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CSI-RS vs SRS Beamforming

In an issue of Signals Flash by Signals Research Group (SRG), they talked about 2 different types of MIMO. Quoting from their journal, "CSI-RS versus SRS. Those operators that have tested or made token use of MU-MIMO leverage a flavor of MU-MIMO that is based on CSI-RS. The MU-MIMO network we tested was based on SRS, which makes it far more likely to observe sixteen spatial layers (versus eight)."

I reached out to Emil Björnson, Visiting Professor at KTH Royal Institute of Technology and Associate Professor at Linköping University to see if he has explained this in any of his videos. Here is what he said:

"I'm not talking about 3GPP terminology in any of my videos. But you can listen to the slides that starts around 12:40 in this video (embedded below). If you are looking for CSI-RS vs SRS based MU-MIMO, then jump to around 12:40 in this video where you can see CSI-RS being referred to as "grid of beams" and SRS is similar to the other option, which is the preferred option, especially for TDD."

You can download the slides from here.

A recent post on Telecoms Infrastructure Blog also has a nice short tutorial on Massive MIMO and Beamforming.

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