1. doc.: IEEE 802.11-10/0487r1 Submission May 2010 Slide 1 Scheduled Spatial Reuse with Collaborative Beamforming Date: 2010-05-16 Authors: Thomas Derham, Orange Labs

2. doc.: IEEE 802.11-10/0487r1 Submission Abstract May 2010 Slide 2Thomas Derham, Orange Labs Spatial reuse is a key aim for 802.11ad [1] –potentially a major increase in aggregate data throughput within a PBSS –mutual interference mitigated by directional antennas Beamforming capability of phased-array antennas can be used to our advantage to optimally mitigate interference –Antenna Weight Vectors (AWVs) can be determined that are optimized taking into account mutual interference due to spatial reuse –based on simple extension of Beam Refinement Procedure (BRP) [2] –resulting SINR of each link can be accurately predicted and used by PCP as the basis for co-scheduling (in addition to Directional Channel Quality reports) Substantial increase in throughput; low complexity and impact

3. doc.: IEEE 802.11-10/0487r1 Submission A typical 802.11ad usage scenario May 2010 Slide 3Thomas Derham, Orange Labs Home Gateway Set-top box Media server FTTH repeater BSS in dense networks, multiple links must share the same channel –but one uncompressed HD video link can exhaust all bandwidth in one channel –video links tend to be continuously active over extended periods –spatial reuse necessary to support all links (e.g. video + data) [3]

4. doc.: IEEE 802.11-10/0487r1 Submission Scheduled spatial reuse May 2010 Slide 4Thomas Derham, Orange Labs beaconservice periods (SPs) contention-based period (CBP) beacon interval (BI) CSMA/CATDMA high-QoS data transmissions are generally scheduled in SPs –since CSMA/CA is inefficient with directional antennas [4] –PCP (PBSS Control Point) schedules SPs and transmits the beacon [5] spatial reuse: PCP may co-schedule overlapping SPs (e.g. 2x spatial reuse) STA1 STA2 STA3 STA4 STA1 => STA2 STA3 => STA4

5. doc.: IEEE 802.11-10/0487r1 Submission Example of co-scheduling process May 2010 Slide 5Thomas Derham, Orange Labs PCP STA1 STA2 STA3 STA4 Extended mmWave TSPEC (Src STA = 3), Dest STA = 4, Length = x Extended Schedule (1) Src STA = 1, Dest STA = 2, Start = 0, Length=x’ (2) Src STA = 3, Dest STA = 4, Start = 0, Length=x (1)STA3 requests SPs for link STA3=>STA4 by sending “Extended mmWave TSPEC” to PCP (2)If no free time in BI, PCP sends “Spatial Reuse BRP Request” to the STAs of a subset of links (STA1=>STA2, STA3=>STA4) that it is considering to co-schedule (3)STAs perform BRPs with other STAs in the subset to determine optimal AWVs (4)Receiver STAs (STA2, STA4) send “Spatial Reuse SINR Report” to PCP (5)PCP determines scheduling (all/part of subset), broadcasts “Extended Schedule” Spatial Reuse BRP Request Co-scheduled links: STA1=>STA2, STA3=>STA4 Spatial Reuse SINR Report SINR 1,2, SINR 3,4 STA1 => STA2 < x STA1 => STA2 STA3 => STA4

6. doc.: IEEE 802.11-10/0487r1 Submission PCP determines a subset of links that it is considering to co-schedule May 2010 Slide 6Thomas Derham, Orange Labs based on two metrics that approximately indicate spatial separation –metrics already known by PCP, so no additional overhead –large receiver spatial separation => greater chance links can be co-scheduled PCP angular separation is beamforming vector used by PCP for PCP Rx STA of ith link range separation is channel strength for PCP Rx STA of ith link

7. doc.: IEEE 802.11-10/0487r1 Submission Each Tx STA performs BRP with all Rx STAs in the subset to determine optimal Tx AWV May 2010 Slide 7Thomas Derham, Orange Labs Tx STA initiates transmit beam refinement with each Rx STA in turn –i.e. Tx STA1 performs transmit BRP for both its own link (STA1=>STA2) and the “cross-link” it may interfere with (STA1=>STA4) Rx STA shall fix its beam to the best known AWV for its own link –all links have already done conventional beam training –i.e. Rx STA4 fixes its beam to AWV chosen in previous SLS/BRP with STA3 Tx STA cycles through an orthogonal codebook matrix of AWVs –CSI “Channel Measurement”/“Tap Delay” fed back for each AWV in codebook STA1 STA2 STA3 STA4 link cross-link Rx beam fixed to best AWV for STA3=>STA4 link TRN-T transmitted M times (number of Tx elements)

8. doc.: IEEE 802.11-10/0487r1 Submission Each Tx STA performs BRP with all Rx STAs in the subset to determine optimal Tx AWV (2) Tx STA estimates effective MISO channel –e.g. MIMO channel model for subcarrier i: –transmit-side spatial covariance matrix of MISO channel given by: Tx STA calculates optimal AWV using max-SLNR criterion –Signal to Leakage & Noise Ratio: “leakage” is interference caused to other Rx May 2010 Thomas Derham, Orange LabsSlide 8 codebook of Tx AWVs MIMO channel fixed Rx AWV channel estimates for Tx AWVs “cross-link” to qth Rx STAown link (eig{X} is dominant eigenvector of X)

9. doc.: IEEE 802.11-10/0487r1 Submission Each Rx STA performs BRP with all Tx STAs in the subset to determine optimal Rx AWV May 2010 Slide 9Thomas Derham, Orange Labs Rx STA initiates receive beam refinement with each Tx STA in turn –i.e. Rx STA2 performs receive BRP for both its own link (STA1=>STA2) and the “cross-link” that may cause it interference (STA3=>STA2) Tx STA shall fix its beam to the best known AWV for its own link –determined in previous stage –i.e. Tx STA3 fixes its beam to AWV chosen for use with STA4 Rx STA cycles through an orthogonal codebook matrix of AWVs STA1 STA2 STA3 STA4 TRN-R transmitted N times (number of Rx elements) Tx beam fixed to best AWV for STA3=>STA4 link link cross-link

10. doc.: IEEE 802.11-10/0487r1 Submission Each Rx STA performs BRP with all Tx STAs in the subset to determine optimal Rx AWV (2) Rx STA estimates effective SIMO channel –e.g. MIMO channel model for subcarrier i: –receive-side spatial covariance matrix of SIMO channel given by: Rx STA calculates optimal AWV using max-SINR criterion –Signal to Interference & Noise Ratio: “interference” is caused by other Tx May 2010 Thomas Derham, Orange LabsSlide 10 fixed Tx AWV MIMO channel codebook of Rx AWVs channel estimates for Rx AWVs “cross-links” from pth Tx STAown link (eig{X} finds dominant eigenvector of X)

11. doc.: IEEE 802.11-10/0487r1 Submission Each Rx STA sends SINR report to PCP and PCP determines scheduling May 2010 Slide 11Thomas Derham, Orange Labs Rx STA calculates SINR assuming subset is co-scheduled PCP schedules links based on these SINRs –links are co-scheduled (overlapping SPs) if all SINR are above a threshold –threshold may be chosen according to QoS requirement for that link –if one or more SINRs are too low, two choices: –(a) remove dominant interfering pair (lowest SLNR) and retry, or –(b) perform iteration of Tx-side and Rx-side BRP and AWV calculation –since optimal Rx AWV are conditional on Tx AWV, and vice versa own link “cross-links” from pth Tx STA

12. doc.: IEEE 802.11-10/0487r1 Submission System-level simulation setup May 2010 Slide 12Thomas Derham, Orange Labs ParameterValue Transmit power+10 dBm Noise figure10 dB Bandwidth2 GHz Antennas4x4 uniform 2D phased arrays Link to system level interface Link level: reference OFDM PHY with LDPC Target PER = 0.1 (effective SNR from MIESM) Traffic modelFull buffer Scheduler2 iterations of Tx/Rx BRP and AWV calculation. Links dropped from subset until all SINR>threshold conference room model –inter-cluster parameters between all pairs of STAs from ray-tracing [7] –correctly models interference between all STAs –TGad channel model code used for intra-cluster parameters [8] Link-n

13. doc.: IEEE 802.11-10/0487r1 Submission STA positions as per Evaluation Methodology May 2010 Slide 13Thomas Derham, Orange Labs –3 STA-STA pairs on table [9]: STA2=>1 (LoS), STA3=>5 (NLoS), STA7=>8 (LoS) –STA-AP links ignored; STA5=>STA3 ignored since direct leakage with STA3=>5 not modeled –beamforming: (a) conventional training, (b) collaborative beamforming complementary CDF of aggregate throughputcomplementary CDF of number of co-scheduled links no. of co-scheduled links increased in approx. 80% of channel instances SINR threshold: 4 dB aggregate throughput increased by 40% @P r =0.5

14. doc.: IEEE 802.11-10/0487r1 Submission STA positions randomized on table May 2010 Slide 14Thomas Derham, Orange Labs –10 pairs of STAs on 2.5 x 1 m table (random orientation) ==> dense network –note: not all pairs are simultaneously active (due to scheduler SINR rule) –beamforming types: (a) conventional training, (b) collaborative beamforming complementary CDF of aggregate throughputcomplementary CDF of number of co-scheduled links SINR threshold: 4 dB aggregate throughput increased by 70% @P r =0.5

15. doc.: IEEE 802.11-10/0487r1 Submission STA positions randomized on table May 2010 Slide 15Thomas Derham, Orange Labs –10 pairs of STAs on 2.5 x 1 m table (random orientation) ==> dense network –note: not all pairs are simultaneously active (due to scheduler SINR rule) –beamforming types: (a) conventional training, (b) collaborative beamforming complementary CDF of aggregate throughputcomplementary CDF of number of co-scheduled links SINR threshold: 9.5 dB aggregate throughput increased by 60% @P r =0.5

16. doc.: IEEE 802.11-10/0487r1 Submission Supporting scheduled spatial reuse with collaborative beamforming in 802.11ad May 2010 Slide 16Thomas Derham, Orange Labs provide basic framework to allow implementation –(1) a field in BRP request which tells the responder STA to fix its AWV to the best known beam for communicating with a specified STA –(2) a supporting STA should maintain a table of best known AWVs for communicating with each STA when specified other links are co-scheduled –e.g. transmitter AWVs receiver AWVs AWVPaired receiver STACo-scheduled links w1w1 STA2none w2w2 STA2STA3=>4 w3w3 STA2STA5=>6 w4w4 STA2STA3=>4; STA7=>8 w5w5 STA3none... AWVPaired receiver STACo-scheduled links d1d1 STA2none d2d2 STA2STA3=>4 d3d3 STA2STA5=>6 d4d4 STA2STA3=>4; STA7=>8 d4d4 STA3none...

17. doc.: IEEE 802.11-10/0487r1 Submission Supporting scheduled spatial reuse with collaborative beamforming in 802.11ad (2) May 2010 Slide 17Thomas Derham, Orange Labs to allow control by PCP –(1) support “Spatial Reuse BRP Request” for both Tx and Rx sides –from PCP to Tx/Rx STAs –(2) support “Spatial Reuse SINR Report” –from Rx STAs to PCP complementary to existing beamforming (SLS/BRP) and measurement reports –predicted SINR reports are more accurate than Directional Channel Quality –not affected by bursty traffic –based on the responder AWV that will actually be used

18. doc.: IEEE 802.11-10/0487r1 Submission Overhead and complexity May 2010 Slide 18Thomas Derham, Orange Labs small additional overhead to perform cross-link BRPs, but... –can allow PCP implementation (or STA) to manage overhead tradeoff –spatial reuse always involves some additional measurements, so is best targeted to low mobility channels (many realistic 11ad scenarios) –all Rx STAs could simultaneously “listen” to TRN if framework supported it computational complexity reduced due to efficient algorithms –calculate AWVs –division by Hermitian matrix, e.g. Cholesky factorization –find dominant eigenvector, e.g. power iteration method –calculate SINRs for scheduling –matrix multiplication

19. doc.: IEEE 802.11-10/0487r1 Submission Conclusion May 2010 Slide 19Thomas Derham, Orange Labs A method of scheduled spatial reuse with collaborative beamforming is proposed –significantly increases aggregate throughput –significantly increases the number of concurrent links that are supported –scheduling guarantees the QoS of each link Low complexity, overhead and impact –only provide framework to enable implementations –shown that low complexity implementations are possible –complementary to existing beamforming and measurement mechanisms

20. doc.: IEEE 802.11-10/0487r1 Submission References May 2010 Slide 20Thomas Derham, Orange Labs [1] C. Cordeiro et al, “Spatial Reuse and Interference Mitigation in 60 GHz”, 802.11- 09/0782r0 [2] C. Cordeiro et al, “PHY/MAC Complete Proposal Specification”, 802.11-10/0433r0 [3] M. Park et al, “QoS Considerations for 60 GHz Wireless Networks, Globecom 2009 [4] S. Nandagopalan et al, “MAC Channel Access in 60 GHz”, 802.11-09/0572r0 [5] C. Cordiero et al, “Implications of Usage Models on TGad Network Architecture”, 802.11-09/0391r0 [6] M. Lim et al, “Spatial Multiplexing in the Multi-user MIMO Downlink Based on Signal-to-Leakage Ratios”, Globecom 2007 [7] M. Park et al, “TGad Interference Modeling for MAC Simulations”, 802.11-10/0067r0 [8] A. Maltsev et al, “Channel Models for 60 GHz WLAN Systems”, 802.11-09/0334r7 [9] E. Perahia et al, “Evaluation Methodology”, 802.11-09/0296r16

21. doc.: IEEE 802.11-10/0487r1 Submission Appendix an additional usage case - two STAs in each device Slide 21Thomas Derham, Orange Labs effectively MxN spatial multiplexing with max. rank 2 –“SU-MIMO” for additional throughput with strong multipath channel –e.g. “bottlenecks” to/from repeater –“MU-MIMO” to allow simultaneous communication between central point and two different destinations –e.g. multi-stream video from media server –the same collaborative beamforming technique optimizes AWVs to minimize interference