submission doc.: ieee 802.11-15/0050r0 january 2015 yu wang et al., ericssonslide 1 modeling...
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Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et al., EricssonSlide 1
Modeling components impacting throughput gain from CCAT adjustment
Date: 2015-01-11
Name Affiliations Address Phone Email Yu Wang Ericsson Farogatan 6,
Stockholm, Sweden yu.a.wang (at)
ericsson.com
Johan Söder Ericsson johan.soder (at) ericsson.com
Hakan Persson Ericsson hakan.z.persson (at) ericsson.com
Guido Hiertz Ericsson guido.hiertz (at) ericsson.com
Filip Mestanov Ericsson filip.mestanov (at) ericsson.com
Sean Coffey Realtek
Masahito Mori Sony
Yuichi Morioka Sony
Authors:
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 2
Background
• Some contributions show moderate gains from Clear Channel Assessment Threshold (CCAT) adjustment• “DSC performance” [1] shows < 50% in both average and 5th
percentile
• Other contributions show much higher gains• “Performance Gains from CCA Optimization” [2] indicates
~200% gain in average throughput
• Question to answer:• What are the important modelling components needed to get a
more realistic estimation of the gain by adjusting CCAT?
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 3
Background
• Simplified traffic modeling used• Full buffer DL only
• Compare the effect of the following modeling components
Component Simplified Realistic
Spatial streams 1 (SISO) 1 to 2 (MIMO)
Link adaptation “Ideal” ACK-based
Preamble reception Always received and decoded
In some cases not received or decoded
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 4
Simulation scenario 2• “Enterprise Scenario” as defined
in [3]• 8 offices, 64 cubicles per office, 2
STAs per cubicle• (8 × 64 × 2) / 32 = 32 STA/AP
• 4 × 80MHz channels (8 APs on the same channel)
• 32 × 8 = 256 STAs on the same channel
• P2P links are not included in the simulation
• DL full buffer traffic
BSS9-12 BSS13-16 BSS24-28 BSS29-32
BSS1-4 BSS5-8 BSS17-19 BSS20-23
20 m
20 m
STA1
STA2
STA3
2 m
2 m
STA4
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 5
Simplified modelling components
• SISO
• ‘Ideal’ link adaptation• SINR@Receiver before transmission used to set MCS
• Preamble Reception• Ideal PLCP preamble decoding
• When two preambles arrive at the same time, both can be decoded
• 802.11 OFDM signal always identified• Even if PLCP has already been
transmitted when the sensing starts
• In the simplified modeling CCA-SD (preamble detection) threshold is always used, although CCA-ED threshold should be used in case the preamble is not decoded
AP A
AP B
PayloadPreamble
SensingPayloadPreamble
AP A
AP B
Preamble Payload
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 6
More realistic modelling components
• MIMO
• Link adaptation• Adaptive auto-rate fallback
• Preamble Reception:• PLCP preamble decoding
• When two preambles arrive at the same time, both can be decoded only if SINR is sufficiently high
• 802.11 signal may not be identified• If a preamble can not be detected,
CCA-ED will be used
AP A
AP B
PayloadPreamble
SensingPayloadPreamble
AP A
AP B
Preamble Payload
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 7
Average throughput gain• Figure shows gain in average throughput for different
CCAT compared to -82 dBm
• Large gains with simplified modeling
• Very small gains with more realistic modeling
-90 -80 -70 -60 -500
50
100
150
CCA Threshold [dBm]
Gai
n in
mea
n t
hro
ug
hp
ut
[%]
simplifiedrealistic
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 8
Modeling impact on throughput• -82 vs. -50 dBm CCAT: gain in average user throughput varies from 6% to 137%
• Model analysis for gain from reduced CCAT:• MIMO: high SINR with -82 dBm can not be fully utilized by SISO transmission,
higher user throughput @ -82 dBm
• LA: lower user throughput @ -50 dBm due to larger variations in interference
• PR: higher user throughput @ -82 dBm since the ED threshold (-62 dBm) is applied when an interferer’s preamble is not correctly decoded
• Moving from simplified to more realistic modeling:• Higher throughput @ -82 dBm and lower throughput @ -50 dBm
• The gain between -82 dBm and -50 dBm is reduced, compared to the simplified modeling gain
-82 dBm -50 dBm0
2
4
6
8
10
Ave
rage
use
r th
roug
hput
(M
b/s)
LA: link adaptationPR: preamble reception (detection & decoding)
MIMO
PRLA
Ideal,SISO
Ideal,MIMO
Non-ideal LA,MIMONon-ideal PR,MIMO
Non-ideal LA+PR,MIMO
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 9
Simplified models
• Ideal LA & PR, SISO
• Gain in average user throughput: 137%• Gain in spatial reuse measured by AP transmitting time: 242%
• Loss in transmission rate: 21%
• Loss due to increased packet loss: 5%
-82 dBm -70 dBm -50 dBm0
0.2
0.4
0.6
0.8
AP
sta
te r
atio
Defer
ReceiveTransmit
-82 dBm -70 dBm -50 dBm0
2
4
6
8
Ave
rage
MC
S r
ate
(bits
/sym
bol)
Relative value: 1 0.99487 0.79235
-82 dBm -70 dBm -50 dBm0
0.02
0.04
0.06
0.08
Pac
ket
loss
rat
e
Relative value: 1 2.0807 5.6983
Collision
Decoding error
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 10
More realistic models
• Non-ideal LA & PR, MIMO
• Gain in average user throughput: 6%• Gain in spatial reuse measured by AP transmitting time: 178%
• Loss in transmission rate: 40%
• Loss due to increased packet loss : 40%
-82 dBm -70 dBm -50 dBm0
0.2
0.4
0.6
0.8
AP
sta
te r
atio
Defer
ReceiveTransmit
-82 dBm -70 dBm -50 dBm0
2
4
6
8
10
12
Ave
rage
MC
S r
ate
(bi
ts/s
ymbo
l)
Relative value: 1 0.95391 0.59807
-82 dBm -70 dBm -50 dBm0
0.1
0.2
0.3
0.4
Pac
ket
loss
rat
e
Relative value: 1 2.0696 5.7037
Collision
Decoding error
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 11
Summary• Factors limiting user throughput gain with CCAT adjustment are
identified
• With SISO and ideal modeling assumptions, high gain has been shown
• The gain in average user throughput of adjusted CCAT is reduced significantly after adding:• MIMO transmission (improves baseline)
• Adaptive auto rate fallback link adaptation
• Realistic preamble detection and decoding
• Analysis was done for full buffer DL-only traffic, for realistic gain estimation realistic traffic model with mix of DL and UL traffic should be considered
• Adjusted CCAT or DSC provides system improvements [1] but more realistic modeling is important to avoid overestimation of gains
Submission
doc.: IEEE 802.11-15/0050r0January 2015
Yu Wang et. al., EricssonSlide 12
References
[1] 11-14/1427r2, “DSC Performance”
[2] 11-14/0889r3, “Performance Gains from CCA Optimization”
[3] 11-14/0980r5, “TGax Simulation Scenarios”
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