Transcript 15-04-0564-00-004a-signal-strength-based-ranging.ppt

September 2004
doc.: IEEE 802.15-04-0564-00-004a
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Signal Strength Based Ranging]
Date Submitted: [August 31, 2004]
Source: [Neiyer Correal] Company [Motorola Inc.]
Address [8000 West Sunrise Boulevard, Plantation, FL, USA]
Voice:[(954)723-8000], FAX: [(954)723-3712], E-Mail:[[email protected]]
Re: []
Abstract: [Focus of the presentation is the application of Received Signal Strength for ranging]
Purpose: [Provide information on RSS ranging.]
Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for
discussion and is not binding on the contributing individual(s) or organization(s). The material in this
document is subject to change in form and content after further study. The contributor(s) reserve(s) the right
to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE
and may be made publicly available by P802.15.
Submission
Slide 1
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Signal Strength Based Ranging
Florida Communications Research Labs
Presented by Neiyer Correal
Motorola Labs
Motorola Inc.
Submission
Slide 2
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Table of Contents
•
•
•
•
•
•
Free Space Propagation
Large Scale Attenuation Mechanisms
Small Scale Attenuation
Converting RSS to Range estimates
Location with RSS
RSS Ranging with 802.15.4
Submission
Slide 3
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Free Space Propagation
Power density flux is given by:
d
Pd (d ) 
Pt Gt
4d 2
Watts/m 2
Power collected by an antenna of effective area Ae is:
Pr (d )  Pd (d)A e Watts
Expressing Ae in terms of antenna gain
Pr (d )  Pt Gt G
 
 2
r 4d
Submission
Slide 4
Ae 
G2
4
Watts
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Free Space Path Loss Attenuation
• In free space energy attenuation obeys an inverse
square law
d
Ld   10 log 10
Pr
Pt
  10 log 10G G  
( 4d ) 2
2
t
r
Model is valid in the far-field when there are no
obstructions – Satellite Communications
In practice received power is referenced with respect to a
reference distance d0 in the far field.
Pr (d )  Pr (d 0 )
Submission
Slide 5
 
d0 2
d
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Mechanisms Impacting Propagation
• In terrestrial settings additional mechanisms
affect wave propagation and received power
• Reflection – From large smooth surfaces
• Diffraction – Secondary waves go around
obstacle edges
• Scattering – Rough surfaces scatter energy
Submission
Slide 6
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Propagation Attenuation Mechanisms
•
•
•
•
Received Signal Strength is attenuated by three propagation loss mechanisms:
Logarithmic power decrease with distance
Slowly varying shadowing component – terrain contours and obstructions
Fast fading component – multipath addition
log(d/d0)
Pr (dBm)
Pr(dBm)
•
log(d/d0)
Pr (dBm)
log(d/d0)
For ranging we would like to mitigate the random small-scale attenuation and
distill the more deterministic large-scale attenuation
Submission
Slide 7
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Mean Large-scale Path Loss
• The mean received power decreases
logarithmically with distance
Pr (d )  Pr (d 0 )
 
d0 n
d
log(d/d0)
Pr(dBm)
Pr(d0)
n
Pr (d ) dBm  Pr (d0 ) dBm  10n log
Submission
Slide 8
 
d0
d
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Large-scale Fading
• Variation of individual measurements around
the mean have a normal distribution in dB
log(d/do)
P(dBm)

2
Pi , j (dBm) ~  Pi , j (dBm),  dB
Pr (d0 )dBm  Pr (d )dBm  
Submission
Slide 9
Neiyer Correal, Motorola Inc.

September 2004
doc.: IEEE 802.15-04-0564-00-004a
Impulse Response
• Small-scale behavior is directly related to impulse
response of the channel
h( )   ai e
 ji
 (  i )
• RMS delay spread
   2  2
• where

  a2
k
a k2
Submission
ak2 2

  a2
k
2
Slide 10
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Effects of signal time-spreading
Channel
Channel
Signal
Signal
FLAT FADING CHANNEL
Delay spread < Symbol Period
Spectral characteristics preserved
Copies of the signal add vectorially
Received power fluctuates significantly
over a local area
Submission
Slide 11
FREQUENCY SELECTIVE CHANNEL
Delay spread > Symbol Period
Intersymbol interference
Multipath can be resolved
Received power does not fluctuate
significantly over a local area
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Mitigating Fading Effects
• Diversity Techniques are useful for
mitigating fading effects
• Frequency
• Spatial
• Temporal
• Equalizer/Rake filters mitigate
frequency selective fading.
Submission
Slide 12
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Measuring Received Power
• With wideband signals mean received power
can be calculated summing the powers of the
multipath in the power delay profile.
• With narrowband signals, received power
experiences large fluctuations over a local
area. Averaging must be used to estimate
mean received power.
Submission
Slide 13
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
RSS Measurements
•
Measurements
– 2.4 GHZ band 40 MHz BW
– Mot. Labs Plantation FL, office
environment
– 13 by 15 m area
– Multipoint to multipoint
– 9460 RSS measurements
 di , j 
  X 
pˆ i , j  po  10n log 10 
 d0 
n = 2.3
σ = 3.92
Submission
p0 is path loss at
X is Log-Normal
reference distance d0 medium scale fading error
Slide 14
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Validating the log-normal assumption
If

2
pˆ i , j   pi , j ,  dB

then

2
pˆ i , j  pi , j   0,  dB

There is a good fit to the model.
Submission
Slide 15
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Converting RSS to Range
• Range can be estimated via:
dˆ  d 010
p0  pˆ ( d )
10 n
 d10
X
10 n
• Estimated range has a log-normal
distribution
 ( , 2 )
Submission
Slide 16
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Range Variance and Distance
d=10
d=20
d=10
d=10
d=20
d=20
Range estimate distribution variance decreases with distance
Submission
Slide 17
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Multi-hop RSS Ranging
• Multiple short range measurements are
more accurate than a long one
Normalized Error
1
k
Number of hops
Submission
Slide 18
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
802.15.4 Implementation
• Take advantage of LQI or ED for ranging purposes.
• Configure Link Quality Indicator to provide Received
Signal Strength.
• LQI is reported to the MAC via PD-DATA.indication.
• LQI values range from 0x00 to 0xff. 0x00
corresponding to lowest quality signal.
• LQ values are uniformly spaced in between.
• At least 8 values of LQ are required.
• Channel model parameters are needed.
• TX Power and RSS circuitry calibration.
Submission
Slide 19
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Sources of Error
•
•
•
•
Small-scale and large-scale fading
Propagation model parameters
Device variabililty
Antenna, temperature and frequency
effects
• Quantization
Submission
Slide 20
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Location with RSS
• Coarse location can be achieved via
connectivity information
• RSS can be effectively used for location
fingerprinting
• Traditional multilateration is feasible with
RSS information
• Relative Location improves accuracy/range
Submission
Slide 21
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
CRLB: One Unknown-Location Device
•
RSS case
– Scales proportionally with distance
d and with σdB /n
– RSS performance can exceed TOA
at certain density of devices.
– Min value  σ1  27% of d.
Average bound is 0.3
– Traditionally RSS is coarse,
however one can take advantage
of high density of devices
y
y1
RSS Case: 1 for location estimate for the 1-blindfolded
device example. Assumes dB/n = 1.7. Scales with d,
distance between reference devices.
d
Reference Device
x1
Submission
x
Blindfolded Device
Slide 22
Neal Pawari et al, Relative Location in Wireless Sensor Networks.
IEEE Trans. Sig. Proc.
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
Relative Location
central
computer
d
d
d
d
d
d
d
d
d
d
data
link
Devices calculate ranges to their
neighbors
Location is jointly estimated using
collective information
d
d
z9
d
d
d
d
Architectural Blueprint
NeuRFons
Benefits
Location Accuracy/Range
Extension
‘Reference’
‘Blind’
Submission
Slide 23
Neiyer Correal, Motorola Inc.
September 2004
doc.: IEEE 802.15-04-0564-00-004a
REFERENCES
[1] T.S. Rappaport, Wireless Communications 2nd
Edition, Prentice Hall, 2001.
[2] Patwari Neal et al, Relative Location in Wireless
Networks, IEEE Transactions on Signal Processing,
vol. 51, no. 8, August 2003, pp. 2137-2148.
[3] Patwari Neal et al, Using Proximity and Quantized
RSS for Sensor Location in Wireless Networks,
Proceedings of the 2nd International ACM Workshop
on Wireless Sensor Networks and Applications
(WSNA), San Diego, CA, Sept. 19, 2003.
Submission
Slide 24
Neiyer Correal, Motorola Inc.