laboratory for communications engineering engineering department, university of cambridge location...
TRANSCRIPT
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Location of Mobile Devices Using
Networked Surfaces
James Scott Frank Hoffmann [email protected] [email protected]
http://www-lce.eng.cam.ac.uk/
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Overview
• Quick intro to Networked Surfaces
• Location process
• Simulations, measurements and visualisations
• Improving accuracy
• Applications
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Networked Surfaces Concept• Provide network connectivity using physical surfaces
• Such as desks, floors, etc.• Make use of gravity
• No “plug”; no special position/alignment required• Provides mobility for devices• Offers transparency of connection for users
• Support a range of services• Ethernet-style inter-computer networks• Slower serial busses for peripherals• Power
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Networked Surfaces Implementation• Augment surface and objects with conductive pads
•Different object “footprints” guarantee different numbers of channels
• When connecting, “pad mappings” are discovered
• Prototype characteristics:– PCMCIA interface to notebooks – Connection in ~0.2s– Disconnection in ~0.1s– 5Mbit/s networking
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Object Pad Configurations
Links Required
Object Pads
Footprint Diameter
(mm)
2 5 26
3 9 46
4 12 68
5 16 88
6 19 110
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Location Process
Object Placement
Surface Strip Object Pad
3
16
5
10
7
4
Pad Mapping
LocationAlgorithm
Object Location
y
x
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Location Algorithm
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Location Characteristics
• Location available for 100% of connected objects
• Expect guarantee of bounded maximum error
• Algorithm is fast: ~1ms on modest hardware
• Tested using simulations, measurements and visualisation…
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Simulations• Simulation process:
– Simulate random placement
– Calculate pad mappings
– Execute location algorithm
– Compare result with original placement
• Allows fast testing of many placements– 1,000,000 locations tested for each data point
• Other advantages– Testing of various footprints
– Evaluation of possible improvements
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Simulation Results
17mm
61mm
10°
41°
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Comparison with Measurements
• 50 manual measurements
• 4 link object
• Est. 5mm accuracy
• Results very close to simulation
Variable Mean Simulated Error
Mean Measuremen
t Error
Difference
X 15mm 13mm 2mm
Y 3.6mm 3.0mm 0.6mm
(X,Y) vector
16mm 14mm 2mm
7.8° 6.3° 1.5°
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Visualisation Tool• Circle shows est. position,
rectangle shows bounds
• Lines show est. orientation and max orientation range
• Y accuracy >> X accuracy
• 2 column accuracy >> 1 column accuracy
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Improving Location Accuracy
• Current prototype does not provide full pad mapping info• Only as many links as necessary, and only one object pad per link
• Can augment with information on “Duplicate Pads”• For each surface pad used, list all object pads touching it (instead of just
one)
• Can also augment with information on “All Links”• Provide mappings for all surface pads sensed, not just those used for
connection
• Possible to implement in current prototype• Changes only required in FPGA programs, not in hardware• Use simulation to test improved performance
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Improved Simulations — (X,Y) vector
17mm
61mm
8mm
32mm
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Improved Simulations — Orientation
9°2°
10°
41°
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Integration and Applications
• Integration with context-aware middlewares– E.g. QoS DREAM Flame, SPIRIT (both at LCE)
• APP: Auto-configuration of devices– Automatically connect devices appropriately– e.g. keyboard connects to closest monitor
• APP: Interface mobility– Remote interfaces using devices with better I/O hardware– e.g. ad-hoc docking station for a notebook computer
Laboratory for Communications EngineeringEngineering Department, University of Cambridge
Conclusions
• Networked Surface prototype is capable of locating devices with a mean error of 8mm and 2º
• Also guarantees maximum errors of 32mm and 9º
• Beats most “dedicated” location systems!
• Many useful applications, including surface-centric ones