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

Jyh-How Huang Saqib Amjad Shivakant MishraDept. of Computer Science, University of Colorado at Boulder

Presented by: Yi Zhang

Most slides taken from Jyh-How Huang’s slides athttp://csel.cs.colorado.edu/~huangjh/Cenwits/CenwitsSlides.ppt

IntroductionIntroduction

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 actions2

Last Seen PointLast Seen Point

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Current Search and Rescue Current Search and Rescue Technologies 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 system4

Design GoalsDesign 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

requirements5

CenWitsCenWits

A Connection-less Sensor-Based Tracking System Using Witnesses

Comprised of RF sensors GPS receivers Access points Location points Control center

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How it Works (I)How it Works (I)

Node ID Coordinate Time

10

3

Node ID Coordinate Time

8

6

8

6

2

10

3

1

1 2

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How it Works (II)How it Works (II)

Node ID Coordinate Time

10

3

8

6 x3, y3, z3 16:58

2

1

Node ID Coordinate Time

…

6 x1, y1, z1 12:31

…

…

6 x2, y2, z2 14:09

…

6 x3, y3, z3 16:58

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How it Works (III)How it Works (III)

Hiker 6 is reported missing at23:59

Node ID Coordinate Time

…

6 x1, y1, z1 12:31

…

…

6 x2, y2, z2 14:09

…

6 x3, y3, z3 16:58

x1, y1, z1

x2, y2, z2

x3, y3, z3

Inferred location at 23:59

Hot Search Zone

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System ArchitectureSystem Architecture

Witness

Witness

Search & Rescue Team Control Center10

Memory ManagementMemory 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 ManagementPower 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

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Grouping to Save EnergyGrouping to Save Energy

One active leader at any time; others sleepLeadership time-multiplexed

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More Memory More Memory ManagementManagement

Partitions: sub-groups containing >= 2 nodesEach of the K partitions receives/sends 1/K of total dataWhen nodes dies: split large partition or merge with small partition

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Prototype ImplementationPrototype 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

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

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Experiment 2 (Indirect Inference):Experiment 2 (Indirect Inference): Hiker 1: A to B and beyondHiker 1: A to B and beyondHiker 2: Does not come in contact with any APHiker 2: Does not come in contact with any APHiker 3: C to B and beyondHiker 3: C to B and beyond

Path of hiker 2 is drawn successfully

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1

3

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 Experiment 3 (Identifying Hot Search Areas)Hot Search Areas)

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ConclusionsConclusions

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

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Discussion (1)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!

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Discussion (2)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 issues22

Comments?Comments?

Thanks!

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