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Wireless Networks

Wireless Networks. Asstt. Professor Adeel Akram. Introduction to Wireless Communication. Course Outline: Basic topics. Transmission Fundamentals Analog and digital transmission Channel capacity Antennas, propagation modes, and fading Signal encoding techniques Spread spectrum technology

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Wireless Networks

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  1. Wireless Networks Asstt. Professor Adeel Akram

  2. Introduction to Wireless Communication

  3. Course Outline: Basic topics • Transmission Fundamentals • Analog and digital transmission • Channel capacity • Antennas, propagation modes, and fading • Signal encoding techniques • Spread spectrum technology • Coding and error control • Cellular networks • Wireless LANs • IEEE 802.11 • Bluetooth

  4. Course Outline: Advanced topics • Mobile IP • Multihop ad hoc networks • MAC and routing protocols • Power control and topology control • Capacity of ad hoc networks • Sensor networks • Infrastructure, MAC, and routing protocols • Synchronization Protocols • Algorithms for query processing

  5. Tentative Course Schedule

  6. Text Books • Wireless Communications and Networks, by William Stallings,Prentice Hall, 2nd Edition, 2005 • This textbook will be followed for most of the course.  • The material on multihop and sensor networks will be taken from research papers, and other collections. 

  7. Wireless Comes of Age • Guglielmo Marconi invented the wireless telegraph in 1896 • Communication by encoding alphanumeric characters in analog signal • Sent telegraphic signals across the Atlantic Ocean • Communications satellites launched in 1960s • Advances in wireless technology • Radio, television, mobile telephone, communication satellites • More recently • Satellite communications, wireless networking, cellular technology, adhoc networks, sensor networks

  8. Network Network Layered Architecture Application Application Transport Transport Network Network Data Link Data Link Data Link Data Link Physical Physical Physical Physical Medium Radio Scope of this course: Anything above and related protocols

  9. Wireless communication systems • Target information systems: “Anytime, Anywhere, Anyform” • Applications: Ubiquitous computing and information access • Market in continuous growth: • 35-60% annual growth of PCS(Personal Communications Services) • Number of subscribers: • by 2001: over 700M mobile phones • by 2003: 1 billion wireless subscribers (source Ericsson) • 300% growth in wireless data from 1995-1997 • Large diversity of standards and products • Confusing terminology

  10. Number of Subscribers in Hong Kong Fixed Telephone Mobile Phone Broadband Internet Will wireless Internet take off?

  11. Mobile Subscribers in Pakistan More than15,511,045 subscribers of Cellular Networks *From Telecom Indicators section of PTA Website

  12. Limitations and difficulties • Wireless is convenient and less expensive • Limitations and political and technical difficulties inhibit wireless technologies • Lack of an industry-wide standard • Device limitations • E.g., small LCD on a mobile telephone can only displaying a few lines of text • E.g., browsers of most mobile wireless devices use wireless markup language (WML) instead of HTML

  13. Wireless around us… WLAN, DAB, GSM, etc… Personal Travel Assistant, PDA, Laptop, GSM, cdmaOne, WLAN, Bluetooth, ...

  14. PDA • simple graphical displays • character recognition • simplified WWW • Laptop • fully functional • standard applications • Palmtop • tiny keyboard • simple versions of standard applications • Mobile phones • voice, data • simple text displays Portable Devices performance

  15. Radio frequency spectrum • Wireless technologies have gradually migrated to higher frequencies

  16. Wireless & Mobility • Wireless: • Limited bandwidth • Broadcast medium: requires multiple access schemes • Variable link quality (noise, interference) • High latency, higher jitter • Heterogeneous air interfaces • Security: easier snooping • Mobility: • User location may change with time • Speed of mobile impacts wireless bandwidth • Need mechanism for handoff • Security: easier spoofing • Portability • Limited battery, storage, computing, and UI

  17. Challenges in Mobile Computing • Three major challenges: • Wireless Channel • Mobility • Device Limitation

  18. Wireless Channel The 1st challenge

  19. Communication Channel Transmitter Receiver Channel The medium used to transmit the signal from the transmitter to the receiver Wireline / Wireless channel

  20. Wireline Channel Transmitter Wireline Channel, e.g. copper wire Receiver Shielded against electromagnetic noise Too many noises? Large signal attenuation? Use repeaters Upgrade to coaxial cable Data speed too low? Data speed still too low? Upgrade to optical fiber

  21. Fading Effect • Typical Indoor Wireless Environment • Signal strength fluctuates significantly • Wireless channel cannot be engineered. • You can only improve your transmission and reception techniques.

  22. Bit Error Rate • Optical fiber: 10-11 or 10-12 • Mobile channel: • Good quality: 10-6 • Actual condition: 10-2 or worse

  23. Implication • For wireline systems, it is assumed that the channel is error free • Many protocols are designed with this assumption • These protocols do not work well in a wireless environment • e.g. TCP (why?)

  24. What if more than 1 transmitter? Every user accesses the network by means of a dedicated channel Switching Center or Network Access Point Dedicated Channel New user is served by a new wire-line circuit Access capacity is “unlimited”.

  25. How about wireless networks? Wireless users access the network by means of a shared channel Shared Channel Access capacity is inherently limited. Base Station

  26. Implication • For wire-line systems, we can simply install new cables to increase capacity. • For wireless systems, the channel can only be shared by the users. • Capacity does not increase.

  27. Interference • Multiuser Interference • Radio signals of different users interfere with each other • Self-Interference • Multipath effect • Phase-shifted images of the signal at the receiver interact and may cancel the entire signal, (i.e. destructive interference).

  28. Interference Management • How to manage multiuser interference? • i.e. how to share the channel? • Multiple Access Problem • FDMA, TDMA, CDMA, etc. • Media Access Control • Aloha, CSMA, etc. • How to manage self-interference? • Physical layer issue • Equalization, coding, diversity, etc. • These issues will NOT be considered in this course

  29. Mobility The 2nd challenge

  30. User Mobility • Location Management Problem • How does the network know where the intended recipient of a message is currently located?

  31. Cellular Scenario Where is 5008011? Send broadcast messages from every base station?

  32. Dest. Net router Nhops interface B E A 223.1.1 - 1 223.1.1.4 223.1.2 - 1 223.1.2.9 223.1.3 - 1 223.1.3.27 223.1.1.1 223.1.2.1 223.1.1.2 223.1.2.9 223.1.1.4 223.1.2.2 223.1.1.3 223.1.3.27 223.1.3.2 223.1.3.1 Internet Scenario Forwarding table in router Suppose A sends a datagram to E misc fields data 223.1.1.1 223.1.2.2 The router sends the datagram to 223.1.2.2 via interface 223.1.2.9 What happens if E moves to elsewhere?

  33. Ad hoc Network Scenario S E F B C M L J A G H D K I N How to find a suitable path from source S to destination D?

  34. Device Limitation The 3rd challenge

  35. Device Limitation • Resource Limitation • Limited memory • Limited computational power • Small display • Limited battery life • This issue will NOT be considered at the moment but may be extended later

  36. Classification of Wireless Systems • Personal communication systems • Focus on voice communication • Limited bit-rate data transmission • Large-scale mobility and coverage • Operate over licensed frequency bands • Wireless LANs • Designed for high bit-rate transmission • IP oriented • Low-scale coverage • Use unlicensed ISM frequency bands • Multihop ad hoc networks • Have little or no infrastructure • Low-scale coverage • Need new routing protocols • Emerging applications

  37. Transmission fundamentals • Electromagnetic signals • Time domain • Frequency domain • Data rate and bandwidth • Analog and digital data transmission • Channel capacity • Nyquist theorem [Sampling Rate >2fmax ] • Shannon capacity theorem [C≤Wlog2(1+S/N)] • Transmission media

  38. Analog signaling

  39. Digital signaling

  40. Classification of transmission media • Transmission medium • Physical path between transmitter and receiver • Guided media • Waves are guided along a solid medium • E.g., copper twisted pair, copper coaxial cable, optical fiber • Unguided media • Provides means of transmission but does not guide electromagnetic signals • Usually referred to as wireless transmission • E.g., atmosphere, outer space

  41. Unguided media • Transmission and reception are achieved by means of an antenna • Configurations for wireless transmission • Directional • Omnidirectional

  42. General frequency ranges • Microwave frequency range • 1 GHz to 40 GHz • Directional beams possible • Suitable for point-to-point transmission • Used for satellite communications • Radio frequency range • 30 MHz to 1 GHz • Suitable for omnidirectional applications • Infrared frequency range • Roughly, 3x1011 to 2x1014 Hz • Useful in local point-to-point multipoint applications within confined areas

  43. Terrestrial microwave • Description of common microwave antenna • Parabolic "dish", 3 m in diameter • Fixed rigidly and focuses a narrow beam • Achieves line-of-sight transmission to receiving antenna • Located at substantial heights above ground level • Applications • Long haul telecommunications service • Short point-to-point links between buildings

  44. Microwave antenna Parabolic “Dish”

  45. Satellite microwave • Description of communication satellite • Microwave relay station • Used to link two or more ground-based microwave transmitter/receivers • Receives transmissions on one frequency band (uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink) • Applications • Television distribution • Long-distance telephone transmission • Private business networks

  46. Broadcast radio • Description of broadcast radio antennas • Omni directional • Antennas not required to be dish-shaped • Antennas need not be rigidly mounted to a precise alignment • Applications • Broadcast radio • VHF and part of the UHF band; 30 MHZ to 1GHz • Covers FM radio and UHF and VHF television

  47. Infrared • Beyond the EHF spectrum • 1012 to 1014 Hz • Transceivers must be within line of sight or reachable via reflection • Does not penetrate walls

  48. Next Lecture • Antennas & PropagationSignal Encoding

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