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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2009/
Module Title: Telecommunications
Module Code: ELTR
School: ELECTRICAL & ELECTRONIC ENGINEERING
Programme Titles: Bachelor of Engineering in Electronic Engineering, Year 2 Bachelor of Engineering in Electronic Systems Engineering, Year 2
Programme Codes: EELXE_7_Y EELES_8_Y
External Examiner(s): Dr. A. Donnellan Dr. P. O’Sullivan Internal Examiner: Mr M. O’Gorman
Instructions: Answer Question 1 and TWO other questions. Question 1 (worth 40 marks) is compulsory. Questions 2, 3, and 4 are each worth 30 marks.
Duration: 2 Hours
Sitting: Summer 2010
Requirements for this examination: N/A
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you are attempting the correct examination paper. If in doubt please contact an Invigilator.
COMPULSORY QUESTION
Q.1 (a) Briefly describe the difference between natural and flat-top sampling. [10 Marks] (b) Explain why pulse width modulation (PWM) is described as an analogue pulse system rather than a digital pulse system. [10 Marks] (c) Briefly describe what is meant by time division multiplexing (TDM). [10 Marks]
(d) Assuming that a dash occurs with half the probability of a dot in Morse code, calculate the following:- (i) The information in a dot, [3 Marks] (ii) The information in a dash, [3 Marks] (iii) The entropy of the code. [4 Marks]
CHOOSE TWO QUESTIONS FROM Q.2, Q.3, OR Q.4.
Q. 2 (a) Draw the circuit diagram of a simple pulse amplitude modulator and briefly explain its operation. [10 Marks]
(b) Sketch the frequency spectrum of a typical PAM waveform and label each of the frequency components contained in the sketch. [10 Marks]
(c) Explain why the minimum sampling rate that can be used if the information signal is to be reconstructed is 2fm, where fm is the highest frequency component in the signal. [10 Marks]
Q. 3 (a) Describe the process of quantisation of a continuous information signal into a finite set of discrete values. [15 Marks]
(b) Explain how quantisation noise is produced and why the signal-to-quantisation noise ratio deteriorates at low signal magnitudes. [8 Marks]
(c) Explain what is meant by non-linear quantisation and describe its effect on the signal-to-quantisation noise ratio of voice channels. [7 Marks]
