research directions in wireless sensor networks sandeep gupta

Research Directions in Wireless Research Directions in Wireless Sensor NetworksSensor Networks

Sandeep Gupta

CSE534- Advanced Computer Networks2

TopicsTopics

Types of ApplicationsDifference between WSN & traditional

sensor and ad hoc networksResearch Issues


Types of ApplicationsTypes of Applications

According to Culler et al. [CES04]:– Monitoring space

• Habitat monitoring, precision agriculture, indoor climate control, surveillance, treaty verification, intelligent alarms

– Monitoring things• Structural monitoring, ecophysiology, condition-based

equipment maintenance, medical diagnostics, urban terrain mapping

– Monitoring the interactions of things with each other and the encompassing space

• Wildlife habitat monitoring, disaster management, emergency response, ubiquitous computing environments, tracking asset, healthcare, manufacturing process flow.


Types and Features of Traditional Types and Features of Traditional Sensor Networks [SAC04]Sensor Networks [SAC04] Types I -Remote deployment:

– Sensors are placed far from sensing phenomenon.– Large sensors use complex signal processing

techniques to distinguish the targets (sensed objects) from environmental noise.

Type II – in-situ depolyment:– Several sensors that perform only sensing task– Position of sensors and communications topology

is carefully engineered– Sensors transmit time-series of the sensed

phenomenon to the central node which performs computations and fuses data.


Features of Wireless Features of Wireless (Micro/Embedded) Sensor Networks(Micro/Embedded) Sensor Networks

In-situ or embedded– Sensor are deployed either close or inside the

object of study

Dense deployment Ad hoc topology Sensors are resource constrained (energy,

bandwidth, processing, memory) In-network processing (data aggregation,

fusion, array signal processing)


Differences between Ad Hoc Differences between Ad Hoc Networks and Sensor NetworksNetworks and Sensor Networks #nodes several order of magnitude higher

– Sensor nodes may not have global identification (ID) Sensor nodes densely deployed Sensor nodes more prone to failure

– Topology changes frequently Sensor nodes mainly use broadcast communication

paradigm whereas ad hoc networks use point-to-point communication

Sensor nodes are more limited in power, computational capabilities, and memory

Sensor networks are usually application-specific


Research Directions: Sensor Research Directions: Sensor Network OrganizationNetwork Organization

How should the sensor networks be organized?– Hierarchical (Tiered) is preferred from

energy consumption perspective– How many levels?

• E.g. Two Tiered: Sensor -> PDA (microserver) -> Basestation (sink)


Research Direction: Routing and In-Research Direction: Routing and In-network processingnetwork processing

Routing “responses to attributed-based queries” as opposed to “data from one network address to another”.

Efficiency demands in-network processing

Routing needs to be integrated with and influenced by the application– Different from Internet-style routing


Research Direction: Automatic Research Direction: Automatic LocalizationLocalization Needed for integration of information gleaned by

various sensors Location information of sensors in phenomenon P’s

region can be used to determine additional information such as it’s size and speed.

– E.g. combining binary decision (within P or outside P) to determine it’s shape.

sensor

target


Research Direction: Automatic Time Research Direction: Automatic Time SynchronizationSynchronization Useful for sensing time-varying or mobile

phenomenon. Timestamped data from different sensors can

be combined to estimate phenomenon's velocity.

In some cases GPS can provide position and a global clock– Requires line-of-sight to several satellites

• Does not work inside building, underwater, when jammed by enemy, on Mars

– May be too expensive – high cost, energy consumption


Research Direction: Distributed Research Direction: Distributed Signal ProcessingSignal Processing

Traditionally, centralized sensor fusion Signal processing resolve low-level sensor

signals (acoustic or seismic) into higher level sensors (e.g. “cars” or “earthquake”).– Target tracking, signal enhancement

(beamforming – combining signals from several sensors to reduce noise)

Challenge: how to get best signal processing results within the bandwidth and computational constraints of the sensing platforms?


Research Direction: Storage, Search Research Direction: Storage, Search and Retrievaland Retrieval

Sensor network can produce large volume of data

Limited amount of data may be stored locally at sensors

Challenge: Data mining over a massively distributed database which is under energy, bandwidth, and storage constraints

Data mining over data streams rather than data stored on secondary storage


Research Direction: ActuationResearch Direction: Actuation

Actuation extend the capability of network in two ways:

1. can enhance sensing task pointing camera, aiming antenna, repositioning

sensors

2. can affect the environment Opening valves, emitting sound

Common actuation task is sensor mobility– Size and shape of a target can be determined

more accurately if the sensors can move Challenge: making the right actuation

decisions.


Research Direction: Simulation, Research Direction: Simulation, Monitoring, and DebuggingMonitoring, and Debugging How can a designer evaluate a system where, by

definition, the information necessary for the evaluation is not available?– Most of the raw data is not seen outside the network

How can we be sure that the final, high-level sensing results delivered by the system is an accurate reflection of the state of the environment – when sensors are deployed where there is insufficient energy and bandwidth to record all the raw data?

Simulation becomes crucial– simulators may be the only environment in which a sensor

network can both run at a large scale and record each raw datum.


Research Direction: Security and Research Direction: Security and PrivacyPrivacy Physical security of nodes embedded in the

environment cannot be ensured– Security protocols different from those in Internet servers– Attackers can modify node h/w, replace it with malicious

counterpart, fool the sensors in making observations that do not accurately reflect the environment

Limited resources End-to-end encryption prohibits in-networking

processing (data aggregation) Sensor network can be used to gather private data

(record location, time, action etc. of individuals).


Research Issues at various LayersResearch Issues at various Layers

Application Layer:– Sensor Management Protocol– Task Assignment and Data Advertisement– Sensor Query and Data Dissemination

Transport Layer:– Event to Sink (or Base Station)– Sink to Event

Network Layer– Data-centric, energy-efficient routing protocols

Data Link Layer– medium access with built in power conservation, mobility

management, and failure recovery strategies– Application specific Error control

Physical layer– Efficient frequency selection, carrier frequency generation,

modulation and data encryption


Sensor Management ProtocolSensor Management Protocol

Allows accessing a sensor network remotely via Internet

Makes underlying h/w and s/w transparent to sensor management application

Uses attribute-based naming and location-based addressing to access nodes

Perform several management tasks e.g.– Introduce rules related to data aggregation, attribute-based

naming and clustering to the sensor nodes– Time synchronization– Turning sensor nodes on and off– Authentication, key distribution – Moving sensor nodes– Localization


Transport LayerTransport Layer

Traditional transport layer issues:– Bridge application and network layers by

application multiplexing and demultiplexing– Provide data delivery service between the

source and the sink with error control mechanism tailored to the reliability requirements of application layer

– Regulate the amount of traffic injected in the network using flow and congestion control.


Event-to-Sink TransportEvent-to-Sink Transport

Event-to-Sink reliability (reliable event detection at sink) rather than end-to-end reliability (reliable delivery of individual packets from a source to destination)

Sink is only interested in the collective information of sensor nodes within the event radius and not their individual data

sensor

Event radius

sink


Sink to Sensors TransportSink to Sensors Transport

Sink to sensors (reverse) path used to send operational or application-specific data from sink to sensors– OS binaries, programming retasking

configuration files, application-specific queries and commands

– Requires 100% reliability• Requires retransmissions and acks

– Local retransmisions and nacks preferred

Requires multihop one-to-many (multicast) communication

Some Approaches to Some Approaches to Routing in Wireless Sensor Routing in Wireless Sensor

NetworksNetworks


Directed DiffusionDirected Diffusion

Used for Event-Driven Queries

1. Inject a Query into the Sensor Network

2. Flood the Request throughout the Network

3. Transmit Responses from Observers to Sink

4. Combine Similar Responses for Efficiency

5. Provide Data Aggregation at Junctions

6. Maintain Efficient Paths from Observer

7. Develop Alternative Paths around Faulty or Sleeping Nodes


Tree-Based ForwardingTree-Based Forwarding

Tree is created – root is the base station

Most communication is localized.

Hierarchical structure.

Workload of sensors is not balanced.

Limited fault tolerance.


LeachLeach

Used for Periodic Communication

1. Set-up Phase picks ClusterheadsA. Number of Clusterheads Predefined

B. Randomly choose Clusterheads

2. Steady-State Phase supports communication

A. Nodes listen for Clusterhead advertisements

B. Join “closest” Cluster-head

C. Clusterhead Aggregates Data

D. Clusterhead Transmits to the Base Station


Trajectory-Based ForwardingTrajectory-Based Forwarding

Path follows a Sine wave

Useful for dense sensor networks– Requires position

information– Sensors follow a

parametric path– No routing tables or

routing information– Local computation

to find next hop– Highly scalable


Redundant NodesRedundant Nodes

Extra wireless sensors can aid routing protocols in several ways:– Compensates for unbalanced loads– Allows double-checking of sensor readings– Extends sensor network lifespan

Useful for sensors with passive power supplies– Enables sensors to recharge– Reduces overall energy demands


ReferencesReferences

[CES04] D. Culler, D. Estrin, and M. Sirvastava, “Overview of Sensor Networks”, IEEE Computer, 41-49, 37(8), Aug. 2004.

[SAC04] W. Su, O. Akan, and E. Cayirci, “Chapter 2: Communication Protocols for Sensor Networks”, in Book “Wireless Sensor Networks”, Raghavendra, Shivalingam, Znati (Eds), KAP, 2004.

[ES04] J. Elson and D. Estrin, “Chapter 1: Sensor Networks: A Bridge to the Physical World”, in Book “Wireless Sensor Networks”, Raghavendra, Shivalingam, Znati (Eds), KAP, 2004.

research directions in wireless sensor networks sandeep gupta

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