doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 1 Project: IEEE P 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) ], FAX: [(954) ], 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 P 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 P

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 2 Signal Strength Based Ranging Florida Communications Research Labs Presented by Neiyer Correal Motorola Labs Motorola Inc.

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 3 Table of Contents Free Space Propagation Large Scale Attenuation Mechanisms Small Scale Attenuation Converting RSS to Range estimates Location with RSS RSS Ranging with

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 4 Free Space Propagation d Power collected by an antenna of effective area A e is: Expressing A e in terms of antenna gain Power density flux is given by:

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 5 Free Space Path Loss Attenuation In free space energy attenuation obeys an inverse square law d 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 d 0 in the far field.

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 6 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

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 7 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/d 0 ) Pr(dBm) log(d/d 0 )

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 8 Mean Large-scale Path Loss The mean received power decreases logarithmically with distance log(d/d 0 ) Pr(dBm) P r (d 0 ) n

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 9 Large-scale Fading Variation of individual measurements around the mean have a normal distribution in dB log(d/do) P(dBm)

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 10 Impulse Response Small-scale behavior is directly related to impulse response of the channel RMS delay spread where

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 11 Effects of signal time-spreading Signal Channel Signal Channel FLAT FADING CHANNEL Delay spread < Symbol Period Spectral characteristics preserved Copies of the signal add vectorially Received power fluctuates significantly over a local area FREQUENCY SELECTIVE CHANNEL Delay spread > Symbol Period Intersymbol interference Multipath can be resolved Received power does not fluctuate significantly over a local area

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 12 Mitigating Fading Effects Diversity Techniques are useful for mitigating fading effects Frequency Spatial Temporal Equalizer/Rake filters mitigate frequency selective fading.

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 13 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

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 14 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 X  is Log-Normal medium scale fading error p 0 is path loss at reference distance d 0 n = 2.3 σ = 3.92

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 15 Validating the log-normal assumption If then There is a good fit to the model.

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 16 Converting RSS to Range Range can be estimated via: Estimated range has a log-normal distribution

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 17 Range estimate distribution variance decreases with distance Range Variance and Distance d=10 d=20 d=10

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 18 Multi-hop RSS Ranging Multiple short range measurements are more accurate than a long one Number of hops Normalized Error

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 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.

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 20 Sources of Error Small-scale and large-scale fading Propagation model parameters Device variabililty Antenna, temperature and frequency effects Quantization

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 21 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

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 22 CRLB: One Unknown-Location Device RSS case –Scales proportionally with distance d and with σ dB /n –RSS performance can exceed TOA at certain density of devices. –Min value  σ 1  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 x1x1 y1y1 Neal Pawari et al, Relative Location in Wireless Sensor Networks. IEEE Trans. Sig. Proc.

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 23 Relative Location Devices calculate ranges to their neighbors Location is jointly estimated using collective information Benefits Location Accuracy/Range Extension

doc.: IEEE a Submission September 2004 Neiyer Correal, Motorola Inc.Slide 24 REFERENCES [1] T.S. Rappaport, Wireless Communications 2 nd Edition, Prentice Hall, [2] Patwari Neal et al, Relative Location in Wireless Networks, IEEE Transactions on Signal Processing, vol. 51, no. 8, August 2003, pp [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.