1. DATA COMMUNICATION
Lecture-27

2. Recap of Lecture 26 Guided Media Optical Fiber Cable Unguided Media
Radio Frequency Allocation
Propagation of Radio Waves

3. Overview of Lecture 27 Frequency Ranges Microwave Communication
Satellite Communication
Cellular Telephony

4. Frequency Ranges
The type of propagation used in radio transmission depends upon the frequency of the signal

5. Very Low Frequency (VLF)

6. Low Frequency (LF)

7. Middle Frequency (MF)

8. High Frequency (HF)

9. Very High Frequency (VHF)

10. Ultra High Frequency (UHF)

11. Ultra High Frequency (UHF)

12. Super High Frequency (SHF)

13. Extremely High Frequency (EHF)

14. Terrestrial Microwave
Microwaves do not follow the curvature of earth
Line-of-sight transmission
Height allows the signal to travel farther

15. Terrestrial Microwave

16. Terrestrial Microwave Antennas

17. Satellite Communication
Line-of-sight microwave communication using satellite
Satellite acts as a very tall antenna and a repeater

18. Satellite Communication

19. Geosynchronous Satellites

20. Satellite Frequency Bands
Each satellite sends and receives over two bands
Uplink: From the earth to the satellite
Downlink: From the satellite to the earth

21. Satellite Frequency Bands
Band Downlink Uplink
C GHz GHz
Ku GH GHz
Ka GHz GHz

22. Cellular Telephony
Each service area is divided into small ranges called cells
Each cell office is controlled by a switching office called MTSO

23. Cellular Telephony

24. Operations of Cellular Telephony
Transmitting
Mobile phone sends the number to the closest cell office
Cell office  MTSO  Telephone office
MTSO assigns an unused voice channel

25. Operations of Cellular Telephony
Receiving
Telephone office sends the signal to MTSO
MTSO sends queries to each cell (paging)
If mobile phone is found and available, assigns a channel

26. Operations of Cellular Telephony
Handoff
MTSO monitors the signal level every few seconds
If the strength diminishes, MTSO seeks a new cell and changes the channel carrying the call

27. Transmission Impairments
Transmission media are not perfect
What is sent is not what is received

28. Transmission Impairments

29. Attenuation Attenuation means loss of energy
Some of electrical energy is converted to heat

30. Attenuation

31. Decibel (dB)
Relative strengths of two signals or a signal at two points
dB = 10 log10 (P2/P1)
P2 and P1 are signal powers
Negative dB means attenuation
Positive dB means amplification

32. Example 7.1
Imagine a signal travels through a transmission medium and its power is reduced to half. This means P2=(1/2)P1. Calculate Attenuation?
Solution:
10log10(P2/ P1)= 10log10(0.5 P1/ P1)
=10(-0.3)= -3 dB

33. Distortion Distortion means that the signal changes its form or shape
Distortion occurs in a composite signal

34. Summary Frequency Ranges Microwave Communication
Satellite Communication
Cellular Telephony
Transmission Impairments

35. Suggested Reading
Section 7.2, 7.3 “Data Communications and Networking” 2nd Edition by Behrouz A. Forouzan