Download Digital Communications Exam, ELTR 8008, Cork Institute of Technology, 2009/10 and more Exams Digital Communication Systems in PDF only on Docsity!
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2009/
Module Title: Digital Communications
Module Code: ELTR 8008
School: Electrical & Electronic Engineering
Programme Title: Bachelor of Engineering (Honours) in Electronic Systems Engineering - Award
Programme Code: EELES_8_Y
External Examiner(s): Dr. Andrew Donnellan, Dr. Paula O Sullivan Internal Examiner(s): Dr. R. A. Guinee
Instructions: Answer THREE questions.
Duration: 2 Hours
Sitting: Winter 2009
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Q1 (a) Draw the block diagram of an 8-PSK modulator. Determine the baud rate and double- sided Nyquist bandwidth in terms of the incoming bit rate to the modulator. (11%) (b) Using the (QIC) tribit symbols “000” and “001” from the incoming modulating binary data determine the output of the 8-PSK modulator and use this information to fill in the phasor and constellation diagrams. Determine the error distance and phase margin for this PSK scheme. (11.33%) (c) An 8-PSK modulator operating at 70MHz is fed with a 10MBPS binary data waveform. Draw the modulator output spectrum and determine the maximum and minimum side frequencies. Determine minimum Nyquist bandwidth and calculate the Baud rate. Compare these results with those for BPSK, QPSK and 8 QAM systems. (11%)
Q2 (a) Draw the block diagram of an 8-QAM transmitter and explain its operation. What is the main advantage of this system compared to an 8-PSK system. (11%) (b) Determine the 8-QAM modulator output for the following (QIC) tribits (000) and (001). Use this information to construct the phasor diagram complete with a table of amplitudes and phases. What is the phase margin of error for this system and compare it with that for an 8-PSK system. Determine the error distance. Use the amplitude levels ±0.25 and ±0.6 in the D/A converters when encoding. (11%) (c) Using the graph in Fig.Q2 determine the minimum bandwidth necessary to achieve an error probability of 10-7^ for an 8-QAM system operating at 10MBPS with a CNR of 10dB. (11.33%)
P ( e )
Eb /N 0 ( dB )
8-Level
Fig.Q2: Error rates of QAM modulation systems.
