Digital Communication MCQs Quiz Multiple Choice Questions & Answers

1. Two binary values are represented by two different frequencies in :

1. frequency-shift-keying
2. phase-shift-keying
3. amplitude-shift-keying
4. none of these above

2. Codec uses

1. Delta modulation only
2. PCM and Delta modulation
3. Pulse code modulation technique only
4. None of these

3. ASK is a result of combination of Shift keying and

1. Analog modulation
2. Amplitude modulation
3. Digital modulation
4. None of these above

4. ASK is rarely used in modems because

1. it is highly susceptible to noise
2. it takes care of amplitude only
3. it shifts only between ON and OFF states
4. none of the above

5. The qualifier differential to PSK means that

1. it uses phase shifts of 180 degree
2. phase shift is with reference to the previous bit transmitted
3. it uses phase shifts of multiple of 90 degree
4. none of these above

6. In PCM

1. Pulse Amplitude modulation samples are quantized
2. Non-linear coding scheme is undertaken
3. Digital signal is converted into analog signal
4. None of these

7. In modems

1. A digital signal changes some characteristics of a carrier wave
2. Digital signal is amplified
3. Several digital signal are multiplexed
4. None of these above

8. Modulation is used to

1. Separate differing transmission
2. Ensure that information may be transmitted over long distances
3. Reduce the bandwidth
4. Allow the use of practicable antennas

9. One factor in the accuracy of a reconstructed PCM signal is the

1. Carrier frequency
2. Number of bits used for quantization
3. Signal bandwidth
4. Baud rate

10. The modulation techniques used to convert analog signal into digital signal are

1. Delta modulation
2. Adaptive delta modulation
3. Pulse code modulation
4. All of the above

11. In PCM, the parameter varied in accordance with the amplitude of the modulating signal is

1. Frequency
2. Phase
3. Amplitude
4. None of the above

12. The error probability of a PCM is

1. Gaussian noise + error component due to inter symbol interference
2. Calculated using power spectral density
3. Calculated using noise and inter symbol interference
4. All of the above

13. In Delta Modulation, the bit rate is

1. N times the modulating frequency
2. N times the nyquist criteria
3. N times the sampling frequency
4. None of the above

14. DPCM is a technique

1. Where difference between successive samples of the analog signals are encoded into n-bit data streams
2. Where digital codes are the quantized values of the predicted value
3. To convert analog signal into digital signal
4. All of the above

15. Granular noise occurs when

1. Step size is too large
2. There is interference from the adjacent channel
3. Step size is too small
4. Bandwidth is too large

16. The digital modulation technique in which the step size is varied according to the variation in the slope of the input is called

1. PCM
2. Adaptive delta modulation
3. Delta modulation
4. PAM

17. In Adaptive Delta Modulation, the slope error reduces and

1. Quantization error increases
2. Quantization error remains same
3. Quantization error decreases
4. None of the above

18. Matched filters may be used

1. In parameter estimation problems
2. To estimate the distance of the object
3. To estimate the frequency of the received signal
4. All of the above

19. Information rate is defined as

1. Average number of bits of information per second
2. rH
3. Information per unit time
4. All of the above

20. Entropy is

1. Information in a signal
2. Amplitude of signal
3. Average information per message
4. All of the above

21. Timing jitter is

1. Change in frequency
2. Deviation in location of the pulses
3. Change in amplitude
4. All of the above

22. A linear code

1. All-zero code word is a code word
2. Minimum hamming distance between two code words is equal to weight of any non zero code word
3. Sum of code words is also a code word
4. All of the above

23. Parity bit coding may not be used for

1. Which bit is in error
2. Both a & b
3. Error in more than single bit
4. None of the above

24. Parity check bit coding is used for

1. Error detection
2. Error correction and detection
3. Error correction
4. None of the above

25. Run Length Encoding is used for

1. Bit error correction
2. Correction of error in multiple bits
3. Reducing the repeated string of characters
4. All of the above

26. The number of bits of data transmitted per second is called

1. Modulation rate
2. Coding
3. Data signaling rate
4. None of the above

27. Pulse shaping is done

1. by limiting the bandwidth of transmission
2. after line coding and modulation of signal
3. to control Inter Symbol Interference
4. All of the above

28. Nyquist criterion helps in

1. Reduction in transmission bandwidth
2. Increase in transmission bandwidth
3. Transmitting the signal without ISI
4. Both a and b

29. The Nyquist theorem is

1. Helps in quantization
2. Limits the bandwidth requirement
3. Relates the conditions in time domain and frequency domain
4. Both a and c

30. ASK modulated signal has the bandwidth

1. Half the bandwidth of baseband signal
2. Double the bandwidth of baseband signal
3. Same as the bandwidth of baseband signal
4. None of the above

31. The probability of error of DPSK is …………. than that of BPSK

1. Lower
2. Same
3. Higher
4. Not predictable

32. BPSK system modulates at the rate of

1. 2 bit/ symbol
2. 4 bit/ symbol
3. 1 bit/ symbol
4. None of the above

33. The technique that may be used to reduce the side band power is

1. BPSK
2. Gaussian minimum shift keying
3. MSK
4. BFSK

34. The process of converting the analog sample into discrete form is called

1. Multiplexing
2. Quantization
3. Modulation
4. Sampling

35. The sequence of operations in which PCM is done is

1. Quantizing, encoding, sampling
2. Quantizing, sampling, encoding
3. Sampling, quantizing, encoding
4. None of the above

36. In Delta modulation,

1. All the coded bits used for sampling are transmitted
2. The step size is fixed
3. One bit per sample is transmitted
4. Both a and c are correct

37. In digital transmission, the modulation technique that requires minimum bandwidth is

1. PCM
2. DPCM
3. Delta modulation
4. PAM

38. DPCM suffers from

1. Quantization noise
2. Both a & b
3. Slope over load distortion
4. None of the above

39. The digital modulation scheme in which the step size is not fixed is

1. Adaptive delta modulation
2. DPCM
3. Delta modulation
4. PCM

40. The maximum synchronizing capability in coding techniques is present in

1. Polar NRZ
2. Polar RZ
3. Manchester format
4. Polar quaternary NRZ