Wireless Sensor Network Dr. Monir Hossen ECE, KUET Department of Electronics and Communication Engineering, KUET

Wireless Sensor Network

Dr. Monir HossenECE, KUET

Department of Electronics and Communication Engineering, KUET

Department of Electronics and Communication Engineering, KUET 2

Introduction Differences with ad hoc networks Applications Characteristics Challenges Future Motes Hardware Setup Overview

Agendas of This Lecture


Introduction Wireless Sensor Networks (WSNs) are networks that consists

of sensor nodes which are distributed in an ad hoc manner WSN consisting of spatially distributed autonomous devices

using sensors to cooperatively monitor physical or environmental conditions:

- Temperature - Sound - Pressure - Home automation - Traffic control - Healthcare application

Main Devices of WSN

Sensor Nodes and PANC


Characteristics of Wireless Sensor Networks

Wireless Sensor Networks mainly consists of sensor nodes. Sensor nodes are -o Low power deviceo Consist of limited memoryo Energy constrained due to their small size.

Wireless networks can also be deployed in extreme environmental conditions and may be prone to enemy attacks.

Although deployed in an ad hoc manner they need to be self organized and self healing and can face constant reconfiguration.


Design Challenges of WSN (1/2)

Heterogeneity => The devices deployed maybe of various types

and need to collaborate with each other.

Distributed Processing=> The algorithms need to be centralized as the

processing is carried out on different nodes.

Low Bandwidth Communication=> The data should be transferred efficiently

between sensor nodes.


Design Challenges of WSN (2/2) Large Scale Coordination

=> The sensors need to coordinate with each other to produce required results.

Utilization of Sensors=> The sensors should be utilized in a ways that

produce the maximum performance and use less energy.

Real Time Computation=> The computation should be done quickly as

new data is always being generated.


Operational Challenges of WSNs Energy Efficiency Limited storage and computation Low bandwidth and high error rates Errors are common

Wireless communication Noisy measurements Node failure are expected

Scalability to a large number of sensor nodes

Survivability in harsh environments Experiments are time- and space-

intensive


The Growth of Sensor Networks WSNs grown from simple point-to-point networks with simple interface protocols providing sensing and control informationThe sensor node has increased onboard intelligence and processing capabilities thus providing it with different computing capabilities The development of the Manufacturing Automation Protocol (MAP), reduced the cost of integrating various networking schemes into a plant wide system The development of other communication protocols allowed simultaneous analog and digital communications created a sensor network


Enabling Technologies

Embedded

Control system w/Small form factorUntethered nodes

Networked

Exploitcollaborative

Sensing, action

Sensing

Tightly coupled to physical world

Embed numerous distributed devices to monitor and interact

with physical world

Network devices to coordinate and perform higher-level tasks

Exploit spatially and temporally dense, in situation of sensing and actuation


Future of WSNSmart Home / Smart Office

Sensor nodes controlling appliances and electrical devices in the house.

Better lighting and heating in office buildings.

The Pentagon building has used sensors extensively.


Biomedical / Medical Health Monitors

Glucose Heart rate Cancer detection

Chronic Diseases Artificial retina Cochlear implants

Hospital Sensors Monitor vital signs Record

irregularities


Military

Remote deployment of sensors for tactical monitoring of enemy troop movements.


Industrial & Commercial

Numerous industrial and commercial applications:o Agricultural Crop Conditionso Inventory Trackingo In-Process Parts Trackingo Automated Problem Reportingo RFID – Theft Deterrent and Customer

Tracingo Plant Equipment Maintenance Monitoring


Traffic Management & Monitoring Future cars could use

wireless sensors to:Handle AccidentsHandle Thefts

Sensors embedded in the roads to:=> Monitor traffic flows=> Provide real-time route

updates=> Monitor the speed of a

car


Typical Multi-hop WSN Architecture

PANC

Sensor Node

Since area of u-City is increasing: Diameter of WSN is

increased (> 10 Km)

Number of sensor nodes are increased ( > multi-decades of thousands)

Number of wireless hopes are increased (>15)

Reverse time delay is increased

WSN Normally Constitutes an Multi-hop Wireless Network


Limitations of Multi-hop WSNs

The Multi-hop WSN Possess the Following Limitations:

- Large Time Delay

- Huge Traffic Overcrowding

- Data Repetition Multiple Times

- Huge Energy Loss

- Difficult to Protect The Failure of a Node

- Large Time for Fault Analysis


Data Transmission Protocol in WSN

PNC Sensor Node 1

Beacon

Data

Acknowledgment

Beacon

Beacon

Data

DataAcknowledgmentAcknowledgment

Sensor Node 4

Sensor Node 2

Sensor Node 3

Beacon

Data

Acknowledgment

(optional)

(optional)

(optional)

(optional)

Two Types of Data Transaction Exist:

- PANC Sensor Node

- Sensor Nodes PANC

DS

US


Routing Protocols in WSNs

Hierarchical-Based

Location-Based

Flat-Based

Routing Protocols

Traditional Routing Current Routing

Flooding Gossiping


Flooding Protocol A classical mechanisms to relay data in sensor

networks without the need for any routing algorithms and topology maintenance. It broadcasts data.

Drawbacks:• Implosion (duplicate packet

may receive)• Overlap (two sensors send

a packet and at the same time) • Resource blindness (without checking node’s

status it transmits packets)


Gossiping Protocol A slightly enhanced version

of flooding where the transmitting node sends the packet to a randomly selected neighbor which picks another neighbor to forward the packet to and so on. Advantage: avoid the

collapse Drawback:

Transmission delay


Flat-Based Routing Protocols (1/2) All the nodes are treated equally and have the

same functionality

1. Sensor Protocol for Information Negotiation (SPIN): Sending meta -data to neighboring nodes, instead of data Requesting for the desired data

Avoid redundant data transmission Adaptation to remaining energy increase network

lifetime

2. Directed Diffusion: BS continuously sends query to the neighboring nodes Node with the desired data transmit all the way back to BS

Saving energy by selecting the optimal return path Not practical for continuous data demand cases


Flat-Based Routing Protocols (2/2) 3. Rumor Routing:

Variation of Directed Diffusion Each node has an event table Event agent flooding instead of query flooding

Significant energy saving Good for when number of events is less than queries

4. Minimum Cost Forwarding Algorithm (MCFA): Each node knows the least cost path between itself and BS Least cost path can be acquired via initialization

Saving energy by selecting the optimal return path Good for small networks


Hierarchical Routing (1/3) Higher energy nodes for transmission, lower

energy nodes for sensing Two layer routing Increasing the life time

1. Low Energy Adaptive Clustering Hierarchy (LEACH): Random and variation Cluster Head (CH) selection Compression and transmission of arriving data at CHs

Constant monitoring applications Good for small networks Extra overhead because of clustering


Hierarchical Routing (2/3)

2. Self Organizing Protocol (SOP): Mobile sensors to probe the environment Stationary nodes as the routers LML algorithm for routing Energy consumption is less than SPIN

3. Virtual Grid Architecture Symmetric, non-overlapping clusters with optimal CH Local and global data aggregation

Hard to find the optimal global aggregators


Hierarchical Routing (3/3)

4. Hierarchical power-aware routing Proximate nodes form zones Routes through the zones

which has maximum minimum residual energy Extra algorithm can be

exploited


Location-Based Routing o Sensor nodes are addressed based on their locationo Location are acquired by GPS or via coordination

among nodes1. Geographical Adaptive Fidelity (GAF):

Network divided into zones Only one node is awake in each zone, the rest sleep

Conserves energy by turning off unnecessary nodes Increases the network life time

2. SPAN: Some nodes are selected as coordinators based on their

positions Enough coordinators such that network is three-hop

reachable Not energy efficient as the others


Routing Protocols Based on Protocol Operation

1. Multipath routing Increases fault tolerance Sophisticated case: have back up paths

2. Query-based routing Query transmitted and the date is sent back

3. Negotiation-based routing High-level data description Elimination of redundant data transmission

4. QoS-based routing Balance between data quality and energy consumption


Hidden Terminal Problem

A

BC

Hidden terminalsA and C cannot hear each other.A sends to B, C cannot receive A. C wants to send to B, C senses a “free” medium (CS fails)Collision occurs at B.A cannot receive the collision (CD fails).A is “hidden” for C.

Solution?Hidden terminal is peculiar to wireless (not found in wired)Need to sense carrier at receiver, not sender!“virtual carrier sensing”: Sender “asks” receiver whether it can hear something. If so, behave as if channel busy.


Exposed Node Problem Exposed node problem occurs when a node is prevented

from sending packets to other nodes due to a neighboring transmitter.

If a transmission between S1 and R1 is taking place, node S2 is prevented from transmitting to R2 as it will interfere with the transmission by its neighbor S1

However note that R2 could still receive the transmission of S2 without interference because it is out of range of S1


IEEE 802.11 MAC Protocol: CSMA/CA

802.11 CSMA: SenderIf sense channel idle for DIFS (Distributed Inter Frame Space) then transmit entire frame (no collision detection)If sense channel busythen binary back off

802.11 CSMA: ReceiverIf received OKreturn ACK after SIFS --Short IFS (ACK is needed due to hidden terminal problem)

NAV: network allocation vector


Collision Avoidance Mechanisms

Problem: Two nodes, hidden from each other, transmit complete frames to base stationWasted bandwidth for long duration!

Solution: Small reservation packets: RTS+CTSNodes track reservation interval with internal (NAV)

Thanks for Your Kind Attention

Department of Electronics and Communication Engineering, KUET

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Wireless Sensor Network Dr. Monir Hossen ECE, KUET Department of Electronics and Communication Engineering, KUET