doc.: IEEE 802.11-14/1207r0

Submission Imad Jamil (Orange)Slide 1

OBSS reuse mechanism which preserves fairness

Date: 2014-09-15

Name Company Address Phone email Imad Jamil Orange 4 rue du clos Courtel

35512 Cesson Sévigné France

imad.jamil@orange.com

Laurent Cariou Orange 4 rue du clos Courtel 35512 Cesson Sévigné France

+33 299124350 Laurent.cariou@orange.com

Thomas Derham Orange 9F Keio Shinjuku Oiwake Bldg. Shinjuku 3-1-13, Tokyo, Japan

+81 3 5312 8563

thomas.derham@orange.com

Authors:

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

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)Slide 2

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

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)

Imad Jamil (Orange)Slide 3

STAs at 3m: CCA=-50dBmSTAs at 5m: CCA =-60dBmAPs: CCA =-60dBm

margin 20dBMax CCA -50dBm

STAs at 3m: CCA=-40dBmSTAs at 5m: CCA =-60dBmAPs: CCA =-60dBm

margin 20dBMax CCA -40dBm

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

TPC algorithm

• TPC (Transmit Power control):– each receiving STA requests transmitting STA to adjust its TP so that

Rx Power = CCA + Margin

• We took a margin of 20dB

Imad Jamil (Orange)Slide 4

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

Tx :15 dBmTx :15 dBm

Tx : 15 dBmTx : 15 dBm

[21 m][21 m]

Close to scenario 3

- First tier only (7 BSSs), 8 STAs per BSS, frequency reuse 3 pattern

Simulation scenario

Imad Jamil (Orange)Slide 5

[7 m][7 m]

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

ParametersPHYoIEEE 802.11noPath Loss: ITU UMi (23.3+36.7log10(d)+ 21log10(2400/900MHz))oBand: 5 GhzoChannel: 20 MHzoTx power: 15 dBm

TrafficoFull buffer UDP trafficoDL (AP->STA): 4Mbps per STAoUL (STA->AP): 4Mbps per STA

MetricAggregate throughput, per user throughput CDF

Rate adaptationAARF with selection of set of MCSs (link adaptation)

Simulation scenario

Imad Jamil (Orange)Slide 6

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

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

Slide 7

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

1 - DSC fairness improvements with max CCA threshold optimization

Slide 8

• Unfairness between STAs at different range in UL

• We changed the max CCA threshold to limit the CCA difference between STAs, which limits the unfairness

STAs at 3m: CCA=-50dBmSTAs at 5m: CCA =-60dBmAPs: CCA =-60dBm

margin 20dBMax CCA -50dBm

STAs at 3m: CCA=-40dBmSTAs at 5m: CCA =-60dBmAPs: CCA =-60dBm

margin 20dBMax CCA -40dBm

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

2 - Fairness comparison with Fixed CCA

Slide 9

• Same simulation scenario (7 11ax, 1 legacy per AP), comparing:– fixed CCA: -82, -70, -60, -50dBm– DSC with max CCA threshold (-50dBm): (STAs at 3m: CCA=-50dBm, STAs at 5m: CCA =-60dBm, APs: CCA =-60dBm)

11ax STAs legacy STAs

-82 -70 -60: best fixed CCA

-50

CCAC: DSC

UL User throughput CDF results for 11ax devices:Curve slope is a good indication of fairness

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

2 - Fairness comparison with Fixed CCA

Slide 10

• Conclusion:

at saturation state:

– fixed CCA is not more fair than DSC between 11ax STAs

– fixed CCA is unfair with legacy devices

Without legacy STAs With legacy STAs

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

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

Slide 11

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

Reuse scheme: balanced CCAC/TPCExample with an equal modification of CCA and TP

Slide 12

• STA calculates a Delta_x value, which is the amount of dB by which CCA and TP will be changed– this delta_x value would be equal to delta_CCA if CCA adaptation only is performed and to delta_TP if TPC only is performed

– if the STA uses the concept of DSC on this first Delta_x calculation, we have: Delta_x = Rx_power – Margin – standard_CCA (ex: Margin= 20dB, standard_CCA = -79dBm for 40MHz)

• STA applies a specific formula for the calculation of delta_CCA and delta_TP, based on Delta_x– in our example, we considered the rule as being an equal change of CCA and TP

Delta_CCA=Delta_TP=Delta_x / 2

• STA applies CCA adaptation using Delta_CCA

• STA requests AP to apply TP adaptation using Delta_TP– or applies TP adaptation using Delta_TP

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

Fairness comparison with balanced CCAC/TPC (1/4)

Slide 13

• Same simulation scenario, comparing:– best fixed CCA: -60 dBm– DSC with max CCA threshold (-50dBm): (STAs at 3m: CCA=-50dBm, STAs at 5m: CCA =-60dBm, APs: CCA =-60dBm)

– TPC

– balanced CCAC/TPC (equal change between CCA and TP)

Aggregate throughput results, with and without legacy devies:All solutions present similar results (expect TPC, which collapses in the presence of legacy devices

TPC in presence of legacy devices

September 2014

doc.: IEEE 802.11-14/1207r0

Submission Slide 14

• Same simulation scenario, comparing:– best fixed CCA: -60 dBm– DSC with max CCA threshold (-50dBm): (STAs at 3m: CCA=-50dBm, STAs at 5m: CCA =-60dBm, APs: CCA =-60dBm)

– TPC

– balanced CCAC/TPC (equal change between CCA and TP)

Without legacy STAs(8 11ax STA per AP)

With legacy STAs(7 11ax STA and 1 legacy STA per AP

Balanced CCAC/TPC and TPC

DSC and fixed CCA

Balanced CCAC/TPC

DSC and fixed CCA

UL User throughput CDF results for 11ax devices:Curve slope is a good indication of fairness

Fairness comparison with balanced CCAC/TPC (2/4)

September 2014

doc.: IEEE 802.11-14/1207r0

Submission Slide 15

• Same simulation scenario, comparing:– best fixed CCA: -60 dBm– DSC with max CCA threshold (-50dBm): (STAs at 3m: CCA=-50dBm, STAs at 5m: CCA =-60dBm, APs: CCA =-60dBm)

– balanced CCAC/TPC (equal change between CCA and TP)

legacy STAs throughput(7 11ax STA and 1 legacy STA per AP)

Balanced CCAC/TPC

DSC

Legacy throughput are better preservedthan with DSC

UL User throughput CDF results for legacy devices:

Fairness comparison with balanced CCAC/TPC (3/4)

September 2014

doc.: IEEE 802.11-14/1207r0

Submission Slide 16

• Conclusion:– Balanced CCAC/TPC seems the best solution with regards to fairness between 11ax and with

legacy devices

– It gives equal area throughput gains than CCAC (DSC, fixed CCA..) and TPC

• Further advantages:– It preserves the benefit of being directly beneficial for the STA to implement (compared to

TPC)

– It can be very simple to define in 11ax:• we can define in 11ax only the proportion rule to respect between Delta_CCA and Delta_TPC: gives every STA the

possibility to use its own algorithm (need to see what proportion rule is the optimum)

• this proportion rule could be parametrized in case of a managed network (need simulations to evaluate if different proportion rules are required depending on the environments, or depending on the proportion of legacy/11ax devices)

• Note that such proportion rule would need to be adapted when combined with UL OFDMA and UL MU-MIMO, as TP adaptation will be required also for those schemes.

Fairness comparison with balanced CCAC/TPC (4/4)

September 2014

doc.: IEEE 802.11-14/1207r0

Submission

Conclusion

• Fairness has to be considered for OBSS reuse mechanisms– even if it only arises at saturation state

• Fairness analysis with CCA control– We previously showed fairness issues with DSC

– fixed CCA is not more fair than DSC between 11ax STAs

– fixed CCA is unfair with legacy devices

• New solution to consider: balanced CCAC/TPC– in our simulation scenario, Balanced CCAC/TPC performs way better with regards to fairness

between 11ax and with legacy devices

– and It gives equal area throughput gains than CCAC (DSC, fixed CCA..) and TPC

– Need to evaluate it on other scenarios, and to optimize the ratio between CCAC and TPC

Imad Jamil (Orange)Slide 17

September 2014