UNIVERSITY OF MANITOBA
FINAL EXAMINATION (FALL 2019)
COURSE CODE: ECE4260 DATE: December 19, 2019
TITLE: Communication Systems TIME: 1.30 PM
INSTRUCTOR: Pradeepa Yahampath DURATION: 3 hours
Academic Integrity Contra
...
UNIVERSITY OF MANITOBA
FINAL EXAMINATION (FALL 2019)
COURSE CODE: ECE4260 DATE: December 19, 2019
TITLE: Communication Systems TIME: 1.30 PM
INSTRUCTOR: Pradeepa Yahampath DURATION: 3 hours
Academic Integrity Contract
I understand that cheating is a serious offense. As members of the University Community,
Students have an obligation to act with academic integrity. Any Student who engages in Academic Misconduct in relation to a University Matter will be subject to discipline. (2.4 - Student
Academic Misconduct Procedure).
Student name:
Signature:
Instructions
• This is a closed-book exam.
– No printed or hand written material of any form allowed.
– No Internet access or the use of any other form of electronic media permitted.
– A non-programmable calculator may be used.
• Answer all 6 questions. All questions carry equal marks.
– Write ONLY on right hand pages.
– Use left hand pages ONLY for scratch work.
– For full credit, you must clearly show all relevant calculations. Answers without
intermediate steps receive zero marks.
– In problems involving the Q-function (given on page 5), you may express the final
solution in terms of Q(x) (it is not required to evaluate the numerical value).
• Return this exam paper with your answer booklet.
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UNIVERSITY OF MANITOBA
FINAL EXAMINATION (FALL 2019)
COURSE CODE: ECE4260 DATE: December 19, 2019
TITLE: Communication Systems TIME: 1.30 PM
INSTRUCTOR: Pradeepa Yahampath DURATION: 3 hours
5 Marks 1. (a) Name two key advantages of digital communication over analog communication.
(b) Draw a labeled block diagram of a synchronous demodulator that can be used to demodulate an SSB-AM signal.
(c) Phase-shift keying (PSK) and differential phase-shift keying (DPSK) are closely related
binary digital modulation methods. What is the motivation for using DPSK?
(d) What is a weakly (or wide-sense) stationary random process?
9 Marks 2. (a) The signal 5 sin(1200πt) is used as the message input to a conventional AM modulator
whose modulation index is 60%. The total power of the AM signal is found to be 4 W.
The carrier frequency is 100 kHz.
i. Determine the fraction of total power in the sidebands.
ii. Find a time-domain expression for the AM signal.
iii. What is the bandwidth of the AM signal?
(b) The message signal m(t) = 5 cos(300πt) + sin(1200πt), is used in a single sideband
modulator (SSB) which transmits only the upper sideband. The total power of the SSB
signal is 10 W. The carrier frequency is 100 kHz.
i. Plot and correctly label the magnitude spectrum of the SSB signal.
ii. What is the bandwidth of the SSB signal?
9 Marks 3. (a) Determine the 95%-power bandwidth of the following signal.
m(t)
t(sec.)
0.5
+0.5
0.1 0.05 0 0.05 0.1
(b) When the above signal is used as the message input to a frequency modulator (FM), a
maximum frequency deviation of 125 Hz is observed at the output of the modulator.
i. Determine the instantaneous frequency deviation of the carrier at t = 80 ms.
ii. Assuming carrier phase at t = 0 to be 0 radians, determine the instantaneous phase
deviation at t = 80 ms.
iii. Find a reasonable
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