doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 1 Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs) Submission Title: IEEE Relative Location Date Submitted: May 2004 Source: Neiyer Correal, Frederick Martin, Motorola, Inc. Contact: F. Martin, Motorola, Inc., 8000 W. Sunrise Blvd. Plantation, FL Voice: , FAX: , Re: Technical Contribution to TG4A Abstract:Relative location based on received signal strength ranging can be used for 2 dimensional location in personal area networks. Purpose:To provide information on potential location performance of networks based on IEEE 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 /XXX Submission May 2004 Correal, Motorola, Inc.Slide 2 Motivation for Relative Location Techniques Device data must be accompanied by its location –Actuator must know where to act –Alarm must be localized to be useful to a human operator Placing & locating every device is labor-intensive Cost of device location must be considered –GPS cost, power consumption can be prohibitive Only an outdoor solution –Local Positioning Systems (LPS) need intensive installation High Cost of wiring Labor intensive

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 3 Relative Location Goal: Self-location with few known-location nodes –Without wired infrastructure –Applicable to any environment data link central computer A B C 7 ‘Blindfolded’ Wireless Sensors ‘Reference’ 3 Difficulties –Ad hoc connectivity Advantages –Reference devices are the ‘infrastructure’ –Peer-to-peer range measurement possible –Accuracy/range extension

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 4 Relative Location Conventional Location –Devices are located only with respect to fixed base stations Relative Location –All devices calculate the distance to their neighbors Architectural Blueprint d z9z9 d d d d ddd d dd d dd d d data link central computer Architectural Blueprint zBzB zAzA zCzC z 12 d 9,B d 9,C data link central computer d 9,A Benefits Higher rates Location Accuracy/Range Extension Characteristics Long path lengths Complex installation zn:zn: devices range estimates d a,b : Legend Synch / data ‘Blind’ NeuRFons ‘Reference’ v

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 5 Relative Location in 1 Dimension

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 6 Relative Location – Physical Analogy Relative location analogy: –Nails represent absolute location information –Springs’ natural lengths are the estimated range between nodes –Spools are nodes Location Mapping Algorithm Relative Range Data Reference and Blind NeuRFons Spools will move in the direction of force until sum of forces equals zero

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 7 Range Estimation Techniques Time Difference of Arrival (TDOA) relies on time synch –(ns) time-synch unlikely Time-of-Arrival (TOA) can be measured via round-trip At 1 meter range resolution for 3 ns time resolution (RF signal), wide bandwidth signal is needed. Received Signal Strength (RSS) is considered coarse due to the multipath channel Range estimate variance increases with range WE WILL FOCUS ON RSS ON RF SIGNALS Various media are possible RF Infrared Ultrasound Acoustic Time-Based Techniques Signal Strength Techniques

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 8 Relative Location Simulation Path Loss Errors of  = 6 dB Single room, 20 m by 10 m 3, 4, or 6 Reference devices 1 to 10 Blindfolded devices Reference devices located in corners Other devices placed at random Simulation of Indoor Relative Location –Signal Strength as a Ranging Technology Location Accuracy improves with either –More Reference devices –More Blindfolded devices.

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 9 Relative Location Experiment Set-up Measurements –Mot. Labs Plantation FL, office environment –13 by 15 m area –44 devices (0.2 /m 2 ) –4 reference devices in corners of area –Nodes at 1m height –Multipoint to multipoint –44*43*5 = 9460 measurements –2.4 GHz signal, 40 MHz BW Figure: Area Map, Device # and Location

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 10 Relative Location Experiment Set-up RMS Location Error of 2.14 m Histogram of Errors #T #R True Location Relative Location Estimate Key: RMS is 15% of Ref. device separation

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 11 Relative Location Radio Testbed Testbed Device –900 MHz, 50 kbit/s FM –8 channels –Sensor Suite RSS Ranging

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 12 Relative Location Measurement Results Environments –Outdoor Parking Lot –Residential Home 9m x 9m area, 4 by 4 grid –Reference nodes at corners RMS location errors –1.0m in parking lot –2.1m in house Above: Map of the Perkins home and grid of 16 device locations. Side: Parking lot experiment. Devices are located on top of blue upside-down recycling bins.

doc.: IEEE /XXX Submission May 2004 Correal, Motorola, Inc.Slide 13 Summary can be used for location under some conditions RSSI appears to be a viable method for location resolution Cooperative location can enhance location estimation -- higher density of nodes results in improved location estimation For reference node separation on order of 10m, 2D location with RMS errors on order of 2m is possible For more information, see N. Patwari, A. O. Hero, III, M. Perkins, N. Correal, R. J. O’Dea, “Relative location estimation in wireless sensor networks,” IEEE Trans. On Signal Processing, vol. 51, no. 8, August, 2003, pp