NATIONAL OPEN UNIVERSITY OF NIGERIA
14/16 AHMADU BELLO WAY, VICTORIA ISLAND, LAGOS
SCHOOL OF SCIENCE AND TECHNOLOGY
MARCH/APRIL 2014 EXAMINATION
COURSE CODE: CIT754
COURSE TITLE: DIGITAL COMMUNICATIONS
TIME ALLOWED: 3HOURS
INSTRUCTION: ANSWER ANY FOUR (5) QUESTIONS. EACH QUESTION CARRIES 14MARKS.
1. (a.) Discuss briefly Channel codes and Convolutional codes (6 Marks)
(b.) Write short notes on the following (8 marks)
i. Hamming Codes
ii. Golay Code
2. (a.) State the properties for which A set G and a binary operation denoted by + constitute an Abelian group holds (8 Marks)
(b.) Describe two algorithms for performing the optimization automatically and adaptively (6 marks)
3. (a.) Using a well labeled diagram explain a Finite-State Channel (8 Marks)
(b.) State the alternative methods which are often used to describe a convolutional code (6 marks)
4. (a.) Define a lowpass/ baseband signal Signal (4 marks)
(b.) Using a well labeled Block diagram, briefly discuss the Multiple Trellis-Coded Modulations. (10 Marks)
5. (a.) Define the capacity of a channel (2 Marks)
(b.) Show the expression for a power-constrained discrete-time AWGN channel. For a Gaussian noise with a power spectral density of S,(f) show the expression for which the capacity of the channel is given by. (12 Marks)
6. Using a well labeled block diagram illustrate the specific model for the multichannel digital signaling system. Show the expression for the signal waveforms (14 marks)
7. (a.) If s, (t) be the equivalent lowpass signal transmitted over the channel and let Sl(f) denote its frequency content. Express in terms of the time-domain variables c(T;t) and sl(t) the equivalent lowpass received signal, exclusive of additive noise. (10 marks)
(b.) Write short notes on any of the following (4 marks)
i. Phase fitter
ii. Spread spectrum signal
For the 2015 – till date past questions for this course CLICK HERE
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