Information Theory and Elements of Digital Communication (CSCT2208)
Computer Science - COS
Semester: Second Semester
Level: 200
Year: 2018
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REPUBLIC OF CAMEROON THE UNIVERSITY OF BAMENDA
Peace-Work-Fatherland P.O. Box 39 Bambili
Second Semester Examinations
School: HTTTC Department: Computer Science Option: ICT Level: 100
Course Code: ICT125 Course Title: Information theory and element of digital communication
Lecturer: Dr. DADA Jean-Pierre Credit Value: 2
Date: Time: 1:30 hour Start Time: End Time:
Instructions: Answer Exercises 1, 2, 3 and 4 or 5
Exercise 1: Convert in base 2, the following decimal numbers: 121; 18; 155 (9 marks)
Exercise 2: Convert in base 2, the following Hexadecimal numbers: 89h; A1h; 55h (9 marks)
Exercise 3: Perform the following operations:
A) (3 marks)
B) (3 marks)
C) (3 marks)
D) (3 marks)
E) (3 marks)
Exercise 4: Hamming codes (7,4): syndrome decoding
To apply Hamming codes, let
a message to be sent. We should add on this message,
the code
. Then the message (code word) to send becomes
. The pictorial
representation of encoding for Hamming (7,4) codes is:
1) How do you call the code
? (4 marks)
2) Give the relation helping to calculate
;
and
(12 marks)
3) Let us assume that the message received
. The position of the errors is given
by:
•
•
•
Give the formulae to calculate the position of the error (6 marks)
4) Application of Hamming codes: The original message to be sent using Hamming code is 0000.
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4.1) Using hamming codes, what is the message to be really transmitted by the system? (6 marks)
4.2) During transmission, errors can occur. Let us assume that the message received is 1000000.
4.2.1) Where the errors coming from during transmission? (1 mark)
4.2.2). Demonstrate using Hamming procedure that you can detect the error and correct it? (8
marks)
Exercise 5: Let us image an information system using a word of 9 bits where 8 bits are reserved for
information and one bit for parity. Let us consider the information Dada is here to be sent by this system.
This information is divided into blocks of 8 bits per row (one letter per row).
1) Using ASCC codes, complete the following table with the initial message (8 marks)
0 1 0 0 0 1 0 0 D
0 1 1 0 0 0 0 1 a
0 1 1 0 0 1 0 0 d
0 1 1 0 0 0 0 1 a
i
s
h
e
r
e
2) Using VRC and LRC methods, and odd generator, generate the message to be sent (6 marks)
3) During transmission, some errors occur. Let us imagine that the message received is:
1 1 0 1 1 1 1 1 0
0 1 0 0 0 1 0 0 1
0 1 1 0 0 0 0 1 0
0 1 1 0 0 1 0 0 0
0 1 1 0 0 0 0 1 0
0 0 1 0 0 0 0 0 0
0 1 1 0 1 0 0 1 1
0 1 1 1 0 0 1 1 0
0 0 1 0 0 0 0 0 0
0 1 1 0 0 1 1 1 0
0 1 1 0 1 1 1 1 1
0 1 1 0 1 1 1 0 1
0 1 1 0 0 1 0 1 1
3.1. What is the message received? (8 marks)
3.2. Demonstrate that you can detect and correct these errors using VRC and LRC (7 marks)
3.3. Give the message after correction (4 marks)
3.4. Have you corrected all errors? (2 marks)
3.5. List one limit of this method (2 marks)
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HANDOUT: ASCII codes
The ASCII (American Standard Code for Information Interchange) code is the most used in
computer science. It is used for the international transmission of information. Let us extract it as:
0 1 2 3 4 5 6 7
0 Space P ‘ p
1 A Q a q
2 B R b r
3 C S c s
4 D T d t
5 E U e u
6 F V f v
7 G W g w
8 H X h x
9 I Y i y
A J Z j z
B K k
C L l
D M m
E N n
F O o
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