Rong Wang CGS3285 January 2004

1. Wireless Transmission Rong Wang CGS3285 January 2004

2. Recommended Reading • From textbooks: • Chapter 7 of Data Communications and Networking, 3rd Edition, by Behrouz A. Forouzan (ISBN: 0-07-251584-8) • Page 78~81 of Data Communications: From Basics to Broadband, 3rd Edition, by William J. Beyda (ISBN: 0-13-096139-6) • From references: • Chapter 4 of Data and Computer Communications, 7th Edition, by William Stallings (ISBN:0-13-100681-9) Unguided Transmission Media

3. Unguided Media: Wireless Antennas Satellite Terrestrial Broadcast Radio Infrared Unguided Transmission Media

4. Wireless Transmission Frequencies Unguided Transmission Media

5. Antenna • Electrical conductor (or system of..) used to radiate electromagnetic energy or collect electromagnetic energy • Transmission • Electrical energy is converted into electromagnetic energy by antenna • Radiated into surrounding environment • Reception • Electromagnetic energy impinging on antenna • Converted to electrical energy • Fed to receiver • Same antenna often used for both Unguided Transmission Media

6. Radiation Pattern • Power radiated in all directions • Not same performance in all directions • Isotropic antenna is (theoretical) point in space • Radiates in all directions equally • Gives spherical radiation pattern Unguided Transmission Media

7. Omnidirectional antennas Unguided Transmission Media

8. Figure 7.21Unidirectional antennas Unguided Transmission Media

9. Wireless Propagation Methods • Signal travels along three routes • Ground wave • Sky wave • Line of sight Unguided Transmission Media

10. Ground Wave Propagation • Follows contour of earth • Up to 2MHz • AM radio Unguided Transmission Media

11. Sky Wave Propagation • Signal reflected from ionosphere layer of upper atmosphere • Amateur radio, BBC world service, Voice of America • (Actually refracted) Unguided Transmission Media

12. Line-of-Sight • Above 30Mhz • May be further than optical line of sight due to refraction Unguided Transmission Media

13. Satellite • Satellite is a relay station • Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency • GEO (geosynchronous-earth orbit) satellites • Height of 22,230 miles • Requires 3 GEO satellites • LEO (low – earth orbit) satellites • A few hundred miles above the earth • Require more 66 LEO satellites • MEO (medium-earth orbit) satellites • 6434 miles above the earth • Require 12 MEO satellites • Advantage: cheaper over long distances than fiber optics or twisted pair • Problem: • susceptible to noise and interference caused by a variety of sources • Security risk Unguided Transmission Media

14. Satellite Communication Configurations • Point-to-Point • Multipoint Unguided Transmission Media

15. Point-to-Point Transmission Unguided Transmission Media

16. Satellite Broadcast Link Unguided Transmission Media

17. Satellite – Transmission Characteristics • Optimum frequency range • 1~10 GHz • Point-to-point service 4/6-GHz band • 5.925 ~ 6.425GHz (uplink) • 3.7 ~ 4.2GHz (downlink) • Point-to-point service 12/14-GHz band • 14 ~ 14.5GHz (uplink) • 11.7~12.2GHz(downlink) • Point-to-point service 23/30-GHz band • 27.5 ~ 30GHz (uplink) • 17.7 ~ 20.2GHz(downlink) • Subject to noise and delays Unguided Transmission Media

18. Satellite Applications • Television • Satellites are well suited to television distribution because its broadcast nature • TV programs are transmitted to the satellite and then broadcast down to a number of stations • Stations then distribute the programs to individual viewers • PBS (Public Broadcasting Service) • Commercial networks • Cable television • DBS (direct broadcast satellite) • Long distance telephone: point-to-point trunks Unguided Transmission Media

19. Terrestrial Microwave • Parabolic dish • Fixed rigidly • Focused beam • Line of sight • Antennas are located above ground level to • Extend the range between antennas • Be able to transmit over intervening obstacles • Microwave relay towers are used Unguided Transmission Media

20. Terrestrial Microwave Unguided Transmission Media

21. Terrestrial Microwave - Applications • Long haul telecommunications • Less amplifiers or repeaters than coaxial cable • Short point-to-point links between buildings • Closed-circuit TV • LAN data link • Bypass application • Cellular systems • Higher frequencies give higher data rates Unguided Transmission Media

22. Terrestrial Microwave – Transmission Characteristics • Long-haul telecommunication • 4 ~ 6 GHz bands • Cable TV system • 12-GHz band • Short point-to-point buildings • 22-GHz band Unguided Transmission Media

23. Broadcast Radio • Physical description • Omnidirectional • Does not require dish-shaped antennas and antennas need not to be rigidly mounted to a precise alignment • Transmission characteristics • 3kHz ~ 1GHz • Line of sight • Less sensitive to attenuation from rainfall • Suffers from multipath interference • Reflections • Applications • FM radio • UHF and VHF television Unguided Transmission Media

24. Infrared • Frequencies from 300Ghz to 400ThZ • Used only for short ranged communications • Can not penetrate walls and require line of sight (or reflection • Can not used outside a building • e.g. TV remote control, wireless keyboard Unguided Transmission Media

25. Note: Radio waves are used for multicast communications, such as radio and television, and paging systems.

26. Note: Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

27. Note: Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.