introduction to wireless sensor networks - system architecture of networked sensor platforms and...

Introduction to Wireless Sensor Networks

-System Architecture of Networked Sensor Platforms and Applications

Wireless sensor networksWireless sensor networks consists of group of sensor nodes consists of group of sensor nodesto perform distributed sensing task using wireless medium.to perform distributed sensing task using wireless medium.

CharacteristicsCharacteristics- low-cost, low-power, lightweight- low-cost, low-power, lightweight

- densely deployed- densely deployed

- prone to failures- prone to failures

- two ways of - two ways of deploymentdeployment: randomly, pre-determined or engineered: randomly, pre-determined or engineered

ObjectivesObjectives-- Monitor activitiesMonitor activities- Gather and fuse information- Gather and fuse information

- Communicate with global data processing unit- Communicate with global data processing unit

Sensor Networks

Application Areas Application Areas [Akyildiz+ 2002][Akyildiz+ 2002]

1.1. Military:Military: Monitoring equipment and ammunitionMonitoring equipment and ammunition Battlefield surveillance and damage assessmentBattlefield surveillance and damage assessment Nuclear, biological, chemical attack detection and reconnaissanceNuclear, biological, chemical attack detection and reconnaissance

Sensor Networks

2.2. Environmental:Environmental: Forest fire / flood detectionForest fire / flood detection

3.3. Health:Health: Tracking and monitoring doctors and patients inside a hospitalTracking and monitoring doctors and patients inside a hospital Drug administration in hospitalsDrug administration in hospitals

Sensor Networks

5.5. Other Commercial Applications:Other Commercial Applications: Environmental control in office buildingsEnvironmental control in office buildings Detecting and monitoring car theftsDetecting and monitoring car thefts Managing inventory controlManaging inventory control Vehicle tracking and detectionVehicle tracking and detection

Application Areas Application Areas [Akyildiz+ 2002][Akyildiz+ 2002]

4.4. Home:Home: Home automationHome automation Smart environmentSmart environment

Sensor Networks Preliminaries – For large scale environment monitoring applications, dense For large scale environment monitoring applications, dense

sensor networks are mainly used sensor networks are mainly used

– Sensing capabilities should be distributed and coordinated Sensing capabilities should be distributed and coordinated amongst the sensor nodesamongst the sensor nodes

– Algorithms deployed should be localized since transmissions Algorithms deployed should be localized since transmissions between large distances are expensive and lowers networks life between large distances are expensive and lowers networks life timetime

– These networks should be self-configuring, scalable, redundant These networks should be self-configuring, scalable, redundant and robust during topology changesand robust during topology changes

ClusteringClustering– Partitioning of the network Partitioning of the network – Identification of vital nodes (clusterheads)Identification of vital nodes (clusterheads)

RoutingRouting– Discovering routes from source to destinationDiscovering routes from source to destination– Maintaining the routesMaintaining the routes– Rediscovery and repair of routesRediscovery and repair of routes

Topology managementTopology management– Maintain the linksMaintain the links– Minimize the changes in underlying graphMinimize the changes in underlying graph

SecuritySecurity

Research Problems in Sensor Networks

Medium Access Control ProtocolsMedium Access Control Protocols

Sensor data managementSensor data management

Power conservation/energy consumptionPower conservation/energy consumption

Data fusion and dissemination of sensor dataData fusion and dissemination of sensor data

New applications for ad hoc and sensor networksNew applications for ad hoc and sensor networks

Research Problems in Ad hoc and Sensor Networks

– Compared to analysis and simulation techniques, designing a system Compared to analysis and simulation techniques, designing a system platform has the following advantages:platform has the following advantages: Provides genuine executive environment: various proposed Provides genuine executive environment: various proposed

algorithms can be exactly evaluated; good way to examine existing algorithms can be exactly evaluated; good way to examine existing design principles and discover new ones under different design principles and discover new ones under different configurationsconfigurations

More attention can be focused on the application-layerMore attention can be focused on the application-layer A real system platform can accelerate the pace of research and A real system platform can accelerate the pace of research and

developmentdevelopment

Why Sensor Platforms?

– Constructing a platform for WSN falls into the area of embedded system Constructing a platform for WSN falls into the area of embedded system development which usually consists of developing environment, development which usually consists of developing environment, hardware and software platforms.hardware and software platforms.

1.1. Hardware PlatformHardware Platform

Consists of the following four components:Consists of the following four components:

a) Processing Unita) Processing Unit

Associates with small storage unit (tens of kilo bytes order) and Associates with small storage unit (tens of kilo bytes order) and

manages the procedures to collaborate with other nodes to carry out themanages the procedures to collaborate with other nodes to carry out the

assigned sensing taskassigned sensing task

b) Transceiver Unitb) Transceiver Unit

Connects the node to the network via various possible transmissionConnects the node to the network via various possible transmission

medias such as infra, light, radio and so onmedias such as infra, light, radio and so on

General WSN System Architecture

1.1. Hardware PlatformHardware Platform

c) Power Unitc) Power Unit

Supplies power to the system by small size batteries which makes the Supplies power to the system by small size batteries which makes the

energy a scarce resourceenergy a scarce resource

d) Sensing Unitsd) Sensing Units

Usually composed of two subunits: sensors and analog-to-digitalUsually composed of two subunits: sensors and analog-to-digital

Converters (ADCs). The analog signal produced by the sensors areConverters (ADCs). The analog signal produced by the sensors are

converted to digital signals by the ADC, and fed into the processing unitconverted to digital signals by the ADC, and fed into the processing unit

e) Other Application Dependent Componentse) Other Application Dependent Components

Location finding system is needed to determine the location of sensor Location finding system is needed to determine the location of sensor

nodes with high accuracy; mobilizer may be needed to move sensor nodes with high accuracy; mobilizer may be needed to move sensor

nodes when it is required to carry out the tasknodes when it is required to carry out the task


2.2. Software PlatformSoftware Platform

Consists of the following four components:Consists of the following four components:

a) Embedded Operating System (EOS)a) Embedded Operating System (EOS)

Manages the hardware capability efficiently as well as supportsManages the hardware capability efficiently as well as supports

concurrency-intense operations. Apart from traditional OS tasks such asconcurrency-intense operations. Apart from traditional OS tasks such as

processor, memory and I/O management, it must be real-time to rapidlyprocessor, memory and I/O management, it must be real-time to rapidly

respond the hardware triggered events, multi-threading to handle respond the hardware triggered events, multi-threading to handle

concurrent flows concurrent flows

b) Application Programming Interface (API)b) Application Programming Interface (API)

A series of functions provided by OS and other system-level components A series of functions provided by OS and other system-level components

for assisting developers to build applications upon itselffor assisting developers to build applications upon itself


2.2. Software PlatformSoftware Platform

c) Device Driversc) Device Drivers

A series of routines that determine how the upper layer entities A series of routines that determine how the upper layer entities

communicate with the peripheral devicescommunicate with the peripheral devices

d) Hardware Abstract Layer (HAL)d) Hardware Abstract Layer (HAL)

Intermediate layer between the hardware and the OS. Provides uniformIntermediate layer between the hardware and the OS. Provides uniform

interfaces to the upper layer while its implementation is highly dependentinterfaces to the upper layer while its implementation is highly dependent

on the lower layer hardware. With the use of HAL, the OS and on the lower layer hardware. With the use of HAL, the OS and

applications easily transplant from one hardware platform to anotherapplications easily transplant from one hardware platform to another


– Motes are tiny, self-contained, battery powered computers with radio Motes are tiny, self-contained, battery powered computers with radio links, which enable them to communicate and exchange data with one links, which enable them to communicate and exchange data with one another, and to self-organize into ad hoc networksanother, and to self-organize into ad hoc networks

– Motes form the building blocks of wireless sensor networksMotes form the building blocks of wireless sensor networks

– TinyOS TinyOS [TinyOS][TinyOS], component-based runtime environment, is designed to , component-based runtime environment, is designed to provide support for these motes which require concurrency intensive provide support for these motes which require concurrency intensive operations while constrained by minimal hardware resourcesoperations while constrained by minimal hardware resources

Berkeley Motes [Hill+ 2000]

Figure 3: Berkeley MoteFigure 3: Berkeley Mote

IntroductionIntroduction

– Habitat and environmental monitoring represent essential class of sensor Habitat and environmental monitoring represent essential class of sensor network applications by placing numerous networked micro-sensors in an network applications by placing numerous networked micro-sensors in an environment where long-term data collection can be achievedenvironment where long-term data collection can be achieved

– The sensor nodes perform filtering and triggering functions as well as The sensor nodes perform filtering and triggering functions as well as application-specific or sensor-specific data compression algorithms thru application-specific or sensor-specific data compression algorithms thru the integration of local processing and storagethe integration of local processing and storage

– The ability to communicate allows nodes to cooperate in performing The ability to communicate allows nodes to cooperate in performing tasks such as statistical sampling, data aggregation, and system health tasks such as statistical sampling, data aggregation, and system health and status monitoringand status monitoring

– Increased power efficiency assists in resolving fundamental design Increased power efficiency assists in resolving fundamental design tradeoffs, e.g., between sampling rates and battery lifetimestradeoffs, e.g., between sampling rates and battery lifetimes

Wireless Sensor Networks for Habitat Monitoring [Mainwaring+ 2002]


– The sensor nodes can be reprogrammed or retasked after deployment in The sensor nodes can be reprogrammed or retasked after deployment in the field by the networking and computing capabilities providedthe field by the networking and computing capabilities provided

– Nodes can adapt their operation over time in response to changes in the Nodes can adapt their operation over time in response to changes in the environmentenvironment

– The application context helps to differentiate problems with simple and The application context helps to differentiate problems with simple and concrete solutions from open research areasconcrete solutions from open research areas

– An effective sensor network architecture and general solutions should be An effective sensor network architecture and general solutions should be developed for the domaindeveloped for the domain

– The impact of sensor networks for habitat and environmental monitoring The impact of sensor networks for habitat and environmental monitoring is measured by their ability to enable new applications and produce new is measured by their ability to enable new applications and produce new resultsresults



– This paper develops a specific habitat monitoring application, but yet a This paper develops a specific habitat monitoring application, but yet a representative of the domainrepresentative of the domain

– It presents a collection of requirements, constraints and guidelines that It presents a collection of requirements, constraints and guidelines that serve as a basis for general sensor network architectureserve as a basis for general sensor network architecture

– It describes the core components of the sensor network for this domain– It describes the core components of the sensor network for this domain– hardware and sensor platforms, the distinct networks involved, their hardware and sensor platforms, the distinct networks involved, their interconnection, and the data management facilitiesinterconnection, and the data management facilities

– The design and implementation of the essential network services – The design and implementation of the essential network services – power management, communications, re-tasking, and node management power management, communications, re-tasking, and node management can be evaluated in this contextcan be evaluated in this context


Habitat MonitoringHabitat Monitoring

– Researchers in the Life Sciences are concerned about the impacts of Researchers in the Life Sciences are concerned about the impacts of human presence in monitoring plants and animals in the field conditionshuman presence in monitoring plants and animals in the field conditions

– It is possible that chronic human disturbance may adversely effect results It is possible that chronic human disturbance may adversely effect results by changing behavioral patterns or distributionsby changing behavioral patterns or distributions

– Disturbance effects are of concern in small island situations where it may Disturbance effects are of concern in small island situations where it may be physically impossible for researchers to avoid some impact on an be physically impossible for researchers to avoid some impact on an entire populationentire population

– Seabird colonies are extreme sensitive to human disturbanceSeabird colonies are extreme sensitive to human disturbance

– Research in Maine [Anderson 1995], suggests that a 15 minute visit to a Research in Maine [Anderson 1995], suggests that a 15 minute visit to a cormorant colony can result in up to 20% mortality among eggs and cormorant colony can result in up to 20% mortality among eggs and chicks in a given breeding year. Repeated disturbance can lead to the chicks in a given breeding year. Repeated disturbance can lead to the end of the colonyend of the colony


Habitat MonitoringHabitat Monitoring

– On Kent Island, Nova Scotia, research learned that Leach’s Storm Petrels On Kent Island, Nova Scotia, research learned that Leach’s Storm Petrels are likely to desert their nesting burrows in case of disturbance during the are likely to desert their nesting burrows in case of disturbance during the first two weeks of incubationfirst two weeks of incubation

– Sensor networks advances the monitoring methods over the traditional Sensor networks advances the monitoring methods over the traditional invasive onesinvasive ones

– Sensors can be deployed prior to the breeding season or other sensitive Sensors can be deployed prior to the breeding season or other sensitive period or while plants are dormant or the ground is frozen on small islets period or while plants are dormant or the ground is frozen on small islets where it would be unsafe or unwise to repeatedly attempt field studieswhere it would be unsafe or unwise to repeatedly attempt field studies

– Sensor network deployment may be more economical method for Sensor network deployment may be more economical method for conducting long-term studies than traditional personnel-rich methodsconducting long-term studies than traditional personnel-rich methods

– A “deploy ‘em and leave ‘em” strategy of wireless sensor usage would A “deploy ‘em and leave ‘em” strategy of wireless sensor usage would decrease the logistical needs to initial placement and occasional servicingdecrease the logistical needs to initial placement and occasional servicing


Great Duck IslandGreat Duck Island

– The College of Atlantic (COA) is field testing in-situ sensor networks for The College of Atlantic (COA) is field testing in-situ sensor networks for habitat monitoringhabitat monitoring

– Great Duck Island (GDI) is a 237 acre island located 15 km south of Great Duck Island (GDI) is a 237 acre island located 15 km south of Mount Desert Island, MaineMount Desert Island, Maine

– At GDI, three major questions in monitoring the Leach’s Storm Petrel At GDI, three major questions in monitoring the Leach’s Storm Petrel [Anderson 1995]:[Anderson 1995]:

1.1. What is the usage pattern of nesting burrows over the 24-72 hour What is the usage pattern of nesting burrows over the 24-72 hour cycle when one or both members of a breeding pair may alternate cycle when one or both members of a breeding pair may alternate incubation duties with feeding at sea?incubation duties with feeding at sea?

2.2. What changes can be observed in the burrow and surface What changes can be observed in the burrow and surface environmental parameters during the course of the approximately 7 environmental parameters during the course of the approximately 7 month breeding season (April-October)?month breeding season (April-October)?


Great Duck IslandGreat Duck Island

3.3. What are the differences in the micro-environments with and without What are the differences in the micro-environments with and without large numbers of nesting petrels?large numbers of nesting petrels?

– Presence/absence data is obtained through occupancy detection and Presence/absence data is obtained through occupancy detection and temperature differentials between burrows with adult birds and burrows temperature differentials between burrows with adult birds and burrows that contain eggs, chicks, or are emptythat contain eggs, chicks, or are empty

– Petrels will most likely enter or leave during the daytime; however, 5-10 Petrels will most likely enter or leave during the daytime; however, 5-10 minutes during late evening and early morning measurements are minutes during late evening and early morning measurements are needed to capture the entry and exit timingsneeded to capture the entry and exit timings

– More general environmental differentials between burrow and surface More general environmental differentials between burrow and surface conditions can be captured by records every 2-4 hours during the conditions can be captured by records every 2-4 hours during the extended breeding season; whereas, the differences between “popular” extended breeding season; whereas, the differences between “popular” and “unpopular” sites benefit from hourly samplingand “unpopular” sites benefit from hourly sampling


Great Duck Island RequirementsGreat Duck Island Requirements

1.1. Internet AccessInternet Access

– The sensor networks at GDI must be accessible via the Internet since the The sensor networks at GDI must be accessible via the Internet since the ability to support remote interactions with in-situ networks is essentialability to support remote interactions with in-situ networks is essential

2.2. Hierarchical NetworkHierarchical Network

– Habitats of interest are located up to several kilometers away. A second Habitats of interest are located up to several kilometers away. A second tier of wireless networking provides connectivity to multiple patches of tier of wireless networking provides connectivity to multiple patches of sensor networks deployed at each of the areas.sensor networks deployed at each of the areas.

3.3. Sensor Network LongevitySensor Network Longevity

– Sensor networks that runs for several month from non-rechargeable Sensor networks that runs for several month from non-rechargeable power sources would be desirable since studies at GDI can span multiple power sources would be desirable since studies at GDI can span multiple field seasonsfield seasons



4.4. Operating off-the gridOperating off-the grid

– Every level of the network must operate with bounded energy suppliesEvery level of the network must operate with bounded energy supplies

– Renewable energy such as solar power may be available some locations, Renewable energy such as solar power may be available some locations, disconnected operation is a possibilitydisconnected operation is a possibility

– GDI has enough solar power that run the application 24x7 with small GDI has enough solar power that run the application 24x7 with small probabilities of service interruptions due to power lossprobabilities of service interruptions due to power loss

5.5. Management at-a-distanceManagement at-a-distance

– Remoteness of the field sites requires the ability to monitor and manage Remoteness of the field sites requires the ability to monitor and manage sensor networks over the Internet. The goal is no on-site presence for sensor networks over the Internet. The goal is no on-site presence for maintenance and administration during the field season, except for maintenance and administration during the field season, except for installation and removal of nodesinstallation and removal of nodes



6.6. Inconspicuous operationInconspicuous operation

– It should not disrupt the natural processes or behaviors under studyIt should not disrupt the natural processes or behaviors under study

– Removing human presence from the study areas would eliminate a Removing human presence from the study areas would eliminate a source of error and variation in data collection and source of disturbancesource of error and variation in data collection and source of disturbance

7.7. System behaviorSystem behavior

– Sensor networks should present stable, predictable, and repeatable Sensor networks should present stable, predictable, and repeatable behavior at all times since unpredictable system is difficult to debug and behavior at all times since unpredictable system is difficult to debug and maintainmaintain

– Predictability is essential in developing trust in these new technologies Predictability is essential in developing trust in these new technologies for life scientistsfor life scientists



8.8. In-situ interactionsIn-situ interactions

– Local interactions are required during initial development, maintenance Local interactions are required during initial development, maintenance and on-site visits and on-site visits

– PDAs can be useful in accomplishing these tasks – they may directly PDAs can be useful in accomplishing these tasks – they may directly query a sensor, adjust operational parameters and so onquery a sensor, adjust operational parameters and so on

9.9. Sensors and samplingSensors and sampling

– The ability to sense light, temperature, infrared, relative humidity, and The ability to sense light, temperature, infrared, relative humidity, and barometric pressure are essential set of measurementsbarometric pressure are essential set of measurements

– Additional measurements may include acceleration/vibration, weight, Additional measurements may include acceleration/vibration, weight, chemical vapors, gas concentrations, pH, and noise levelschemical vapors, gas concentrations, pH, and noise levels



10.10. Data archivingData archiving

– Sensor readings must be achieved for off-line data mining and analysisSensor readings must be achieved for off-line data mining and analysis

– The reliable offloading of sensor logs to databases in the wired, powered The reliable offloading of sensor logs to databases in the wired, powered infrastructure is essentialinfrastructure is essential

– It is desirable to interactively “drill-down” and explore sensors in near It is desirable to interactively “drill-down” and explore sensors in near real-time complement log-based studies. In this mode of operation, the real-time complement log-based studies. In this mode of operation, the timely delivery of sensor data is the keytimely delivery of sensor data is the key

– Nodal data summaries and periodic health-and-status monitoring also Nodal data summaries and periodic health-and-status monitoring also requires timely delivery of the datarequires timely delivery of the data


System ArchitectureSystem Architecture

– A tiered architecture is developedA tiered architecture is developed

– The lowest level consists of the The lowest level consists of the sensor nodessensor nodes that perform general that perform general purpose computing and networking as well as application-specific sensingpurpose computing and networking as well as application-specific sensing

– The sensor nodes may be deployed in dense patches and transmit their The sensor nodes may be deployed in dense patches and transmit their data through the sensor network to the sensor network data through the sensor network to the sensor network gatewaygateway

– Gateway is responsible for transmitting sensor data from the Gateway is responsible for transmitting sensor data from the sensor patchsensor patch through a local through a local transit networktransit network to the remote to the remote base stationbase station that provides that provides WAN connectivity and data loggingWAN connectivity and data logging

– The base station connects to database replicas across the internetThe base station connects to database replicas across the internet

– At last, the data is displayed to researchers through a user interfaceAt last, the data is displayed to researchers through a user interface




Figure 1: System architecture for habitat monitoringFigure 1: System architecture for habitat monitoring


– The autonomous sensor nodes are placed in the areas of interest where The autonomous sensor nodes are placed in the areas of interest where each sensor node collects environmental data about its immediate each sensor node collects environmental data about its immediate surroundingssurroundings

– Since these sensors are placed close to the area of interest, they can be Since these sensors are placed close to the area of interest, they can be built using small and inexpensive individual sensors – high spatial built using small and inexpensive individual sensors – high spatial resolution can be achieved through dense deployment of sensor nodesresolution can be achieved through dense deployment of sensor nodes

– This architecture offers higher robustness compared to traditional This architecture offers higher robustness compared to traditional approaches which use a few high quality sensors with complex signal approaches which use a few high quality sensors with complex signal processingprocessing

– The computational module is a programmable unit that provides The computational module is a programmable unit that provides computation, storage and bidirectional communication with other nodescomputation, storage and bidirectional communication with other nodes



– The computational module interfaces with the analog and digital sensors The computational module interfaces with the analog and digital sensors on the sensor module, performs basic signal processing and dispatches on the sensor module, performs basic signal processing and dispatches the data according to the needs of the applicationthe data according to the needs of the application

– Compared to traditional data logging systems, networked sensors offer Compared to traditional data logging systems, networked sensors offer two main advantages: they can be re-tasked in the field and they can two main advantages: they can be re-tasked in the field and they can communicate with the rest of the systemcommunicate with the rest of the system

– In-situ re-tasking gives researchers the ability to refocus their observations In-situ re-tasking gives researchers the ability to refocus their observations based on the analysis of the initial results – initially, absolute temperature based on the analysis of the initial results – initially, absolute temperature readings are desired, after a while, only significant temperature changes readings are desired, after a while, only significant temperature changes exceeding a threshold may become more usefulexceeding a threshold may become more useful



– Individual sensor nodes communicate and coordinate with one another Individual sensor nodes communicate and coordinate with one another

– These nodes form a multi-hop network by forwarding each other’s These nodes form a multi-hop network by forwarding each other’s messages and if needed, the network can perform in-network aggregation messages and if needed, the network can perform in-network aggregation (e.g., relaying the average temperature across the region)(e.g., relaying the average temperature across the region)

– Eventually, data from each sensor needs to be propagated to the InternetEventually, data from each sensor needs to be propagated to the Internet

– The propagated data may be raw, filtered or processed dataThe propagated data may be raw, filtered or processed data

– Since direct wide area connectivity cannot be brought to each sensor path Since direct wide area connectivity cannot be brought to each sensor path due to several reasons (e.g., cost of equipment, power, disturbance due to several reasons (e.g., cost of equipment, power, disturbance created by the installation of the equipment in the environment), wide are created by the installation of the equipment in the environment), wide are connectivity is brought to a connectivity is brought to a base stationbase station instead instead



– The base station may communicate with the sensor patch using a wireless The base station may communicate with the sensor patch using a wireless LAN where each sensor patch is equipped with a LAN where each sensor patch is equipped with a gatewaygateway that can that can communicate with the sensor network and provides connectivity to the communicate with the sensor network and provides connectivity to the transit networktransit network

– The transit network may consist of a single hop link or series of networked The transit network may consist of a single hop link or series of networked wireless nodes and each transit network design has different wireless nodes and each transit network design has different characteristics with respect to expected robustness, bandwidth, energy characteristics with respect to expected robustness, bandwidth, energy efficiency, cost and manageabilityefficiency, cost and manageability

– To provide data to remote end-users, the To provide data to remote end-users, the base stationbase station includes WAN includes WAN connectivity and persistent data storage for the collection of sensor connectivity and persistent data storage for the collection of sensor patchespatches



– It is expected that WAN connection will be wirelessIt is expected that WAN connection will be wireless

– The architecture needs to address the disconnection possibilitiesThe architecture needs to address the disconnection possibilities

– Each layer (sensor nodes, gateways, base stations) has some persistent Each layer (sensor nodes, gateways, base stations) has some persistent storage to protect against data loss due to power outage as well as data storage to protect against data loss due to power outage as well as data management servicesmanagement services

– At the sensor level, these will be primitive, taking the form of data loggingAt the sensor level, these will be primitive, taking the form of data logging

– The base station may provide relational database service while the data The base station may provide relational database service while the data management at the gateways falls somewhere in betweenmanagement at the gateways falls somewhere in between

– When it comes to data collection, long-latency is preferable to data lossWhen it comes to data collection, long-latency is preferable to data loss

– Users interact with the sensor network in two waysUsers interact with the sensor network in two ways



– Remote users access the replica of the base station database Remote users access the replica of the base station database

– This approach assists on integration with data analysis and mining tools This approach assists on integration with data analysis and mining tools while masking the potential wide area disconnections with the base while masking the potential wide area disconnections with the base stationsstations

– On-site users may require direct interaction with the network and this can On-site users may require direct interaction with the network and this can be accomplished with a small, PDA-sized device, referred to as be accomplished with a small, PDA-sized device, referred to as gizmogizmo

– Gizmo allows the user to interactively control the network parameters by Gizmo allows the user to interactively control the network parameters by adjusting the sampling rates, power management parameters and other adjusting the sampling rates, power management parameters and other network parametersnetwork parameters

– The connectivity between any sensor node and gizmo may or may not rely The connectivity between any sensor node and gizmo may or may not rely on functioning on multi-hop sensor network routingon functioning on multi-hop sensor network routing



– Focus is on issues related to dynamic sensor networks with mobile Focus is on issues related to dynamic sensor networks with mobile nodes and wireless communication between themnodes and wireless communication between them

– In this system, the sensor nodes collars carried by the animals under In this system, the sensor nodes collars carried by the animals under study; wireless ad hoc networking techniques are used to swap and store study; wireless ad hoc networking techniques are used to swap and store data in a peer-to-peer manner and to pass it towards a mobile base data in a peer-to-peer manner and to pass it towards a mobile base station that sporadically traverses the area to upload datastation that sporadically traverses the area to upload data

– Biology and biocomplexity research has been focused on gathering data Biology and biocomplexity research has been focused on gathering data and observations on a range of species to understand their interactions and observations on a range of species to understand their interactions and influences on each otherand influences on each other

– For example, how human development into wilderness areas affects For example, how human development into wilderness areas affects indigenous species there; understand the migration patterns of wild indigenous species there; understand the migration patterns of wild animals and how they may be affected by changes in weather patterns or animals and how they may be affected by changes in weather patterns or plant life, by introduction of non-native species, and by other influencesplant life, by introduction of non-native species, and by other influences

Energy-Efficient Computing for Wildlife Tracking: Design Tradeoffs and Early Experiences with ZebraNet [Juang+ 2002]


– Finding and learning these details require long-term position logs and Finding and learning these details require long-term position logs and other biometric data such as heart rate, body temperature, and frequency other biometric data such as heart rate, body temperature, and frequency feedingfeeding

– Current wildlife tracking studies rely on simple technology, for example, Current wildlife tracking studies rely on simple technology, for example, many studies rely on collaring a sample subset of animals with simple many studies rely on collaring a sample subset of animals with simple VHF transmittersVHF transmitters

– Researchers periodically drive through and/or fly over an area with a Researchers periodically drive through and/or fly over an area with a receiver antenna, and listen for pings from previously collared animalsreceiver antenna, and listen for pings from previously collared animals

– Once animal is found, its behavior can be observed and its observed Once animal is found, its behavior can be observed and its observed position can be logged; however, there are limits to such studiesposition can be logged; however, there are limits to such studies

– First, data collection is infrequent and can miss many “First, data collection is infrequent and can miss many “interesting eventsinteresting events””



– Second, data collection is mostly limited to daylight hours, but animal Second, data collection is mostly limited to daylight hours, but animal behavior and movements in night hours can be differentbehavior and movements in night hours can be different

– Third, data collection is impossible or very limited for secluded species Third, data collection is impossible or very limited for secluded species that avoid human contactthat avoid human contact

– The most elegant trackers commercially available use GPS to track The most elegant trackers commercially available use GPS to track position and use satellite uploads to transfer data to a base stationposition and use satellite uploads to transfer data to a base station

– These systems also suffer from several limitationsThese systems also suffer from several limitations

– First, at most a log of 3000 position samples can be logged and no First, at most a log of 3000 position samples can be logged and no biometric databiometric data

– Second, since satellite uploads are slow and uses high power Second, since satellite uploads are slow and uses high power consumption, they are done infrequently – this limits how often position consumption, they are done infrequently – this limits how often position samples can be gathered without overflowing 3000-entry log storagesamples can be gathered without overflowing 3000-entry log storage



– Third, downloads of data from the satellite to the researchers are both Third, downloads of data from the satellite to the researchers are both slow and expensive, therefore, constraining the amount of data collectedslow and expensive, therefore, constraining the amount of data collected

– Finally, these systems operate on batteries without recharge – when Finally, these systems operate on batteries without recharge – when power is drained, the system become unusable unless it is retrieved, power is drained, the system become unusable unless it is retrieved, recharged and re-deployedrecharged and re-deployed

– ZebraNetZebraNet project is building tracking nodes that include a low-power project is building tracking nodes that include a low-power miniature GPS system with user-programmable CPU, non-volatile miniature GPS system with user-programmable CPU, non-volatile storage for data logs, and radio transceivers for communicating either storage for data logs, and radio transceivers for communicating either with other nodes or with a base stationwith other nodes or with a base station



– One of the key principles of ZebraNet is that the system should work in One of the key principles of ZebraNet is that the system should work in arbitrary wilderness locations; no assumptions are made about the arbitrary wilderness locations; no assumptions are made about the presence of of fixed antenna towers or cellular phone servicepresence of of fixed antenna towers or cellular phone service

– The system uses peer-to-peer data swaps to move the data around; The system uses peer-to-peer data swaps to move the data around; periodic researcher drives bys and/or fly-overs can collect logged data periodic researcher drives bys and/or fly-overs can collect logged data from several animals despite encountering relatively few within rangefrom several animals despite encountering relatively few within range

– Even though ad hoc sensor networks have been heavily studied, not Even though ad hoc sensor networks have been heavily studied, not much has been published about the characteristics of mobile sensor much has been published about the characteristics of mobile sensor networks with mobile base stations and very few studies focus on networks with mobile base stations and very few studies focus on building real systemsbuilding real systems



– This paper has the following unique contributions:This paper has the following unique contributions:

o To the best knowledge of authors, this is the first study of mobile To the best knowledge of authors, this is the first study of mobile sensor networks protocols in which the base station is also sensor networks protocols in which the base station is also mobilemobile. It . It is presumed that researchers will upload data while driving or flying is presumed that researchers will upload data while driving or flying by the regionby the region

o Zebra-tracking is a domain in which the node mobility models are Zebra-tracking is a domain in which the node mobility models are unknown which makes it a research goal. Understanding how, when unknown which makes it a research goal. Understanding how, when and why zebras undertake long-term migrations is the most essential and why zebras undertake long-term migrations is the most essential biological question of this work. biological question of this work.

o ZebraNet’s data collection has communication patterns in which data ZebraNet’s data collection has communication patterns in which data can be cooperatively passed towards a base stationcan be cooperatively passed towards a base station

o Energy tradeoffs are examined in detail using real system energy Energy tradeoffs are examined in detail using real system energy measurements for ZebraNet prototype hardware in operationmeasurements for ZebraNet prototype hardware in operation



– Some of the interesting research questions to be explored are:Some of the interesting research questions to be explored are:

o How to make the communications protocol both effective and power-How to make the communications protocol both effective and power-efficient?efficient?

o To what extent can we rely on ad hoc, peer-to-peer transfers in a To what extent can we rely on ad hoc, peer-to-peer transfers in a sparsely-connected spatially-huge sensor network?sparsely-connected spatially-huge sensor network?

o How can we provide comprehensive tracking of a collection of How can we provide comprehensive tracking of a collection of animals, even if some of the animals are reclusive and rarely are animals, even if some of the animals are reclusive and rarely are close enough to humans to have their data logs updated directly?close enough to humans to have their data logs updated directly?

– This research work gives quantitative explorations of the design This research work gives quantitative explorations of the design decisions behind some of these questionsdecisions behind some of these questions


ZebraNet Design GoalsZebraNet Design Goals

– The ZebraNet project is a direct and ongoing collaboration between The ZebraNet project is a direct and ongoing collaboration between researchers in experimental computer systems and in wildlife biologyresearchers in experimental computer systems and in wildlife biology

– The wildlife biologists have determined the tracker’s overall design goals:The wildlife biologists have determined the tracker’s overall design goals:

o GPS position samples are taken every three minutesGPS position samples are taken every three minutes

o Detailed activity logs taken for three minutes every hourDetailed activity logs taken for three minutes every hour

o One year of operation without direct human intervention – that is, not One year of operation without direct human intervention – that is, not counting on tranquilizing and re-collaring an animal more than once counting on tranquilizing and re-collaring an animal more than once per yearper year

o No fixed base stations, antennas, or cellular service No fixed base stations, antennas, or cellular service

o A high success rate for A high success rate for eventuallyeventually delivering all logged data is delivering all logged data is essential while latency is not as criticalessential while latency is not as critical

o For a zebra collar, a weight limit of 3-5 lbs is recommendedFor a zebra collar, a weight limit of 3-5 lbs is recommended


ZebraNet Design GoalsZebraNet Design Goals

– Ultimately, this detailed information may include several position Ultimately, this detailed information may include several position estimates, temperature information, weather data, environmental data, estimates, temperature information, weather data, environmental data, and body movements that will serve as signatures of behavior; however, and body movements that will serve as signatures of behavior; however, in this initial system, the focus is only on position datain this initial system, the focus is only on position data

– Overall, the key goal is to deliver to researchers a very high fraction of the Overall, the key goal is to deliver to researchers a very high fraction of the data collected over the months or years that the system is in operationdata collected over the months or years that the system is in operation

– Therefore, ZebraNet must be power-efficient, designed with appropriate Therefore, ZebraNet must be power-efficient, designed with appropriate data log storage, and must be rugged to ensure reliability under tough data log storage, and must be rugged to ensure reliability under tough environmental conditionsenvironmental conditions


ZebraNet Problem StatementZebraNet Problem Statement

– The biologists design goals need to be translated into the engineering The biologists design goals need to be translated into the engineering task at handtask at hand

– Success rate at delivering position data to the researchers –data homing Success rate at delivering position data to the researchers –data homing rate– should approach 100%rate– should approach 100%

– Weight limits on each node translate almost directly to computational Weight limits on each node translate almost directly to computational energy limits since weight of the battery and solar panel takes bulk of the energy limits since weight of the battery and solar panel takes bulk of the total weight of a ZebraNet node; therefore, collar and protocol design total weight of a ZebraNet node; therefore, collar and protocol design decisions must manage the number and size of data transmissions decisions must manage the number and size of data transmissions requiredrequired

– System design choices must be made that limit the range of System design choices must be made that limit the range of transmissions since the required transmitter energy increases transmissions since the required transmitter energy increases dramatically with the distance transmitteddramatically with the distance transmitted



– The amount of storage needed to hold position logs must be limited – if The amount of storage needed to hold position logs must be limited – if many redundant copies are stored and swapped, the storage many redundant copies are stored and swapped, the storage requirements can scale as requirements can scale as O(nO(n22))

– Although the energy cost of storage is small compared to that of Although the energy cost of storage is small compared to that of transmissions, it is still necessary to develop storage-efficient designtransmissions, it is still necessary to develop storage-efficient design

– Due to limited transceiver, coverage and a base station only sporadically Due to limited transceiver, coverage and a base station only sporadically available, ZebraNet must forward data through other nodes in peer-to-available, ZebraNet must forward data through other nodes in peer-to-peer manner and store redundant copies of position logs in other tracking peer manner and store redundant copies of position logs in other tracking nodesnodes

– Some of the key challenges in ZebraNet come from the spatial and Some of the key challenges in ZebraNet come from the spatial and temporal scale of the systemtemporal scale of the system



– In terms of temporal scale, keeping a system running autonomously In terms of temporal scale, keeping a system running autonomously months at a time is challenging; it requires tremendous design-time months at a time is challenging; it requires tremendous design-time attention to both hardware and software reliabilityattention to both hardware and software reliability

– In terms of spatial scale, ZebraNet is also aggressive; it is the specific In terms of spatial scale, ZebraNet is also aggressive; it is the specific intent of the system to operate over an area of hundreds or thousands of intent of the system to operate over an area of hundreds or thousands of square square kilometerssquare square kilometers

– Due to the large distances involved and sparse sensor coverage, Due to the large distances involved and sparse sensor coverage, energy/connectivity tradeoffs become keyenergy/connectivity tradeoffs become key



– These challenges mentioned here tackles several open problems:These challenges mentioned here tackles several open problems:

– ZebraNet protocol promises good communication behavior on mobile ZebraNet protocol promises good communication behavior on mobile sensors forwarding data towards a mobile base stationsensors forwarding data towards a mobile base station

– ZebraNet explores design issues for sensors that are more coarse-ZebraNet explores design issues for sensors that are more coarse-grained than many prior sensor proposals. Larger the weight limits grained than many prior sensor proposals. Larger the weight limits and storage budgets allow researchers to consider different protocols and storage budgets allow researchers to consider different protocols with improved leverage for sparsely-connected, physically-with improved leverage for sparsely-connected, physically-widespread sensorswidespread sensors


[Abrach+ 2003] H. Abrach, S. Bhatti, J. Carlson, H. Dai, J. Rose, A. Sheth, B. Shucker, J, Deng and R. Han, MANTIS: System Support for MultimodAl NeTworks of In-Situ Sensors, 2nd ACM International Workshop on Wireless Sensor Networks and Applications (WSNA 2003), September 2003.

[Akyildiz+ 2002] I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, A Survey on Sensor Networks, IEEE Communications Magazine, Vol. 40, No. 8, pp. 102-114, August 2002.

[Anderson 1995] J.G.T. Anderson, Pilot survey of mid-coast Maine seabird colonies: an evaluation of techniques, Bangor, ME, 1995. Report to the State of Maine Dept. of Inland Fisheries and Wildlife.

[Hill+ 2000] J. Hill, R. Szewczyk, A. Woo, S. Hollar, D. Culler, and K. Pister, System Architecture Directions for Networked Sensors, Architectural Support for Programming Languages and Operating Systems (ASPLOS) 2000.

[Juang+ 2002] P. Juang, H. Oki, Y. Wang, M. Martonosi, L-S Peh, and D. Rubenstein, Energy-Efficient Computing for Wildlife Tracking: Design Tradeoffs and Early Experiences with ZebraNet, ACM SIGARCH Computer Architecture News, vol. 30, no. 5, December 2002 .

[Mainwaring+ 2002] A. Mainwaring, J. Polastre, R. Szewczyk, D. Culler, and J. Anderson, Wireless Sensor Networks for Habitat Monitoring, 1st ACM International Workshop on Wireless Sensor Networks and Applications (WSNA 2002), Atlanta, Georgia, September 28, 2002.

[TinyOS] TinyOS: a component-based OS for the networked sensor regime.

References

http://webs.cs.berkeley.edu/tos

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