unit iii - mr.rajiv bhandari · unit iii basic concepts of wireless sensor networks (wsn) unit iii...

Unit III

Basic concepts of Wireless Sensor Networks (WSN)

Unit III 1 Prof. Prashant Lahane

Wireless Sensor Network

“A wireless sensor network (WSN) is a wireless network consisting of spatially distributed

autonomous devices using sensors to cooperatively monitor physical or environmental conditions, such as

temperature, sound, vibration, pressure, motion or pollutants, at different locations.”

- Wikipedia


Motes & Wireless Sensor Networks

• A very low cost low power computer- on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals.

• It performs tasks, processes data and controls the functionality of other components in the sensor node.

• Monitors one or more sensors. • A Radio Link to the outside world. • Are the building blocks of Wireless Sensor Networks (WSN).

External Memory

Dig

ital

I/O

po

rts

Radio Transceiver

An

alo

g I/

O P

ort

s

Microcontroller

A/D

D/A

Sensor

Sensor


WSN Overview (Cont.)

CPU

• The Microcontroller Unit (MCU) is the primary choice for in-node processing.

• Power consumption is the key metric in MCU selection.

• The MCU should be able to sleep whenever possible, like the radio.

• Memory requirements depend on the application

• ATmega128L and MSP430 are popular choices


Example Microcontrollers

• Texas Instruments MSP430

– 16-bit RISC core, 4 MHz

– Up to 120 KB flash

– 2-10 KB RAM

– 12 ADCs, RT clock

• Atmel ATMega

– 8-bit controller, 8 MHz

– Up to 128KB Flash

– 4 KB RAM

•


Communication Device

• Medium options

– Electromagnetic, RF

– Electromagnetic, optical

– Ultrasound

Radio

Transceiver

radio wave

bit stream


Transceiver Characteristics

• Service to upper layer: packet, byte, bit

• Power consumption

• Supported frequency, multiple channels

• Data rate

• Modulation

• Power control

• Communication range

• etc. Unit III 7 Prof. Prashant Lahane

Transceiver States

• Transceivers can be put into different operational states, typically:

– Transmit

– Receive

– Idle – ready to receive, but not doing so

– Sleep – significant parts of the transceiver are switched off

Rx Tx Idle

Sleep


Wakeup Receivers • When to switch on a receiver is not clear

– Contention-based MAC protocols: Receiver is always on

– TDMA-based MAC protocols: Synchronization overhead, inflexible

• Desirable: Receiver that can (only) check for incoming messages

– When signal detected, wake up main receiver for actual reception

– Ideally: Wakeup receiver can already process simple addresses

– Not clear whether they can be actually built, however



Sensors

• The power efficiency of the sensors is also crucial, as well as their duty cycle.

• MEMS(micro electro-mechanical system) techniques allow miniaturization(manufacture ever smaller mechanical, optical and electronic products and devices).


Sensors

• Main categories

– Passive, omnidirectional

• Examples: light, thermometer, microphones, hygrometer, …

– Passive, narrow-beam

• Example: Camera

– Active sensors

• Example: Radar

• Important parameter: Area of coverage

– Which region is adequately covered by a given sensor?


IWING-MRF Motes

Radio transceiver

8-bit AVR Microcontroller

USB Connector (for reprogramming

and power)

Analog/Digital sensor connectors

External battery connector

Digital sensor connectors

Morakot Saravanee, Chaiporn Jaikaeo, 2010. Intelligent Wireless Network Group (IWING), KU Unit III 12 Prof. Prashant Lahane

Characteristics of WSN

• Requirements: small size, large number, and low cost.

• Constrained by – Energy, computation, and communication

• Small size implies small battery

• Low cost & energy implies low power CPU, radio with minimum bandwidth and range

• Ad-hoc deployment implies no maintenance or battery replacement

• To increase network lifetime, no raw data is transmitted


WSN Overview (Cont.) Distinguishing Features

WSNs are ad hoc networks (wireless nodes that self-organize into an infrastructure less network).

• Sensing and data processing are essential

• WSNs have many more nodes and are more thickly deployed

• Hardware must be cheap; nodes are more prone to failures

• WSNs operate under very strict energy constraints

• WSN nodes are typically static.

• The communication scheme is many-to-one (data collected at a base station) rather than peer-to-peer



Lifetime

• Nodes are battery-powered.

• Nobody is going to change the batteries. So, each operation brings the node closer to death.

"Lifetime is crucial!”

To save energy:

• Sleep as much as possible.

• Acquire data only if crucial.

• Use data synthesis and compression.

• Transmit and receive only if necessary. Receiving is just as costly as sending.



Scalability and Reliability

WSNs should

• self-configure and be robust to topology changes (e.g., death of a node)

• maintain connectivity: can the Base Station reach all nodes?

• ensure coverage: are we able to observe all phenomena of interest?

Maintenance

• Reprogramming is the only practical kind of maintenance.

• It is highly desirable to reprogram wirelessly.


WSN Overview (Cont.) Data Collection

• Centralized data collection puts extra burden on nodes close to the base station. Clever routing can ease that problem

• Clustering: data from groups of nodes are compound before being transmitted, so that fewer transmissions are needed.

• Often getting measurements from a particular area is more important than getting data from each node.

• Security and authenticity should be guaranteed. However, the CPUs on the sensing nodes cannot handle fancy encryption schemes.



Power Supply • AA batteries power the vast majority of existing platforms.

They dominate the node size. • Alkaline batteries offer a high energy density at a cheap price.

The discharge curve is far from flat, although. • Lithium coin cells are more compact and boast a flat discharge

curve. • Rechargeable batteries: Who does the recharging? • Solar cells are an option for some applications. • Fuel cells may be an alternative in the future. • Energy scavenging techniques are a hot research topic

(mechanical, thermodynamical, electromagnetic).



Radio

• Commercially-available chips

• Available bands: 433 and 916MHz, 2.4GHz ISM bands

• Typical transmit power: 1 milliwatt =0 decibal milliwatt(dBm).

Power control

• Sensitivity: as low as -110dBm

• Narrowband (FSK) or Spread Spectrum communication. DS-SS (e.g., ZigBee) or FH-SS (e.g., Bluetooth)

• Relatively low rates (<100 kbps) save power.


Ad Hoc Wireless Networks • It is decentralized type of wireless network.

• Each node participates in routing by forwarding data for other nodes, so the determination of which nodes forward data is made dynamically on the basis of network connectivity.

• Large number of self-organizing static or mobile nodes that are possibly randomly deployed.

• Near(est)-neighbor communication.

• Sensor Networks and Sensor-Actuator Networks are a prominent example.


https://en.wikipedia.org/wiki/Wireless_network

https://en.wikipedia.org/wiki/Node_%28computer_science%29

Wireless Sensor Networks

• Formed by hundreds or thousands of motes that communicate with each other and pass data along from one to another

• Research done in this area focus mostly on energy aware computing and distributed computing


Types of Sensors

1. Acoustic, sound, vibration a. Geophone (converts ground movement (displacement)

into voltage)

b. Hydrophone(listening to underwater sound)

c. Microphone (converts sound in air into an electrical signal)

2. Automotive, transportation a. Radar gun (to detect the speed of other objects)

b. Parking sensors (to alert the driver of unseen obstacles during parking military exercises)

c. Speedometer


http://en.wikipedia.org/wiki/Geophone

http://en.wikipedia.org/wiki/Hydrophone

http://en.wikipedia.org/wiki/Microphone

http://en.wikipedia.org/wiki/Radar_gun

http://en.wikipedia.org/wiki/Parking_sensors

http://en.wikipedia.org/wiki/Speedometer

Types of Sensors

4. Electric current, electric potential, magnetic, radio

5. Environment, weather, moisture, humidity

6. Flow, fluid velocity

7. Ionizing radiation, subatomic particles

8. Navigation instruments

9. Position, angle, displacement, distance, speed, acceleration

10.Optical, light, imaging, photon

11.Pressure, Force, density, level


Sensor Network Architecture

• The two basic kinds of sensor network architecture

– Layered Architecture

– Clustered Architecture


1 Layered Architecture

• A layered architecture has a single powerful base station, and the layers of sensor nodes around it correspond to the nodes that have the same hop-count to the BS.

• In the in-building scenario, the BS acts an access point to a wired network, and small nodes form a wireless backbone to provide wireless connectivity.

• The advantage of a layered architecture is that each node is involved only in short-distance, low-power transmissions to nodes of the neighboring layers.


Figure 1 Layered architecture


Unified Network Protocol Framework (UNPF)

• UNPF is a set of protocols for complete implementation of a layered architecture for sensor networks

• UNPF integrates three operations in its protocol structure:

– Network initialization and maintenance

– MAC protocol

– Routing protocol


Network initialization and maintenance

• The BS broadcasts its ID using a known CDMA code on the common control channel.

• All node which hear this broadcast then record the BS ID. They send a beacon signal with their own IDs at their low default power levels.

• Those nodes which the BS can hear form layer one

• BS broadcasts a control packet with all layer one node IDs. All nodes send a beacon signal again.

• The layer one nodes record the IDs which they hear (form layer two) and inform the BS of the layer two nodes IDs.

• Periodic beaconing updates neighbor information and change the layer structure if nodes die out or move out of range.


MAC protocol

• During the data transmission phase, the distributed TDMA receiver oriented channel (DTROC) assignment MAC protocol is used.

• Two steps of DTROC : – Channel allocation : Each node is assigned a reception channel by the

BS, and channel reuse is such that collisions are avoided.

– Channel scheduling : The node schedules transmission slots for all its neighbors and broadcasts the schedule. This enables collision-free transmission and saves energy, as nodes can turn off when they are not involved on a send/receive operation.


2 Clustered Architecture • A clustered architecture organizes the sensor nodes into

clusters, each governed by a cluster-head. The nodes in each cluster are involved in message exchanges with their cluster-heads, and these heads send message to a BS.

• Clustered architecture is useful for sensor networks because of its inherent suitability for data fusion. The data gathered by all member of the cluster can be fused at the cluster-head, and only the resulting information needs to be communicated to the BS.

• The cluster formation and election of cluster-heads must be an autonomous, distributed process.


Figure 2 Clustered architecture


WSN Applications

• Building Automation • Sensors and Robots • Healthcare • Military surveillance • Environmental/Habitat monitoring • Inventory tracking

Evolution of Sensor Hardware Platform


Building Automation Application • Measuring temperature and humidity

• Controlling heating, ventilation, air-conditioning unit, shades blinds and lighting

• Controlling access and providing security etc.


Sensors Applications

Low-power microscopic sensors with wireless communication capability

• Miniaturization of computer hardware Intelligence

• Micro Electro-Mechanical Structures (MEMS) Sensing

• Low-cost CMOS-based RF Radios Wireless Communications


Sensors Applications

• Even though wireless sensors has limited resources in memory, computation power, bandwidth, and energy.

• With small physical sizeCan be embedded in the physical environment.

• Support powerful service in aggregated form (interacting/collaborating among nodes)


Robot Application

• A ring of robots to fight fires.

• Robots that are connected to communicate with each other by Wireless Sensor Network to fight the fire by sensing the fire and locate it to make a ring shape around it and each Fire Fighter Robot will fight fire from one direction so that the fire will be easily stopped.


Healthcare Applications

• In Medical health care field, WSN are used with embedded systems to monitor the health of the patients in the hospital

• Or outside the hospital through the internet.

1) Wireless pulse Oximeter sensor 2) Wireless muscle movements monitor


Wireless pulse Oximeter sensor • Devices collect the heart pulse rate and the Oxygen

saturation and send these data over a short range(100m) Wireless Network to any number of receiving devices, including PDAs, laptops, or ambulance-based terminals which in turn can display the receiving data and record them .

• The device can alarms if data fall out of specific parameter.

• Easy to wear like hand watch.


Wireless movements monitor

• This device can monitoring the limb movements and muscle activity when they exercise.

• Sensor nodes in all the muscles of the body to create a network and send all the recorder info to the

master.

• Master sends the info to the device that monitor.


Military Applications • Shooter Localization

• Perimeter Defense (Oil pipeline protection)

• Insurgent Activity Monitoring (MicroRadar)

• Sensors measuring: electromagnetic energy / signals, light, pressure, sound – explosions

• Also: chemical, biological and explosive vapor; presence of people or objects

• Use of WSNs can reduce uncertainty: where enemy forces will be deployed; their role

• OTW (Other than War): Areas at risk of natural disaster; location of population to be protected


Military Applications

• .


Unit III 44

What is RFID?

• RFID = Radio Frequency IDentification.

• An ADC (Automated Data Collection) technology that:

– uses radio-frequency waves to transfer data between a reader and a movable item to identify, categorize, track..

– Is fast and does not require physical sight or contact between reader/scanner and the tagged item.

– Performs the operation using low cost components.

– Attempts to provide unique identification and backend integration that allows for wide range of applications.

• Other ADC technologies: Bar codes, OCR(optical character Reorganization ).

Prof. Prashant Lahane

Unit III 45

RFID system components

Eth

ern

et

RFID

Reader

RFID Tag RF Antenna Network Workstation


Unit III 46

RFID systems: logical view

3 2 4 5 6 7 8

Application

Systems

RF Write data

to RF tags

Trading

Partner

Systems

Read

Manager Transaction

Data Store

Items with

RF Tags Reader

Antenna

Antenna

EDI /

XML

10

1

Tag/Item

Relationship

Database 9

Internet ONS

Server

Product

Information

(PML Format)

11 12

Other Systems RFID Middleware Tag Interfaces


Unit III 47

RFID tags: Smart labels

… and a chip

attached to it

… on a substrate

e.g. a plastic

foil ...

an antenna,

printed, etched

or stamped ...

A paper label

with RFID inside

Source: www.rfidprivacy.org Prof. Prashant Lahane

Unit III 48

Some RFID tags

Source: www.rfidprivacy.org Prof. Prashant Lahane

Unit III 49

•Tags can be attached to almost anything: – Items, cases or pallets of products, high value goods

– vehicles, assets, livestock or personnel

•Passive Tags – Do not require power – Draws from Interrogator Field

– Lower storage capacities (few bits to 1 KB)

– Shorter read ranges (4 inches to 15 feet)

– Usually Write-Once-Read-Many/Read-Only tags

– Cost around 25 cents to few dollars

•Active Tags – Battery powered

– Higher storage capacities (512 KB)

– Longer read range (300 feet)

– Typically can be re-written by RF Interrogators

– Cost around 50 to 250 dollars

RFID tags


Unit III 50

Tag block diagram

Antenna

Power Supply

Tx Modulator

Rx

Demodulator

Control Logic

(Finite State

machine)

Memory

Cells

Tag Integrated Circuit (IC)


Unit III 51

RFID tag memory

• Read-only tags – Tag ID is assigned at the factory during manufacturing

• Can never be changed

• No additional data can be assigned to the tag

• Write once, read many (WORM) tags – Data written once, e.g., during packing or manufacturing

• Tag is locked once data is written

• Similar to a compact disc or DVD

• Read/Write – Tag data can be changed over time

• Part or all of the data section can be locked


Unit III 52

RFID readers • Reader functions:

– Remotely power tags

– Establish a bidirectional data link

– Inventory tags, filter results

– Communicate with networked server(s)

– Can read 100-300 tags per second

• Readers (interrogators) can be at a fixed point such as – Entrance/exit

– Point of sale

• Readers can also be mobile/hand-held


Unit III 53

Some RFID readers

Source: www.buyrfid.org Prof. Prashant Lahane

Unit III 54

Reader anatomy

915MHz

Radio

Network

Processor

Digital Signal

Processor

(DSP)

13.56MHz

Radio

Power

Supply


Unit III 55

RFID application points

• Assembly Line

Shipping Portals

Handheld Applications

Bill of Lading

Material Tracking

Wireless


Unit III 56

RFID applications • Manufacturing and Processing

– Inventory and production process monitoring

– Warehouse order fulfillment

• Supply Chain Management – Inventory tracking systems

– Logistics management

• Retail – Inventory control and customer insight

– Auto checkout with reverse logistics

• Security – Access control

– Counterfeiting and Theft control/prevention

• Location Tracking – Traffic movement control and parking management

– Wildlife/Livestock monitoring and tracking Prof. Prashant Lahane

Unit III 57

Smart groceries

• Add an RFID tag to all items in the grocery.

• As the cart leaves the store, it passes through an RFID transceiver.

• The cart is rung up in seconds.


Unit III 58

1. Tagged item is removed

from or placed in

“Smart Cabinet”

3. Server/Database is

updated to reflect

item’s disposition

4. Designated individuals

are notified regarding

items that need

attention (cabinet and

shelf location, action

required)

2. “Smart Cabinet”

periodically

interrogates to assess

inventory

Passive

read/write tags

affixed to caps

of containers

Reader antennas placed under each shelf

Smart cabinet

Source: How Stuff Works Prof. Prashant Lahane

Unit III 59

Smart fridge

• Recognizes what’s been put in it

• Recognizes when things are removed

• Creates automatic shopping lists

• Notifies you when things are past their expiration

• Shows you the recipes that most closely match what is available


Unit III 60

Smart groceries enhanced

• Track products through their entire lifetime.

Source: How Stuff Works Prof. Prashant Lahane

Unit III 61

Some more smart applications

• “Smart” appliances: – Closets that advice on style depending on clothes available.

– Ovens that know recipes to cook pre-packaged food.

• “Smart” products: – Clothing, appliances, CDs, etc. tagged for store returns.

• “Smart” paper: – Airline tickets that indicate your location in the airport.

• “Smart” currency: – Anti-counterfeiting and tracking.

• “Smart” people ??


Unit III 62

RFID advantages over bar-codes

• No line of sight required for reading

• Multiple items can be read with a single scan

• Each tag can carry a lot of data (read/write)

• Individual items identified and not just the category

• Passive tags have a virtually unlimited lifetime

• Active tags can be read from great distances

• Can be combined with barcode technology


Unit III 63

Outline • Overview of RFID

– Reader-Tag; Potential applications

• RFID Technology Internals

– RF communications; Reader/Tag protocols

– Middleware architecture; EPC standards

• RFID Business Aspects

• Security and Privacy

• Conclusion Prof. Prashant Lahane

Unit III 64

RFID communications

Tags

Reader

Power from RF field

Reader

Antenna

Reader->Tag Commands

Tag->Reader Responses

RFID Communication

Channel


Unit III 65

RFID communication

Host manages Reader(s) and issues Commands

Reader and tag communicate via RF signal

Carrier signal generated by the reader

Carrier signal sent out through the antennas

Carrier signal hits tag(s)

Tag receives and modifies carrier signal

– “sends back” modulated signal (Passive Backscatter – also referred to

as “field disturbance device”)

Antennas receive the modulated signal and send them to the

Reader

Reader decodes the data

Results returned to the host application


Unit III 66

Antenna fields: Inductive coupling

Transceiver

Tag Reader

antenna

RFID

Tag

IC or microprocessor

antenna


Unit III 67

Antenna fields: Propagation coupling

Transceiver

Tag Reader

antenna

RFID

Tag

IC or microprocessor

antenna


Unit III 68

Operational frequencies Frequency

Ranges LF

125 KHz HF

13.56 MHz

UHF 868 - 915

MHz

Microwave 2.45 GHz &

5.8 GHz

Typical Max Read Range

(Passive Tags)

Shortest 1”-12”

Short 2”-24”

Medium 1’-10’

Longest 1’-15’

Tag Power Source

Generally passive tags only, using

inductive coupling

Generally passive tags only, using

inductive or capacitive coupling

Active tags with integral battery or passive tags

using capacitive storage,

E-field coupling

Active tags with integral battery or passive tags using capacitive storage, E-field coupling

Data Rate Slower Moderate Fast Faster

Ability to read near

metal or wet surfaces

Better Moderate Poor Worse

Applications

Access Control & Security

Identifying widgets through

manufacturing processes or in

harsh environments Ranch animal identification Employee IDs

Library books Laundry

identification Access Control Employee IDs

supply chain tracking

Highway toll Tags

Highway toll Tags Identification of private vehicle

fleets in/out of a yard or facility Asset tracking


Unit III 69

Reader->Tag power transfer

Reader

Reader

Antenna Tag

Q: If a reader transmits Pr watts, how much power Pt does the

tag receive at a separation distance d?

A: It depends-

UHF (915MHz) : Far field propagation : Pt 1/d2

HF (13.56MHz) : Inductive coupling : Pt 1/d6

Separation

distance d


Unit III 70

Limiting factors for passive RFID

1. Reader transmitter power Pr (Gov’t. limited)

2. Reader receiver sensitivity Sr

3. Reader antenna gain Gr (Gov’t. limited)

4. Tag antenna gain Gt (Size limited)

5. Power required at tag Pt (Silicon process limited)

6. Tag modulator efficiency Et


Unit III 71

RFID Summary

Strengths

Advanced technology

Easy to use

High memory capacity

Small size

Weaknesses

Lack of industry and application

standards

High cost per unit and high RFID

system integration costs

Weak market understanding of

the benefits of RFID technology

Opportunities

Could replace the bar code

End-user demand for RFID

systems is increasing

Huge market potential in many

businesses

Threats

Ethical threats concerning

privacy life

Highly fragmented competitive

environment


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