1. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Determination of Ng in MU mode (CID 3432) Date: 2011-01-05 Authors: Slide 1

2. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Abstract We suggest means to facilitate usage of Ng<4 in MU mode Slide 2

3. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Problem Description In current draft BFee can use any Ng value in both SU and MU –Ng value is not conveyed in advance to BFer BFer is “surprised” by Ng value in each new Beamforming Matrix report Using Ng<4 incurs high complexity in case where user is first in NDPA list and needs to reply within SIFS –It is expected many vendors will opt for Ng=4 to reduce complexity –Users that reply to a Poll should have no problem using Ng<4 Ng value has implications on performance in MU mode –A small Ng value involves high protocol overheads –A large Ng value impacts performance ([1], and slides ahead)  Ng value should be taken into account in MU grouping decision Slide 3

4. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Discussion Only the AP has the full picture of the implications of Ng value, in terms of both MU performance (since it depends on stream/power allocation for all users), and feedback overhead Optimal Ng value should be determined dynamically according to SNR, group size, stream allocation, overhead (sounding frequency), channel flatness, etc. From feedback overhead perspective, determination of matrix dimension size and tone grouping should be taken jointly. While it is true that a user with Ng=4 harms its own performance, if all users tend to use Ng=4, the entire network performance will be impacted and MU mode effectiveness will be seriously compromised Slide 4

5. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Simulation Results We show effect of grouping with a 4T Bfer and three users in channel D. Each user is served by one stream. Performance of single antenna users is compared to that of dual antenna users Degradation effect of Ng=4 is drastic with single antenna users. Interference cancelation in dual antenna users partially limits loss Slide 5

6. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Simulation Results, cont’ With 4 users, effect is even more drastic Ng=2 performance is almost identical to Ng=1. Ng=4 is distinctively inferior Usage of Ng=1 or 2 enables single antenna clients to effectively participate in MU-MIMO operation Slide 6

7. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Impact on Single Antenna User, cont’ Usage of Ng=4 degrades 2-antenna users’ performance to that of a single antenna user employing Ng=1 Would be a pity to invest in 2 RF chains and get the effective performance of a single antenna device in MU mode Slide 7

8. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Suggested Solution We suggest two alternative solutions Solution A: –Ng Value in MU mode must be less than 4 (can be 1 or 2) –Optionally, BFer sends a bit per user in NDPA to signal “Ng=4 allowed” (to control overhead in cases where Ng=4 is tolerable). If set, BFee is encouraged to use Ng=4 Solution B: –BFer sends bit per user in NDPA to signal “Ng=4 allowed” –In case the bit is not set, a BFee that cannot reply with Ng<4 (for whatever reason) returns a Null VHT Compressed Beamforming Report (Remaining Segments = 7) –No need for BFee to declare Ng capabilities in advance Slide 8

9. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Signaling “Ng=4 Allowed” in NDPA Use one reserved bit in Sounding Sequence field to signal:  0 – Nc index in STA Info field has 3 bits (as in spec today)  1 – Nc index in STA Info field has 2 bits (max Nc=3). The remaining bit signals “Ng=4 allowed” In SU mode STA Info field remains as in spec today Slide 9 B13 signals “Ng=4 Allowed”

10. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Summary We showed simulation results indicating usage of Ng=4 will seriously compromise MU performance Two alternative solutions were presented to enable BFer to get matrix with Ng<4 when needed “Ng=4 Allowed” bit per user was suggested in NDPA The suggested schemes do not impact SU operation Slide 10

11. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Straw Poll 1 Do you support mandating BFee support for Ng<4 in MU mode? Slide 11

12. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Straw Poll 2 Do you support mandating BFee support for Ng<4 in MU mode and dedicating a bit in STA Info field in NDPA to indicate “Ng=4 allowed”? Slide 12

13. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications Straw Poll 3 Do you support dedicating a bit in the STA Info field in the NDPA frame to indicate “Ng=4 allowed” and that a STA that is unable to comply to this dictum will feedback an empty VHT Compressed Beamforming Report frame? Slide 13

14. doc.: IEEE 802.11-11/0995r0 Submission July 2011 Nir Shapira, Celeno Communications References [1] Hongyuan Zhang et al. “11ac Explicit Sounding and Feedback”, 11-10-1105-01-00ac-explicit- sounding-and-feedback.ppt, Nov 2010 Slide 14