1
Validation of Radio Channel Models using an Anechoic Chamber
Yuhao Zheng, David M. NicolUniversity of Illinois at Urbana-Champaign
Outline
• Introduction & anechoic chamber• Experimental framework• Radio channel models• Experiment results• Conclusions & future works
2
Introduction
• Wireless network simulation is popular• Fidelity is a problem– Especially for radio channel model– Higher layers depend on physical layer
• Tradeoff: accuracy ↔ computational cost– Simple models: free space, two ray– Complex models: raytracing, Transmission Line
Matrix (TLM)
3
Our Focus
• Complex models: Raytracing, TLM– Received signal strength
• Sensitivity experiments– Small changes in environment– How does a model reflect this?
• Problems– Need accurate measured value for validation– Anechoic chamber
4
Tx
Rx
Anechoic Chamber
• Illinois Wireless Wind Tunnel (iWWT)
• Characteristics– No outside interferences– No inside reflections
• Ideal wireless testbed– “Free space” inside
5
record RSStransmit pkts
Experimental Framework
6
chamber wall
Soekris Engineering net4521wireless node
attenuator (directional)
reflector (material varies)
20 ft
11 ft
experiment measured
model predicted
compare& validate
Simple Raytracing Model
7
• Wireless node single point– Assumption: omnidirectional antenna
• Attenuator fixed pathloss coefficient– Depends on direction
• Reflector line– Material-dependent reflection rate, tuned offline
N
ai aedi
de
n points
k=1n ∗k ref∗ cos (a i−ae)∗pathloss (d i+de )
Contribution of this single reflection path:
a series of points
Advanced Raytracing Model
• Consider path loss & path delay– Revision to single reflection path
– Complex number addition
8
direct pathreflected path
Im
Re
• More general radio model– Single point point matrix
N
ai aedi
de
n points
Transmission Line Matrix Model
• Even-based Transmission Line Matrix [Nutaro’06]• Space cells displacement state• A cell can change state when– External event: from adjacent cells– Internal event: when not at equilibrium position
• Implementation details– Grid size = λ/D, D is tunable– Source: sinusoidal– RSS: average over time
9
Experimental Results
10
20 ft
11 ft
large-scale movement
small-scale movement
direction A
direction B
Results – Large-scale Movement
11
0 2 4 6 8 10 12 14 16 18 20-60
-59
-58
-57
-56
-55
measured simplified RT normal RT event TLMX Position (ft)
Rece
ived
Sig
nal
Stre
ngth
(dBm
)
0 2 4 6 8 10 12 14 16 18 20-68-67-66-65-64-63-62
measured simplified RT normal RT event TLMX Position (ft)
Rece
ived
Sig
nal S
tren
gth
(dBm
)
direction A
direction B
can capture the peakbut not exact shape
~2dB error
Results – Small-scale Movement
12
120 122 124 126 128 130 132-64
-62
-60
-58
-56
-54
measured simplified RT normal RT event TLM
Y Position (in)Rece
ived
Sig
nal S
tren
gth
(dBm
)
120 122 124 126 128 130 132-70
-68
-66
-64
-62
measured simplified RT normal RT event TLM
Y Position (in)
Rece
ived
Sig
nal S
tren
gth
(dBm
)
direction A
direction B
cannot capture the shape~2dB error
Results – Radio Beamform
13
wireless box @rotating table
spectrum analyzer
Results – Radio Beamform
14
-180 -135 -90 -45 0 45 90 135 180-80
-70
-60
-50
-40
-30
VPol HPol Total
Angle
Pow
er L
evel
(dBm
)
up to 10dB variation!
Results – Resolution of Raytracing
15
120 122 124 126 128 130 132-69
-68
-67
-66
-65
-64
-63
measured RT n=9 RT n=25 RT n=49
Y Position (in)
Rece
ived
Sig
nal S
tren
gth
(dBm
)converged, n=9 is good
Results – Resolution of TLM
16
120 122 124 126 128 130 132-72-71-70-69-68-67-66-65-64-63-62-61-60
measured TLM D=1.5 TLM D=5 TLM D=8
Y Position (in)
Rece
ived
Sig
nal S
tren
gth
(dBm
)not converged, D=8 is the best
Conclusions & Future Works
• Conclusions– 2dB error of both raytracing & TLM– Model uncertainty > error eliminated by chamber– Validation outside the chamber may be okay
• Future works– Quantify the speed of different models– Consider the beamform of antenna
17
Backup Slides
18
Result – Antenna Shape
19
120 122 124 126 128 130 132-67
-66
-65
-64
real point h-line v-line s-rect l-rect
Y Position (in)
Rece
ived
Sig
nal S
tren
gth
(dBm
)
Title
• text
20
Title
• text
21