CS 525M – Mobile and Ubiquitous Computing...
Transcript of CS 525M – Mobile and Ubiquitous Computing...
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CS 525M – Mobile and Ubiquitous Computing Seminar
Mark FiguraMike Scaviola
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Introduction
• Real-world measurement of 802.11b wireless performance– Signal/noise ratio– Average bandwidth
• Divided into 4 phases– Phase 0 – distance– Phase 1 – building materials– Phase 2 – environmental effects– Phase 3 – interference
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How we tested (equipment)
• Proxim ORiNOCO 802.11b pcmcia card• Linksys “Instant Wireless” Wireless Access
Point Router• Two laptops from the ATC
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And the power?
• A car starter battery along with a power inverter does wonders!
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Software
• 2 measurements taken…– Signal/noise with NetStumbler– Average bandwidth with QCheck
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Why?
• NY Stock Exchange• Short of “ray-tracing” how can you tell what
factors are involved in 802.11b performance?– Are there any simple rules for planning
the design of your home wireless network?
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Phase 0 - distance
•First test on the football field•As expected, SNR drops as distance increases•At about 15 yards, throughput started to become erratic. By 30 yards, we could not get an accurate measurement.
SNR
0
10
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Distan
ce (ya
rds)
2 3 4 6 7 9 11 13 15 18 20 21 23 24 25 28 30
Throughput
00.5
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33.5
44.5
5
Dis
tanc
e (y
ards
) 2 3 4 6 7 9 11 13 15 18 20 21 23 24 25 28 30
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Phase 0 – distance
Our setup on the football field
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Phase 0 – distance
• Second test in a long hallway in the Campus Center
• Throughput is erratic, but confined to two distinct plateaus
throughput
00.5
11.5
22.5
33.5
4
dist
ance 3 6 9 12 15 18 21 24 27 30 33 36 39
throughput
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Phase 0 – distance
• Just like in the football-field experiment, the SNR decreases as one would expect with distance…
• At the maximum distance tested which was longer than the distance on the football field, we had 2x the SNR
SNR
010203040506070
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MT
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02:3
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MT)
02:3
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02:4
7:12
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0:13
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6:15
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SNR
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Phase 0 – distance
• Third test in a large open room (Harrington Auditorium)
• At about 15 yards, bandwidth dropped significantly just like in the previous experiments.
• At 53 yards, it returned to full bandwidth!– Shape of the room
Bandwidth
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1 5 9 13 17 21 25 29 33 37 41 45 49 53
Bandwidth
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Phase 0 – distance
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Phase 1 – building materials
• Unfortunately, by the time that we were about to conduct the building materials test, we realized it was ill conceived
• Learned from the distance tests that radio waves are much less line-of-sight than we thought
• We didn’t have the resources to do a better test, so we decided to continue with the test as-is.
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Phase 1 – building materials
4
4.1
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4.7
Material
Mbp
s
No Obstruction
3/4" Particle Board
Cement Board
Sheetrock
Polyisocyanurate Insulation
Ceiling tile (hard)
Ceiling tile (foam)
1/2" 3ply birch plywood
3/8" 3ply Pine
3/4" 4ply Plywood
3/8" 4ply Plywood
Insulation (pink panther)
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Phase 1 – building materials
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Phase 2 – environmental
• What are the effects of humidity on wireless, if any?
• Very slight downward trend
SNR
010203040506070
Tim
e (G
MT
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23:5
9:27
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MT)
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MT)
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MT)
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MT)
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MT)
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MT)
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MT)
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(G
MT)
SNR
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Phase 3 – interference
• Tested with two sources of noise in the 2.4ghz band– Microwaves– Roommate’s phone that ruins my
wireless headphones
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Phase 3 – interference
Effect of Microwave Oven on Throughput
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Channel
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ps Microwave Off
Microwave On
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Phase 3 – interference
Effect of 2.4Ghz Phone on Throughput
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Channel
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s No Phone
Idle Phone
In Use
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Conclusions
• Wireless signals may be too complex to conduct research with based solely on empirical evidence
• Although we did not reach many of out goals, we learned a lot about wireless– Line of sight is less important than
structures that tend to “focus” radio waves such as the ends of Harrington
– Without surfaces to bounce off of, 802.11b behaves very poorly as shown by our outdoor test
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Conclusions
– Interference with other devices using the same band is a big problem
– If you get poor performance, try moving just a little bit – small changes in position or orientation can have huge effects on performance
– Always keep a close watch on your laptop
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Questions?