http://nesl.ee.ucla.edu/ http://nesl.ee.ucla.edu 1 Dynamic Location Discovery in Ad-Hoc Networks Andreas Savvides, Athanassios Boulis and Mani B. Srivastava (asavvide,boulis,[email protected]) Networked and Embedded Systems Lab(NESL) http://nesl.ee.ucla.edu Electrical Engineering Department Session 7
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Http://nesl.ee.ucla.edu/ 1 Dynamic Location Discovery in Ad-Hoc Networks Andreas Savvides, Athanassios Boulis and Mani B. Srivastava.
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– report event origins– evaluate network coverage– assist with routing
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Basic Concepts
• Distance measuring methods– Signal Strength
• Uses RSSI readings and wireless propagation model
– Time based methods• ToA, TDoA• Used with radio, IR, acoustic, ultrasound
– Angle of Arrival (AoA)• Measured with directive antennas or
arrays
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Basic Concepts II
Hyperbolic Trilateration
Triangulation
Multi-lateration– Considers all available beacons
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Existing TechnologiesINFRASTRUCTURE:• Automatic Vehicle Location system (AVL)
– Base stations keep track of police cars ( uses time based and signal strength methods)
• GPS, Loran• 911 Emergency Location System (ToA, TDoA)
• BAT System(AT&T Cambridge Labs), Cricket (MIT) • RADAR – indoor, uses signal strength maps• RFID tags – IR proximityAD-HOC:• Picoradio (UC Berkeley) – indoor, based on signal strength
maps• GPS-less outdoor localization (Bulusu et. al) – proximity based
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Location Discovery in Ad-Hoc Networks
• No infrastructure support• GPS may not always work
– Costly, Power Hungry, does not work everywhere
• Our Approach– Use RSSI for measuring node separation– But how should the beacons be placed?
• Multiple tradeoffs still an open problem
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Long Range Beaconing
• Long Range BeaconingAdvantages:– Multi-hop Coverage– Works well even in low densities
• Disadvantages:– Low fault tolerance– Requires Dedicated Beacons– Some infrastructure is required
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Our Approach
• Single hop beaconing• Iterative multilateration• Dynamic estimate the wireless channel
parameters• Can be done in conjunction with routing
Advantages:• Data packets are also act as beacon signals• Distributed – relies on neighborhood information• Fault tolerant• Location discovery is almost free!!
Two-Phase Approach• Obtain a propagation model estimate based on initial set of beacons• Certainly of node estimates used as weights for the channel estimate• Follow a rip-up and retry method until a predefined set of constraints