Tracking issues in the Wireless sensor Network Presented By Vinay Kumar Singh Date:

Outline Introduction. Localization.

Tracking  Specify target’s past trajectory.  Predict future position of target. Collaborative tracking  Individual or a small group of sensors to track target in neighboring region.  Hand-off to the next group of sensors where the target is heading to next. Multiple target tracking.

Outdoors 1. GPS. Indoors 1.Active Badge (cellular proximity, infrared badges, central server). 2.Active BAT ( ultrasound-based, more accurate location Based; more accurate location identification). 3.Cricket (ultrasound emitters and object receivers, objects self- localize). 4. RADAR (IEEE based, uses signal strength and S/N ratio to deduce 2D position of wireless devices indoors). 5. Laser Range Finder. 6. Electro Motive Force Method. 7. Smart Floor method. 8. Motion Star Tracking Approaches

Location Technique Triangulation  Lateration 1. Direct 2. Time-of-Flight(e.g.GPS,Active Bat location system,Cricket,Bluesoft etc.) 3. Attenuation. (e.g. Spot on Ad hoc location system).  Angulations (e.g. ominidirectional Ranging) Scene Analysis (e.g. RADAR location system) Proximity  Monitoring wireless cellular access points. (e.g. Active Badge system)  Observing automatic ID systems. (e.g. E-Toll system, EPC etc)  Detecting physical contact. (e.g. Capacitive field detection, Smart Floor method)

Triangulation (x3, y3) (x1,y1)(x2,y2) y x a b c (x-x1) 2 + (y-y1) 2 = a 2 (x-x2) 2 + (y-y2) 2 = b 2 (0,0) (x,y) (x-x3) 2 + (y-y3) 2 = c 2

Angulations

Distance Measurement Technologies Comparisons Ultrasonic time-of-flight  Common frequencies 25 – 40KHz, range few meters (or tens of meters), avg. case accuracy ~ 2-5 cm, lobe-shaped beam angle in most of the cases  Wide-band ultrasonic transducers also available, mostly in prototype phases Acoustic ToF  Range – tens of meters, accuracy =10cm RF Time-of-flight  Ubinet UWB claims = ~ 6 inches Acoustic angle of arrival  Average accuracy = ~ 5 degrees (e.g. acoustic beam former, MIT Cricket) Received Signal Strength Indicator  Motes: Accuracy 2-3 m, Range = ~ 10m  : Accuracy = ~30m Laser Time-of-Flight Range Measurement  Range =~ 200, accuracy =~ 2cm very directional RFID and Infrared Sensors – many different technologies  Mostly used as a proximity metric

Possible Implementations/ Computation Models 2. Locally Centralized Some of unknown nodes compute 1.Centralized Only one node computes 3. (Fully) Distributed Every unknown node computes Computing Nodes Each approach may be appropriate for a different application. Centralized approaches require routing and leader election. Fully distributed approach does not have this requirement.

GPS(Global Positioning System) For outdoor use, we have the Global Positioning System (GPS). GPS basics: GPS determines the distance by measuring the time it takes a signal to propagate from satellite to receiver Need to have very good synchronization of clocks Satellite clock is atomic Need to know satellite location Receive signal from three satellites to determine location Need a fourth satellite to estimate elevation and for accuracy Satellite GPS accuracy is getting reasonable (10-20 meters) BTW, there is intended noise Why? Don’t want weapons

GPS Requirement GPS Constellation  24 satellites (Space Vehicles or SVs)  20,200km altitude (12 hour orbit period)  6 orbital planes (55° inclination)  4 satellites in each plane GPS Satellite Details  Manufactured by Rockwell International, later by Lockheed M&S  ~1900 lbs (in orbit)  2.2m body, 7m with solar panels  7-10 year expected lifetime

GPS problems GPS doesn’t work indoors because the satellite signal is weak or reflected which means lowers accuracy. Indoor location systems is an active research area. Ideal location sensor in indoor environments have the following properties:  Provide fine-grain spatial information at a high update rate.  Unobtrusive, cheap, scalable and robust

Cricket: System Architecture Deploy actively transmitting beacons on walls and/or ceilings, and attach listeners to host devices (handhelds, laptops, etc.) A beacon is a small device attached to some location within the geographic space it advertises. Configure beacons with space Identifiers, and optionally with position coordinates

How Cricket work? Each beacon periodically broadcasts its space identifier and position coordinates on a radio frequency (RF) channel. Each beacon also broadcasts an ultrasonic pulse at The same time as the RF message Listeners that have line-of-sight connectivity to the beacon and are within the ultrasonic range will receive this pulse. RF travels about 10 6 times faster than ultrasound, the listener calculate Time difference of arrival between the start of the RF message from a beacon and the corresponding ultrasonic pulse.

RADAR RADAR attempts to use common off-the-shelf components. For example, b base stations. Basically, RADAR makes use of WLAN technology. RADAR assumes that the access points (AP)s provide overlapping coverage over area of interest. The user carries a mobile device which helps in determining location e.g. laptop, palmtop, badge. Practical signal strength model. Radio Propagation Model

RADAR Approach It is a RF based Indoor location tracking system. It provides the information based on various base station range overlapping areas and their signal measurement. It combines empirical measurements with signal propagation modeling to determine user location. RADAR uses signal strength information gathered at multiple receiver locations to triangulate the user’s coordinates. Triangulation is done using both empirically-determined and theoretically computed signal strength information.

Active Badge First indoor badge system Based on infrared technology Each locatable wears a badge Emits a unique ID periodically Server collects data from fixed sensors (base stations) System provides symbolic absolute location information Sunlight and fluorescent light interfere with infrared Infrared limits cell sizes to small- or medium-sized room. Users wear infrared badges Badge emits GUID every 10 seconds

Active Bat system Based on ultrasound Locatable carry Active Bat tags Request/Response protocol  Controller sends request via short-range radio  Bat replies with ultrasonic pulse  Controller resets ceiling sensors via wired network  Ceiling sensor measures distance using time from reset to ultrasonic pulse arrival  Estimated distance

Active Bat System Radio transceiver, controlling logic and an ultrasonic transducer. Periodically transmits a radio message containing a single identifier (corresponds to a Bat unit). Placed at known points on the ceiling of the rooms to be instrumented. Receivers are connected by a wired daisy-chain network. Receivers monitor the incoming ultrasound and record the time of arrival for any bat signal.

Acoustic Target Tracking Operation

Acoustic Target Tracking

Motion Star Virtual reality and motion capture Fixed antenna generates Axial DC magnetic-field pulses Receiving antennas measure Field pulse in three orthogonal Axes (combined with earth magnetic field) Pro: Accurate resolution of 1mm, 1ms, and 0.1° Cons: implementation costs, object tethered to control unit, sensors must remain within 1-3m of transmitter, sensitive to metallic objects Motion Star Wireless (Magnetic pulse transmitting antennas receiving antennas and Controller )

Smart Floor method Embedded Pressure Sensors  Capture Footfalls.  Data used for position Tracking and pedestrian recognition Unobtrusive system Does not require people to carry any device or tag Poor scalability and high incremental cost Many users in one room?

Spot-On Implement ad hoc Lateration with low-cost tags Ad-hoc location sensing is a fusion of concepts from object location tracking and the theories of ad-hoc networking Spot-On tags use radio signal strength information (RSSI) as a distance estimator to perform ad-hoc Lateration.

E911 FCC is requiring wireless phone providers to locate any phone that makes an E911 call Different approaches  proximity  angulations with phased antenna arrays  GPS-enabled handsets Leads to numerous new consumer services

Easy Living Keeps track of devices etc. in a room Uses real time 3D cameras for vision positioning. Monitoring from the Internet to control lights, audio video, watch television. lots of processing power used to analyze frames captured, difficult to maintain accuracy, since vision struggles with analysis accuracy

Comparison

Modern applications Physical security  Detecting intruders Medical  Patients in a hospital Habitat monitoring  Wildlife, plants Environmental  Tracking forest fires, pollution Smart buildings Air traffic control Surveillance Required in most applications: Location of the sensor

Target tracking problem Problem statement A varying number of targets Arise at random in space and time Move with continuous motions Persist for a random time and possibly disappear Positions of targets are sampled at random intervals Measurements are noisy and Detection probability < 1.0 False alarms Goal: detect, alert, and track for each target

Tracking Challenges Data dissemination and storage Localization. Resource allocation and control Operating under uncertainty Real-time constraints Data fusion (measurement interpretation) Multiple target disambiguation Track modeling, continuity and prediction Target identification and classification

Which one of these approaches is better? Difficult to compare error rate. RF is not robust, ultrasound systems are better but only if ceiling mounted. Lots of start-up cost with Active Bats; same with Cricket. RADAR is relatively inexpensive in terms of hardware but extremely time-consuming to do calibration. RADAR needs network cards. Conclusion

References P. Bahl, V. Padmanabhan, "RADAR: An In-Building RF-based User Location and Tracking System" IEEE INFOCOM 2000, vol. 2, pp "RADAR: An In-Building RF-based User Location and Tracking System" Nissanka B. Priyantha, Anit Chakraborty and Hari Balakrishnan, " The Cricket Location-Support System " Proc. 6th ACM MOBICOM, A ugust 2000, pp " The Cricket Location-Support System " Andy Hopper, Pete Steggles, Andy Ward, Paul Webster, " The Anatomy of a Context-Aware Applica tion " Proceedings of the 5th Annual ACM/IEEE International Conference on Mobile Computing and Networking (Mobicom '99), Seattle, Washington, USA, August 1999." The Anatomy of a Context-Aware Applica tion " Special Notes: Special thanks goes to MIT for a presentation that has great pictures. Location Sensing Techniques Jerey Hightower and Gaetano Borriello UW-CSE University of Washington, Computer Science and Engineering