1. Laboratory for Communications Engineering Engineering Department, University of Cambridge Location of Mobile Devices Using Networked Surfaces James Scott Frank Hoffmann jamesscott@acm.orgfh215@cam.ac.uk http://www-lce.eng.cam.ac.uk/

2. Laboratory for Communications Engineering Engineering Department, University of Cambridge Overview Quick intro to Networked Surfaces Location process Simulations, measurements and visualisations Improving accuracy Applications

3. Laboratory for Communications Engineering Engineering 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

4. Laboratory for Communications Engineering Engineering 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

5. Laboratory for Communications Engineering Engineering Department, University of Cambridge Prototype Photo

6. Laboratory for Communications Engineering Engineering Department, University of Cambridge Object Pad Configurations Links Required Object Pads Footprint Diameter (mm) 2526 3946 41268 51688 619110

7. Laboratory for Communications Engineering Engineering Department, University of Cambridge Location Process

8. Laboratory for Communications Engineering Engineering Department, University of Cambridge Location Algorithm

9. Laboratory for Communications Engineering Engineering 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…

10. Laboratory for Communications Engineering Engineering 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

11. Laboratory for Communications Engineering Engineering Department, University of Cambridge Simulation Results 17mm 61mm 10° 41°

12. Laboratory for Communications Engineering Engineering Department, University of Cambridge Comparison with Measurements 50 manual measurements 4 link object Est. 5mm accuracy Results very close to simulation VariableMean Simulated Error Mean Measurement Error Difference X15mm13mm2mm Y3.6mm3.0mm0.6mm (X,Y) vector 16mm14mm2mm  7.8°6.3°1.5°

13. Laboratory for Communications Engineering Engineering 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

14. Laboratory for Communications Engineering Engineering 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

15. Laboratory for Communications Engineering Engineering Department, University of Cambridge Improved Simulations — (X,Y) vector 17mm 61mm 8mm 32mm

16. Laboratory for Communications Engineering Engineering Department, University of Cambridge Improved Simulations — Orientation 9° 2° 10° 41°

17. Laboratory for Communications Engineering Engineering 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

18. Laboratory for Communications Engineering Engineering 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

19. Laboratory for Communications Engineering Engineering Department, University of Cambridge 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, LED’s for output Can interact with users directly e.g. Confirmation dialogues Huge application space