1. Reducing Channel Dimension in MU-MIMO CSI Feedback
September 2010
doc.: IEEE /1114r0
September 2010
Reducing Channel Dimension in MU-MIMO CSI Feedback
Date:
Authors:
Nir Shapira et al, Celeno Communications

2. September 2010
doc.: IEEE /1114r0
September 2010
Abstract
CSI feedback overhead is a major issue in MU mode effectiveness
Last meeting [1] was presented. Reducing channel dimension per user was shown as a good method for grouping MU users for increased performance
Explicit Dimension Reduction (DR) was defined – AP notifies each user on its allocated dimension size
[1] showed that DR done locally by user has good performance with less management overhead
In this submission we present detailed suggestion for inclusion in Specification Framework document
Nir Shapira et al, Celeno Communications

3. Explicit DR Principles
September 2010
doc.: IEEE /1114r0
Explicit DR Principles
September 2010
AP controls just the dimension size per user
AP sends dimension νk to the k’th user
νk ≤nk (nk number of user antennas)
User makes reduction operation on CSI feedback
User only sees channel from AP to user. DR decision is suboptimal
Simulations show ([1]) performance loss vs. a “know-all” user is small
User has several options to reduce dimension, amongst them:
Opt 1 (V/CV feedback): return first rows corresponding to best eigenmodes of V matrix
Opt 2 (CSI FB): receive chain (antenna) selection. User deletes rows of unused antennas from CSI matrix
Opt 3 (CSI FB) : Eigen-mode selection. User returns rows corresponding to largest eigenmodes of effective channel , where U is the receive matrix in the SVD of the channel matrix (H=UDV*)
Nir Shapira et al, Celeno Communications

4. Detailed Suggestion AP allocates dimension size νk per user
September 2010
doc.: IEEE /1114r0
September 2010
Detailed Suggestion
AP allocates dimension size νk per user
Allocation is part of MU group definition ([2]).
Allocation can be changed using dedicated action frame for dimension control:
Each user returns a channel of dimension νk as a response to subsequent NDPs
In case user belongs to several MU groups, it can have a different reduced dimension in each group
Group ID
AID1
AID2 …
AIDN ν1 ν2 … νN
AID stands for Associated Identifier
AID may be replaced by some other field that identifies STAs
Group ID ν1 ν2 … νN
Nir Shapira et al, Celeno Communications

5. Override Reduction Option
September 2010
doc.: IEEE /1114r0
September 2010
Override Reduction Option
Add bit in HTC field in sounding announcement to indicate DR override for the upcoming NDP
Enables AP to occasionally sound entire channel without having to redefine MU group
Nir Shapira et al, Celeno Communications

6. Resolvable and non-Resolvable LTFs
September 2010
doc.: IEEE /1114r0
September 2010
Resolvable and non-Resolvable LTFs
With resolvable LTFs DR operation mainly effects sounding operation
AP is free to make any further DR decision on top of Users’. User can detect actual DR operation from LTFs in each DL-MU frame
In the non-resolvable case the AP must use entire reduced channel as returned by user
User must store DR information (DR receive matrix) for proper MU packet decoding
Nir Shapira et al, Celeno Communications

7. September 2010
doc.: IEEE /1114r0
September 2010
Straw Poll #1
Do you support adding dimension reduction capabilities, whereby the AP allocates dimension size per user and user performs dimension reduction operation to the specifications framework document (IEEE /0992)?
Nir Shapira et al, Celeno Communications

8. September 2010
doc.: IEEE /1114r0
September 2010
Straw Poll #2
Do you support controlling dimension size allocation by adding fields to MU Group definition frame, and by a specific Dimension Allocation action frame, as detailed in slide 4, to the specifications framework document (IEEE /0992)?
Nir Shapira et al, Celeno Communications

9. September 2010
doc.: IEEE /1114r0
September 2010
Straw Poll #3
Do you support adding a Reduction Override bit to NDP Announcement to enable AP to sound entire channel as detailed in slide 5, to the specifications framework document (IEEE /0992)?
Nir Shapira et al, Celeno Communications

10. September 2010
doc.: IEEE /1114r0
September 2010
References
[1] Nir Shapira, et. al., Channel Dimension Reduction in MU Operation, TGac, IEEE /0803r0 [2] Joonsuk Kim, et. al., Group ID Concept for Downlink MU_MIMO Transmission, TGac, IEEE /0073
Nir Shapira et al, Celeno Communications