Range-free localization schemes for large scale sensor networks
Proceedings of the 9th annual international conference on Mobile computing and networking
Robust distributed network localization with noisy range measurements
SenSys '04 Proceedings of the 2nd international conference on Embedded networked sensor systems
Proceedings of the 13th annual ACM international conference on Mobile computing and networking
Devices that tell on you: privacy trends in consumer ubiquitous computing
SS'07 Proceedings of 16th USENIX Security Symposium on USENIX Security Symposium
Nericell: rich monitoring of road and traffic conditions using mobile smartphones
Proceedings of the 6th ACM conference on Embedded network sensor systems
VTrack: accurate, energy-aware road traffic delay estimation using mobile phones
Proceedings of the 7th ACM Conference on Embedded Networked Sensor Systems
Cooperative transit tracking using smart-phones
Proceedings of the 8th ACM Conference on Embedded Networked Sensor Systems
Locating sensors in the wild: pursuit of ranging quality
Proceedings of the 8th ACM Conference on Embedded Networked Sensor Systems
Mapping the urban wireless landscape with Argos
Proceedings of the 8th ACM Conference on Embedded Networked Sensor Systems
USENIX Security'10 Proceedings of the 19th USENIX conference on Security
Real-time measurement of link vehicle count and travel time in a road network
IEEE Transactions on Intelligent Transportation Systems
Stochastic radio interferometric positioning in the 2.4 GHz range
Proceedings of the 9th ACM Conference on Embedded Networked Sensor Systems
Place lab: device positioning using radio beacons in the wild
PERVASIVE'05 Proceedings of the Third international conference on Pervasive Computing
A traceability attack against e-passports
FC'10 Proceedings of the 14th international conference on Financial Cryptography and Data Security
License Plate Recognition From Still Images and Video Sequences: A Survey
IEEE Transactions on Intelligent Transportation Systems
Signals from the crowd: uncovering social relationships through smartphone probes
Proceedings of the 2013 conference on Internet measurement conference
Smart cities software: customized messages for mobile subscribers
WiFlex'13 Proceedings of the First international conference on Wireless Access Flexibility
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Smartphones with Wi-Fi enabled periodically transmit Wi-Fi messages, even when not associated to a network. In one 12-hour trial on a busy road (average daily traffic count 37,000 according to the state DOT), 7,000 unique devices were detected by a single road-side monitoring station, or about 1 device for every 5 vehicles. In this paper, we describe a system for passively tracking unmodified smartphones, based on such Wi-Fi detections. This system uses only common, off-the-shelf access point hardware to both collect and deliver detections. Thus, in addition to high detection rates, it potentially offers very low equipment and installation cost. However, the long range and sparse nature of our opportunistically collected Wi-Fi transmissions presents a significant localization challenge. We propose a trajectory estimation method based on Viterbi's algorithm which takes second-by-second detections of a moving device as input, and produces the most likely spatio-temporal path taken. In addition, we present several methods that prompt passing devices to send additional messages, increasing detection rates an use signal-strength for improved accuracy. Based on our experimental evaluation from one 9-month deployment and several single-day deployments, passive Wi-Fi tracking detects a large fraction of passing smartphones, and produces high-accuracy trajectory estimates.