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Mobile and Sensor Networks : Prospects, Challenges and Social Implications

Mobile and Sensor Networks : Prospects, Challenges and Social Implications

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Mobile and Sensor Networks : Prospects, Challenges and Social Implications

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  1. Mobile and Sensor Networks : Prospects, Challenges and Social Implications Bhabani P. Sinha Advanced Computing and Microelectronics Unit Indian Statistical Institute, Calcutta email : bhabani@isical.ac.in

  2. Organization • Introduction • Present Scenario • Cellular Mobile Networks • Ad hoc Mobile Networks • Sensor Networks • Future Challenges • Social Implications

  3. 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

  4. 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

  5. Types of Mobile Networks Two different types of mobile networks Cellular • • Ad Hoc

  6. 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) : concentrating • points to which base stations are connected • Mobile switching centre (MSC) : to switch calls to • mobiles of the networks MSC BSC BSC cell X Y base station

  7. 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

  8. • Bandwidth management • • Mobility management • Location management • Handoff management • Exact location identification • Internetworking • • Security Cellular Networks : Major Research Areas

  9. Ad hoc Networks : Major Research Areas • Initialization • Assign distinct IDs (1 to n) to Mobile Terminals 3 5 1 4 7 6 2

  10. Ad hoc Networks : Major Research Areas • Leader Election • Identify a Mobile Terminal as Leader • Inform all others Nodes in the Network

  11. Ad hoc Networks : Major Research Areas • Clustering • Reduce Information Update Overhead (e.g. Routing Tables)

  12. Ad hoc Networks : Major Research Areas • Time Slot assignment • Avoiding collision • Detecting and resolving collision • Communication Protocols • Broadcasting • Multicasting • Gossiping

  13. Present Scenario

  14. Bandwidth Management

  15. 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

  16. 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.

  17. 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

  18. 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) Comparisons between 3G and 4G

  19. 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

  20. 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].

  21. 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

  22. Bandwidth Management (Contd.) • 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

  23. Mobility Management

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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

  29. Location Management (contd.) Distributed Database Architectures - Distributed Hierarchical Tree-based Database - Partitioning - Database Hierarchy

  30. 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

  31. 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

  32. 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

  33. 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

  34. 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)

  35. Handoff Management

  36. Handoff Management Handoff Management Initiation New Connection Generation Data Flow Control Resource Allocation Buffering/ Sequencing User Movement Multicast Network Conditions Connection Routing

  37. 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

  38. Location Identification • Wide Range of Applications • Military Maneuvers • Emergency Search & Rescue Operations • Tracking Targets and Users • Location Sensitive Commercial & Residential Services

  39. 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 Environments

  40. 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

  41. Location Identification (contd.) • Existing Approaches attempt Location Estimation • Least Squares Method • Residual Weighing Algorithm (RWGH) • Computationally Intensive • Probabilistic Measure • No Error Bound Guaranteed

  42. 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

  43. Location Identification (contd.) Location Sensing Techniques • Triangulationor 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

  44. 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

  45. Location Identification (contd.) • VHF Omni-directional Ranging • Technique: Angulation • Accuracy: 1 degree radial (100 %) • Scale • Several Transmitters per Metropolitan Area • Cost • Expensive Infrastructure, Inexpensive Aircraft Receivers • Comments: Range of 30 to 140 Nautical Miles, Line-of- sight Required

  46. 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

  47. 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

  48. 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

  49. 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

  50. 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