Bhabani P. Sinha Advanced Computing and Microelectronics Unit Indian Statistical Institute, Calcutta...

Bhabani P. Sinha

Advanced Computing and Microelectronics Unit

Indian Statistical Institute, Calcutta

email : [email protected]

Mobile and Sensor Networks : Prospects, Challenges and Social Implications

Organization

• Introduction

• Present Scenario

• Cellular Mobile Networks

• Ad hoc Mobile Networks

• Sensor Networks

• Future Challenges

• Social Implications

Introduction

• Wireless communication services

– Cordless Telephones

– High-Speed Wireless Local-Area Networks

– Wide-Area Wireless Data Systems

– Cellular Mobile Radio systems

– Satellite-Based Mobile Systems

Introduction (Contd.)

• Characterization of Mobile Networks

– Mobile elements are resource-poor relative to static elements

– Mobility is inherently hazardous

– Mobile connectivity is highly variable in performance and reliability

– Mobile elements rely on a finite energy source

• Sensor Networks

- Both Mobile and Static depending on application

- Energy constraint is more important

Types of Mobile Networks

Two different types of mobile networks

• Cellular

• Ad Hoc

Introduction (Cont.)

Overview of a Cellular System

• Cells : overlapping regions of circular, hexagonal, or any arbitrary shape

• Base stations : transceivers in each cell

for communication among mobiles using wireless links

• Base station controllers (BSC) : concentratingpoints to which base stations are

connected

• Mobile switching centre (MSC) : to switch calls to

mobiles of the networks

MSC

BSC BSC

cell

base station

XY

Introduction (Contd.)

– Ad hoc Network• No existing Robust Communication Infrastructure

• No Wired Communication Links

• Only Wireless Communication between Mobile Terminals

• Distributed System with no Central Arbiter

• Mostly Single Channel Networks

– Communication over Unique Common Radio Frequency

– usually TDMA

• Bandwidth management

• Mobility management

– Location management

– Handoff management

– Exact location identification

– Internetworking

• Security

Cellular Networks : Major Research Areas

Ad hoc Networks : Major Research Areas

• Initialization Assign distinct IDs (1 to n) to Mobile

Terminals

1

2

3

4

5

6 7

– Leader Election• Identify a Mobile Terminal as Leader • Inform all others Nodes in the Network



ClusteringClustering Reduce Information Update Overhead (Reduce Information Update Overhead (e.g. e.g.

Routing Tables) Routing Tables)


– Time Slot assignment

• Avoiding collision

• Detecting and resolving collision

– Communication Protocols• Broadcasting • Multicasting• Gossiping

Present Scenario

Bandwidth Management


Wireless Communication constitutes the fastest growing segment of communication industry

• 200 million subscribers of cellular communication systems listed in 1997 (Akilydiz et al., Proc. IEEE, Aug. 1999)

• 1,50,000 new subscribers joining every day• more than 1000 million subscribers all over the world

Increasing demand for mobile multimedia services - voice- data- image- video conferencing


Fourth Generation Wireless Systems

Characteristics : • Support interactive multimedia services

- teleconferencing, wireless Internet, etc.

• Wider bandwidths, higher bit rates

• Global mobility and service portability

• Scalability of mobile networks.


New Features in 4G

• Entirely packet-switched networks

• All network elements are digital

• Higher bandwidths to provide multimedia services at lower cost (up to 100Mbps)

• Tight network security

Comparisons between 3G and 4G

3G• Back compatible to 2G

• Circuit and packet switched networks

• Combination of existing

& evolved equipment

• Data rate up to 2 Mbps

4G• Extend 3G capacity by

one order of magnitude

• Entirely packet switched networks

• All network elements are digital

• Higher bandwidth (up to 100 Mbps)

Bandwidth Management (Contd.)

Frequency Allocation (1992 World Administrative Radio Conference)

• Total spectrum : 1885 - 2025 MHz , 2110 - 2200 MHzfrequency gaps between 2025-2110 MHz and beyond 2200 MHz used for remote sensing, cable TV, space research

Available bandwidth : 230 MHz

• 170 MHz bandwidth reserved for terrestrial use• 60 MHz for satellite

satellite band : 1980 - 2010 MHz, 2170 - 2200 MHz

Revised Frequency Allocation (1995 ITU World Radio Conference)

• Satellite allocation for America and Carribean : 1990-2025 MHz and 2160-2200 MHz (total 75 MHz)Difficult for US service providers to support Mobile Terminals

Bandwidth management is a crucial issue


The Channel Assignment Problem (CAP) :

Assigning frequency channels to the cells :-

• Satisfying :

– Channel requirement for each cell– Frequency separation constraints

• Avoiding :– Channel interference

• Using :– As small bandwidth as possible.

In its most general form the problem is NP-Complete [Hale, 1980].


Essential to develop :

• Heuristic Algorithms / Approximation Algorithms

• Lower Bounds on Bandwidth

• Simulation of algorithms on benchmark problems

Engineering Approach :Exploit the hexagonal symmetry of cellular networks

Static / Long-term assignments : maximum execution time is of the order of 10 to 20 seconds

Short-term assignments : maximum execution time is ~ 0.5 sec

• Design a hierarchy of algorithms (with low overhead ~ 1%) to be used in a practical situation

• long term assignment (say, every hour)

optimal, execution time ~ 10 seconds

• intermediate term assignment (say, every 10 minutes)

near-optimal, possibly with some blocked calls

execution time ~ 1 second

• short term assignment (say, every minute or on demand for handoff)

execution time ~ few tens of milliseconds


Mobility Management

Location Management

Location Management : a two-stage process

• Location update : time, movement and distance based

MT periodically notifies the network of its new access point

- mobile user is authenticated by the network

- user location profile is revised

• Call delivery

- network is queried for the user location profile

- current position of the mobile host is found

Location Management

Two commonly used standards for location management in PLMN

• IS - 41 (Interim Standard - 41)

(Electronic and Telephone Industry Association EIA/ TIA)

used in North America, Personal Access Communication Services (PACS)

• GSM MAP (Global System for Mobile Telecommunications - Mobile Application Part)

used in Europe, Digital Cellular System - 1800 (DCS - 1800) & pcs - 1900 networks

Both are similar, but GSM MAP facilitates personal mobility and user selection of network providers

Every mobile has an entry in a database in the MSC to keep track of its last known location which is periodically updated:

HLR : Home Location Register - keeps information about each user

VLR : Visitor Location Register- stores information about users visiting its associated area

Location Management

Location Management (contd.)

Two possible situations

• An MT can be far away from its HLR

a large number of message communication may be involved

• An MT can be called from a nearby MT

no need to refer to the HLR of the called MT

Research Objectives

- Minimization of overall signaling traffic (particularly because of the rapid increase in the number of mobile subscribers)

- Minimization of registration and call setup time

Strategy

- design of a suitable database architecture

- design of efficient update algorithms


Design of database architecture

- Centralized Database (extension of IS - 41 strategy)

- Distributed Database

Centralized Database Architectures

Dynamic hierarchical database architecture

Directory register (DR)

each covers a number of MSC’s

DR periodically computes and stores the location pointer configuration for MT

Three types of pointers in a DR

- local pointer (indicating the current serving MSC of MT)

- direct remote pointer to the currently serving DR

- indirect remote pointer pointing to the currently serving DR


Distributed Database Architectures

- Distributed Hierarchical Tree-based Database

- Partitioning

- Database Hierarchy

Location Management for Mobile IP

Mobile IP Architecture

Mobile Node Home Agent Correspondent

(before move) Node

Subnet A

Subnet C

Internet

Subnet B

Mobile Node

(after move) Foreign Agent

Location Management for Mobile IP

Two IP addresses assigned to a mobile node

while it visits a foreign link

• Its own identification

• Care of Address (CoA)

Association between CoA and Mobile Node’s home address

done by a Mobility binding table

with an associated life time

Location Management for LEO Satellite Networks

LEO satellite altitudes : 500 -1500 Km

MEO satellite altitudes : 5,000 - 13,000 Km

Geostationary satellite : 35,823 Km

LEO satellites are used for covering regions where terrestrial wireless systems are economically infeasible (rough terrain or insufficient population)

Iridium provided service for voice and low bit-rate data transfer

Teledesic : proposed for broad-band access

Location Management for LEO Satellites (contd.)

High mobility of LEO Satellites needs ISL (intersatellite links) for routing messages

- Handoff is very frequent

- Coverage area of a single satellite consists of

small-sized cells : Spotbeams

- Different spotbeams use different frequencies

Handoffs in LEO satellites :

• Intersatellite handoff

• Spotbeam (intrasatellite) handoff

• Link handoff


Research Issues on Location Management

• Security (user authentication)

• Dynamic updates (delay constraints)

• Centralized vs. Distributed database architecture

• Paging delay minimization

All these issues are network independent (independent of protocols used in PLMN, PSTN, ISDN, IP, X.25 or ATM networks)

Handoff Management

Handoff Management

Initiation

Handoff Management

Resource Allocation

New Connection Generation

Data Flow Control

User MovementBuffering/ Sequencing

Network Conditions

Connection Routing

Multicast

Handoff Management (contd.)Handoff management may be of two types

• intracell handoff

transfer of the on-going call to a new radio channel at the same BS

• intercell handoff

handoff to a new BS

Two phases of handoff :

• Soft handoff

mobile terminal may be connected to multiple BS’s simultaneously

during handoff

Some form of signaling diversity is used to combine multiple signals

• Hard Handoff

Only one BS is connected at a time

Before handoff - the old BS After handoff - the new BS

Location IdentificationLocation Identification Wide Range of ApplicationsWide Range of Applications

Military ManeuversMilitary Maneuvers

Emergency Search & Rescue OperationsEmergency Search & Rescue Operations

Tracking Targets and UsersTracking Targets and Users

Location Sensitive Commercial & Location Sensitive Commercial &

Residential ServicesResidential Services

Location Identification (contd.)Location Identification (contd.)

Global Positioning System (GPS)Global Positioning System (GPS)

Provide accurate locationProvide accurate location

High infrastructure costHigh infrastructure cost

Constellation of satellites Constellation of satellites

Suitable only for outdoor rural Suitable only for outdoor rural environmentsenvironments

Suffers from NLOS errorsSuffers from NLOS errors

Signal Reflection and Obstruction in Signal Reflection and Obstruction in Indoor Indoor EnvironmentsEnvironments


Modeling of indoor environments difficultModeling of indoor environments difficult Environments vary widelyEnvironments vary widely

NLOS Error time and location dependentNLOS Error time and location dependent Requires Non-parametric ApproachesRequires Non-parametric Approaches

Prohibitive Time and Cost FactorsProhibitive Time and Cost Factors


Existing Approaches attempt Location Existing Approaches attempt Location EstimationEstimation

Least Squares MethodLeast Squares Method Residual Weighing Algorithm (RWGH)Residual Weighing Algorithm (RWGH) Computationally IntensiveComputationally Intensive Probabilistic MeasureProbabilistic Measure No Error Bound GuaranteedNo Error Bound Guaranteed


Computational Geometric Approach Computational Geometric Approach (IWDC 2005, Sinha and (IWDC 2005, Sinha and

DattaChowdhury) DattaChowdhury)

Returns Region, instead of Point Returns Region, instead of Point EstimateEstimate Node Node Guaranteed Guaranteed to be found in to be found in RegionRegion ObjectiveObjective: Minimize Region of : Minimize Region of Residence of All Residence of All Nodes in NetworkNodes in Network


Location Sensing TechniquesLocation Sensing Techniques

TriangulationTriangulation or or TrilaterationTrilateration Multi-lateration Multi-lateration for better Accuracyfor better Accuracy

AngulationAngulation Measure Angle or Bearing Relative to Points Measure Angle or Bearing Relative to Points with known with known SeparationSeparation

ProximityProximity: Measure Nearness to known : Measure Nearness to known Set of PointsSet of Points Scene AnalysisScene Analysis: Examine View from : Examine View from Particular Particular Vantage PointVantage Point


Survey of Location SystemsSurvey of Location Systems

Global Positioning System (GPS)Global Positioning System (GPS) TechniqueTechnique: Radio time-of-flight Lateration: Radio time-of-flight Lateration AccuracyAccuracy: 1-5 meters 95% to 99%: 1-5 meters 95% to 99% ScaleScale: 24 Satellites Worldwide: 24 Satellites Worldwide CostCost: Expensive Infrastructure, $100 per : Expensive Infrastructure, $100 per ReceiverReceiver LimitationsLimitations: Not Suitable for Indoors: Not Suitable for Indoors

Research on Improving Indoor GPS Systems and Research on Improving Indoor GPS Systems and AccuracyAccuracy


VHF Omni-directional Ranging VHF Omni-directional Ranging TechniqueTechnique: Angulation: Angulation AccuracyAccuracy: 1 degree radial (100 %): 1 degree radial (100 %) ScaleScale

Several Transmitters per Metropolitan AreaSeveral Transmitters per Metropolitan Area CostCost

Expensive Infrastructure, Inexpensive Aircraft Expensive Infrastructure, Inexpensive Aircraft ReceiversReceivers

CommentsComments: Range of 30 to 140 Nautical : Range of 30 to 140 Nautical Miles, Line-of-Miles, Line-of- sight Requiredsight Required


Emergency 911 Service (E911)Emergency 911 Service (E911) TechniqueTechnique: Triangulation: Triangulation AccuracyAccuracy: 150 to 300 m : 150 to 300 m ScaleScale: Density of Cellular : Density of Cellular InfrastructureInfrastructure CostCost

Upgrading Phone Hardware, Cell Upgrading Phone Hardware, Cell InfrastructureInfrastructure


Active Badge SystemActive Badge System TechniqueTechnique: Infra-red, Cellular Proximity: Infra-red, Cellular Proximity AccuracyAccuracy: Room Size: Room Size ScaleScale

1 Base per Room1 Base per Room10 sec to Process Badge per Base10 sec to Process Badge per Base

CostCost Administration, Setup CostAdministration, Setup CostCheap Tags and BasesCheap Tags and Bases

LimitationsLimitations: Sunlight and Fluorescent Light: Sunlight and Fluorescent Light


Active Bats SystemActive Bats System TechniqueTechnique: Ultrasound and RF, Time-of-: Ultrasound and RF, Time-of-flight, Lateration, flight, Lateration, Statistical Pruning to Statistical Pruning to Eliminate NLOS ErrorsEliminate NLOS Errors AccuracyAccuracy: 9cm (95%): 9cm (95%) ScaleScale

1 Base per 10 sq. meter1 Base per 10 sq. meter25 Computations per Room per Sec25 Computations per Room per Sec

CostCost Administration, Setup CostAdministration, Setup CostCheap Tags and SensorsCheap Tags and Sensors

LimitationsLimitations: Required Ceiling Sensor Grid, : Required Ceiling Sensor Grid, Sensitive to Sensitive to Precise Placement of SensorsPrecise Placement of Sensors


Microsoft RADARMicrosoft RADAR TechniqueTechnique: 802.11 RF Scene Analysis and : 802.11 RF Scene Analysis and TriangulationTriangulation AccuracyAccuracy: 3m (Scene Analysis) to 4.3m : 3m (Scene Analysis) to 4.3m ScaleScale: 3 Base Stations per Floor : 3 Base Stations per Floor CostCost

802.11 Installation802.11 Installation

Location Identification (contd.)Location Identification (contd.) SummarySummary

Most Existing Commercial Products use Signal Most Existing Commercial Products use Signal Strength Strength Attenuation Based SolutionsAttenuation Based Solutions

Cheaper HardwareCheaper HardwareNot Very Accurate, Especially for IndoorsNot Very Accurate, Especially for Indoors

Signal Strength Database Systems for Office, Signal Strength Database Systems for Office, Hospitals & Hospitals & Warehouse Environments – Warehouse Environments – Relatively Static ParametersRelatively Static Parameters Ongoing Research in TOA, TDOA, AOA Ongoing Research in TOA, TDOA, AOA Techniques – More Techniques – More Promising than Signal Promising than Signal Strength Based SolutionStrength Based Solution

Bottomline Bottomline : : Still No Ubiquitous, Scalable Still No Ubiquitous, Scalable

High Precision High Precision Location SystemLocation System

Sensor NetworksSensor Networks

What are Sensor Networks ?

Sensor Networks (contd.)


Major Applications

• Environmental Monitoring– Monitoring air, soil and water, condition based maintenance

• Habitat Monitoring– Determining the plant and animal species population and behavior

• Seismic detection• Military surveillance• Inventory tracking


Major Issues and Features

Size of Node:Size of Node: Sensor node is small in size. It is difficult to accommodate Sensor node is small in size. It is difficult to accommodate

sophisticate hardware.sophisticate hardware. Limited energy resources :Limited energy resources :

It requires power control in software level e.g., It requires power control in software level e.g., Power aware routing protocol.Power aware routing protocol.

Low Computational Efficiency: Low Computational Efficiency: Requires robustness in calculationsRequires robustness in calculations


Major Issues and Features Low Bandwidth:Low Bandwidth:

Reduction of traffic overhead in the network.Reduction of traffic overhead in the network. Limited Memory:Limited Memory:

An operating system suitable for sensor nodes.An operating system suitable for sensor nodes. Fault tolerance: Fault tolerance:

Due to short lifetime Due to short lifetime limited power supply limited power supply environmental changeenvironmental change

Security:Security: Nodes are very vulnerable in nature. Intruder (possibly nature) can Nodes are very vulnerable in nature. Intruder (possibly nature) can

inject malicious informationinject malicious information


Major Issues and Features

Ad-Hoc Network:Ad-Hoc Network: Probably the sensor nodes dropped from air Probably the sensor nodes dropped from air Sensor network has no pre-defined structure.Sensor network has no pre-defined structure.

Localization of Nodes: Localization of Nodes: No unique ID as Internet. The position with respect to some No unique ID as Internet. The position with respect to some

reference can identify a sensor node. reference can identify a sensor node. To react to the target, it is necessary to know the location of the To react to the target, it is necessary to know the location of the

target.target. Calibration: Calibration:

Needs high accuracy in estimation of location of objects.Needs high accuracy in estimation of location of objects.

Future Challenges

Topics for Exploration

Interoperability of Mobile Devices

• Different technologies : CDMA, GSM

• Different backbone Networks

– PLMN, WATM, MIP, Satellite

• Different Communication Protocols

– Deterministic / Randomized Algorithms


Efficient Global Roaming Capability

• Fast and Low Cost Location Management Technology

• Fast and Low Cost Handoff Technology

• More Accurate Location Identification Methodology

– Outdoor and Indoor locations


Effective Utilization of Sensors

• Fast and Efficient Routing Strategy

• Improvement of Life Time

Social Implications

Social Implications

• Benefits– Connectivity to remote rural areas

• land line telephone links are either infeasible (difficult – to – access terrain) or uneconomical

– Ubiquitous connectivity even when people are on the move

– Business promotion and economic growth

through continuous awareness of the market condition

– Continuous remote medical facilities

through on-line connectivity to the doctors / hospitals

Social Implications

• Benefits– Agricultural promotion through information broadcast

among the farmers

– Disaster relief (Earthquakes, Flood, Cyclones)

– Defense Applications in remote inaccessible places

– Exact location identification - useful for tourists, emergency medical service on highways, request for police protection when attacked by terrorists/ robbers

– Aids in criminal investigation

Social Implications

• Hazards

– Health hazards due to continuous exposure to harmful radio signals ***

– Noise pollution

Roads, public vehicles, meeting rooms, theater halls

– Security threat (if the mobile device is stolen or lost)

Conclusion

• Most popular and widely used technology during the last decade

– Great impact on the society as a whole

– But not without any associated hazards

• Scientists need to work not only for the technological advances for the next generation mobile communication and computing, but also to find ways to eliminate health hazards, in particular

THANK YOU !

Bhabani P. Sinha Advanced Computing and Microelectronics Unit Indian Statistical Institute, Calcutta...

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