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Abstract-This paper addresses deafness -a problem that appears when MAC protocols are designed using directional antennas. Briefly, deafness is caused when a transmitter fails to communicate to its intended receiver, because the receiver is beamformed towards a direction away from the transmitter. Existing CSMA/CA protocols rely on the assumption that congestion is the predominant cause of communication failure, and adopt backoff schemes to handle congestion. While this may be appropriate for omnidirectional antennas, for directional antennas, both deafness and congestion can be the reason for communication failures. An appropriate directional MAC protocol needs to classify the actual cause of failure, and react accordingly. This paper quantifies the impact of deafness on directional medium access control, and proposes a tone-based mechanism as one way of addressing deafness. The tone-based mechanism, ToneDMAC, assumes congestion as the default reason for communication failures, and applies a corrective measure whenever the cause is deafness. Simulation results indicate that ToneDMAC can alleviate deafness, and perform better than existing directional MAC protocols.

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We present the results, experiences and lessons learned from comparing a diverse set of technical approaches to indoor localization during the 2014 Microsoft Indoor Localization Competition. 22 different solutions to indoor localization from different teams around the world were put to test in the same unfamiliar space over the course of 2 days, allowing us to directly compare the accuracy and overhead of various technologies. In this paper, we provide a detailed analysis of the evaluation study's results, discuss the current state-ofthe-art in indoor localization, and highlight the areas that, based on our experience from organizing this event, need to be improved to enable the adoption of indoor location services.

This paper identifies the possibility of using electronic compasses and accelerometers in mobile phones, as a simple and scalable method of localization without war-driving. The idea is not fundamentally different from ship or air navigation systems, known for centuries. Nonetheless, directly applying the idea to human-scale environments is non-trivial. Noisy phone sensors and complicated human movements present practical research challenges. We cope with these challenges by recording a person's walking patterns, and matching it against possible path signatures generated from a local electronic map. Electronic maps enable greater coverage, while eliminating the reliance on WiFi infrastructure and expensive war-driving. Measurements on Nokia phones and evaluation with real users confirm the anticipated benefits. Results show a location accuracy of less than 11m in regions where today's localization services are unsatisfactory or unavailable. 1 Updates are necessary because WiFi access points change over time as people shift in/out of apartments, homes and offices.978-1-4244-5837-0/10/$26.00

As mobile begins to overtake the fixed Internet access, ad networks have aggressively sought methods to track users on their mobile devices. While existing countermeasures and regulation focus on thwarting cookies and various device IDs, this paper submits a hypothesis that smartphone/tablet accelerometers possess unique fingerprints, which can be exploited for tracking users. We believe that the fingerprints arise from hardware imperfections during the sensor manufacturing process, causing every sensor chip to respond differently to the same motion stimulus. The differences in responses are subtle enough that they do not affect most of the higher level functions computed on them. Nonetheless, upon close inspection, these fingerprints emerge with consistency, and can even be somewhat independent of the stimulus that generates them. Measurements and classification on 80 standalone accelerometer chips, 25 Android phones, and 2 tablets, show precision and recall upward of 96%, along with good robustness to realworld conditions. Utilizing accelerometer fingerprints, a crowdsourcing application running in the cloud could segregate sensor data for each device, making it easy to track a user over space and time. Such attacks are almost trivial to launch, while simple solutions may not be adequate to counteract them. Permission to freely reproduce all or part of this paper for noncommercial purposes is granted provided that copies bear this notice and the full citation on the first page. Reproduction for commercial purposes is strictly prohibited without the prior written consent of the Internet Society, the firstnamed author (for reproduction of an entire paper only), and the author's employer if the paper was prepared within the scope of employment.

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