Unit III - Mr.Rajiv Bhandari · Unit III Basic concepts of Wireless Sensor Networks (WSN) Unit III Prof. Prashant Lahane 1
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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
Unit III 2 Prof. Prashant Lahane
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
Unit III 3 Prof. Prashant Lahane
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
Unit III 4 Prof. Prashant Lahane
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
•
Unit III 5 Prof. Prashant Lahane
Communication Device
• Medium options
– Electromagnetic, RF
– Electromagnetic, optical
– Ultrasound
Radio
Transceiver
radio wave
bit stream
Unit III 6 Prof. Prashant Lahane
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
Unit III 8 Prof. Prashant Lahane
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
Unit III 9 Prof. Prashant Lahane
WSN Overview (Cont.)
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).
Unit III 10 Prof. Prashant Lahane
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?
Unit III 11 Prof. Prashant Lahane
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
Unit III 13 Prof. Prashant Lahane
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
Unit III 14 Prof. Prashant Lahane
WSN Overview (Cont.)
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.
Unit III 15 Prof. Prashant Lahane
WSN Overview (Cont.)
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.
Unit III 16 Prof. Prashant Lahane
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.
Unit III 17 Prof. Prashant Lahane
WSN Overview (Cont.)
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).
Unit III 18 Prof. Prashant Lahane
WSN Overview (Cont.)
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.
Unit III 19 Prof. Prashant Lahane
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.
Unit III 20 Prof. Prashant Lahane
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
Unit III 21 Prof. Prashant Lahane
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
Unit III 22 Prof. Prashant Lahane
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
Unit III 23 Prof. Prashant Lahane
Sensor Network Architecture
• The two basic kinds of sensor network architecture
– Layered Architecture
– Clustered Architecture
Unit III 24 Prof. Prashant Lahane
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.
Unit III 25 Prof. Prashant Lahane
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
Unit III 27 Prof. Prashant Lahane
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.
Unit III 28 Prof. Prashant Lahane
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.
Unit III 29 Prof. Prashant Lahane
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.
Unit III 30 Prof. Prashant Lahane
WSN Applications
• Building Automation • Sensors and Robots • Healthcare • Military surveillance • Environmental/Habitat monitoring • Inventory tracking
Evolution of Sensor Hardware Platform
Unit III 32 Prof. Prashant Lahane
Building Automation Application • Measuring temperature and humidity
• Controlling heating, ventilation, air-conditioning unit, shades blinds and lighting
• Controlling access and providing security etc.
Unit III 33 Prof. Prashant Lahane
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
Unit III 34 Prof. Prashant Lahane
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)
Unit III 35 Prof. Prashant Lahane
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.
Unit III 36 Prof. Prashant Lahane
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
Unit III 38 Prof. Prashant Lahane
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.
Unit III 39 Prof. Prashant Lahane
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.
Unit III 40 Prof. Prashant Lahane
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
Unit III 42 Prof. Prashant Lahane
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
Prof. Prashant Lahane
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
Prof. Prashant Lahane
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 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
Prof. Prashant Lahane
Unit III 50
Tag block diagram
Antenna
Power Supply
Tx Modulator
Rx
Demodulator
Control Logic
(Finite State
machine)
Memory
Cells
Tag Integrated Circuit (IC)
Prof. Prashant Lahane
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
Prof. Prashant Lahane
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
Prof. Prashant Lahane
Unit III 54
Reader anatomy
915MHz
Radio
Network
Processor
Digital Signal
Processor
(DSP)
13.56MHz
Radio
Power
Supply
Prof. Prashant Lahane
Unit III 55
RFID application points
• Assembly Line
Shipping Portals
Handheld Applications
Bill of Lading
Material Tracking
Wireless
Prof. Prashant Lahane
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.
Prof. Prashant Lahane
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
Prof. Prashant Lahane
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 ??
Prof. Prashant Lahane
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
Prof. Prashant Lahane
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
Prof. Prashant Lahane
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
Prof. Prashant Lahane
Unit III 66
Antenna fields: Inductive coupling
Transceiver
Tag Reader
antenna
RFID
Tag
IC or microprocessor
antenna
Prof. Prashant Lahane
Unit III 67
Antenna fields: Propagation coupling
Transceiver
Tag Reader
antenna
RFID
Tag
IC or microprocessor
antenna
Prof. Prashant Lahane
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
Prof. Prashant Lahane
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
Prof. Prashant Lahane
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
Prof. Prashant Lahane
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
Prof. Prashant Lahane
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