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A Survey of Wireless Communications

A Survey of Wireless Communications. Professor S. Olariu Department of Computer Science Old Dominion University Norfolk, VA 23529 U.S.A. olariu@cs.odu.edu http://www.cs.odu.edu/~olariu. In case you haven’t noticed…. Tethered communication does not scale

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A Survey of Wireless Communications

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  1. A Survey of Wireless Communications Professor S. Olariu Department of Computer Science Old Dominion University Norfolk, VA 23529 U.S.A. olariu@cs.odu.edu http://www.cs.odu.edu/~olariu NATO-ARW, Suceava, Romania, September 4-8, 2006 1

  2. In case you haven’t noticed… • Tethered communication does not scale • End-user mobility is becoming the norm rather than the exception • Anytime/anywhere communication is here to stay • Paradigm shift – the way we view communication and computation must change if we want to remain competitive • Are we ready for it?? NATO-ARW, Suceava, Romania, September 4-8, 2006 2

  3. Recent trends • One billion wireless communication devices in use worldwide (2005) • 400 million wireless telephone handsets (purchased annually) • Users want (need?) anytime/anywhere communications • Emerging PCS services, multimedia, mobile commerce, etc. NATO-ARW, Suceava, Romania, September 4-8, 2006 3

  4. Networks 101 • Wired networks • static: no mobility • e.g. LAN, MAN, WAN, and Internet • Wireless networks • mobility is becoming the norm • name of the game: Hide mobility from the application! NATO-ARW, Suceava, Romania, September 4-8, 2006 4

  5. Wireless networks 101 • Infrastructure-based networks • cellular networks • satellite networks • HALO-type networks • Infrastructure-free networks • Mobile Ad hoc Networks (MANET) • wireless sensor networks • other rapidly-deployable networks • Hybrid networks • Wireless Internet NATO-ARW, Suceava, Romania, September 4-8, 2006 5

  6. The vision: an integrated global communication system NATO-ARW, Suceava, Romania, September 4-8, 2006 6

  7. Hybrid wireless networks NATO-ARW, Suceava, Romania, September 4-8, 2006 7

  8. Major issues (1) • Mobility management • addressing and routing • location tracking: GPS, E-911 • Network management • virtual infrastructure • Resource management • network resource allocation • energy management • QoS management • dynamic resource reservation and adaptive error control techniques NATO-ARW, Suceava, Romania, September 4-8, 2006 8

  9. Major issues (2) • MAC protocols • contention control and resolution • Middleware • measurement and experimentation • Security • authentication, encryption, anonymity, and intrusion detection • Error control and fault tolerance • error correction and retransmission management • deployment of back-up systems NATO-ARW, Suceava, Romania, September 4-8, 2006 9

  10. Cellular networks • A Mobile Host (MH) communicates with • A Base Station (BS) that controls • A Cell - the BS’s area of coverage NATO-ARW, Suceava, Romania, September 4-8, 2006 10

  11. Channel assignment • Co-channel interference between frequencies used in neighboring cells • Fixed assignment • poor for hotspots • good in uniformly high loads • Dynamic assignment • complex • Hybrid assignment • fixed assignment plus dynamic pool NATO-ARW, Suceava, Romania, September 4-8, 2006 11

  12. A1 B A2 B A3 B Increasing system capacity A: Channels used at full power B: Channels used at reduced power NATO-ARW, Suceava, Romania, September 4-8, 2006 12

  13. A B Handoff NATO-ARW, Suceava, Romania, September 4-8, 2006 13

  14. Wireless QoS • QoS in wireless networks difficult due to user mobility, limited bandwidth, various impairments, etc. • Demand for new services yields multi-class traffic with different resource and QoS requirements: • telephony • web • e-mail • video NATO-ARW, Suceava, Romania, September 4-8, 2006 14

  15. Classification of QoS parameters • Packet level: • packet delay • jitter • packet dropping probability • Call level: • call dropping probability (CDP) • call blocking probability (CBP) • supplied bandwidth • Session level NATO-ARW, Suceava, Romania, September 4-8, 2006 15

  16. LEO satellites • Description: • Low Earth Orbit: 500km-2000km • high, constant, velocity • deployed in constellations of multiple satellites • Benefits • low power requirements at the end-user level • low signal propagation delay • global coverage NATO-ARW, Suceava, Romania, September 4-8, 2006 16

  17. LEO satellites • Satellite footprint • coverage area on the surface of the surface of the Earth • Footprint • divided into spotbeams, forming a pattern of overlapping circles, similar to a cellular network NATO-ARW, Suceava, Romania, September 4-8, 2006 17

  18. The HALO network NATO-ARW, Suceava, Romania, September 4-8, 2006 18

  19. Multi-hop self-organized networks Peer to peer networks Ad hoc networks Sensor networks Rapidly deployable networks (1) NATO-ARW, Suceava, Romania, September 4-8, 2006 19

  20. Wireless mesh NATO-ARW, Suceava, Romania, September 4-8, 2006 20

  21. Brief history of rapid deployment • The concept of rapidly-deployable networks dated back to 1970s • DARPA packet radio networks • Development languished in 1980s • due to the lack of low cost CPU and memory for ad hoc routing • Rekindled about 1995 • DARPA vision – late 1990s –Smart Dust consisting of mm3 devices NATO-ARW, Suceava, Romania, September 4-8, 2006 21

  22. MANET: an intro • MANET consist of mobile nodes that form a network in an ad hoc manner • The nodes intercommunicate using single or multi-hop wireless links • Each node in MANET can operate as a host as well as a router • The topology, locations, connectivity, transmission quality are variable NATO-ARW, Suceava, Romania, September 4-8, 2006 22

  23. Characteristics of MANET • Self-organizing: no central control • Scarce resources: bandwidth and batteries • Dynamic network topology NATO-ARW, Suceava, Romania, September 4-8, 2006 23

  24. MANET applications • Civilian • Wireless LANs/WANs – mobile and stationary • Remote data collection and analysis • Taxi cabs • Disaster recovery • Vehicular ad hoc network (VANET) • Defense • Battlefield communications and data transfer • Surveillance • Early warning systems NATO-ARW, Suceava, Romania, September 4-8, 2006 24

  25. MANET ­ issues and challenges • Operating in presence of unpredictable mobility • Operating in an error-prone media • Low bandwidth channels • Low power devices with limited resources • Maintaining and retaining connectivity and state info • Security: infrastructure and communication NATO-ARW, Suceava, Romania, September 4-8, 2006 25

  26. MAC for MANET • Special requirements • Avoid interferences among simultaneous transmissions • Yet, enable as many non-interfering transmissions as possible • Fairness among transmissions • No centralized coordinators, should function in full distributed manner • No clock synchronization, asynchronous operations NATO-ARW, Suceava, Romania, September 4-8, 2006 26

  27. Carrier-sensing in MANET • Problems • Hidden terminal problem • Exposed terminal problem • Possible solution: Busy tone NATO-ARW, Suceava, Romania, September 4-8, 2006 27

  28. B A X Hidden terminal problem A is transmitting a packet to B Node X finds that the medium is free, and transmits a packet No carrier does not imply OK to transmit! NATO-ARW, Suceava, Romania, September 4-8, 2006 28

  29. B A Y X Exposed terminal problem A is transmitting a packet to B X will not transmit to Y, even though it will not interfere at B Presence of carrier does not imply to hold off transmission! NATO-ARW, Suceava, Romania, September 4-8, 2006 29

  30. B B A X A Y X Busy tone B is receiving a packet from A X OK to transmit X not OK to transmit • Receiver transmits busy tone when receiving data • All nodes hearing busy tone keep silent • Requires a separate channel for busy tone NATO-ARW, Suceava, Romania, September 4-8, 2006 30

  31. Topology control • Neighbor discovery • Network organization • choosing transmission radii • choosing neighbors • Scheduling node activity • Clustering • Select cluster-heads • assign nodes to clusters • Dominating sets: each node in set or neighbor of some node in the set • Bluetooth scatternet formation NATO-ARW, Suceava, Romania, September 4-8, 2006 31

  32. Data communication • Routing: find a path from source to destination • Location update: maintain destination information • Broadcasting: send from source to all nodes • Multicasting: send from source to some nodes • Geocasting: send from source to all nodes inside a region • Network partitioning: data/service replication • IP-based addressing and routing NATO-ARW, Suceava, Romania, September 4-8, 2006 32

  33. X D Z S MANET – Effect of dynamic topology D Y X S NATO-ARW, Suceava, Romania, September 4-8, 2006 33

  34. Dominating sets NATO-ARW, Suceava, Romania, September 4-8, 2006 34

  35. Wireless Sensor Networks NATO-ARW, Suceava, Romania, September 4-8, 2006 35

  36. How it all started … • SmartDust program sponsored by DARPA defined sensor networks as: A sensor network is a deployment of massive numbers of small, inexpensive, self-powered devices that can sense, compute, and communicate with other devices for the purpose of gathering local information to make global decisions about a physical environment NATO-ARW, Suceava, Romania, September 4-8, 2006 36

  37. SmartDust – the vision • An airplane traverses a battlefield and deploys massive numbers of tiny sensors • The sensors randomly scatter spatially as they land • They self-organize into an ad hoc network such that information can be transmitted multi-hop to a collection point • The sensors monitor and report on troop movements, armaments, mine fields, etc NATO-ARW, Suceava, Romania, September 4-8, 2006 37

  38. What are sensors? • Miniature devices with modest capabilities linked by some wireless medium (e.g. radio, ultrasound, laser) • Non-renewable energy budget • Disposable: tiny, mass-produced, dust cheap! • Mass production implies: • testing is not an option • anonymity: no fabrication-time IDs NATO-ARW, Suceava, Romania, September 4-8, 2006 38

  39. Typical sensor diagram - 1Kbps-10Kbs transmission range 3-10m Transceiver Transceiver - Limited storage 4-8Kb Memory Memory Embedded Slow processor Embedded 4bit, 5-10 MHz Processor Processor Sensor Sensor Low-power special-purpose Non-renewable Battery Battery NATO-ARW, Suceava, Romania, September 4-8, 2006 39

  40. Types of sensors • Pressure • Temperature • Light • Biological • Chemical • Strain, fatigue • Tilt • Acceleration • Seismic • Metal detectors Sensors you can buy off-the-shelf NATO-ARW, Suceava, Romania, September 4-8, 2006 40

  41. Thus, sensors can measure… • Distance to an object • Direction of object • Ambient temperature • Presence of chemicals • Light intensity • Vibrations • Motion • Seismic tremors • Noise (acoustic data) NATO-ARW, Suceava, Romania, September 4-8, 2006 41

  42. Sensors – modus operandi • Must work unattended • Modest non-renewable energy budget • Name of the game – prolong longevity of network • sleep a lot, wake up periodically • work locally, communicate sparingly • optimize transmission radius when communicating! • Supplement modest energy budget by scavenging • Hopefully, energy will not be a major problem NATO-ARW, Suceava, Romania, September 4-8, 2006 42

  43. Sensor networks • Distributed systems with no central control • Massive number of tiny sensors densely deployed in the area of interest • Random deployment: individual sensor positions cannot be engineered • Main goal: produce globally-meaningful information from locally-collected data • Only as good as the information produced • information quality • information security NATO-ARW, Suceava, Romania, September 4-8, 2006 43

  44. Homeland security applications • Battlefield surveillance - monitoring critical terrain, routes, bridges and straits for enemy activity • Battle damage assessment - field reports from attached sensors afford real-time assessment • Early detection of biological, chemical, or nuclear attack • Early warning systems • Containment of terrorist attacks - in metropolitan areas guide public and first aid providers NATO-ARW, Suceava, Romania, September 4-8, 2006 44

  45. Early warning systems Networked sensors make monitoring and early warning systems more accurate and affordable NATO-ARW, Suceava, Romania, September 4-8, 2006 45

  46. Traffic control Can networked sensors control traffic flow better than a loose network of people? NATO-ARW, Suceava, Romania, September 4-8, 2006 46

  47. Securing US ports Only 2% of the containers entering our ports are checked! NATO-ARW, Suceava, Romania, September 4-8, 2006 47

  48. Securing container transit NATO-ARW, Suceava, Romania, September 4-8, 2006 48

  49. … and handling NATO-ARW, Suceava, Romania, September 4-8, 2006 49

  50. Two views of sensor networks • Centrally controlled • the user pushes queries/interests • sensor network provides answers • does not scale well • prone to creation of energy holes • Autonomous • assumes a pervasive instrumentation • organized ad hoc in service-centric fashion • scales well • less prone to the creation of energy holes NATO-ARW, Suceava, Romania, September 4-8, 2006 50

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