Thiagarajan-VTrack - VTrack: Accurate, Energy-Aware Road...

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Unformatted text preview: VTrack: Accurate, Energy-Aware Road Traffic Delay Estimation Using Mobile Phones Arvind Thiagarajan, Lenin Ravindranath, Katrina LaCurts, Sivan Toledo Jakob Eriksson Samuel Madden, Hari Balakrishnan Tel-Aviv University U. Illinois Chicago MIT CSAIL stoledo@tau.ac.il jakob@cs.uic.edu { arvindt,lenin,katrina,madden,hari } @csail.mit.edu Abstract Traffic delays and congestion are a major source of ineffi- ciency, wasted fuel, and commuter frustration. Measuring and localizing these delays, and routing users around them, is an important step towards reducing the time people spend stuck in traffic. As others have noted, the proliferation of commod- ity smartphones that can provide location estimates using a variety of sensorsGPS, WiFi, and/or cellular triangulation opens up the attractive possibility of using position samples from drivers phones to monitor traffic delays at a fine spatio- temporal granularity. This paper presents VTrack, a system for travel time estimation using this sensor data that addresses two key challenges: energy consumption and sensor unreliability. While GPS provides highly accurate location estimates, it has several limitations: some phones dont have GPS at all, the GPS sensor doesnt work in urban canyons (tall buildings and tunnels) or when the phone is inside a pocket, and the GPS on many phones is power-hungry and drains the bat- tery quickly. In these cases, VTrack can use alternative, less energy-hungry but noisier sensors like WiFi to estimate both a users trajectory and travel time along the route. VTrack uses a hidden Markov model (HMM)-based map matching scheme and travel time estimation method that interpolates sparse data to identify the most probable road segments driven by the user and to attribute travel times to those segments. We present experimental results from real drive data and WiFi access point sightings gathered from a deployment on several cars. We show that VTrack can tolerate significant noise and outages in these location estimates, and still successfully iden- tify delay-prone segments, and provide accurate enough delays for delay-aware routing algorithms. We also study the best sampling strategies for WiFi and GPS sensors for different energy cost regimes. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. SenSys09, November 46, 2009, Berkeley, CA, USA....
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This note was uploaded on 08/25/2011 for the course EEL 6788 taught by Professor Boloni,l during the Spring '08 term at University of Central Florida.

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Thiagarajan-VTrack - VTrack: Accurate, Energy-Aware Road...

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