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Towards Collaborative Localization of Mobile Users with Bluetooth Alexandre Barreira CSIRO ICT Centre, Brisbane, Australia Philipp Sommer Brano Kusy Raja.

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Presentation on theme: "Towards Collaborative Localization of Mobile Users with Bluetooth Alexandre Barreira CSIRO ICT Centre, Brisbane, Australia Philipp Sommer Brano Kusy Raja."— Presentation transcript:

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

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 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 Bluetooth Localization Overview

4 Infrastructure-based Bluetooth Localisation X Bluetooth Coverage Gaps

5 Collaborative Bluetooth Localisation Can fill coverage gaps X X X

6 Infrastructure-based Bluetooth Localisation X Sparse coverage

7 Collaborative Bluetooth Localisation X Can provide denser coverage

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

9 Bluetooth neighbor discovery A has list of neighbor MAC addresses A B C Neighbor Address MAC B MAC c

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

11 Bluetooth neighbor discovery for localization name = (LOCx, LOCy, LOCz) A B C name? (name, RSSI, class) NeighbourLocationRSSIclass BCBC 2,3,4 4,3, Phone Desktop

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 name = (LOCx, LOCy, LOCz, t) A B C name? (name, RSSI, class) Neighbou r Locatio n timeMin offset RSSIclass BCBC 2,3,4 4,3, Phone Desktop

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 name = (LOCx, LOCy, LOCz, t) A B C name? (name, RSSI, class) Neighbou r Locatio n timeMin offset RSSIclass BCBC 2,3,4 4,3, Phone Desktop

17 Rejecting cached device names Include timestamp into device name Receiver can estimate time offset between remote device and local clock name = (LOCx, LOCy, LOCz, t) A B C name? (name, RSSI, class) NeighbourLocatio n timeMin offset RSSIclass BCBC 2,3,4 4,3, Phone Desktop

18 Experiments 2 Samsung Nexus S phones Both running Android 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.

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20 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

21 Thank you Dr. Raja Jurdak CSIRO ICT Centre Principal Research Scientist Research Group Leader Phone: +61 (0) Web: University of Queensland Adjunct Associate Professor


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