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Enhanced Massive MIMO
Massive MIMO has been a key component for achieving such a high throughput promised by 5G/NR. So you may guess that Enhancement of Massive MIMO would be for even higher throughput, but it is not. In terms of throughput, we already have almost all the capability with Release 15. We already got max 8 CC CA in FR2 and 256 QAM. The only remaining technology to push up the throughput even further would be 2 codewords in both FR1 and FR2, 8 layers in FR1 and 400 Mhz bandwidth in FR2, but it doesn't seem to be the target for Release 16.
Major focus for Release 16 is to increase the stability of MIMO connection and more robust recovery process for beam failure.
The list of the feature to enhance Massive MIMO in Release 16 in comparison to Release 15 is described as follows in RP-200474 and Ref .
Multi TRP (Transmission and Reception Point)
One of the most frequently mentioned feature related to enahanced massive MIMO would be the featured called Multi TRP. This is a feature that enable gNB to use more than one TRP to communicate to a UE. There are a couple of different ways for this type of communication and it can be summarized as in the following illustration.
(A) TRP1 and TRP2 is transmitting two two different PDSCH but control signal (PDCCH/DCI) for the two PDSCH is transmitted by TRP1. In this case, if there is some problem in radio link with TRP1 and PDCCH reception fails, the communication via TRP2 is impacted as well.
(B) TRP1 and TRP2 is transmitting two two different PDSCH and each TRP is transmitting its own corresponding PDCCH/DCI. In this case, if there is any problem in radio link with one of the TRPs, the communication via other TRP can be intact.
(C) This scenario shows the case where TRP1 and TRP2 is used to jointly process the DL and UL signal (Similar scenario as CoMP)
Codebook Type II Enhancement
This is not a new feature. It is an enhanced feature for an existing feature. Type II codebook is already there in Release 15. Then what will be changed in Release 16 ? Unfortunately it is not each to precisely point out the difference unless you look into the codebook equation itself.
A new DMRS sequence is introduced in release 16 mainly which can be summarized as below.