1. 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. Contents • One Line Summary • Introduction • RIPS (Radio Interferometric Positioning System) • Source of Error • Implementation Issues • Range Calculation • Localization • Experiment • Conclusion

3. One Line Summary • Introduce novel ranging technique (RIPS) for wireless sensor networks using application of the interference signal

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. 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. 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. RIPS (Radio Interferometric Positioning System) Phase Offset Caculate dABCD Central LocalizationAlgorithm Localization

8. Interferometric Positioning

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. RIPS implementation Steps • Selecting a pair of transmitters & scheduling • Calibration of the radios of senders • Transmission of a pure sine wave • Analysis of the RSSI samples of the interference signal at each of the receivers • Calculation of the actual dABCD range from the measured relative phase offset • Localization algorithm

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. 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. Range Calculation • Final dABCD = the solution with the minimum error value

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 dABCD 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. Experiments • Setup • 16 sensor nodes • Area : 18 x 18 meter • 3 anchor points • Compare with high resolution DFT-based tone parameter estimation

16. Experiments • Error Distribution of all the ranges • Calculating dABCD

17. Experiments • Error distribution of Localization • Average : 3cm

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