1. Network Computing Laboratory Radio Interferometric Geolocation Miklos Maroti, Peter Volgesi, Sebestyen Dora Branislav Kusy, Gyorgy Balogh, Andras Nadas Karoly Molnar, Akos Ledeczi (Vanderbilt Univ.) 2006. 11. 07. Tue. Presentor : Kim, Chanho

2. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 2 Contents One Line Summary Introduction RIPS (Radio Interferometric Positioning System) Source of Error Implementation Issues Range Calculation Localization Experiment Conclusion

3. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 3 One Line Summary Introduce novel ranging technique (RIPS) for wireless sensor networks using application of the interference signal

4. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 4 Introduction Many application of the WSN require individual nodes’ location State of Art Ultrasound method, Ultrasonic method, … Limitation : cannot have adequate accuracy, acceptable range at the same time / work in 2D only Radio Interferometry High accuracy, long range Work in 3D environment

5. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 5 Introduction Terms Ranging: determine distances between nodes Localization: find physical 3-D locations of nodes Interference: superposition of two or more waves resulting in a new wave pattern Interferometry: cross-correlates a signal from a single source recorded by 2 observers, used in geodesy, astronomy, …

6. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 6 RIPS (Radio Interferometric Positioning System) RIPS no processing power to correlate high freq radio signals in WSN utilize two transmitters to produce low frequency interference signal directly Feasible on the highly resource constrained Achieve high accuracy

7. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 7 RIPS (Radio Interferometric Positioning System) Phase Offset Caculate d ABCD Localization Central Localization Algorithm

8. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 8 Interferometric Positioning

9. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 9 Sources of Error Carrier Frequency Inaccuracy Carrier Frequency Drift and Phase Noise Multipath effects Antenna Orientation RSSI measurement delay jitter RSSI Signal-to-Noise Ratio Signal Processing Error Time Synchronization Error

10. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 10 RIPS implementation Steps 1. Selecting a pair of transmitters & scheduling 2. Calibration of the radios of senders 3. Transmission of a pure sine wave 4. Analysis of the RSSI samples of the interference signal at each of the receivers 5. Calculation of the actual d ABCD range from the measured relative phase offset 6. Localization algorithm

11. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 11 RIPS Implementation Issue (1/2) Radio Chip Chipcon CC1000 (433MHz) Time Synchronization Crucial Operation : sampling of the RSSI signal (need to be aligned microseconds precision) Using external Synchronization protocol

12. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 12 RIPS Implementation Issue (2/2) Tuning To measure interference accurately Implement a frequency tuning algorithm Frequency & Phase estimation RSSI values need to be processed on the motes Scheduling High Level Scheduling Responsible for selecting the pair of transmitters Should minimize the number of interference measurement Low Level Scheduling : Coordinates the activities of the two transmitters and multiple Frequency tuning algorithm, phase offset estimation requires proper timing

13. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 13 Range Calculation Final d ABCD = the solution with the minimum error value

14. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 14 Localization Use an optimization method based on genetic algorithms (GA) Goal : find the relative positions of the nodes Requirement for this algorithm Given a set of nodes with unknown locations A set ‘M’ of d ABCD ranges Output A node placement represented by a vector of (x,y,z) coordinates Using genetic operators to fix the error of solution Crossing over Mutations

15. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 15 Experiments Setup 16 sensor nodes Area : 18 x 18 meter 3 anchor points Compare with high resolution DFT-based tone parameter estimation

16. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 16 Experiments Error Distribution of all the ranges Calculating d ABCD

17. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 17 Experiments Error distribution of Localization Average : 3cm

18. Korea Advanced Institute of Science and Technology Network Computing Laboratory | 18 Conclusion Introduce RIPS (Radio Interferometric Position System) which is the novel ranging technique for wireless sensor networks Achieve high accuracy, long range simultaneously Support 3D localization, does not require extra HW or calibration Key Idea the application of interference signal