Wireless Ad-Hoc Sensor Networks forWireless Ad-Hoc Sensor Networks forMonitoring Endangered Plant SpeciesMonitoring Endangered Plant Species

Edo BiagioniEdo Biagioni

University of Hawaii at ManoaUniversity of Hawaii at ManoaAlso Kim Bridges, Brian Chee, Anders Host-Madsen, Also Kim Bridges, Brian Chee, Anders Host-Madsen, Galen Sasaki, and many more, including Chen, Fan, Galen Sasaki, and many more, including Chen, Fan, Morton, Xie, and DARPAMorton, Xie, and DARPA

OverviewOverview

An ecological wireless sensor An ecological wireless sensor networknetwork

Overall challengesOverall challenges

Current solutionsCurrent solutions

Future solutionsFuture solutions

Protecting Endangered Protecting Endangered PlantsPlants

Hard to do Hard to do without knowing without knowing plants' needs, soplants' needs, so

Study the Study the environmentenvironment

See how the See how the plants are doingplants are doing

Use sensors and Use sensors and hi-res camerashi-res cameras

ChallengesChallengesEnergy: batteries, solar, windEnergy: batteries, solar, wind

Sleep, wake up, transmit, go back to Sleep, wake up, transmit, go back to sleepsleep

Low bit-rate, but over a wide areaLow bit-rate, but over a wide area

Low cost, unobtrusiveLow cost, unobtrusive● Fading: bad geometry, plants (2.4GHz)Fading: bad geometry, plants (2.4GHz)● Collisions and CongestionCollisions and Congestion● Sensors: sunlight, rain, windSensors: sunlight, rain, wind

• Issues common to most sensor Issues common to most sensor networks!networks!

The PODS projectThe PODS project

Hawaii: endangered species “capital”Hawaii: endangered species “capital”

Microclimates: rapid weather changesMicroclimates: rapid weather changes

Pods communicate over many hops Pods communicate over many hops with internet-connected base stationwith internet-connected base station

Assembly of COTS hardware (IPAQ w/ Assembly of COTS hardware (IPAQ w/ Linux), 802.11Linux), 802.11

Custom software, protocols: MOR, LususCustom software, protocols: MOR, Lusus

Transmission range typically ~ Transmission range typically ~ PowerPower--44

Pod placementPod placement

Intensive deployment Intensive deployment where plant growswhere plant grows

Also interested in where Also interested in where the plant does the plant does notnot grow grow

Connection to the Connection to the internet is also a line of internet is also a line of sensorssensors

Many interesting Many interesting topologies [Biagioni and topologies [Biagioni and Sasaki, 2003]Sasaki, 2003]

Sub-region

Ad-hoc Wireless Ad-hoc Wireless Communication:Communication:

Multipath On-Demand RoutingMultipath On-Demand RoutingProtocol provides routing information Protocol provides routing information as well as transport for data (IP) as well as transport for data (IP) packetspackets

Multiple paths with retransmission Multiple paths with retransmission perform well in the face of congestion – perform well in the face of congestion – good performance means low powergood performance means low power

Application-level broadcast supports Application-level broadcast supports synchronizationsynchronization

Low or high mobilityLow or high mobility

Sensor Network ArchitectureSensor Network Architecture

More powerful pods form a “backbone”, More powerful pods form a “backbone”, may have better communications and may have better communications and sensors (cameras), may be always onsensors (cameras), may be always on

Smaller sensors are cheaper, use less Smaller sensors are cheaper, use less energy, may have less range and lower energy, may have less range and lower speedspeed

Two-tiered (or multi-tiered) architectureTwo-tiered (or multi-tiered) architecture

Protocol for Simple NodesProtocol for Simple NodesLususLusus

Routing on a gradient towards base Routing on a gradient towards base station or nearest high-level nodestation or nearest high-level node

Link-layer reliabilityLink-layer reliability

Joining separate data into one packetJoining separate data into one packet

Low speed serial radiosLow speed serial radios

PIC microcontrollerPIC microcontroller

Application-Level Data Application-Level Data Protocol:Protocol:

SNDTSNDTFeatures:Features:

ReliableReliable

Low-overheadLow-overhead

EncryptionEncryption

Faster than using SSH/TCP to transfer Faster than using SSH/TCP to transfer small amounts of datasmall amounts of data

Rate-limited transmissionRate-limited transmission

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Cooperative DiversityCooperative DiversityAnders Host-MadsenAnders Host-Madsen

Ad-hoc networksAd-hoc networks

Users communicate directly with Users communicate directly with each othereach other

Interference Among Different Interference Among Different connectionsconnections

Fading due to distanceFading due to distance

– Fading

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Cooperative TDMACooperative TDMA

Cooperative TDMACooperative TDMA

Nodes use TDMA multiple-accessNodes use TDMA multiple-access

While a transmitter is passive, it can act While a transmitter is passive, it can act as relayas relay

One node One node transmits first transmits first and the other and the other helps, then helps, then switchswitch

Research PlanResearch PlanAnders Host-MadsenAnders Host-Madsen

ResultsResultsFading Relay channel capacity (with J. Zhang, ASU)Fading Relay channel capacity (with J. Zhang, ASU)Theoretical bounds for 4-node cooperative diversityTheoretical bounds for 4-node cooperative diversityNSF fundingNSF funding

CurrentCurrentMIMO Relay Channel (with J. Zhang, ASU)MIMO Relay Channel (with J. Zhang, ASU)Multinode relay channelMultinode relay channelConstruction of experimental 4-node networkConstruction of experimental 4-node networkPractical coding methods for the relay channelPractical coding methods for the relay channel

FutureFutureLow power regimeLow power regimeExperimentation on wireless testbedExperimentation on wireless testbedGeneralization to larger networksGeneralization to larger networks

Routing/clusteringRouting/clustering

Application to environmental sensor networkApplication to environmental sensor network

Open Research IssuesOpen Research Issues

Theoretical models for wireless ad-hoc Theoretical models for wireless ad-hoc network performancenetwork performance

Practical, reproducible performance testsPractical, reproducible performance tests

Lessen power needs by moving away from Lessen power needs by moving away from COTS (or by COTS moving closer)COTS (or by COTS moving closer)

Micropower generation and conservationMicropower generation and conservation

Wireless that works well near the groundWireless that works well near the ground

Wireless Ad-Hoc Network Wireless Ad-Hoc Network PerformancePerformance

In typical multi-hop networks, at most 1 In typical multi-hop networks, at most 1 out of 3 nodes can transmit at any timeout of 3 nodes can transmit at any time

Interference range is usually greater Interference range is usually greater than transmission rangethan transmission range

Fading varies over time, and it is hard to Fading varies over time, and it is hard to reproduce any actual testreproduce any actual test

““Quantum” testing: observe what Quantum” testing: observe what actually happens, run in actual actually happens, run in actual environmentsenvironments

Power Research IssuesPower Research Issues

COTS keeps getting lower power, COTS keeps getting lower power, smaller, cheapersmaller, cheaper

Microcontrollers can do 90% of the job Microcontrollers can do 90% of the job at a fraction of the (cost, size, weight)at a fraction of the (cost, size, weight)

Solar works well, expensive, hard to Solar works well, expensive, hard to concealconceal

Wind works sometimes, hard to concealWind works sometimes, hard to conceal

Future WorkFuture Work

More applications: science, agriculture, More applications: science, agriculture, even tourismeven tourism

Better visualization of dataBetter visualization of data

Evaluation with larger actual networksEvaluation with larger actual networks

Protocol improvementsProtocol improvements

Better, lower power, less conspicuous, Better, lower power, less conspicuous, cheaper sensors and camerascheaper sensors and cameras

SummarySummary

Experience building, deploying wireless ad-Experience building, deploying wireless ad-hoc sensor networkshoc sensor networks

Multi-tiered sensor network architectureMulti-tiered sensor network architecture

Power may cost more than computer+sensorPower may cost more than computer+sensor

Most protocols work (e.g. MANET), but some Most protocols work (e.g. MANET), but some (e.g. MOR) may work better(e.g. MOR) may work better

Cooperative diversity improves range in a Cooperative diversity improves range in a flexible mannerflexible manner

Performance testing is difficult but essentialPerformance testing is difficult but essential