What is multi-user MIMO (MU-MIMO) in 5G?

My friend: Hi Ibrahim, I have a question for you.

Me: Go ahead, please.

My friend: During the trial of MU-MIMO currently running at one site, we didn’t notice an increase of user peak throughput, why?

Me: Actually, we aren’t expecting increase of peak user throughput rather than increase of cell throughput which already was higher as simply MU-MIMO means assigning same resource blocks to different users, so spectral efficiency increases and cell capacity increases also. For example, spectral efficiency can be doubled if same resource blocks are allocated to 2 UEs and spectral efficiency can be 4 times if same resource blocks are allocated by 4 UEs and so on.

My friend: But, how can we allocate same resource blocks to different users? They will interfere each other, right?

Me: Yes, you are right, that’s why those users should be distributed across the cell area and thanks to beamforming, so each user should be served by separate beam and so beamforming can generate significant performance gains from MU-MIMO because the highly directional beams are able to increase the spatial separation between UEs.

My friend: Thanks a lot. 

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Source: Ibrahim Sayed

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