Reducing Channel Dimension in MU-MIMO Explicit Feedback Operation September 2010 doc.: IEEE 802.11-10/1114r1 September 2010 Reducing Channel Dimension in MU-MIMO Explicit Feedback Operation Date: 2010-09-15 Authors: Nir Shapira et al, Celeno Communications

September 2010 doc.: IEEE 802.11-10/1114r1 September 2010 Abstract Explicit sounding 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

DR Principles – AP Allocation September 2010 doc.: IEEE 802.11-10/1114r1 DR Principles – AP Allocation September 2010 AP controls the maximum dimension size per user (MU mode) Enables AP to control maximum feedback overhead AP makes grouping decisions, hence should be able to control dimension AP has knowledge of all users’ channels, hence can make globally optimal dimension decision User sees only narrow part of full composite channel User can still decide to further reduce dimension In case of LOS or ill conditioned channels For power save reasons Nir Shapira et al, Celeno Communications

DR Principles – User Reduction September 2010 doc.: IEEE 802.11-10/1114r1 DR Principles – User Reduction September 2010 User makes reduction operation on sounding 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, depending on type of feedback, amongst them: Opt 1 (V/CV feedback): return first rows corresponding to best eigenmodes of V matrix Opt 2 (V+S feedback): return first rows corresponding to best eigenmodes of V & S matrices (best DR option) Opt 3 (CSI FB): receive chain (antenna) selection. User deletes rows of unused antennas from CSI matrix Opt 4 (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

Dimension Reduction Control September 2010 doc.: IEEE 802.11-10/1114r1 September 2010 Dimension Reduction Control NDPA frame was defined for NDP announcement [3] NDPA already include a list of stations ids to be sounded We suggest to add to NDPA a list of dimension allocation, one for each participating user Gives AP maximum flexibility in dimension allocation AP can occasionally sound individual users for full channel rank to update dimension allocation decision Nir Shapira et al, Celeno Communications

Resolvable and non-Resolvable LTFs September 2010 doc.: IEEE 802.11-10/1114r1 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 802.11-10/1114r1 September 2010 Straw Poll #1 Do you support adding the following sentence to the Specifications Framework document: “A user shall have the ability to reduce the feedback dimension from the sounded dimensions with explicit MU-MIMO feedback”? Nir Shapira et al, Celeno Communications

September 2010 doc.: IEEE 802.11-10/1114r1 September 2010 Straw Poll #2 Do you support enabling the AP to allocate the maximum explicit feedback dimension for each user in MU-MIMO operation? Nir Shapira et al, Celeno Communications

September 2010 doc.: IEEE 802.11-10/1114r1 September 2010 Straw Poll #3 Do you support adding TBD dimension allocation information per user in MU-MIMO operation to the NDPA frame, and update the Specifications Framework document accordingly? Nir Shapira et al, Celeno Communications

September 2010 doc.: IEEE 802.11-10/1114r1 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 [3] Simone Merlin, et. al., Protocol for SU and MU Sounding Feedback, TGac, IEEE 802.11-10/1091 Nir Shapira et al, Celeno Communications