MIMO huge increase in transmit antenna array increases spatial dimension rapidly thereby increasing spectral efficiency. But in such a scenario, how will the service being provided to multiple users that are separated by a certain distance and residing outside the sharp beam?
With Massive MIMO you create an individual "sharp beam" for each user. This is possible since the "beams" are created electronically, by selecting a particular combination of phase and power differences over the array for each signal. The signals intended for the multiple users are added up in the digital domain before being transmitted.
Note that that the "beam" analogy is only valid for line-of-sight communication. In practice there will be many non-line-of-sight users. These are served in the same way, but the phase and power variations over the array will not form a sharp angular beam - it will just make sure that signals from the multiple antennas add coherently at the spatial location of the user.
Dear,
In Massive MIMO you can give all resource blocks to everyone - if they have data buffers to transmit. The separation between users is done spatially by the downlink precoding and uplink detection, instead of making them orthogonal in the time/frequency space.
There is no one-to-one correspondence between users and antennas in Massive MIMO. All the antennas at a base station are used to serve a user, by precoding.
One example: The base station has 100 antennas and decides on that it will serve up to Kmax users. If there KKmax, you can divide the resources in some simple way between them - there is no need to use current channel knowledge since the small-scale fading averages.
source:Massive MIMO: Ten Myths and One Critical Question
Emil Björnson
With Massive MIMO you create an individual "sharp beam" for each user. This is possible since the "beams" are created electronically, by selecting a particular combination of phase and power differences over the array for each signal. The signals intended for the multiple users are added up in the digital domain before being transmitted.
Note that that the "beam" analogy is only valid for line-of-sight communication. In practice there will be many non-line-of-sight users. These are served in the same way, but the phase and power variations over the array will not form a sharp angular beam - it will just make sure that signals from the multiple antennas add coherently at the spatial location of the user.
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