Location of Mobile Devices Using Networked Surfaces James Scott Frank Hoffmann [e-mail][e-mail] http://www-lce.eng.cam.ac.uk/

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Location of Mobile Devices Using Networked
Surfaces James Scott Frank Hoffmann
jamesscott_at_acm.org fh215_at_cam.ac.ukhttp//www-l
ce.eng.cam.ac.uk/
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Overview

• Quick intro to Networked Surfaces
• Location process
• Simulations, measurements and visualisations
• Improving accuracy
• Applications

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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

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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

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Prototype Photo
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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
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Location Process
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Location Algorithm
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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

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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

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Simulation Results
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Comparison with Measurements
Variable Mean Simulated Error Mean Measurement 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

• 50 manual measurements
• 4 link object
• Est. 5mm accuracy
• Results very close to simulation

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Visualisation Tool

• Circle shows est. position, rectangle shows
  bounds
• Lines show est. orientation and max orientation
  range
• Y accuracy gtgt X accuracy
• 2 column accuracy gtgt
• 1 column accuracy

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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

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Improved Simulations (X,Y) vector
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Improved Simulations Orientation
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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

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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

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Applications Continued

• Ubiquitous interfaces using Networked Surfaces
• Use location as user input and device as
  pointer
• Position, orientation, vector of movement, and
  velocity can all be provided
• Outputs using the capabilities of the devices
  themselves, or
• Direct HCI with Surfaces
• Use pressure sensors in the Surface for input,
  LEDs for output
• Can interact with users directly
• e.g. Confirmation dialogues
• Huge application space