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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 [1].

 

Release 15

Release 16

Support of Beam-Based Operation  
CSI codebook : Upto 32 ports  
CSI Type I Codebook : Basic Closed Loop MIMO  
CSI Type II Codebook : High Resulution, MU-MIMO

Enhanced Type II Codebook

  • Overhead reduction by compressing the CSI report in the frequency domain.
  • Extending the CSI type II codebook to rank larger than two
 

Multi-TRP/Multi-Panel transmission enhancements

  • Single PDCCH scheduling multiple TRP
  • Individual PDCCH scheduling each individual TRP
  • Uplink control signaling for non-coherent joint transmission
  • Max two TRP/panel for simultaneous multi-TRP/panel reception
 

Multi-beam operation enhancement

  • Reduced latency and overhead
  • Beam Failure Recovery for SCell
  • Measurement Report of L1-SINR
 

Low PAPR Reference Signal

  • New Sequences for PDSCH/PUSCH DMRS
  • New DMRS sequences for PI/2-BPSK-based PUSCH/PUCCH

 

 

 

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.

  • Number of supported layers is increased from 2 (Rel 15) to 4 (Rel 16).
  • Codebook itself will get more sophisticated in Rel 16 comparing to Rel 15. This would not look obvious unless you analyze the codebook equation to the very detailed level. I did this analysis in my codebook page. If you take a close at the equation and compare it to Rel 15 equation, you would notice that the granularity of amplitude and phase parameter is improved in Rel 16.

 

 

 

 

 

 

PDSCH DMRS

 

A new DMRS sequence is introduced in release 16 mainly which can be summarized as below.

 

 

 

 

Reference :

 

[1] The 5G Evolution:3GPP Releases 16-17 (5G Americas)