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

1. 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:[n.correal@motorola.com] 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. Neiyer Correal, Motorola Inc.

2. Signal Strength Based Ranging Florida Communications Research Labs Presented by Neiyer Correal Motorola Labs Motorola Inc. Neiyer Correal, Motorola Inc.

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 802.15.4 Neiyer Correal, Motorola Inc.

4. d Free Space Propagation Power density flux is given by: Power collected by an antenna of effective area Ae is: Expressing Ae in terms of antenna gain Neiyer Correal, Motorola Inc.

5. d Free Space Path Loss Attenuation • In free space energy attenuation obeys an inverse square law 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. Neiyer Correal, Motorola Inc.

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 Neiyer Correal, Motorola Inc.

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/d0) log(d/d0) log(d/d0) Pr(dBm) Pr (dBm) Pr (dBm) Neiyer Correal, Motorola Inc.

8. Mean Large-scale Path Loss • The mean received power decreases logarithmically with distance log(d/d0) Pr(d0) n Pr(dBm) Neiyer Correal, Motorola Inc.

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

10. Impulse Response • Small-scale behavior is directly related to impulse response of the channel • RMS delay spread • where Neiyer Correal, Motorola Inc.

11. 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 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.

12. Mitigating Fading Effects • Diversity Techniques are useful for mitigating fading effects • Frequency • Spatial • Temporal • Equalizer/Rake filters mitigate frequency selective fading. Neiyer Correal, Motorola Inc.

13. 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. Neiyer Correal, Motorola Inc.

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 p0 is path loss at reference distance d0 Xs is Log-Normal medium scale fading error n = 2.3 σ = 3.92 Neiyer Correal, Motorola Inc.

15. Validating the log-normal assumption then If There is a good fit to the model. Neiyer Correal, Motorola Inc.

16. Converting RSS to Range • Range can be estimated via: • Estimated range has a log-normal distribution Neiyer Correal, Motorola Inc.

17. Range Variance and Distance Range estimate distribution variance decreases with distance d=10 d=10 d=10 d=20 d=20 d=20 Neiyer Correal, Motorola Inc.

18. Multi-hop RSS Ranging • Multiple short range measurements are more accurate than a long one Normalized Error Number of hops Neiyer Correal, Motorola Inc.

19. 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. Neiyer Correal, Motorola Inc.

20. Sources of Error • Small-scale and large-scale fading • Propagation model parameters • Device variabililty • Antenna, temperature and frequency effects • Quantization Neiyer Correal, Motorola Inc.

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 Neiyer Correal, Motorola Inc.

22. Reference Device Blindfolded Device 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: s1 for location estimate for the 1-blindfolded device example. AssumessdB/n = 1.7. Scales with d, distance between reference devices. d Neal Pawari et al, Relative Location in Wireless Sensor Networks. IEEE Trans. Sig. Proc. x1 x Neiyer Correal, Motorola Inc.

23. central computer data link z9 d d d d d d d d d d d d d d d d NeuRFons Architectural Blueprint ‘Reference’ ‘Blind’ Relative Location • Devices calculate ranges to their neighbors • Location is jointly estimated using collective information • Benefits • Location Accuracy/Range Extension Neiyer Correal, Motorola Inc.

24. 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. Neiyer Correal, Motorola Inc.