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July 2009
Hart (Cisco Systems)Slide 1
doc.: IEEE 802.11-09-0816r2
Submission
Enterprise Simulation Scenario
Date: 2009-07-11
Name Affiliation Address Phone Email Brian Hart Cisco Systems 170 West Tasman Drive,
San Jose, CA 95134 +1-408-526-3346 [email protected]
Hajime Suzuki (source of much data but not editorially responsible)
CSIRO PO Box 76 Epping, NSW 1710, Australia
July 2009
Hart (Cisco Systems)Slide 2
doc.: IEEE 802.11-09-0816r2
Submission
Improvements to the enterprise simulation scenario
Situation
• The Enterprise Network simulation scenario (#4) is derived from 802.11n scenario with 1 AP with 30 clients
• The Enterprise Network simulation scenario (#4) assumes no fluorescent light effect because recent measurements have not replicated this effect.
Complication
• 11ac has 5 or 6 channels at 5GHz whereas 11n had 12 channels. Overlapping APs are much more likely with 5 or 6 channels.
• We freshly present measurements of the fluorescent light effect showing that typically it is absent, yet is significant when present.
Key Line
• We should make improvements to the simulation scenarios in the functional requirements of 09/451 in order to account for overlapping APs and the fluorescent light effect.
Summary
July 2009
Hart (Cisco Systems)Slide 3
doc.: IEEE 802.11-09-0816r2
Submission
There are only five or six 80 MHz channels
• There are five 80MHz channels at 5 GHz
− 36-48, 52-64, 100-112, 116-128, 149-161
− Plus a sixth, 132-144, with a regulatory change
• Typical channel plan with six channels is:
36 -48
36 -48
36 -48
36 -48
36 -48
36 -48
36 -48
-20 0 20
0
40
-40
x (m)
y (m)
July 2009
Hart (Cisco Systems)Slide 4
doc.: IEEE 802.11-09-0816r2
Submission
So we expect two overlapping BSSs
• APs co-channel with the (0,0) AP are at
−(-20,-40), (20,40)m [44m range]−(-40,40), (40,40)m [57m range]−(0,60), (-60,0)m [60m range]
• Now range with -76dBm CCA (for 80MHz) is 50m:
17dBm + 3dBi - 47dB[1m] - 20log10(5m/1m) - 35log10(50m/5m) = -76dBm
• With multistorey deployments, 20dBm TX power, 6dBi antennas, cubes, realistic sensitivities, 10 or 20m breakpoint, the actual overlap is worse
• But let’s assume 2 overlapping BSSs for simplicity
36 -48
36 -48
36 -48
36 -48
36 -48
36 -48
36 -48
-20 0 20
0
40
-40
x (m)
y (m)
July 2009
Hart (Cisco Systems)Slide 5
doc.: IEEE 802.11-09-0816r2
Submission
Proposal: let’s allow comparability in OBSS behavior• Uplink/downlink MU-MIMO / SDMA and OFDMA are valuable technologies
that we should be exploring, yet they are more challenging in an OBSS world
• We should include OBSS as an “impairment” because otherwise there is a risk we will make suboptimal design choices based on false optimism
• The simplest proposal is to triplicate the APs and clients in scenario #4, keep the first copy at (0,0), translate the second copy by (20,40) and translate the third copy by (-20,-40)m
−E.g. Note) It is encouraged that TGac technology proposals describe its impact on OBSS. The preferred simulation scenario is the Enterprise Simulation Scenario with the BSS triplicated then each copy translated by (0,0), (20,40) and (-20,-40)m
−We could reduce the number of clients per BSS since 90 clients may be overkill (e.g. reduce to 15-20 clients per BSS).
• Note: multiple APs is more in harmony with Usage Model 2d in 09/161r2
July 2009
Hart (Cisco Systems)Slide 6
doc.: IEEE 802.11-09-0816r2
Submission
A Fresh Look at Fluorescent Light Measurements
• 09/537r0 and 09/538r0 did not observe any Doppler spread from fluorescent tubes, and 09/537r0 reported a lack of literature on this topic.
• In the next few slides we share Cisco-sponsored measurements from the literature obtained in the 2003-2004 timeframe on this topic
• We agree that 11n erred by making the fluorescent light effect a pervasive property of channels D and E. In our experience, there are locations where the fluorescent light effect is negligible
− Yet when present the fluorescent light effect can be significant
July 2009
Hart (Cisco Systems)Slide 7
doc.: IEEE 802.11-09-0816r2
Submission
Requirements for a fluorescent light effect
• From practical considerations, a significant fluorescent light effect requires:
1. Fluorescent lights (most typical of enterprise environment)
2. Preferably downward-pointed, uncovered(?) fluorescent light fixtures
3. Light fixtures which capture RF reflections and pass them through the fluorescent tube (akin to design goal of light dispersion)
4. A location with suitable multipath: e.g. a dominant fluorescent path, or two paths of similar strength with one affected by fluorescent tubes
• 1 is typical of enterprise, 2 is out of our control yet seems to happen in a proportion of customer sites (e.g. 1/3 sites with 11ac submissions), 3 is reasonably typical for downward-pointed fixtures due to coincident design, 4 is a statistical property (that is hard to capture, but see next slides)
July 2009
Hart (Cisco Systems)Slide 8
doc.: IEEE 802.11-09-0816r2
Submission
Measurement Environment• Three areas were tested; they were not cherry picked: they were
simply chosen as a typical desktop location for a laptop
• Each area was tested in detail: the RX antennas were scanned over a local area of 4 x 4 wavelengths with a 0.05 wavelength increment (6400 locations).
• 2TX (2λ separation) x 2RX (0.5λ) antennas, all located in the same (cluttered) office room with clear LOS
• At each antenna position, 4 MIMO sub-channels (Tx1-Rx1, Tx1-Rx2, Tx2-Rx1, Tx2-Rx2) are measured 100 times every 1.3 ms while the antennas are stationary. (1.3ms due to HW behavior)
• Fluorescent lights using 50Hz electricity were ON
• Measured during the night (2 hours per measurement) when no human activity was present
• As can be seen from the photo, the fluorescent tubes are surrounded by metal plates which might enhance the fluorescent light effect
July 2009
Hart (Cisco Systems)Slide 9
doc.: IEEE 802.11-09-0816r2
Submission
Doppler variations only affect selected locations within the area• Plot of power deviation between 1.3ms-separated samples of a single subcarrier
• Most locations for this subcarrier exhibit little power deviation
• About 10% of locations for this subcarrier show 5-10-15 dB deviation
• Across the band (not shown), about 20% of locations are affected
July 2009
Hart (Cisco Systems)Slide 10
doc.: IEEE 802.11-09-0816r2
Submission
At this location, the channel across the whole band can change
• Here we look at the subcarrier power (y axis) over time at one location.
• The weakest subcarriers (2-6MHz) vary the most (from circa 0dB to -10 dB and back to 0dB)
• Even the strongest subcarriers (-8 to -6 MHz) jump in time: mostly +6dB, then a brief period down towards 4dB, then 8dB, back to 4dB, then back at the start to +6dB
July 2009
Hart (Cisco Systems)Slide 11
doc.: IEEE 802.11-09-0816r2
Submission
Example impact of fluorescent light effect on channel estimation
• Assume the channel at a subcarrier is estimated initially during the LTFs then kept fixed for the packet duration. What impact does the fluorescent light effect have on the constellation after a ZF equalizer?
• Use an EVM-like measure:
where E|x|y indicates the expectation of x over y.
• With fluorescent lights on, the channel is disturbed cyclostationarily, and the EVM degrades to about -20dBm at 10ms intervals = 1/(2x50Hz)
• With fluorescent lights off, coherence is well maintained and EVM is a flat -25dB even after 60ms
0 10 20 30 40 50 60 70-27.5
-27
-26.5
-26
-25.5
-25
-24.5
T ime (ms)
EV
M (
dB)
T x1-Rx1T x1-Rx2T x2-Rx1T x2-Rx2
0 10 20 30 40 50 60 70-25
-24
-23
-22
-21
-20
-19
T ime (ms)
EV
M (
dB)
T x1-Rx1T x1-Rx2T x2-Rx1T x2-Rx2
xft
xftH
xftHxfttHEt
,,
10 ,,
,,,,log20EVM
July 2009
Hart (Cisco Systems)Slide 12
doc.: IEEE 802.11-09-0816r2
Submission
What is the overall incidence of amplitude and phase variation?
• At 50% of locations and subcarriers, 1.5dB absolute maximum power variation across 1.3ms
• At 10% of locations and subcarriers, 3.5dB absolute maximum power variation
• At 1% of locations and subcarriers, 10dB absolute maximum power variation [3.2dB with lights off]
• At 50% of locations and subcarriers, 22deg absolute maximum subcarrier phase deviation across 1.3ms
• At 10% of locations and subcarriers, 32deg absolute maximum subcarrier phase deviation
• At 1% of locations and subcarriers, 80deg absolute maximum subcarrier phase deviation [32deg with lights off]
July 2009
Hart (Cisco Systems)Slide 13
doc.: IEEE 802.11-09-0816r2
Submission
Yet, the fluorescent light effect is most dramatic with faded subcarriers
• Plot of power deviation between 1.3ms samples of a single subcarrier versus median RSSI of that subcarrier (130ms)
• More faded subcarriers vary the most
−E.g. when the main static paths superimpose destructively, a weaker dynamic fluorescent path has more influence
• Even so, variations of 5 dB are very common
• Thus analysis of measurements should be extended to consider impact on the overall impact on capacity
July 2009
Hart (Cisco Systems)Slide 14
doc.: IEEE 802.11-09-0816r2
Submission
Summary of the fluorescent light effect
• We have shared additional fluorescent measurements with 802.11ac
• The fluorescent light effect is reasonably well-established:−There is peer reviewed literature: e.g. references [36-37] in 03/940r4; plus Hajime Suzuki, Mark Hedley, Graham Daniels, and Colin Jacka, "Spatial distribution of temporal variation caused by active fluorescent lights in office environment," In Proceedings of the URSI Commission F Triennium Open Symposium, pp. 181-186, Cairns, Australia, June 2004.
−There are previous positive IEEE submissions: e.g. [33-35] in 03/940r4 although the realism of these is not always clear-cut
• Of the measurements submitted to 11ac, 1 out of 3 buildings exhibit the effect. In the one building that showed the effect, 3 out of 3 typical laptop areas showed the effect. Within these typical laptop areas, the effect was present at about 20% of locations
− Unlike the 11n model
• 1 out of 3 buildings is not very statistically significant; but it is high enough to be a concern: extrapolating, a non-negligible proportion of buildings are affected, and can degrade the benefits of TXBF & especially null-steering
−Narrow nulls are more sensitive to time variation than broad beamforming peaks−The customer-facing vendor perspective is that this stuff should “just work”, whatever the customer’s building construction
July 2009
Hart (Cisco Systems)Slide 15
doc.: IEEE 802.11-09-0816r2
Submission
Proposal for the fluorescent light effect
• Uplink/downlink MU-MIMO / SDMA are valuable technologies that we should be exploring, yet they are more challenging in a time-varying world
• We should include the fluorescent light effect as an impairment because otherwise there is a risk we will make suboptimal design choices based on false optimism
• As an initial proposal, we could assume some percentage of client locations are subject to the fluorescent light effect, and reinstate the 11n fluorescent Doppler model for these clients in the enterprise scenario−An initial proposal is 7% (1/3 buildings x 20% of locations at 1 building)
• Or take a data-driven approach: measurements of more buildings & multiple locations within these buildings, recording the level of the effect
July 2009
Hart (Cisco Systems)Slide 16
doc.: IEEE 802.11-09-0816r2
Submission
Questions
?
July 2009
Hart (Cisco Systems)Slide 17
doc.: IEEE 802.11-09-0816r2
Submission
Strawpoll 1
•OBSS investigations should be comparable, so the OBSS Note in 09/451 should propose studying OBSS via the Enterprise Simulation Scenario, with the original BSS copy/pasted to (20,40) and (-20,-40)•Y34, N0, A30
July 2009
Hart (Cisco Systems)Slide 18
doc.: IEEE 802.11-09-0816r2
Submission
Strawpoll 2
•There is sufficient evidence of the fluorescent light effect that it merits further study as a candidate for insertion into the 11ac channel model for enterprise environments. •Y43, N0, A27
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