A Hybrid Indoor Tracking System for First Responders

Transcription

1 A Hybrid Indoor Tracking System for First Responders Precision Indoor Personnel Location and Tracking for Emergency Responders Technology Workshop August 4, 2009 Marc Harlacher Director, Location Solutions Lin Haas Navigation Programs Lead

2 Introduction DHS S&T is developing a precision indoor location and tracking device for first responders: GLANSER program Argon ST, in conjunction with our partners, has offered a solution that extends the hybrid approach with new technologies Solution integrates personnel tracking and status reporting with an open and extensible communications infrastructure Includes an incident command and monitoring interface suitable for local and/or remote operation Function GLANSER BAA Requirement (Goal) 3D Position 1.0 (0.5) meter Operating Range NLOS 15 (30) meters Operating Range LOS 30 (100) meters Connectivity 90% (99%) Dimensions 2 x 4 x 6 Weight 1 lb. Life 4 (12) hours Data Storage 45 (240) mins. Max # Nodes 500 2

3 Indoor Navigation Approach Hybrid peer-to-peer networking, A-GPS and inertial sensors to deliver sub-meter positioning accuracy Precise urban and indoor location of individuals Accurate absolute positioning Advantageous operating range Reliable and adaptive communication Automatic operation Desired line of sight signal Undesired multipath signal 3

4 Indoor RF Navigation Challenges Line of Sight (LOS) signal attenuation 5 to 20+dB of signal attenuation per wall or floor Reduces operating range Rapidly eliminates reliable use of GPS Non-uniform frequency attenuation distorts the signal Multipath signal reflections Complex indoor environments contain large numbers of reflective surfaces Dozens of multipath reflections are generated for any given transmitter/receiver pair geometry Example complex indoor environment Line of sight (red path) 4

5 Variation of Multipath and Line of Sight Signal Amplitudes for Mobile Users Black lines: LOS < -140 dbm Red: LOS 20 db weaker than at least one other path Transmitter Intermediate colors: LOS is weaker than MP, but may be usable Blue: LOS is the strongest path (multipath can still be present) 80 Time (sec) 90 Comparison of LOS signal strength relative to the strongest multipath signal Assume LOS must be above -140 dbm to be tracked Typically 5-15 paths modeled between a transmitter and receiver Note rapid changes in LOS availability and amplitude challenging environment LOS amplitude often changes abruptly within each second 5

6 Multipath and Ranging Receivers Without multipath, the receiver s estimate for signal time of arrival is unambiguous over time Navigation uses the time (or delay) measurement at the peak of this gabled roof Line of sight signal is easily obtained from the peak Multipath creates ambiguities in the time of arrival measurement These ambiguities distort the delay estimate and lead to inaccurate navigation Can you find the line of sight signal? Time Correlator Delay Signal Profile without Multipath Time Signal Profile with Multipath Correlator Delay 6

7 Time Domain Techniques Multipath Mitigation Employed by Indoor RF Navigation Systems Observation: Multipath reflections always arrive later than the line of sight Given sufficient time resolution, one can determine which signal arrives first Time resolution is proportional to the inverse of the signal bandwidth Ultra Wide Band (UWB) techniques achieve sufficient time resolution by using extreme signal bandwidth The primary drawback to using very large bandwidth is potential interference caused to (and by) other signals Places practical limits on transmission power Very good for short range applications Spatial Techniques Observation: Multipath reflections tend to arrive from different directions than the line of sight Given sufficient angular resolution, one can determine which signal arrives from the desired direction Solutions include mechanically or electronically-steered directional antennas, and super-resolution techniques 7

8 Synthetic Aperture Line of Sight Assessment (SALSA) Synthetic aperture Beam footprint SALSA concept is analogous to synthetic aperture beamforming: Data from multiple epochs are integrated User motion is used to form large apertures MP Application to multipath mitigation for dynamic users: Complex samples are integrated over multiple data bits LOS signal integrates coherently/optimally Multipath integrates destructively LOS t 0 t 1 8

9 SALSA Separates the LOS and Multipath Signal Components Only the accurate line of sight component is used for navigation Accurate line of sight path is isolated from multipath Current receivers track these stronger multipath signals which results in large positioning errors Angle of Arrival Time of Arrival Both angle and time of arrival are used to identify the line of sight 9

10 Experimental Results SALSA has been demonstrated in a range of relevant environments Controlled experiments in anechoic chamber Indoors (commercial office building) Urban canyon (Rosslyn, VA) Most relevant experiments duplicate a challenging first responder scenario: One node located on a vehicle in a parking lot Second node moving on the 7 th floor of a 10-story office building (far side) ~100 meter LOS separation Signal parameters: Argon BW = ~5 MHz building, Rx EIRP = 0.1 watt 7 th floor Omni antennas Path amplitude Correlation Sample MP Delay, m LOS Correlator Range rate, m/s Tx 10

11 Wrap-Up SALSA is capable of unprecedented multipath mitigation, enabling robust precise indoor navigation Simultaneously addresses the range propagation and multipath mitigation challenges Together with other new technologies, Argon and its partners offer a compelling solution to one of the urgent needs of the first responder community 55 y, m Performance prediction indicating less than 1 meter indoor positioning x, m 11