towards collaborative localization of mobile users with bluetooth
DESCRIPTION
Towards Collaborative Localization of Mobile Users with Bluetooth . Philipp Sommer Brano Kusy Raja Jurdak. UTC/Georgia Tech. Alexandre Barreira. CSIRO ICT Centre, Brisbane, Australia. Localisation. Indoors Specialized tracking devices Infrastructure deployment cost Setup phase - PowerPoint PPT PresentationTRANSCRIPT
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: [email protected]: http://jurdak.com
University of QueenslandAdjunct Associate Professor