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Cankaya University - ECE Department - ECE 373 (MT)Student Name:Student Number:
Questions
Date: 21.11.2011Open Book Exam
1. (70 Points) Two continuous time waveforms XI (t) and x2 (t) are given as message signals,
where XI (t) = Alcos (2000Jrt) , x2 (t) = Az sin (4000Jrt + Jr/ 4) . Answer the following questions.a. Find Xl (t) and X2 (t) , plot them and make appropriate comments.b. X (t) = Xl (t) + x2 (t) is to be sampled by periodic delta functions at 5 (five) time the
Nyquist rate, Is. Determine Is. With this Nyquist rate, describe how you wouldarrange for XI (t) and x2 (t) to be time division multiplexed (TDM). Plot the resultingTDM waveform.
c. Again assuming Is to be five times the Nyquist rate and number of quantization levelsto be 8, plot and calculate for XI (t) and x2 (t), the code of each sample andcorresponding binary encoded representation in the time interval 0:0; t :0;1 mseconds.
d. Are XI (t) and x2 (t) power or energy signals? Find their mean and normalized powersor energies. Find the autocorrelation function, R
X2(r) .
e. By changing X2 (t) to a carrier signal in the form of X2 (t) = Ac sin [2Jr.fct + e(t) J,keeping Xl (t) the same and using XI (t) as message signal to modulate X2 (t) as PMand FM, explain how you would relate e(t) to XI (t) in the two cases. Plot theresulting time waveforms of modulated PM and FM signals.
f. By setting X2 (t) = Ac sin (2Jr Ii) and using XI (t) to modulate X2 (t) in the form of AMand DSBSC, find the resulting time waveforms and frequency spectrums of modulatedsignals.
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2. (30 Points) Answer the following questions as True or False. For the False ones givethe correct answer or the reason. For the True ones, justify your answer
a) Carrier frequencies of GSM networks are between 500 MHz and 600 MHz: ;=-o;j e....
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