CS 525M – Mobile and Ubiquitous Computing...

CS 525M – Mobile and Ubiquitous Computing Seminar

Mark FiguraMike Scaviola

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

How we tested (equipment)

• Proxim ORiNOCO 802.11b pcmcia card• Linksys “Instant Wireless” Wireless Access

Point Router• Two laptops from the ATC

And the power?

• A car starter battery along with a power inverter does wonders!

Software

• 2 measurements taken…– Signal/noise with NetStumbler– Average bandwidth with QCheck

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?

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

20

30

40

50

60

Distan

ce (ya

rds)

2 3 4 6 7 9 11 13 15 18 20 21 23 24 25 28 30

Throughput

00.5

11.5

22.5

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

Phase 0 – distance

Our setup on the football field

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

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

Tim

e (G

MT

)

02:3

2:01

(G

MT)

02:3

5:04

(G

MT)

02:3

8:06

(G

MT)

02:4

1:07

(G

MT)

02:4

4:10

(G

MT)

02:4

7:12

(G

MT)

02:5

0:13

(G

MT)

02:5

3:13

(G

MT)

02:5

6:15

(G

MT)

02:5

9:17

(G

MT)

03:0

2:29

(G

MT)

03:0

5:31

(G

MT)

03:0

8:40

(G

MT)

03:1

1:43

(G

MT)

03:1

4:49

(G

MT)

SNR

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

0

1

2

3

4

5

6

1 5 9 13 17 21 25 29 33 37 41 45 49 53

Bandwidth

Phase 0 – distance

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.

Phase 1 – building materials

4

4.1

4.2

4.3

4.4

4.5

4.6

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)

Phase 1 – building materials

Phase 2 – environmental

• What are the effects of humidity on wireless, if any?

• Very slight downward trend

SNR

010203040506070

Tim

e (G

MT

)

23:5

9:27

(G

MT)

00:0

5:24

(G

MT)

00:1

1:18

(G

MT)

00:1

7:11

(G

MT)

00:2

3:03

(G

MT)

00:2

8:54

(G

MT)

00:3

4:46

(G

MT)

00:4

0:41

(G

MT)

00:4

6:34

(G

MT)

00:5

2:29

(G

MT)

00:5

8:23

(G

MT)

01:0

4:16

(G

MT)

01:1

0:08

(G

MT)

01:1

6:00

(G

MT)

01:2

1:55

(G

MT)

SNR

Phase 3 – interference

• Tested with two sources of noise in the 2.4ghz band– Microwaves– Roommate’s phone that ruins my

wireless headphones

Phase 3 – interference

Effect of Microwave Oven on Throughput

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10 11

Channel

Mb

ps Microwave Off

Microwave On

Phase 3 – interference

Effect of 2.4Ghz Phone on Throughput

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 2 3 4 5 6 7 8 9 10 11

Channel

Mbp

s No Phone

Idle Phone

In Use

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

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

Questions?