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CenWits: A Sensor-Based Loosely Coupled Search and Rescue System Using Witnesses

CenWits: A Sensor-Based Loosely Coupled Search and Rescue System Using Witnesses. Jyh-How Huang Saqib Amjad Shivakant Mishra Dept. of Computer Science, University of Colorado at Boulder Presented by: Yi Zhang Most slides taken from Jyh-How Huang’s slides at

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CenWits: A Sensor-Based Loosely Coupled Search and Rescue System Using Witnesses

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  1. CenWits: A Sensor-Based Loosely Coupled Search and Rescue System Using Witnesses Jyh-How Huang Saqib Amjad Shivakant Mishra Dept. of Computer Science, University of Colorado at Boulder Presented by: Yi Zhang Most slides taken from Jyh-How Huang’s slides at http://csel.cs.colorado.edu/~huangjh/Cenwits/CenwitsSlides.ppt

  2. Introduction • Goal: To build a search and rescue system that can pinpoint missing person’s last seen point in wilderness areas • Lost hikers, stranded climbers, injured skiers, … • Difficult because of lack of timely information about the current location • “Last seen point” is critical for search and rescue actions

  3. Last Seen Point

  4. Current Search and Rescue Technologies • The Old School Way – Ask • Personal GPS receiver and Satellite transmitter – Power greedy; Must operate manually to send your location • Localization system and GSM transmitter – Need GSM network coverage • Avalanche beacon/RFID reflector – Limited usage • Need a better, cheaper, reliable system

  5. Design Goals • Self-Operate, long life time • Small and light weight • Non intrusive; no infrastructure needed • Power and memory efficient • Cheap($20~$50) • Meets security and privacy requirements

  6. CenWits • A Connection-less Sensor-Based Tracking System Using Witnesses • Comprised of • RF sensors • GPS receivers • Access points • Location points • Control center

  7. 1 2 How it Works (I)

  8. 1 How it Works (II)

  9. Hot Search Zone x3, y3, z3 x2, y2, z2 Inferred location at 23:59 x1, y1, z1 How it Works (III) Hiker 6 is reported missing at 23:59

  10. System Architecture Witness Witness Search & Rescue Team Control Center

  11. Memory Management • MAX RECORD COUNT • Replace the old record with new one of the same node and keep the total records # of a node less than MAX_RECORD_COUNT • MAX HOP COUNT • Don’t forward a packet that has high probability of reaching AP already • MIN RECORD GAP • When 2 records are recorded in a time gap < MIN_RECORD_GAP, replace the old one with new one.

  12. Power Management • Beacon frequency adjustment based on speed, time of day, etc. • 4-phase hand shake protocol • Only transmit as much as the receiver is willing to take

  13. Grouping to Save Energy • One active leader at any time; others sleep • Leadership time-multiplexed

  14. More Memory Management • Partitions: sub-groups containing >= 2 nodes • Each of the K partitions receives/sends 1/K of total data • When nodes dies: split large partition or merge with small partition

  15. Prototype Implementation • MICA2 sensors • 900 MHz; 4 KB SDRAM; 128 KB flash; and 4-512 KB EEPROM • Mantis OS 0.9.1b • MTS420CA GPS module • Successfully conducted a number of experiments in a indoor environment

  16. Experiment 1 (Direct Contact): One hiker starts from A , goes to B and C, and returns to A

  17. Experiment 2 (Indirect Inference): Hiker 1: A to B and beyond Hiker 2: Does not come in contact with any AP Hiker 3: C to B and beyond 1 3 Path of hiker 2 is drawn successfully

  18. Experiment 3 (Identifying Hot Search Areas) Hiker 1 to 5 walk on designated trails while hiker 6 does a random walk. We successfully depict path of hiker 6

  19. Conclusions • CenWits has several advantages over other search and rescue systems • No need for a connected network of any kind • Power and storage efficiency • Cost effective • Non intrusive • Suitable for deployment in wilderness areas • Applications: Hiking; skiing; wildlife monitoring; vehicular network

  20. Discussion (1) • Simplistic approach to the resource/inference quality tradeoff • How to set memory management parameters? • What’s the impact on inference quality? • Ultimate goal is not to save energy/memory, but lives!

  21. Discussion (2) • Energy really saved by transmitting as much as needed? • 4-phase hand shake protocol itself is an overhead • Or maybe 3-phase? (piggyback) • Lack of analysis/quantification • Transmission energy when changing group/partition leader? • Energy/memory costs in experiments? • Security and privacy issues

  22. Comments? • Thanks!

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