Doc.: IEEE 802.15-04-0564-00-004a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 1 Project: IEEE P802.15 Working Group for Wireless Personal

September 2004

Neiyer Correal, Motorola Inc.Slide 1

doc.: IEEE 802.15-04-0564-00-004a

Submission

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)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.

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Signal Strength Based Ranging

Florida Communications Research Labs

Presented by Neiyer Correal

Motorola LabsMotorola Inc.

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

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

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Free Space Propagation

d 2

4 Watts/m)( 2d

GPd

ttdP

Watts(d)A)( edr PdP

Power collected by an antenna of effective area Ae is:

Expressing Ae in terms of antenna gain

4

2GeA

Watts)( 2

4 drttr GGPdP

Power density flux is given by:

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Free Space Path Loss Attenuation• In free space energy attenuation obeys an inverse

square law

2

2)4(Pr 10log1010log10

rtGG

dPtdL d

Model is valid in the far-field when there are no obstructions – Satellite Communications

200)()( dd

rr dPdP

In practice received power is referenced with respect to a reference distance d0 in the far field.

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

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

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

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

• For ranging we would like to mitigate the random small-scale attenuation and distill the more deterministic large-scale attenuation

log(d/d0)

Pr(

dB

m)

Pr

(dB

m)

Pr

(dB

m)

log(d/d0) log(d/d0)

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Mean Large-scale Path Loss

• The mean received power decreases logarithmically with distance

ndd

rr dPdP 0)()( 0

dddBmrdBmr ndPdP 0log10)()( 0

log(d/d0)

Pr(

dB

m)

Pr(d0)

n

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Large-scale Fading

• Variation of individual measurements around the mean have a normal distribution in dB

dBmrdBmr dPdP )()( 0

log(d/do)P

(dB

m)

2,, ),dBm(~)dBm( dBjiji PP

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Impulse Response

• Small-scale behavior is directly related to impulse response of the channel

• RMS delay spread

• where

)()( ij

iieah

22

2

2

k

k

a

a 2

222

k

k

a

a

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Effects of signal time-spreading

Signal

Channel

Signal

Channel

FLAT FADING CHANNELDelay spread < Symbol Period

Spectral characteristics preservedCopies of the signal add vectorially

Received power fluctuates significantlyover a local area

FREQUENCY SELECTIVE CHANNELDelay spread > Symbol Period

Intersymbol interferenceMultipath can be resolved

Received power does not fluctuatesignificantly over a local area

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Mitigating Fading Effects

• Diversity Techniques are useful for mitigating fading effects

• Frequency

• Spatial

• Temporal

• Equalizer/Rake filters mitigate frequency selective fading.

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

• 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.

Measuring Received Power

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

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

Xd

dnpp ji

oji

0

,10, log10ˆ

X is Log-Normal medium scale fading error

p0 is path loss at reference distance d0

n = 2.3σ = 3.92

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Validating the log-normal assumption

2,, ,ˆ dBjiji pp 2

,, ,0ˆ dBjiji pp If then

There is a good fit to the model.

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Converting RSS to Range

• Range can be estimated via:

• Estimated range has a log-normal distribution

n

X

n

dpp

ddd 1010

)(ˆ

0 1010ˆ0

),( 2

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Range estimate distribution variance decreases with distance

Range Variance and Distance

d=10

d=20 d=20 d=20

d=10 d=10

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Multi-hop RSS Ranging

• Multiple short range measurements are more accurate than a long one

k1

Number of hops

No

rma

lize

d E

rro

r

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

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.

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Sources of Error

• Small-scale and large-scale fading

• Propagation model parameters

• Device variabililty

• Antenna, temperature and frequency effects

• Quantization

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

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

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

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

RSS Case: 1 for location estimate for the 1-blindfolded device example. Assumes dB/n = 1.7. Scales with d,

distance between reference devices.

Blindfolded Device

Reference Device

d

x

y

x1

y1

Neal Pawari et al, Relative Location in Wireless Sensor Networks. IEEE Trans. Sig. Proc.

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

Relative Location

Devices calculate ranges to their neighbors

Location is jointly estimated using collective information

BenefitsLocation Accuracy/Range Extension

Architectural Blueprint

d

z9

d

d

d

d

d

dd

d

dd d

d

d

dd

datalink

central computer

‘Blind’

NeuRFons

‘Reference’

September 2004


doc.: IEEE 802.15-04-0564-00-004a

Submission

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.

Documents

Doc.: IEEE 802.15-04-0564-00-004a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 1 Project: IEEE P802.15 Working Group for Wireless Personal