Reducing Channel Dimension in MU-MIMO CSI Feedback September 2010 doc.: IEEE 802.11-10/1114r0 September 2010 Reducing Channel Dimension in MU-MIMO CSI Feedback Date: 2010-09-15 Authors: Nir Shapira et al, Celeno Communications

September 2010 doc.: IEEE 802.11-10/1114r0 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

Explicit DR Principles September 2010 doc.: IEEE 802.11-10/1114r0 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

Detailed Suggestion AP allocates dimension size νk per user September 2010 doc.: IEEE 802.11-10/1114r0 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

Override Reduction Option September 2010 doc.: IEEE 802.11-10/1114r0 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

Resolvable and non-Resolvable LTFs September 2010 doc.: IEEE 802.11-10/1114r0 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

September 2010 doc.: IEEE 802.11-10/1114r0 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 802.11-09/0992)? Nir Shapira et al, Celeno Communications

September 2010 doc.: IEEE 802.11-10/1114r0 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 802.11-09/0992)? Nir Shapira et al, Celeno Communications

September 2010 doc.: IEEE 802.11-10/1114r0 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 802.11-09/0992)? Nir Shapira et al, Celeno Communications

September 2010 doc.: IEEE 802.11-10/1114r0 September 2010 References [1] Nir Shapira, et. al., Channel Dimension Reduction in MU Operation, TGac, IEEE 802.11-10/0803r0 [2] Joonsuk Kim, et. al., Group ID Concept for Downlink MU_MIMO Transmission, TGac, IEEE 802.11-10/0073 Nir Shapira et al, Celeno Communications