Kiran Joshi, Steven Hong, and Sachin Katti, Stanford University
Abstract:
This paper presents PinPoint, a technique for localizing rogue interfering radios that adhere to standard protocols in the in hospitable ISM band without any cooperation from the interfering radio. PinPoint is designed to be incrementally deployed on top of existing 802.11 WLAN infrastructure, and used by network administrators to identify and troubleshoot sources of interference which may be disrupting the network. PinPoint’s key contribution is a novel algorithm that accurately computes the line of sight angle of arrival (AoA) and cyclic signal strength indicator (CSSI) of the target interfering signal at all APs, even when the line of sight (LoS) component is buried by stronger multipath components, interference and noise. PinPoint leverages this algorithm to design an optimization technique, which can localize interfering radios and simultaneously identify the type of interference. Unlike several localization techniques which require extensive pre-deployment calibration (e.g. RFFingerprinting), PinPoint requires very little calibration by the network administrator, and uses a novel algorithm to self-initialize its bearings, even if the locations of some AP are initially unknown and are oriented randomly. We implement PinPoint on WARP software radios and deploy in an indoor testbed spanning an entire floor of our department. We compare PinPoint with the best known prior RSSI and MUSIC-AoA based approaches and show that PinPoint achieves a median localization error of 0:97 meters, which is around three times lower compared to the RSSI and MUSIC-AoA based approaches.
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BibTeX
@inproceedings {180308,
author = {Kiran Joshi and Steven Hong and Sachin Katti},
title = {{PinPoint}: Localizing Interfering Radios},
booktitle = {10th USENIX Symposium on Networked Systems Design and Implementation (NSDI 13)},
year = {2013},
isbn = {978-1-931971-00-3},
address = {Lombard, IL},
pages = {241--253},
url = {https://www.usenix.org/conference/nsdi13/technical-sessions/presentation/joshi},
publisher = {USENIX Association},
month = apr
}
This paper considers a direct approach to mitigating wireless interference in the ISM band: locating the interfering transmitter and then taking necessary actions. The authors propose PinPoint, a technique allowing multiple collaborating access points to localizeinterfering transmitters with high accuracy. Indoor RF location is challenging because signals travel through complex multi-path propagations. Unlike conventional methods that use signal strength or RSSI, PinPoint uses the cyclostationary feature, an inherent "side-signal" carried by all ISM devices to ensure normal operations. Using cyclostationary analysis, each PinPoint AP first identifies the type of the interfering signal, e.g. WiFi, Bluetooth or Zigbee. With knowledge of the signal type and thus the temporal repeating pattern of the cyclostationary feature, the AP can identify the signal's line of sight (LoS) component and compute its angle of arrival (AoA). The authors also show that this is achievable even when the LoS component is 10dB weaker than the other multi-path components in signal strength. Finally, by aggregating the LoS AoAinformation across multiple APs, a central server can compute the location of the interfering transmitter. The authors implemented and tested PinPoint on WARP radios. In an office environment, PinPoint achieves a median localization error of 0.97m, which is much better than prior RSSI and AoA approaches.
Pinpoint is the latest in a number of papers leveraging the unique properties of cyclostationary features (e.g. DOF in SIGCOMM'11, Gelato in MobiHoc'12, and Network Coordination in JSAC'08). These features are likely to see further use in an expanding range of applications. In practice, a critical mass of applications relying on these features might incentivize sophisticated attackers to modify cyclostationary features to evade detection. This currently requires modifying the end device, but that might change with more research focused on exposing physical layer signal controls.
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