positioning in ad-hoc networks - a problem statement jan beutel computer engineering and networks...
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Positioning in Ad-Hoc Networks-
A Problem Statement
Jan BeutelComputer Engineering and Networks Lab
Swiss Federal Institute of Technology (ETH) Zurich
June 20, 2001
Computer EngineeringComputer Engineeringand Networks Laboratoryand Networks Laboratory
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Positioning: Environment
• Stationary and Dynamic Environments
• Graph Connectivity
– Node Clusters
– Node Depletion
• Variance in
– Initial Position Estimates
– Range Estimates
• Map Data, Lookup Tables
• Multiple Link Reception Capability of Nodes
• Low Duty Cycle Radio Frontend
• Incorporate Positioning System in Communication Framework
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Positioning: The Problem
• Finding the position of networking nodes
Relative vs. Absolute Positioning Mode
Reference Positions, Map
Database
Other Networking Nodes, Distance and Geometric
Constellation
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Positioning: Definitions
• anchor node knows its location at start of algorithm
• unknown node does not know its location
• settled node has discovered its location
• neighborhood all nodes within one hop
• Context dependent on Positioning Mode
– Absolute Coordinates (Xi,Yi) Position
– Relative Coordinates (xi-X0,yi-X0) Orientation, Topology
– Range Value ri Proximity to Neighbors
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Positioning: Granularity
• Granularity of Solution Depends on– Network population (nodes/area)– Geometric constellation (Dilution of Precision)– Amount of settled nodes (convergence)– Dynamics in networking nodes (network links/area)– Bounds of the geometric solution
• Coarse Grain Positioning– Cell based proximity– Coarse topology discovery– Low precision coordinates– Invariants
• Fine Grain Positioning– High precision coordinates– Orientation
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Existing Solutions
• Cell Based Identification
• Triangulation to Base Stations (AOA, TDOA, TOA, RSSI, Carrier Phase…)– Global Positioning System– Radar/VOR– Mobile Phones
• Depending on Uni-/Bi-directional Communication Link
• Probability Spaces• Mapping to RF Reference Mappings• Event Based• Topology Information
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Radio Ranging Methods
TOA – time of arrival
Carrier phase
AOA – angle of arrival
Signal strength
TDOA – time distance of arrival
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Positioning Scenarios
• Initialization– Problem: Convergence
• Iteration– Single connected graphs– No dynamics– Problem: Large Amount of Data
• Motion– Multiple disconnected graphs– Mobile nodes– Additional metric incorporated– Problem: Distributed System
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Algorithms for Positioning
• Case: No Anchors available
Idea: Reuse High Connectivity
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Redundant Triangulation
Iteration on 25 individual ranges with 50% each
0 0.5 10
0.2
0.4
0.6
0.8
1
Delaunay Mesh of 25 Networked Nodes
x
0 0.5 10
0.2
0.4
0.6
0.8
1
Solution on 25 Ranges and 50% Error
x
0 0.5 10
0.2
0.4
0.6
0.8
1
50 Solutions and Mean
x
0.4 0.45 0.5 0.55 0.60.4
0.45
0.5
0.55
0.6
Zoom on Error
x
dx 0.0054
dy 0.0058
1% error
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Triangulation on Real Data
• Application to Wavelan RSSI data shows good average
Solution• Iterative triangulation• Overload systems• Influence of
geometric DOP• Include
environmental information
Yielding sub meter DOP
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Algorithms for Positioning
• Case: Anchors available
Idea: Propagate Reference Data
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Establishing Initial Position Estimates
• Assumption Based Coordinates (ABC)
• n0 assumed to be at (0,0,0)
• n1 assumed to be at (r01,0,0)
r01 = RSSI range between n0 and n1
• n2 at (
Assumptions:
• n3 at (
Assumption:
r012 + r03
2 - r132
2r01
, r032-x3
2-y32 )
r032 – r23
2 + x22 + y2
2 - 2x2x3
2r01
,
r012 + r02
2 - r122
2r01
, r022-x2
2 , 0)x
y
z
n0 n1
n2
n3• positive square root• z2 = 0
• positive square root
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
The TERRAIN Algorithm
• Triangulation via Extended Range and Redundant Association of Intermediate Nodes
• ABC algorithm creates maps
• Target node waits to beincluded in 3 maps
• Extended rangescalculated fromrespective maps
• Triangulation bytarget node basedon extended ranges
• Iterate network-widetriangulation
1
2
3
radio range
extended range
intermediate node
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Status
• Simulations yielding first results– Redundant triangulation works well– Range error impacts more than initial position– Initialization/Convergence a problem
• Testbed in setup phase– Smart it’s – BTnode– Multihop BT Prototype
• Simulation with real data in preperation
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Algorithms for Positioning using Bluetooth
• Appropriate HCI Commands and Events– Find Neighbors
• HCI_INQUIRY
– Classify Neighbors• HCI_READ_REMOTE_SUPPORTED_FEATURES
– Continuity in Neighbors• HCI_READ_CLOCK_OFFSET• HCI_READ_CONNECTION_ACCEPT_TIMEOUT• HCI_READ_PAGE_TIMEOUT• HCI_READ_LINK_SUPERVISION_TIMEOUT• HCI_READ_FAILED_CONTACT_NUMBER
– Find Ranges • HCI_READ_RSSI
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Bluetooth RSSI Samples Free Space
-25
-20
-15
-10
-5
0
5
10
15
201
30
59
88
11
7
14
6
17
5
20
4
23
3
26
2
29
1
32
0
34
9
37
8
40
7
43
6
46
5
49
4
52
3
55
2
58
1
61
0
63
9
66
8
69
7
72
6
75
5
78
4
81
3
84
2
87
1
90
0
92
9
95
8
98
7
10
16
10
45
Samples/Distance
RS
SI
Series1
Series2
S
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Bluetooth RSSI Samples Office Space
-25
-20
-15
-10
-5
0
5
10
15
201 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103
109
115
121
127
133
139
145
151
157
163
169
175
181
187
193
199
Samples/Distance
RS
SI
Series1
Series2
Series3
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Jan Beutel, March 26, 2001Jan Beutel, March 26, 2001
Wavelan 802.11b RSSI Samples
-120
-100
-80
-60
-40
-20
0
20
40
60
80
-3 -2 -1 0 0 1 2 3 4 5 6 6 7 8 9 10 11 12 12 13 14 15 16 17 18 18 19 20 21 22
Distance [m]
Sig
na
l an
d N
ois
e L
ev
el [
dB
m]
LSNR Avg
LSL Avg
LNL Avg
RSNR Avg
RSL Avg
RNL Avg
Path Loss 1/r 2̂
Path Loss 1/r 4̂