Towards Collaborative Localization of Mobile Users with Bluetooth

Alexandre Barreira

CSIRO ICT Centre, Brisbane, Australia

Philipp SommerBrano KusyRaja JurdakUTC/Georgia Tech.

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

• 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

Infrastructure-based Bluetooth Localisation

X

Bluetooth Coverage Gaps

Collaborative Bluetooth Localisation

Can fill coverage gaps

X

X

X

Infrastructure-based Bluetooth Localisation

X

Sparse coverage

Collaborative Bluetooth Localisation

X

Can provide denser coverage

Bluetooth neighbor discovery

Use frequency hopping to transmit and listen to neighbors

A

B

C

Bluetooth neighbor discovery

A has list of neighbor MAC addresses

A

B

C

Neighbor AddressMACB

MACc

Bluetooth neighbor discovery

A requests friendly name of each neighbor in second step

A

B

C

name? (name, RSSI, class)

Bluetooth neighbor discovery for localization

name = (LOCx, LOCy, LOCz)

A

B

C

name? (name, RSSI, class)

Neighbour Location RSSI class

BC

2,3,44,3,5

-75-66

PhoneDesktop

RSSI to bound distance

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

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)

Neighbour

Location

time Min offset

RSSI class

BC

2,3,44,3,5

2035

1913

-75-66

PhoneDesktop

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

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)

Neighbour

Location

time Min offset

RSSI class

BC

2,3,44,3,5

2035

1913

-75-66

PhoneDesktop

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)

Neighbour

Location

time Min offset

RSSI class

BC

2,3,44,3,5

2035

1913

-75-66

PhoneDesktop

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.

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

Thank you

Thank you

Dr. Raja JurdakCSIRO ICT CentrePrincipal Research ScientistResearch Group Leader

Phone: +61 (0)7 3327 4059Email: raja.jurdak@csiro.auWeb: http://jurdak.com

University of QueenslandAdjunct Associate Professor