Download An Efficient Channel Assignment Technique for Hexagonal Cellular

Mobile and Sensor Networks : Prospects,
Challenges and Social Implications
Bhabani P. Sinha
Advanced Computing and Microelectronics Unit
Indian Statistical Institute, Calcutta
email : [email protected]
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
MSC
BSC
BSC
cell
• Base stations : transceivers in each cell
for communication among mobiles using
wireless links
• Base station controllers (BSC) : concentrating
points to which base stations are connected
• Mobile switching centre (MSC) : to switch calls to
mobiles of the networks
X
Y
base station
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
Cellular Networks : Major Research Areas
• Bandwidth management
• Mobility management
– Location management
– Handoff management
– Exact location identification
– Internetworking
• Security
Ad hoc Networks : Major Research Areas
• Initialization
Assign distinct IDs (1 to n) to Mobile
Terminals
3
5
1
4
6
2
7
Ad hoc Networks : Major Research Areas
– Leader Election
• Identify a Mobile Terminal as Leader
• Inform all others Nodes in the Network
Ad hoc Networks : Major Research Areas

Clustering

Reduce Information Update Overhead (e.g. 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
4G
• Extend 3G capacity by
one order of magnitude
• Entirely packet switched
networks
• Combination of existing
& evolved equipment
• All network elements
are digital
• Data rate up to 2 Mbps
• Higher bandwidth (up to
100 Mbps)
Bandwidth Management (Contd.)
Frequency Allocation (1992 World Administrative Radio Conference)
• Total spectrum : 1885 - 2025 MHz , 2110 - 2200 MHz
frequency 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
Bandwidth Management (Contd.)
• Design a hierarchy of algorithms (with
~ 1%) to be used in a practical situation
low overhead
• 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
Location Management
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 (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
(before move)
Correspondent
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
Handoff
Management
Initiation
User Movement
New Connection
Generation
Resource
Allocation
Network
Conditions
Data Flow
Control
Buffering/
Sequencing
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 Identification

Wide Range of Applications

Military Maneuvers

Emergency Search & Rescue Operations

Tracking Targets and Users

Location Sensitive Commercial & Residential Services
Location Identification (contd.)
Global Positioning System (GPS)

Provide accurate location

High infrastructure cost


Constellation of satellites
Suitable only for outdoor rural environments

Suffers from NLOS errors

Signal Reflection and Obstruction in Indoor
Location Identification (contd.)

Modeling of indoor environments difficult

Environments vary widely

NLOS Error time and location dependent


Requires Non-parametric Approaches
Prohibitive Time and Cost Factors
Location Identification (contd.)

Existing Approaches attempt Location Estimation
Least Squares Method
 Residual Weighing Algorithm (RWGH)
 Computationally Intensive

Probabilistic Measure
 No Error Bound Guaranteed

Location Identification (contd.)

Computational Geometric Approach
(IWDC 2005, Sinha and DattaChowdhury)
Returns Region, instead of Point Estimate
 Node Guaranteed to be found in Region
 Objective: Minimize Region of Residence of All
Nodes in Network

Location Identification (contd.)
Location Sensing Techniques

Triangulation or Trilateration


Multi-lateration for better Accuracy
Angulation

Measure Angle or Bearing Relative to Points with known
Separation
Proximity: Measure Nearness to known Set of
Points
 Scene Analysis: Examine View from Particular
Vantage Point

Location Identification (contd.)

Survey of Location Systems

Global Positioning System (GPS)
Technique: Radio time-of-flight Lateration
 Accuracy: 1-5 meters 95% to 99%
 Scale: 24 Satellites Worldwide
 Cost: Expensive Infrastructure, $100 per Receiver
 Limitations: Not Suitable for Indoors


Research on Improving Indoor GPS Systems and Accuracy
Location Identification (contd.)

VHF Omni-directional Ranging
Technique: Angulation
 Accuracy: 1 degree radial (100 %)
 Scale



Cost


Several Transmitters per Metropolitan Area
Expensive Infrastructure, Inexpensive Aircraft Receivers
Comments: Range of 30 to 140 Nautical Miles, Line-ofsight Required
Location Identification (contd.)

Emergency 911 Service (E911)
 Technique: Triangulation
 Accuracy: 150 to 300 m
 Scale: Density of Cellular Infrastructure
 Cost

Upgrading Phone Hardware, Cell Infrastructure
Location Identification (contd.)

Active Badge System
Technique: Infra-red, Cellular Proximity
 Accuracy: Room Size

Scale

1
Base per Room
10 sec to Process Badge per Base

Cost
Administration,
Setup Cost
Cheap Tags and Bases

Limitations: Sunlight and Fluorescent Light
Location Identification (contd.)

Active Bats System
Technique: Ultrasound and RF, Time-of-flight, Lateration,
Statistical Pruning to Eliminate NLOS Errors
 Accuracy: 9cm (95%)
 Scale

1
Base per 10 sq. meter
25 Computations per Room per Sec

Cost
Administration,
Setup Cost
Cheap Tags and Sensors

Limitations: Required Ceiling Sensor Grid, Sensitive to
Precise Placement of Sensors
Location Identification (contd.)

Microsoft RADAR
Technique: 802.11 RF Scene Analysis and Triangulation
 Accuracy: 3m (Scene Analysis) to 4.3m
 Scale: 3 Base Stations per Floor
 Cost


802.11 Installation
Location Identification (contd.)

Summary
 Most Existing Commercial Products use Signal Strength
Attenuation Based Solutions
Cheaper
Hardware
Not Very Accurate, Especially for Indoors
Signal Strength Database Systems for Office, Hospitals &
Warehouse Environments – Relatively Static Parameters
 Ongoing Research in TOA, TDOA, AOA Techniques – More
Promising than Signal Strength Based Solution


Bottomline : Still No Ubiquitous, Scalable High Precision
Location System
Sensor 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:
 Sensor node is small in size. It is difficult to accommodate
sophisticate hardware.
Limited energy resources :
 It requires power control in software level e.g.,
Power aware routing protocol.
Low Computational Efficiency:
 Requires robustness in calculations
Sensor Networks
(contd.)
Major Issues and Features




Low Bandwidth:
 Reduction of traffic overhead in the network.
Limited Memory:
 An operating system suitable for sensor nodes.
Fault tolerance:
 Due to short lifetime
 limited power supply
 environmental change
Security:
 Nodes are very vulnerable in nature. Intruder (possibly nature) can
inject malicious information
Sensor Networks
(contd.)
Major Issues and Features



Ad-Hoc Network:
 Probably the sensor nodes dropped from air
 Sensor network has no pre-defined structure.
Localization of Nodes:
 No unique ID as Internet. The position with respect to some
reference can identify a sensor node.
 To react to the target, it is necessary to know the location of the
target.
Calibration:
 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 !