towards collaborative localization of mobile users with bluetooth alexandre barreira csiro ict...
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Towards Collaborative Localization of Mobile Users with Bluetooth
Alexandre Barreira
CSIRO ICT Centre, Brisbane, Australia
Philipp SommerBrano KusyRaja Jurdak
UTC/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 Address
MACB
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 Jurdak
CSIRO ICT CentrePrincipal Research Scientist
Research Group Leader
Phone: +61 (0)7 3327 4059
Email: [email protected]
Web: http://jurdak.com
University of QueenslandAdjunct Associate Professor