1. The measure of the amount of redundancy is given by

A. Code size
B. Code weight
C. Code rate
D. Minimum distance

Answer: C

The rate of the code gives the measure of the amount of redundancy. The rate is given by the ratio of the number of data bits that form an input to a block encoder to the total number of bits.

2. The number of k bit shifts over which a single information bit influences the encoder output is given by

A. Code rate
B. Constraint length
C. Code length
D. Code weight

Answer: B

The constraint length represents the number of k bit shifts over which a single information bit influences the encoder output.

3. The method used for representing convolution encoders are

A. Connection pictorial
B. State diagram
C. Tree diagram
D. All of the mentioned

Answer: D

Several methods are used for representing convolution encoders such as connection pictorial, connection vector or polynomials, state diagram, tree diagram, and trellis diagram.

4. Periodic truncation is done by

A. Appending zero to the end of the input data sequence
B. Appending zero to the beginning of the input data sequence
C. Appending one’s to the end of the data sequence
D. Appending one’s to the beginning of the data sequence

Answer: A

Convolution codes are forced into a block structure by periodic truncation which is done by appending zero at the end of the input data sequence, for the purpose of clearing or flushing the encoding shift register of the data bits.

5. Finite state machines have

A. Past memories also
B. Only present and future memories
C. Only future memories
D. Only present memories

Answer: A

A convolution encoder belongs to a class of devices called finite state machines which are those machines that have a memory of past signals.

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6. How many number of transitions can be made at each bit time?

A. One
B. Two
C. Three
D. Half

Answer: B

As a consequence of shifting in one bit at a time, there are only two possible transitions that the register can make at each bit of time.

7. In the trellis diagram, the number of nodes ______ at successive branching.

A. Increases by 1
B. Doubles
C. Triples
D. None of the mentioned

Answer: B

As per the algorithm, in the trellis diagram at successive branching the number of nodes doubles.

8. Example of a convolution encoder state diagram is

A. Tree diagram
B. Trellis diagram
C. Tree & Trellis diagram
D. None of the mentioned

Answer: C

The tree diagram and trellis diagram are both examples of convolution encoding state diagrams.

9. In the maximum likelihood decoding technique, the likelihood function compares the

A. Joint probabilities
B. Individual probabilities
C. Conditional probabilities
D. None of the mentioned

Answer: C

If all input messages are equally likely a decoder that achieves the minimum probability of error is that which compares the conditional probabilities also called the likelihood function.

10. In a maximum likelihood detector the error probability is

A. Maximum
B. Minimum
C. Zero
D. None of the mentioned

Answer: B

The maximum likelihood detector is an Optical Detector that minimizes the error probability.