OBSS reuse mechanism which preserves fairness

1. OBSS reuse mechanism which preserves fairness Date: 2014-09-15 Authors: Imad Jamil (Orange)

2. Context • It has been shown in many presentations that CCA adaptation (DSC, fixed CCA) can lead to very strong per-user throughput increase in dense environments (multiple x-times improvements) • We look at it for a planned freq reuse 3 deployment (close to scenario 3), • In 523r0, we demonstrated the benefits of DSC, but show some fairness warning (even for 11ax devices) • In this presentation • We present fairness analysis with different CCA adaptation (DSC, fixed CCA), with TPC • We propose a mode that optimizes both area throughput and fairness Imad Jamil (Orange)

3. September 2014 How to improve fairness (1/2)with CCA adaptation • DSC presents unfairness issues at saturation state, linked to the fact that different users have different CCA parameters • How to improve fairness? • 1: DSC unfairness can be improved by tuning the max CCA threshold • 2: CCA can also be fixed for the entire zone • We propose to compare these approaches and evaluate fairness • between 11ax STAs • with regards to legacy STAs

4. Simulation scenario Close to scenario 3 - First tier only (7 BSSs), 8 STAs per BSS, frequency reuse 3 pattern Tx : 15 dBm [21 m] [7 m] Tx :15 dBm Imad Jamil (Orange)

5. Simulation scenario PHY • IEEE 802.11n • Path Loss: ITU UMi (23.3+36.7log10(d)+ 21log10(2400/900MHz)) • Band: 5 Ghz • Channel: 20 MHz • Tx power: 15 dBm Traffic • Full buffer UDP traffic • DL (AP->STA): 4Mbps per STA • UL (STA->AP): 4Mbps per STA Metric Aggregate throughput, per user throughput CDF Rate adaptation AARF with selection of set of MCSs (link adaptation) Parameters Imad Jamil (Orange)

6. 1 - DSC fairness improvements with max CCA threshold optimization • UnfairnessbetweenSTAs at different range in UL • Wechanged the max CCA threshold to limit the CCA differencebetweenSTAs, whichlimits the unfairness margin 20dB Max CCA -50dBm margin 20dB Max CCA -40dBm STAs at 3m: CCA=-50dBm STAs at 5m: CCA =-60dBm APs: CCA =-60dBm STAs at 3m: CCA=-40dBm STAs at 5m: CCA =-60dBm APs: CCA =-60dBm

7. 2 - Fairness comparison with Fixed CCA • Same simulation scenario (7 11ax, 1 legacy per AP), comparing: • fixed CCA: -82, -70, -60, -50dBm • DSC with max CCA threshold (-50dBm): (STAsat 3m: CCA=-50dBm, STAsat 5m: CCA =-60dBm, APs: CCA =-60dBm) UL User throughput CDF results for 11ax devices: Curve slope is a good indication of fairness -82 -70 -60: best fixed CCA CCAC: DSC -50 11ax STAs legacy STAs

8. 2 - Fairness comparison with Fixed CCA • Conclusion: at saturation state: • fixed CCA is not more fairthan DSC between 11ax STAs • fixed CCA isunfairwithlegacydevices • itwillbe more unfair in unmanagedenvironments or withlargercells Without legacy STAs With legacy STAs

9. How to improve fairness (2/2)joint CCA/TPC adaptation • DSC and TPC both present unfairness issues, linked to the fact that different users have different CCA/TP parameters • CCA control favors 11ax, TP control favors legacy STAs • How to improve fairness? • propose a scheme that adapts both CCA and TP, following a specific rule • in order that each mechanism (CCAC and TPC) counteracts the unfairness from the other

10. Reuse scheme: balanced CCAC/TPCExample with an equal modification of CCA and TP • STA calculates a Delta_x value, whichis the amount of dB by which CCA and TP willbechanged • thisdelta_x value wouldbeequal to delta_CCA if CCA adaptation onlyisperformed and to delta_TP if TPC onlyisperformed • if the STA uses the concept of DSC on this first Delta_xcalculation, we have: Delta_x = Rx_power – Margin – standard_CCA (ex: Margin= 20dB, standard_CCA = -79dBm for 40MHz) • STA applies a specific formula for the calculationof delta_CCA and delta_TP, based on Delta_x • in ourexample, weconsidered the rule as being an equal change of CCA and TP Delta_CCA=Delta_TP=Delta_x / 2 • STA applies CCA adaptation usingDelta_CCA • STA requests AP to apply TP adaptation usingDelta_TP • or applies TP adaptation usingDelta_TP

11. Fairness comparison with balanced CCAC/TPC (1/4) • Same simulation scenario, comparing: • best fixed CCA: -60 dBm • DSC with max CCA threshold (-50dBm): (STAsat 3m: CCA=-50dBm, STAsat 5m: CCA =-60dBm, APs: CCA =-60dBm) • TPC • balanced CCAC/TPC (equal change between CCA and TP) Aggregate throughput results, with and without legacy devices : All solutions present similar results (expect TPC, which collapses in the presence of legacy devices Without legacy devices: 8 11ax STAs per AP With legacy devices: 7 11ax STAs and 1 legacy STA per AP 11ax reuse mechanisms No reuse mechanisms TPC in presence of legacy devices

12. Fairness comparison with balanced CCAC/TPC (2/4) • Same simulation scenario, comparing: • best fixed CCA: -60 dBm • CCAC: DSC with max CCA threshold (-50dBm): (STAsat 3m: CCA=-50dBm, STAsat 5m: CCA =-60dBm, APs: CCA =-60dBm) • TPC • balanced CCAC/TPC (equal change between CCA and TP) UL User throughput CDF results for 11ax devices: Curve slope is a good indication of fairness Balanced CCAC/TPC and TPC Balanced CCAC/TPC DSC and fixed CCA DSC and fixed CCA Without legacy STAs (8 11ax STA per AP) With legacy STAs (7 11ax STA and 1 legacy STA per AP

13. Fairness comparison with balanced CCAC/TPC (3/4) • Same simulation scenario, comparing: • best fixed CCA: -60 dBm • DSC with max CCA threshold (-50dBm): (STAsat 3m: CCA=-50dBm, STAsat 5m: CCA =-60dBm, APs: CCA =-60dBm) • balanced CCAC/TPC (equal change between CCA and TP) DSC UL User throughput CDF results for legacy devices: Balanced CCAC/TPC Legacy throughput are better preserved than with DSC legacy STAs throughput (7 11ax STA and 1 legacy STA per AP)

14. Fairness comparison with balanced CCAC/TPC (4/4) • Conclusion: • Balanced CCAC/TPC seems the best solution with regards to fairnessbetween 11ax and withlegacydevices • It givesequal area throughput gains than CCAC (DSC, fixed CCA..) and TPC • Furtheradvantages: • It preserves the benefit of beingdirectlybeneficial for the STA to implement (compared to TPC) • It canbevery simple to define in 11ax: • wecandefine in 11ax only the proportion rule to respect betweenDelta_CCA and Delta_TPC: givesevery STA the possibility to use itsownalgorithm(need to seewhat proportion ruleis the optimum) • this proportion rulecouldbeparametrized in case of a managed network (need simulations to evaluate if different proportion rules are requireddepending on the environments, or depending on the proportion of legacy/11ax devices) • Note thatsuch proportion rulewouldneed to beadaptedwhencombinedwith UL OFDMA and UL MU-MIMO, as TP adaptation willberequiredalso for thoseschemes.

15. Conclusion • Fairness has to beconsidered for OBSS reusemechanisms • even if itonly arises at saturation state • Fairnessanalysiswith CCA control • Wepreviouslyshowedfairness issues with DSC • fixedCCA is not more fairthan DSC between 11ax STAs • fixed CCA isunfairwithlegacydevices • New solution to consider: balanced CCAC/TPC • in our simulation scenario, BalancedCCAC/TPC performswaybetterwith regards to fairnessbetween 11ax and withlegacydevices • and It givesequal area throughput gains than CCAC (DSC, fixed CCA..) and TPC • Need to evaluateit on other scenarios, and to optimize the ratio between CCAC and TPC Imad Jamil (Orange)

16. Annex

17. DSC algorithm • DSC (CCA control): • each STA adjust its CCA to CCA = Useful Rx Power – Margin • AP adjust its CCA to CCA = Useful Rx Power from further STA - Margin • CCA adapation is caped by max CCA value (upper limit) margin 20dB Max CCA -50dBm margin 20dB Max CCA -40dBm STAs at 3m: CCA=-50dBm STAs at 5m: CCA =-60dBm APs: CCA =-60dBm STAs at 3m: CCA=-40dBm STAs at 5m: CCA =-60dBm APs: CCA =-60dBm Imad Jamil (Orange)

18. TPC algorithm • TPC (Transmit Power control): • eachreceiving STA requeststransmitting STA to adjustits TP sothat Rx Power = CCA + Margin • Wetook a margin of 20dB Imad Jamil (Orange)