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

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 2

Last Seen Point 3

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 4

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 5

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

How it Works (I) Node IDCoordinateTime 10 3 Node IDCoordinateTime

How it Works (II) Node IDCoordinateTime x3, y3, z316: Node IDCoordinateTime … 6 x1, y1, z112:31 … … 6 x2, y2, z214:09 … 6 x3, y3, z316:58 8

How it Works (III) Hiker 6 is reported missing at 23:59 Node IDCoordinateTime … 6 x1, y1, z112:31 … … 6 x2, y2, z214:09 … 6 x3, y3, z316:58 x1, y1, z1 x2, y2, z2 x3, y3, z3 Inferred location at 23:59 Hot Search Zone 9

System Architecture Witness Search & Rescue TeamControl Center 10

Current Loosely Coupled Systems ZebraNet At each scan for neighbors if node(I am) is within range of BS send data to BS and delete this data else send data to all neighbors 12 Node ID CoordinateTime3 … CoordinateTime3 … 3 …

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 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 Path of hiker 2 is drawn successfully

Hiker 1 to 5 walk on designated trails while hiker 6 does a random walk. We successfully depict path of hiker 6 Experiment 3 (Identifying Hot Search Areas) 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! 23