Digital Communications Multiple Choice Questions on “Structured sequence”.
1. Structured sequences are
A. Block codes
B. Convolutional codes
C. Turbo codes
D. All of the mentioned
Answer: D
Clarification: Structured sequences are those which add structured redundancy to the source code. Examples are turbo codes, block codes, and convolutional codes.
2. In binary symmetric channel, in the demodulator _____ decision is made.
A. Hard
B. Soft
C. Hard & Soft
D. None of the mentioned
Answer: C
Clarification: In binary symmetric channel the demodulator consists of only two discrete elements. Thus it makes hard or firm decision.
3. In Gaussian channel demodulator ______ decision is made.
A. Hard
B. Soft
C. Hard & Soft
D. None of the mentioned
Answer: B
Clarification: In Gaussian channel demodulator consists of continuous alphabet or quantized approximation thus soft decision is made.
4. Which decoders are less complex?
A. Soft decision decoder
B. Hard decision decoder
C. Hard & Soft decision decoder
D. None of the mentioned
Answer: B
Clarification: The design of a soft decision decoder is more complex than the design of hard decision decoder.
5. The ratio of redundant bits to data bits is called as
A. Code rate
B. Redundancy rate
C. Symbol rate
D. Transmission rate
Answer: B
Clarification: The ratio of redundant bits to data bits is called as redundancy of the code and the ratio of data bits to total bits is called as code rate.
6. If the parity bit takes value one then the summation of code-word gives
A. Even result
B. Odd result
C. Even & Odd result
D. None of the mentioned
Answer: A
Clarification: The parity bit takes on the value of one or zero to ensure that the summation of all the bits in the code-word yields even or odd result.
7. The summation operation is performed using _____ logical operation.
A. EX-OR
B. AND
C. OR
D. EX-NOR
Answer: A
Clarification: The summation operation is performed using modulo 2 arithmetic or exclusive OR operation.
8. The probability of message error is written as
A. Block error
B. Word error
C. Block & Word error
D. None of the mentioned
Answer: C
Clarification: We can write the probability of message error also called as block error or word error.
9. In a real time communication system addition of redundant bits leads to
A. More bandwidth requirement
B. Faster rate of transmission
C. More bandwidth requirement & Faster rate of transmission
D. None of the mentioned
Answer: C
Clarification: In a real time communication system the addition of redundant bits dictates a faster transmission rate and which means more bandwidth.
10. Coding gain is defined as
A. Reduction in Eb/N0
B. Increase in Eb/N0
C. Same as Eb/N0
D. None of the mentioned
Answer: A
Clarification: For a given bit error probability coding gain can be defined as reduction in Eb/N0 that can be realized through the use of code.
11. The capacity per cell is ______ Eb/N0.
A. Directly proportional
B. Inversely proportional
C. Double the
D. Half the
Answer: B
Clarification: The capacity that is the number of users per cell is inversely proportional to Eb/N0.