Rong Wang

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 7881 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 (ISBN0-13-100681-9)

3
Unguided Media Wireless
Antennas Satellite Terrestrial Broadcast
Radio Infrared
4
Wireless Transmission Frequencies
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

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

7
Omnidirectional antennas
8
Figure 7.21 Unidirectional antennas
9
Wireless Propagation Methods

• Signal travels along three routes
• Ground wave
• Sky wave
• Line of sight

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Ground Wave Propagation

• Follows contour of earth
• Up to 2MHz
• AM radio

11
Sky Wave Propagation

• Signal reflected from ionosphere layer of upper
  atmosphere
• Amateur radio, BBC world service, Voice of
  America
• (Actually refracted)

12
Line-of-Sight

• Above 30Mhz
• May be further than optical line of sight due to
  refraction

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

14
Satellite Communication Configurations

• Point-to-Point
• Multipoint

15
Point-to-Point Transmission
16
Satellite Broadcast Link
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Satellite Transmission Characteristics

• Optimum frequency range
• 110 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)
• 11.712.2GHz(downlink)
• Point-to-point service 23/30-GHz band
• 27.5 30GHz (uplink)
• 17.7 20.2GHz(downlink)
• Subject to noise and delays

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

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

20
Terrestrial Microwave
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

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

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

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

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.