Example: Obstacle Modeling for Wireless Transmissions Andy Wang CIS 5930-03 Computer Systems Performance Analysis
Feb 23, 2016
Example: Obstacle Modeling for Wireless
TransmissionsAndy WangCIS 5930-03
Computer SystemsPerformance Analysis
2
Motivation• Typical studies of mobile wireless
networks assume an open field– No physical obstacles (e.g., no buildings)– Not reflective of urban settings
Goals• Validate the open-field wireless signal
attenuation model used in NS-2• Model the signal attenuation caused by
physical obstacles
3
Services• Wireless network signal transmissions
– Broadcast signals– Listen to signals
4
Outcomes• Sufficient signal strength for data
transmission– Successful transmissions– Unsuccessful transmissions (e.g., due to
interferences)• Insufficient signal strength for data
transmission– No service
5
Metric• Signal strength
– dBm (decibels relative to 1 mWatt)• Decibels are ratios (no units)
– Log transformed• 1 mW = 10log10(1mW/1mW) = 0 dBm
– Tricky unit conversions• (XWatts* 1000)mWatts
• (XdBW + 30)dBm
• Note: 30 = 10log10(1000mW/1mW)• Measured in electric power
6
Implicit Assumptions• Bandwidth, latency, and packet loss rate
are largely a function of signal strength• Not measured
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Parameters• Open field
– Type of base station and receiver– Distance between sender and receiver– Presence of interference
• Self interference– Ground surface, signal reflections
• Other transmissions– Weather conditions– Height of transmission source
8
Parameters• With obstacles
– Location of obstacles– Type of obstacles
• Different building codes• Problem
– Difficult to quantify obstacles and their relationship to the base station and receiver
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Factors and Evaluation Techniques
• Factors– Distance between sender and receiver– Presence of obstacles
• Evaluation techniques– Empirical measurements
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Workloads• One sender, one receiver
– Continuous transmissions• Open field
– Mike Long Track on campus• With obstacles
– Around a block in downtown Tallahassee– Around Keen Building
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Workloads• Problems
– No interferences– Only measured two scenarios
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Experimental Settings• Base station
– 802.11b Linksys• Receiver
– Linux laptop with wireless PCI card– Used Wavemon to log transmission signals
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Downtown Tallahassee
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Keen Building GPS Coordinates
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30.445825, -84.301432 30.445806, -84.301347
30.446075, -84.301314 30.446056, -84.301239
30.446093, -84.301389
30.445973, -84.301486
30.445862, -84.301486
30.446010, -84.301143
30.445779, -84.301229
30.445880, -84.301175
30.445862, -84.300896
30.445723, -84.300939
30.445779, -84.301089
30.445917, -84.301035
1
3
2g f e
d
cba
h j
ki
Possible base station locations
Experimental Design• Ideally, start with 23r factorial design to
identify major factors and interactions
16
Experimental Design• What really happened
– 22 factorial design
– Had missing data points for temperature– Ground surfaces correlate to the presence
of obstacles17
Experimental Design• Problems
– Cumbersome setup• Needed portable battery• Network measurements drain batteries quickly
– Missing data points for temperature– Ground surfaces correlate to the presence
of obstacles
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Experimental Design• Open-field model validation
– Simple design• Varied the distance between base station and
receiver• Obstacle model
– Simple design• Varied the distance between base station and
receiver
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Data Analysis• 22 factorial design (example 1)• Fractions of variations explained
* 36% due to the presence of obstacles* 60% due to distance* 4% due to the interaction between the two
• Okay to create separate models– With obstacles– Without obstacles
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Open-field Data Analysis
• Simple linear regression (example 2)– Signal = -46 – 0.57(distance)– R2 = 0.78– Both coefficients are significant
21
0 10 20 30 40 50 60 70 80 90
-120
-100
-80
-60
-40
-20
0
yi y_hat90% confidence interval
distance (meters)
dBm
Open-field Data Analysis
• However, ANOVA not satisfactory
22
-100 -90 -80 -70 -60 -50 -40
-10
-5
0
5
10
15
20
25
y_hat
error residuals
0 2 4 6 8 10 12 14 16
-10
-5
0
5
10
15
20
25
experimental number
error residuals
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-10
-5
0
5
10
15
20
25
f(x) = 6.46005695196675 x − 2.23503935841352E-15R² = 0.819196198781606
normal quantiles
observed error residual quan-
tiles
Try Transforms (Ex.3)• distance’ = 1/distance
– Signal = -91 + 682/distance– R2 = 0.98– Both coefficients are significant
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20 30 40 50 60 70 80 90
-90-80-70-60-50-40-30-20-10
0
yi y_hat90% confidence interval
distance (meters)
dBm
Try Transforms (Ex.3)• distance’ = 1/distance
– R2 = 0.98– Weird error patterns
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-85 -80 -75 -70 -65 -60
-1.5
-1
-0.5
0
0.5
1
1.5
2
y_hat
error residuals
0 2 4 6 8 10 12 14
-1.5
-1
-0.5
0
0.5
1
1.5
2
experimental number
error residuals
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-1.5
-1
-0.5
0
0.5
1
1.5
2
f(x) = 0.800580814768194 x − 1.43585620348543E-15R² = 0.892946654243968
normal quantiles
observed error residual quan-
tiles
Try Transforms (Ex. 4)• distance’ = 1/distance2
– Signal = -84 + 12925/distance2
– R2 = 0.92– Both coefficients are significant
25
20 30 40 50 60 70 80 90
-90-80-70-60-50-40-30-20-10
0
yi y_hat90% confidence interval
distance (meters)
dBm
Try Transforms (Ex. 4)• distance’ = 1/distance2
– R2 = 0.92– Weird error patterns
26
-85 -80 -75 -70 -65 -60
-3
-2
-1
0
1
2
3
y_hat
error residuals
0 2 4 6 8 10 12 14
-3
-2
-1
0
1
2
3
experimental number
error residuals-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-3
-2
-1
0
1
2
3f(x) = 1.62457905305534 x − 2.15805052769733E-15R² = 0.969811539510596
normal quantiles
observed error residual quan-
tiles
Try Transforms (Ex. 5)• distance’ = 1/sqrt(distance)
– Signal = -107 + 211/sqrt(distance)– R2 = 0.99– Both coefficients are significant
27
20 30 40 50 60 70 80 90
-100-90-80-70-60-50-40-30-20-10
0
yi y_hat90% confidence interval
distance (meters)
dBm
Try Transforms (Ex. 5)• distance’ = 1/sqrt(distance)
– R2 = 0.99– Errors not normally distributed
28
-85 -80 -75 -70 -65 -60
-1
-0.5
0
0.5
1
1.5
y_hat
error residuals
0 2 4 6 8 10 12 14
-1
-0.5
0
0.5
1
1.5
experimental number
error residuals
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-1
-0.5
0
0.5
1
1.5
f(x) = 0.472267862672277 x + 7.55722898312044E-15R² = 0.758206423633563
normal quantiles
observed error residual quan-
tiles
Try Transforms (Ex. 6)• distance’ = log10(distance)
– Signal= -18 – 35*log(distance)– R2 = 0.99
29
0 10 20 30 40 50 60 70 80 90
-100-90-80-70-60-50-40-30-20-10
0
yi y_hat90% confidence interval
distance (meters)
dBm
Try Transforms (Ex. 6)• distance’ = log10(distance)
– R2 = 0.99
30
-90 -85 -80 -75 -70 -65 -60 -55 -50
-1
-0.5
0
0.5
1
1.5
2
y_hat
error residuals
0 2 4 6 8 10 12 14 16
-1
-0.5
0
0.5
1
1.5
2
experimental number
error residuals
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-1
-0.5
0
0.5
1
1.5
2
f(x) = 0.617459319587706 x + 1.40861403359254E-15R² = 0.920293187741683
normal quantiles
observed error residual quan-
tiles
Validate Open-field Model
• dBmr = -18 – 35*log(distance)• NS-2 model
* Wattr = Watts*α/distance2
* dBmr = 10*log(Powers*α/distance2) + 30= dBms + 10*log(α) – 20*log(distance)
= (dBms + A) – B*log(distance)
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Obstacle Data Analysis• Simple linear regression
– Signal = -50 – 0.64(distance)– R2 = 0.48– The second coefficient is not significant
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Obstacle Data Analysis (Ex. 7)
• ANOVA– Weird error patterns
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-110 -100 -90 -80 -70 -60 -50 -40
-30
-20
-10
0
10
20
30
40
y_hat
error residuals
0 10 20 30 40 50 60 70 80
-30
-20
-10
0
10
20
30
40
experiment number
error residuals
-3 -2 -1 0 1 2 3
-30
-20
-10
0
10
20
30
40
f(x) = 13.3362552680386 x − 2.73649712017034E-15R² = 0.947276427868547
normal quantiles
observed error residual quan-
tiles
Try Log Transform (Ex. 10)
• R2 = 0.24• ANOVA shows patterns
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-92 -90 -88 -86 -84 -82 -80 -78 -76 -74 -72
-20
-15
-10
-5
0
5
10
15
20
25
y_hat
error residuals
0 10 20 30 40 50 60 70 80
-20
-15
-10
-5
0
5
10
15
20
25
experiment number
error residuals
-3 -2 -1 0 1 2 3
-20
-15
-10
-5
0
5
10
15
20
25
f(x) = 9.43169204430789 x + 2.23760437095676E-14R² = 0.919889934362008
normal quantiles
observed error residual quan-
tiles
Analyze a Subset of Data
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30.445825, -84.301432 30.445806, -84.301347
30.446075, -84.301314 30.446056, -84.301239
30.446093, -84.301389
30.445973, -84.301486
30.445862, -84.301486
30.446010, -84.301143
30.445779, -84.301229
30.445880, -84.301175
30.445862, -84.300896
30.445723, -84.300939
30.445779, -84.301089
30.445917, -84.301035
1
3
2g f e
d
cba
h j
ki
Possible base station locations
Focus on this data set
Keen Building Location 1 (Ex. 13)
• Signal = -27 – 36*log10(distance)• R2 = 0.70• Both coefficients are significant
36
20 30 40 50 60 70 80
-140
-120
-100
-80
-60
-40
-20
0
yi y_hat90% confidence interval
distance (meters)
dBm
Keen Building Location 1
• ANOVA so so• Errors not quite normally distributed
37
-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
-10
-8
-6
-4
-2
0
2
4
6
8f(x) = 3.74974884853963 x − 3.52240445076884E-15R² = 0.945171955778447
normal quantiles
observed error residual quan-
tiles
-96 -94 -92 -90 -88 -86 -84 -82 -80 -78 -76
-10
-8
-6
-4
-2
0
2
4
6
8
y_hat
error residuals
0 5 10 15 20 25
-10
-8
-6
-4
-2
0
2
4
6
8
experiment number
error residuals
Downtown Data Set (Ex. 15)
• Signal = -16 – 39*log10(distance)• R2 = 0.71• Only the second coefficient is significant
38
30 40 50 60 70 80 90
-250
-200
-150
-100
-50
0
50
yi y_hat90% confidence interval
distance (meters)
dBm
Downtown Data Set• ANOVA
39
-94 -92 -90 -88 -86 -84 -82 -80 -78 -76 -74
-6
-4
-2
0
2
4
6
8
y_hat
error residuals
0 1 2 3 4 5 6 7
-6
-4
-2
0
2
4
6
8
experiment number
error residuals
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-6
-4
-2
0
2
4
6
8
f(x) = 4.15328384563262 x + 4.736951571734E-15R² = 0.859261278629964
normal quantiles
observed error residual quan-
tiles
Unified Model (Ex. 17)• Signal = -22 - 5.3*(if ob) – 33*log10(dist)• R2 = 0.32• All coefficients are significant• Passed F test
• The presence of obstacles costs 5.3 dBm
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Unified Model (Ex. 17)• Signal = -22 - 5.3*(if ob) – 33*log10(dist)• R2 = 0.32• All coefficients are significant
41
0 10 20 30 40 50 60 70 80 90 100
-140
-120
-100
-80
-60
-40
-20
0
yi y_hati90% confidence interval
distance (meters)
dBm
Unified Model• ANOVA not so good…
42
-95 -90 -85 -80 -75 -70 -65 -60 -55
-20
-15
-10
-5
0
5
10
15
20
25
y_hat
error residuals
0 10 20 30 40 50 60 70 80 90
-20
-15
-10
-5
0
5
10
15
20
25
experiment number
error residuals
-3 -2 -1 0 1 2 3
-20
-15
-10
-5
0
5
10
15
20
25
f(x) = 8.56394129011418 x − 1.96936779102633E-12R² = 0.935379159161522
normal quantiles
observed error residual quan-
tiles
Problems• Need better ways to describe the
relationship between obstacles, sender, and receiver
43
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White Slide