Wireless Sensor Network Prabhakar Dhekne Bhabha Atomic Research Centre

August 24, 2006 Talk at SASTRA 1

Wireless Sensor Network

Prabhakar Dhekne

Bhabha Atomic Research Centre


Why Talk About Wireless?

Wireless communication is not a new technology but cell phones have brought revolution in wireless communication

Wireless Technology has changed the way Organizations & individuals work & live today

In less than 10 years World has moved from fixed to wireless networks Allowing people, mobile devices & computers talk to each other,

connect without a cable Only available option for field data acquisition

Interconnectivity with multiple devices Using radio-waves, sometimes light Frees user from many constrains of traditional computer &

phone system


Ubiquitous Computing

Future State of Computing Technology? Mobile, many computers Small Processors Low Power Consumption Relatively Low Cost


Ubiquitous Computing

Small, mobile, inexpensive computers…..everywhere!

Fade into the background of everyday life Computers everywhere provides potential for data

collection….sensors! Temperature Light Sound Motion Pressure Many others!!!


Growth in Wireless Systems

Rapid growth in cellular voice services Cell phones everywhere!

Several wireless technology options have been available for the last ~10-20 yrs mini cell stations using existing standards like CDMA or

GSM wireless PABX using PCS standards such as DECT or

PHS/PACS satellite and microwave backhaul

Above solutions OK for voice & low-speed data, but do not meet emerging needs for broadband access and mobile data


Mobile Healthcare Technologies

Mobile Healthcare can be regarded as the integration of technologies of medical sensors, mobile computing, and wireless communications into a system of medical assistance.


Application Examples

Monitoring of patient’s vital signs Diabetes Asthma Hypertension ECG

Predictive usage in order to minimize the needs for medication

Improving the quality of life


Potential Benefits Increasing the physician productivity and

efficiency. Wireless sensors enable the patients’

freedom of movements and therefore promote new ways of monitoring the patient.

Providing clinicians remote access to patient’s information eliminates the need to manually locate and search through patient’s data.

Enabling telemonitoring in emergency scenarios and making remote diagnosis possible.


The provision of Real Time patient care. No matter where the clinician is No matter where the patient is To apply physiological and medical knowledge,

advanced diagnostics, simulations, and effector systems integrated with information and telecommunications for the purposes of enhancing operational and medical decision-making, improving medical training, and delivering medical treatment across all barriers

Mobile Healthcare


Typical Demo System

The patient is provided with a wearable wireless sensor. The signal from the sensor is captured in a Node situated in a mobile phone.

The system allows ubiquitous access to patient’s data and medical information in real-time via the mobile phone.

The medical data is stored & processed in a server, and can be used for establishing diagnostics and treatments.


Application server Application server centralises the

received data and presents it to the user as: Raw data Formatted as graphs

DB

App Server


Wireless Technology

Emerging mainstream wireless technologies provide powerful building blocks for next-generation applications

WLAN (IEEE 802.11 “WiFi”) hot-spots for broadband access, Bluetooth PDAs and laptops with integrated WLANs

Broadband Wireless access technology- MAN (Alternative to DSL) IEEE 802.16 10-30 Km 40 Mbps WiMax

Wide area wireless data also growing SMS, GPRS, Edge, CDMA2000 1xEV-DO (2.4 Mbps data optimized) Variety of interesting devices (e.g. Treo, Sidekick)

Networking of embedded devices Smart spaces, sensor networks (IEEE 802.15.4a- ZigBee) Context-aware mobile data services and web caching for information

services Wireless sensor nets for monitoring and control VOIP for integrated voice services over wireless data networks


IrDA: P2P wirelessIrDA: P2P wireless Infra-red Data Association

Based on Half Duplex Point-to-Point concept Frequency below the red end of spectrum

making it invisible Eliminate the need for cables Clear line-of-sight Short-range (few meters)

Simplest, most prevailing wireless standard

No fixed speed 9.6 Kbps, 4Mbps Discovery Mode to find out data rate, size Token based transmission IrDA ports on PDA, Laptops USB sticks Remote Control in TV, VCR, Air-conditioner

Port costs less than Rs. 1000


Bluetooth: Wireless PAN Bluetooth: Wireless PAN

M1

Bluetooth (Named after Danish King Harold Bluetooth)

Based on Master-Slave concept Short-range (10 meters) Eliminate the need for cables Operates in 2.4 GHz ISM band 720 Kbps Three modes of operation park/hold/sniff

Piconet & Scatternet (master+7 slaves) Interference due to multiple piconets

and IEEE 802.15.1 home/person LAN To eliminate interference frequency

hoping technique used Ominidirectional with both voice &

data Port costs about Rs. 2000

Piconet 1 Piconet 2

S1

M 1/S1

S2

S2

S1


Wi-Fi: Wireless LAN (Hot Wi-Fi: Wireless LAN (Hot Spot)Spot)

Wireless Fidelity based LAN Most popular on Laptops Replacement to wired LAN Connectivity on the move Short-range (100 meters) Ad Hoc and Base station mode Security provided at physical layer Operates in 2.4 GHz and 5 GHz

Collection of IEEE standards 802.11a/b/g 11 Mpbs & 54 Mbps

Low range, requires more power hence not suitable for PDA’s

Difficult to control access & security

Set up is expensive

Ad Hoc Net

Access Point Net


Wi-Max: Wireless MAN Wi-Max: Wireless MAN

Wireless Max High Speed 40-70 Mbps Mid-range (30 Kmeters) Eliminate the need for cables Saving of wired cost Operates in 2.4 GHz ISM band

IEEE standard 802.16


Issues in Wireless Networking

Infrastructured networks Handoff location management (mobile IP) channel assignment


Issues in Wireless Networking

Infrastructureless networksWireless MAC Security (integrity, authentication, confidentiality)

Ad Hoc Routing Protocols Multicasting and Broadcasting


Indoor Environments

Three popular technologies

- High Speed Wireless LANs (802.11b (2.4GHz,

11 Mbps), 802.11a (5GHz, 54 Mbps & higher)

- Wireless Personal area Networks PANs (IEEE 804.14)

HomeRF Bluetooth, 802.15

- Wireless device networks Sensor networks, wirelessly networked robots


What is an Ad hoc Network

Collection of mobile wireless nodes forming a network without the aid of any infrastructure or centralized administration

Nodes have limited transmission range Nodes act as a routers


Ad Hoc Networks

Rapidly deployable infrastructure Wireless: cabling impractical Ad-Hoc: no advance planning

Backbone network: wireless IP routers • Network of access devices

• Wireless: untethered

• Ad-hoc: random deployment

• Edge network: Sensor networks, Personal Area Networks (PANs), etc.

• Disaster recovery

• Battlefield

• ‘Smart’ office


Ad Hoc Network Characteristics

Dynamic topologies Limited channel bandwidth Variable capacity links Energy-constrained operation Limited physical security

Applications Military battlefield networks Personal Area Networks (PAN) Disaster and rescue operation Peer to peer networks


Security Challenges in Ad Hoc Networks

Lack of Infrastructure or centralized control Key management becomes difficult

Dynamic topology Challenging to design sophisticated & secure

routing protocols Communication through Radio Waves

Difficult to prevent eavesdropping Vulnerabilities of routing mechanism

Non-cooperation of nodes Vulnerabilities of nodes

Captured or Compromised


Security

Challenges in ad hoc network security The nodes are constantly mobile The protocols implemented are co-operative in nature There is a lack of a fixed infrastructure to collect audit

data No clear distinction between normalcy and anomaly in ad

hoc networks Secure the Routing Mechanism

A mechanism that satisfies security attributes like authentication, confidentiality, non-repudiation and integrity

Secure the Key Management Scheme Robust key certification and key distribution mechanism


Scalable, reliable, consistent, distributed

service

Calendar+ service Integrate dynamic traffic & schedule

Doctor prescription servicetrack health indicatorsDoctor write prescription

Follow me kiosk service receive and transmit messages

Fridge & shopping serviceFridge records stockSuggests shopping based on recipeShopping guide in store

Sensor services exercise monitorbiometrics traffic information

services

Sensors mobile devices

Services while on move


Tourist guide

Stuttgart tourist guide Like MapQuest except on mobile

device Mapping local interests

Museums historical sites Shopping & restaurants Sample Data Small text with description, operating

hours Local map


How it works Info station

Island of wireless station Embedded in area Users have cheap low bandwidth components Integrated to network with high quality connection Requires some overlap to manage transition

between stations for hand off Scaleable by load balancing

Each center contains unique information Overhead of communication

Initialize externally specified; adjusts quickly


Map-on-the-move

Provide appropriate map County resolution driving in car Info stations small area high

bandwidth Remainder lower bandwidth


Problems in a Mobile Environment

Variable Bandwidth Disconnected Operation Limited Power Implications on distributed file

system support?


Constraints in mobile computing

PDA vs. Laptop vs. cell phones Cellular modem connection: Failure

prone Space: office vs. city vs. county Not continuous connectivity required Data such as pictures text files not

streaming audio and video Heterogeneous devices


MANET: Mobile Ad hoc Networks

A collection of wireless mobile nodes dynamically forming a network without any existing infrastructure and the relative position dictate communication links (dynamically changing).

From DARPA Website


Rapidly Deployable Networks

Failure of communication networks is a critical problem faced by first responders at a disaster site

major switches and routers serving the region often damaged cellular cell towers may survive, but suffer from traffic overload

and dependence on (damaged) wired infrastructure for backhaul In addition, existing networks even if they survive may

not be optimized for services needed at site significant increase in mobile phone traffic needs to be served first responders need access to data services (email, www,...) new requirements for peer-to-peer communication, sensor net or

robotic control at the site Motivates need for rapidly deployable networks that

meet both the above needs -> recent advances in wireless technology can be harnessed to provide significant new capabilities


Infostations Prototype: System for Rapid Deployment Applications

Outdoor Infostations with radio backhaul

for first responders to set up wireless communications infrastructure at a disaster site

provides WLAN services and access to cached data

wireless backhaul link includes data cache

Project for development of: high-speed short-range radios 802.11 MAC enhancements content caching algorithm &

software hardware integration including

solar panels, antennas and embedded computing device with WLAN card

WINLAB’s Outdoor Infostations Prototype (2002)


Ad-Hoc Wireless Network

PC-basedLinux routerPC

Router networkwith arbitrary topology

AP

Compute& storageservers

Managementstations

Radio Monitor

Forwarding Node/AP(custom)

Sensor Node(custom)

802.11bPDA

802.11bLinux PC

Commercial 802.11

A flexible, open-architecture ad-hoc WLAN and sensor network testbed ...

open-source Linux routers, AP’s and terminals (commercial hardware)

Linux and embedded OS forwarding and sensor nodes (custom) radio link and global network monitoring/visualization tools prototype ad-hoc discovery and routing protocols


What is a WSN?

A network that is formed when a set of small sensor devices that are deployed in an “ad hoc fashion” no predefined routes, cooperate for sensing a physical phenomenon.

A Wireless Sensor Network (WSN) consists of base stations and a number of wireless sensors.

Is simple, tiny, inexpensive, and battery-powered

Sensor: The device Observer: The end user/computer

Phenomenon: The entity of interest to the observer


Why Wireless Sensors Now?

Moore’s Law is making sufficient CPU performance available with low power requirements in a small size.

Research in Materials Science has resulted in novel sensing materials for many Chemical, Biological, and Physical sensing tasks.

Transceivers for wireless devices are becoming smaller, less expensive, and less power hungry (low power tiny Radio Chips).

Power source improvements in batteries, as well as passive power sources such as solar or vibration energy, are expanding application options.


Typical Sensor Node Features

A sensor node has: Sensing Material

Physical – Magnetic, Light, Sound Chemical – CO, Chemical Weapons Biological – Bacteria, Viruses, Proteins

Integrated Circuitry (VLSI) A-to-D converter from sensor to circuitry

Packaging for environmental safety Power Supply

Passive – Solar, Vibration Active – Battery power, RF Inductance


Portable and self-sustained (power, communication, intelligence). Capable of embedded complex data processing.

Transceiver

Embedded Processor

Sensor

Battery

Memory

Transceiver

Embedded Processor

Sensor

Battery

Memory

1Kbps- 1Mbps3m-300m

Lossy Transmission

8 bit, 10 MHzSlow Computation

Limited Lifetime

Requires Supervision

Multiple sensors

128Kb-1MbLimited Storage

Sensor Node Hardware

Sensor + Actuator + ADC + Microprocessor + Powering Unit + Communication Unit (RF Transceiver) + GPS


Sensors and Wireless Radio Types of sensors:

-Pressure,-Temperature-Light-Biological-Chemical-Strain, fatigue-Tilt

Capable to survive harsh environments (heat, humidity, corrosion, pollution etc).

No source of interference to systems being monitored and/or surrounding systems.

Could be deployed in large numbers.


ZigBee Wireless Communication Protocol

Based on the IEEE 802.15.4 standard

Small form factor Relatively Inexpensive Low Power Consumption Low Data Rate of Communication Self Organising, Self-Healing…

multi-hop nodes Integrated Sensors Ideal for Wireless Sensor Network

Applications

Wireless Sensor Networks


WSN APPLICATIONS

Potential for new intelligent applications: Smart Homes Process monitoring and control Security/Surveillance Environmental Monitoring Construction Medical/Healthcare

Implemented with Wireless Sensor Networks!


Medical and Healthcare Appln

Backbone Network

Backbone Network

Possibility for Remote consulting(including Audio Visual communication)

Net Switch

Wireless Remote consultation

Net Switch

Remote Databases

In HospitalPhysician


Medical and Healthcare Medical and Healthcare ApplicationsApplications

Sensors equipped Sensors equipped

with BlueToothwith BlueTooth

Source: USC Web Site


iBadge - UCLA

Investigate behavior of children/patient

Features: Speech recording / replaying Position detection Direction detection / estimation

(compass) Weather data: Temperature, Humidity,

Pressure, Light


Other Examples

MIT d'Arbeloff Lab – The ring sensor Monitors the physiological status of the

wearer and transmits the information to the medical professional over the Internet

Oak Ridge National Laboratory Nose-on-a-chip is a MEMS-based sensor It can detect 400 species of gases and

transmit a signal indicating the level to a central control station

VERICHIP: Miniaturised, Implanted, Identification Technology


Structural Health Monitoring

Semi-active Hydraulic Damper(SHD), Kajima Corporation, JapanModel bridge with attached wireless sensors,

B.F. Spencer’s Lab, Civil E., U. Illinois U-C

Accelerometer board prototype,Ruiz-Sandoval, Nagayama & Spencer,Civil E., U. Illinois Urbana-Champaign


Application in Environment Monitoring

Measuring pollutant concentration

Pass on information to monitoring station

Predict current location of pollutant volume based on various parameters

Take corrective action

Pollutants monitored by sensors in the river

Sensors report to the base monitoring station

ST



Vehicular Traffic Control


VMesh: Distributed Data Sensing, Relaying, & Computing via Vehicular Wireless Mesh Networks

US FCC allocated 5.850 to 5.925 GHz dedicated short range communication (DSRC)

Road side to Vehicle

Vehicle to vehicle communication

Project at The University of California, Davis


Network characteristics of WSN

Generally, the network: Consists of a large number of sensors (103 to

106) Spread over large geographical region

(radius = 1 to 103 km) Spaced out in 1, 2, or 3 dimensions Is self-organizing Uses wireless media May use intermediate “collators”


Sensor Network Topology Hundreds of nodes require careful handling of

topology maintenance. Predeployment and deployment phase

Numerous ways to deploy the sensors (mass, individual placement, dropping from plane..)

Postdeployment phase Factors are sensor nodes position change,

reachability due to jamming, noise, obstacles etc, available energy, malfunctioning, theft, sabotage

Redeployment of additional nodes phase Redeployment because of malfunctioning of units


Organization into Ad Hoc Net

Individual sensors are quite limited.

Full potential is realized only by using a

large number of sensors.

Sensors are then organized into an ad

hoc network.

Need efficient protocols to route and

manage data in this network.


Network Topologies

Star Single Hop Network All nodes communicate

directly with Gateway No router nodes Cannot self-heal Range 30-100m Consumes lowest power


Network Topologies

Mesh Multi-hopping network All nodes are routers Self-configuring network Node fails, network self-

heals Re-routes data through

shortest path Highly fault tolerant

network Multi-hopping provides

much longer range Higher power

consumption…nodes must always listen!


Network Topologies

Star-Mesh Hybrid Combines of star’s low

power and… …mesh’s self-healing

and longer range All endpoint sensor

nodes can communicate with multiple routers

Improves fault tolerance Increases network

communication range High degree of flexibility

and mobility


Self-Organizing WLAN Opportunistic ad-hoc wireless networking concepts starting to mature…

Initial use to extend WLAN range in user-deployed networks Based on novel auto-discovery and multi-hop routing protocols extends the utility and reach of low-cost/high speed WiFi equipment

Wired Network InfrastructureWired Network InfrastructureAP1 AP2

802.11 Access to AP

Ad-hoc radio link(w/multi-hop routing

Mobile Node (MN)(end-user)

Ad-hoc accessTo FN

Self-organizingAd-hoc WLAN

Forwarding Node (FN)

Forwarding Node (FN)

Ad-hocInfrastructure

links


How to get information from Data-centric Sensor Networks?

Types of Queries: Historical Queries: Analysis of data collected over time One Time Queries: Snapshot view of the network Persistent Queries: Periodic monitoring at long and regular

intervals Routing required to respond to a Query:

Application specific Data centric Data aggregation capability desirable Need to minimize energy consumption


Software Framework

MAC layer (Tiny OS, routing)

Configuration Table

Power consumption status & replacement strategy

Sensor Data Management

Middleware

Application (passing parameters via API)


Technical challenges

Sensor design Self-organizing network, that requires

0-configuration of sensors Random or planned deployment of

sensors, and collators Auto-addressing Auto-service discovery Sensor localization


Power Consumption

Limited Power Source

Battery Lifetime is limited

Each sensor node plays a dual role of data

originator and data router (data processor)

The malfunctioning of a few nodes consumes

lot of energy (rerouting of packets and

significant topological changes)


Environmental Factors

Wireless sensors need to operate in conditions that are not encountered by typical computing devices: Rain, sleet, snow, hail, etc. Wide temperature variations

May require separating sensor from electronics High humidity Saline or other corrosive substances High wind speeds


Historical ComparisonConsider a 40 Year Old Computer

Model Honeywell H-300 Mica 2

Date 6/1964 7/2003

CPU 2 MHz 4 MHz

Memory

32 KB 128 KB

SRAM ??? 512 KB


Advances in Wireless Sensor Nodes

Consider Multiple Generations of Berkeley Motes

Model Rene 2 Rene 2 Mica Mica 2

Date10/200

06/2001 2/2002 7/2003

CPU 4 MHz 8 MHz 4 MHz 4 MHz

Flash Memor

y8 KB 16 KB 128 KB 128 KB

SRAM 32 KB 32 KB 512 KB 512 KB

Radio10

Kbps10

Kbps40

Kbps40 Kbps


Summary Sensor networks will facilitate one to address

several societal issues: Early-warning systems Disaster mitigation

Applications in other sectors Security, transportation, irrigation

Technology is available today Research into new sensors Needs experimentation, pilot deployment Lots needs to be done in Software (OS, MAC, Application) While cost is an issue today, it will not be so tomorrow


References

Wireless & Mobile Systems Prof Dharma Prakash Agrawal and H. Deng

Integrating Wireless Technology in the Enterprise by Williams Wheeler, Elsevier Digital Press

Circuits & Systems for Wireless Communications Edited by Markus Helfenstein and George S. Moschytz, Kluwer Academic Publishers


Any Questions?

Documents

Wireless Sensor Network Prabhakar Dhekne Bhabha Atomic Research Centre