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Towards Collaborative Localization of Mobile Users with Bluetooth

This paper explores a collaborative Bluetooth localization method tailored for mobile users, addressing the challenges of traditional GPS and infrastructure setup costs. It highlights a novel approach that utilizes friendly names to share localization information, enabling accurate tracking both indoors and outdoors without extensive infrastructure. The method leverages existing Bluetooth coverage to fill gaps and achieve denser localization. Furthermore, it proposes solutions for improving device name caching and clock synchronization for better accuracy. This approach balances localization efficacy with energy efficiency, providing an innovative alternative for mobile user tracking.

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Towards Collaborative Localization of Mobile Users with Bluetooth

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  1. Towards Collaborative Localization of Mobile Users with Bluetooth Philipp Sommer Brano Kusy Raja Jurdak UTC/Georgia Tech. Alexandre Barreira CSIRO ICT Centre, Brisbane, Australia

  2. Localisation • Indoors • Specialized tracking devices • Infrastructure deployment cost • Setup phase • Outdoors • GPS! • Reasonably accurate … • …yet energy expensive • Collaborative Bluetooth Localisation • Can help both • Built-in to smart phones/laptops • No infrastructure/setup in office environments • More energy-efficient than GPS

  3. Bluetooth Localization Overview • Problem • Protocol imposes pairing/piconet association • Solution • Avoid expensive handshake • Use friendly name to share location info – up to 248 characters • Embed location info • Indoors: coordinates • Outdoors: GPS • Problem • Infrastructure setup • Solution • Use only existing infrastructure with bluetooth • Laptops • Desktops • Use office directory to map names to locations

  4. Infrastructure-based Bluetooth Localisation X Bluetooth Coverage Gaps

  5. Collaborative Bluetooth Localisation X X X Can fill coverage gaps

  6. Infrastructure-based Bluetooth Localisation X Sparse coverage

  7. Collaborative Bluetooth Localisation X Can provide denser coverage

  8. Bluetooth neighbor discovery A B C Use frequency hopping to transmit and listen to neighbors

  9. Bluetooth neighbor discovery A B C A has list of neighbor MAC addresses

  10. Bluetooth neighbor discovery A name? (name, RSSI, class) B C A requests friendly name of each neighbor in second step

  11. Bluetooth neighbor discovery for localization A name? (name, RSSI, class) B C name = (LOCx, LOCy, LOCz)

  12. RSSI to bound distance

  13. Device Name Caching • Discovery phase every several seconds • Varies per device/manufacturer • In the meantime, node keeps neighbor location information • Risks stale neighbor list • Risks inaccurate location • Smart phone OS limits control • No methods to flush cache • Caching strategies vary per device model/OS version

  14. Rejecting cached device names • Include timestamp into device name • Receiver can estimate time offset between remote device and local clock A name? (name, RSSI, class) B C name = (LOCx, LOCy, LOCz, t)

  15. Simple Approach to Reject Cached Names • Assumption: mobile phone clocks remain stable over short time intervals • Set (or learn) lower bound for time offset with each neighbor • IF a name with offset>lower bound+c • Discard this name

  16. Rejecting cached device names • Include timestamp into device name • Receiver can estimate time offset between remote device and local clock A name? (name, RSSI, class) B C name = (LOCx, LOCy, LOCz, t)

  17. Rejecting cached device names • Include timestamp into device name • Receiver can estimate time offset between remote device and local clock A name? (name, RSSI, class) B C name = (LOCx, LOCy, LOCz, t)

  18. Experiments • 2 Samsung Nexus S phones • Both running Android 2.3.3 • Both phones • continuously update their Bluetooth device names once every second with the current local time • perform periodic Bluetooth device inquiries • Local clocks of the devices are only loosely synchronized with a clock offset of 9.5 seconds.

  19. Summary • Collaborative Bluetooth localization • Indoors • Fill coverage gaps • Increase density • Outdoors • Saves on using GPS frequently • Simple method to avoid device name caching • Establish pairwise clock offsets • Discard names that diverge from these offsets • Open issues • Learning and adapting pairwise offsets • Bounding uncertainty with high mobility • Versatile localization algorithms

  20. Thank you Dr. Raja Jurdak CSIRO ICT Centre Principal Research Scientist Research Group Leader Phone: +61 (0)7 3327 4059 Email: raja.jurdak@csiro.au Web: http://jurdak.com University of Queensland Adjunct Associate Professor Thank you

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