Communicaton system full course Lecture 3.pdf

Communicaton system full course Lecture 3

1. EEE 3105 : Communication Systems
Course Instructor: Dr. Mosabber Uddin Ahmed

2. Purpose and Types of Modulation
▪Modulation is a process that causes a shift in the range of frequencies
in a signal.
▪To modulate means “to change”.
▪Modulation may be done by varying the amplitude, phase or frequency
of a high frequency carrier in accordance with the amplitude of the
message signal.
▪This process involves: Baseband/message signal →Modulating signal
Carrier signal
Modulated signal

3. Baseband and Carrier Communication
The bandwidth B represents a measure of frequency range. It is typically measured in Hz with 1 Hz =1/sec.
❖The bandwidth of a signal indicates the frequency range in which the signal‘s Fourier transform has a power
above a certain threshold (half of the maximum power).
The term baseband designates a frequency range of signal delivered by source/input transducer starting at 0Hz.
Example:
❑In Telephone, the baseband is 0-3.5kHz
❑In Television, the baseband is 0-4.3 MHz

4. Baseband and Carrier Communication
Baseband signals m(t) have sizeable power at low frequencies, they can not be transmitted over a radio link but
are suitable for transmission over a pair of wires, coaxial cables/optical fibers.
Baseband Communication is the communication that does not use modulation i.e. signals are transmitted
without causing shift in the range of its frequencies.
❖For example: In local telephone communication, short and long distance PCM between two exchanges over
optical fibers use baseband communication.
Baseband signals produced by various information sources are not always suitable for direct transmission over a
given channel. These signals are modified for transmission by a process called modulation in which m(t) is used
to modify some parameter of carrier signal.

5. Baseband and Carrier Communication
A carrier is a sinusoid of high frequency, and one of its parameters (amplitude, frequency or phase) is varied in
proportion to the baseband signal m(t).
❖Carrier Signal (or Carrier Wave) is an alternating electromagnetic signal with a steady frequency upon which
information is superimposed by some form of modulation.
❖Communication that uses modulation to shift the frequency spectrum of a signal is known as carrier
communication.
•In carrier communication, one of the basic parameters (amplitude, frequency or phase) of a sinusoidal carrier of
high frequency is varied in proportion to the baseband signal m(t).
•Modulation can be Analog (AM/FM radios) or Digital(2G, 3G cellphones).

6. Purpose of Modulation

7. Purpose of Modulation

8. Purpose of Modulation

9. Purpose of Modulation

10. Purpose of Modulation

11. Purpose of Modulation
Modulation can be helpful in utilizing the vast spectrum
of frequencies. Modulating baseband signal m(t) and
shifting their spectra to non overlapping bands, all the
available bandwidth can be used through frequency
division multiplexing, FDM

12. Typesof Modulation

13. Typesof Modulation

14. Typesof Modulation

15. Typesof Modulation

16. Amplitude modulation and angle modulation

17. Amplitude modulation: Double Sideband (DSB)

18. Amplitude modulation: Double Sideband (DSB)

19. Amplitude modulation: Double Sideband (DSB)

20. Amplitude modulation: Double Sideband (DSB)

21. Modulation/demodulation: Double Sideband (DSB)

22. Demodulation: Double Sideband (DSB)

23. Demodulation: Double Sideband (DSB)

24. Example

25. Example

26. Example

28. expensive