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
Ad hoc Networks : Major Research Areas
Ad hoc Networks : Major Research Areas
ClusteringClustering Reduce Information Update Overhead (Reduce Information Update Overhead (e.g. e.g.
Routing Tables) Routing Tables)
Ad hoc Networks : Major Research Areas
– Time Slot assignment
• Avoiding collision
• Detecting and resolving collision
– Communication Protocols• Broadcasting • Multicasting• Gossiping
Present Scenario
Bandwidth Management
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
Bandwidth Management
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.
Bandwidth Management
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
Bandwidth Management (Contd.)
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].
Bandwidth Management (Contd.)
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
Bandwidth Management (Contd.)
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
Location Management (contd.)
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
Location Management (contd.)
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
Location Management (contd.)
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
Location Identification (contd.)Location Identification (contd.)
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
Location Identification (contd.)Location Identification (contd.)
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
Location Identification (contd.)Location Identification (contd.)
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 Identification (contd.)Location Identification (contd.)
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
Location Identification (contd.)Location Identification (contd.)
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
Location Identification (contd.)Location Identification (contd.)
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
Location Identification (contd.)Location Identification (contd.)
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
Location Identification (contd.)Location Identification (contd.)
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
Location Identification (contd.)Location Identification (contd.)
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
Location Identification (contd.)Location Identification (contd.)
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.)
Sensor Networks (contd.)
Sensor Networks (contd.)
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
Sensor Networks (contd.)
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
Sensor Networks (contd.)
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
Sensor Networks (contd.)
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
Topics for Exploration
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
Topics for Exploration
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 !
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