1. Transmission Media Unguided Media

2. Unguided Media wireless communication No physical conductor
Signals are broadcast through air
Available to anyone who has a device capable of receiving them
Radio Frequency Allocation
Eight ranges
VLF (very low frequency) to Extremely high frequency (EHF)

3. Propagation of Radio Waves
Radio wave transmission utilizes 5 types of propagation
Surface
Tropospheric
aprox. 30 miles from the earth’s surface
Ionospheric
above Tropospheric, below the space
Line-of-sight
Space

4. Radio Frequency Allocation

5. Types of Propagation Ionosphere Propagation Surface Propagation
Troposphere Propagation
Line-of-sight Propagation
Space Propagation

6. Surface Propagation
Radio waves travel through the lowest portion of the atmosphere
Signals emanate in all directions
From transmitting antenna
Follow the curvature of the planet
Distance depends on the amount of power in signal

7. Troposhperic Propagation
Works in two ways
A signal is sent from antenna to antenna (line-of-sight)
A signal is broadcast at an angle into the upper layers of the troposphere, then it is reflected back down to the earth’s surface
Longer distance to cover

8. Ionosphere Propagation
Signals radiate upward into the ionosphere
Reflected back to earth
The density difference between the troposphere and the ionosphere cause each radio wave to speed up and change direction, bending back to earth

9. Line-of-Sight Propagation
Very high frequency signals are transmitted in straight lines directly from antenna to antenna
Antennas facing each other, tall enough

10. Space Propagation Use satellite relays instead of antenna
Signals are received by satellite
Satellite rebroadcasts the signal back to earth

11. Radio Frequency Ranges
Very Low Frequency (VLF) waves
Propagated as surface wave, through air
Do not suffer much attenuation in transmission
Susceptible to the high levels of atmosphere noise (heat and electricity)
Used mostly for long-range radio navigation
Frequency range : 3-30 KHz

12. Radio Frequency Ranges
Low Frequency (LF) waves
Propagated as surface waves
Used for long-range radio navigation
Attenuation is greater during the daytime
(absorption of waves by natural obstacles increases)
Frequency range : KHz

13. Radio Frequency Ranges
Middle Frequency (MF) waves
Propagated in the troposphere
These frequencies are absorbed by the ionosphere
Absorption increases during the daytime
Most of MF transmission rely on line-of-sight antennas to increase control and avoid absorption problem
Used in AM radio, maritime radio
Frequency range : 300 KHz – 3 MHz
(AM Radio : 535 KHz – 1605 MHz)

14. Radio Frequency Ranges
High Frequency (HF) waves
Use ionosphere propagation
Reflected back to earth
Used in
amateur radio (ham radio),
international broadcasting,
military communication,
Long-distance aircraft
Ship communication
Telephone, telegraph

15. Radio Frequency Ranges
Others
VHF (Very High Frequency)
UHF (Ultra High Frequency)
SHF (Super High Frequency)
EHF (Extremely High Frequency)

16. Terrestrial Microwave
Do not follow the curvature of the earth
Require line-of-sight signal transmission and reception equipment
Distance depends of the height of the antennas
The taller antenna, the longer distance
Microwave signals propagate in one direction at a time
Two frequencies are required for two-way communication

17. Repeaters
Repeaters are used to increase the distance by terrestrial microwave
Signal received by one antenna is relayed to the next antenna
Used in telephone system worldwide

18. Antennas Two types Parabolic dish antenna Horn antenna Parabolic dish

19. Satellite Communication
Similar to line-of-sight microwave transmission
Satellites acting as super tall antennas and repeaters

20. Cellular Telephony
Designed to provide stable communications connections between tow moving devices,
Or between one mobile unit and one stationary (land) unit
A service provider must be able to
track a caller
Assign a channel to the call
Transfer the signal from channel to channel as the caller moves out the range of one channel into the range of another

21. Cellular Telephony To make tracking possible
Cellular service area is divided into small regional called cells

22. Transmission Impairment
attenuation
distortion
noise

23. Transmission Impairment
Attenuation
Loss of energy
Some of the energy is converted to heat
Amplifiers are used to amplify the signal
Distortion
Signal changes its form or shape
Frequencies change
Noise
Thermal noise
Induced noise
Crosstalk, etc.

24. Performance Three concepts to measure performance Throughput
Propagation speed
Propagation time
How fast data can pass through a point
The distance a signal or bit can travel through a medium in one second
Depends on the medium and the frequency of the signal

25. Performance Propagation time
Measure the time required for a signal to travel from one point of the transmission medium to another
Calculated by dividing the distance by the propagation speed
Propagation time = distance/propagation speed