**EC6402 CT Notes**

Anna University Regulation 2013 Electronic Communications Engineering (ECE) EC6402 CT Notes for all 5 units are provided below. Download link for ECE 4th SEM EC6402 COMMUNICATION THEORY Lecture Notes are listed down for students to make perfect utilization and score maximum marks with our study materials.

** EC6402 – COMMUNICATION THEORY**

UNIT-V INFORMATION THEORY

2 Marks Questions and Answers

1.What is entropy? Entropy is also called average information per message. It is the ratio of total information to number of messages. i.e., Entropy, H =(Total information)/ Number of messages .

2. What is channel redundancy? Redundancy (γ) = 1 – code efficiency Redundancy should be as low as possible.

3. Name the two source coding techniques. The source coding techniques are, a) prefix coding b) Shannon-fano coding c) Huffman coding

4. State any four properties of entropy. a) For sure event or impossible event entropy is zero. b) For M number of equally likely symbols, entropy is log 2 M c) Upper bound on entropy is H max = log 2 M d) Entropy is lower bound on average number of bits per symbol.

5. State the channel coding theorem for a discrete memory less channel. Statement of the theorem: Given a source of ‘M’ equally likely messages, with M >>1, which is generating information at a rate. Given channel with capacity C. Then if,R ≤ C There exits a coding technique such that the output of the source may be transmitted over the channel with a probability of error in the received message which may be made arbitrarily small.

7. What is memory less source? Give an example. The alphabets emitted by memory less source do not depend upon previous alphabets. Every alphabet is independent. For example a character generated by keyboard represents memory less source.

8. Explain the significance of the entropy H(X/Y) of a communication system where X is the transmitter and Y is the receiver. a) H(X/Y) is called conditional entropy. It represents uncertainty of X, on average, when Y is known. b) In other words H(X/Y) is an average measure of uncertainty in X after Y is received. c) H(X/Y) represents the information lost in the noisy channel.

9. What is prefix code? In prefix code, no codeword is the prefix of any other codeword. It is variable length code. The binary digits (codewords) are assigned to the messages as per their probabilities of occurrence.

10. What is information theory? Information theory deals with the mathematical modeling and analysis of a communication system rather than with physical sources and physical channels

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