This set of Digital Communication Interview Questions & Answers for experienced focuses on “Intersymbol Interference”.

1. The likelihood ratio test is done between

a) Likelihood of s1 by likelihood of s2

b) Likelihood of s2 by likelihood of s1

c) Both of the mentioned

d) None of the mentioned

View Answer

Explanation: The likelihood ratio is given with the help of conditional probabilities.

2. According to the rule of minimizing the error probabilities the hypothesis should be like if the priori probabilities is ________ than the ratio of likelihoods.

a) Lesser

b) Greater

c) Equal

d) None of the mentioned

View Answer

Explanation: The rule of minimizing the error probabilities show that the hypothesis should be like if the ratio of likelihoods should be greater than the priori probabilities.

3. The detector that minimizes the error probability is called as

a) Maximum likelihood detector

b) Minimum likelihood detector

c) Both of the mentioned

d) None of the mentioned

View Answer

Explanation: For the signals that are equally likely , the detector used to minimize the error probability is called as maximum likelihood detector.

4. For a M-ary signal or symbol the number of likelihood functions are

a) M

b) M+1

c) M-1

d) 2M

View Answer

Explanation: For a M-ary signal there will be M likelihood functions representing M signal classes to which a received signal might belong.

5. An error in binary decision making occurs when the channel noise is

a) Greater than the optimum threshold level

b) Lesser than optimum threshold level

c) Both of the mentioned

d) None of the mentioned

View Answer

Explanation: An error will occur when s1(t) or s2(t) is sent and if the channel noise is greater or lesser than the optimum threshold level.

6. Optimum threshold value is given by

a) a0+a1/2

b) a0-a1/2

c) a0/2

d) a1/2

View Answer

Explanation: The optimum threshold level value for error probability reduction is given by a0+a1/2.

7.The symbol of the probability under the tail of Gaussian pdf is called as

a) Complementary error function

b) Co error function

c) Both of the mentioned

d) None of the mentioned

View Answer

Explanation: The co error function or complementary error function is commonly used symbol for probability under the tail of Gaussian pdf.

8. Matched filter provides _____ signal to noise ratio.

a) Maximum

b) Minimum

c) Zero

d) Infinity

View Answer

Explaantion: A matched filter is a linear filter designed to give maximum signal to noise ratio power at the output.

9.The impulse response of the filter is the ________ of the mirror image of the signal waveform.

a) Delayed version

b) same version

c) Both of the mentioned

d) None of the mentioned

View Answer

Explanation: The matched filter’s basic property is that the impulse response of the filter is the delayed version of the mirror image of the the signal waveform.

10. Example for antipodal bandpass signalling is

a) BPSK

b) ASK

c) FSK

d) MSK

View Answer

Explanation : One type of antipodal bandpass signalling is binary phase shift keying.

**Sanfoundry Global Education & Learning Series – Digital Communications.**

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