12_-_Additional_Issues.pdf

Additional Issues
Introduction
This module is a place for all those extra items that crop up after the main material has
been presented. At this time, the only thing we have left is Locationing.
Objectives
ƒ
Locationing
Low Power RF Solutionsp - Additional Issues
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Module Topics
*** no matter how far you go, there you are ***
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Module Topics
Module Topics
Additional Issues ......................................................................................................................................12-1
Module Topics........................................................................................................................................12-3
CC2431 Location Engine ..................................................................................................................12-5
Parameters.............................................................................................................................................12-6
Operation ...............................................................................................................................................12-7
Performance and Expansion..................................................................................................................12-8
Sources of Error.....................................................................................................................................12-9
Documentation.....................................................................................................................................12-10
Low Power RF Solutions - Additional Issues
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Module Topics
*** Then they came for me (Stephen F. Rohde) ***
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Low Power RF Solutions - Additional Issues
Module Topics
CC2431 Location Engine
Location Engine Example
‹
Yellow Nodes
Š
Š
Reference nodes
Known fixed location
‹
Green Node
Š
Š
Blind node
Movable
Parameters ...
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Parameters
Parameters
CC2431 Location Engine Parameters
Xn
Yn
RSSI n
Xn+1
Y n+1
RSSIn+1
..
..
..
X15
Y 15
RSSI15
‹
‹
‹
Location
Engine
X
Y
Engine can accept 3 minimum and 16 maximum
reference nodes (at least 4 suggested for accuracy)
X and Y are in meters [0, 63.75]
Š Resolution: 0.25 m
RSSI is in dBm [-40 dBm, -95 dBm]
Š Resolution: 0.5 dBm
How does it work? ...
4
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Low Power RF Solutions - Additional Issues
Operation
Operation
How Does It Work?
‹
‹
‹
Uses Received Signal Strength Indicator
Š Proportional to distance
Š Measured in dBm
Š Averages reading over several broadcasts
Maximum likelihood (ML) algorithm
Š Performs range estimation using RSSI
Š Uses range estimates from reference nodes to calculate
location
Blind node builds a table with X, Y and RSSI values
Xn
Yn
RSSI n
Xn+1
Y n+1
RSSIn+1
..
..
..
X15
Y 15
RSSI15
Location
Engine
X
Y
Performance and expansion ...
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Performance and Expansion
Performance and Expansion
Performance and Expansion
Time to estimate
location
Reference node
location precision
Location Range
Blind node
location precision
35us - 13ms
0.25 meter
64 x 64 meters
(Software
expandable)
0.5 meter
More range expansion ...
6
More Range Expansion
‹
‹
‹
‹
Map the coordinates of
the red node to (32, 32)
Map the coordinates of
the surrounding nodes
The location engine gives
position relative to the red
node
Range expansion is
automatically handled by
location engine software
(5 4 , 6 3 )
(6 3 , 6 3 )
(7 2 , 6 3 )
(2 3 , 2 3 )
(3 2 , 2 3 )
(4 1 , 2 3 )
(5 4 , 7 2 )
(6 3 , 7 2 )
(7 2 , 7 2 )
(6 7, 7 4 )
(2 3 , 3 2 )
(3 2 , 3 2 )
(4 1 , 3 2 )
(3 6, 3 4 )
(5 4 , 8 1 )
(6 3 , 8 1 )
(7 2 , 8 1 )
(2 3 , 4 1 )
(3 2 , 4 1 )
(4 1 , 4 1 )
Sources of error ...
7
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Low Power RF Solutions - Additional Issues
Sources of Error
Sources of Error
Sources of Localization Error
‹
‹
‹
‹
‹
‹
‹
‹
Small-scale and large-scale fading. Use of diversity and
intelligent scene analysis helps.
Propagation model parameters. Use local reference links to
estimate model. Iterative path loss parameter estimation.
Geometric Dilution Of Precision (GDOP). Use regular shapes for
deployment. Area of interest surrounded by reference nodes
Composite Antenna pattern, temperature and frequency effects.
Adaptive estimation of antenna gain through an iterative
process.
Algorithm Estimation, Local minima, badly conditioned
matrices. Need for low complexity initial coordinate estimates
(i.e. Coarse location can be achieved via connectivity
information). Need for bounding algorithm.
Quantization of observations and algorithm implementation.
RSSI linearity (over range, over frequency), TX, Rx power
accuracy.
Device variability
Courtesy o f Motorola Labs, Plantatio n, Florida
Documentation ...
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Documentation
Documentation
CC2431 ZDK Documentation
Quick Start Guide
Š
CC2431DK_ZDK_Quick_Start.pdf
Application Note
Š
AN042 -- CC2431 Location Engine
User Guide:
Š
CC2431DK Development Kit User Manual.pdf
Private Location Profile:
Š
Z-Stack Location Profile F8W-2006-0002.pdf
Š
Z-Stack Location Profile User's Guide F8W-2006-0008.pdf
9
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