# Digital Modulation schemes Viva Questions

ASK Generation & Detection:

1. Define ASK. Write the practical applications of ASK.
2. Draw the waveforms of ASK scheme.
3. Draw the Phasor diagrams of ASK.
4. Write the equation of ASK wave.
5. What are the applications of ASK?
7. Write the expression for Probability of error of ASK.
8. What is the BW of ASK?
9. Draw the signal constellation diagram of ASK.
10. Draw the block diagram of ASK generator. Explain its working.
11. Draw the block diagram of coherent ASK demodulator. Explain its working.
12. Draw the block diagram of non-coherent ASK demodulator. Explain its working.
13. How ASK is different from AM?
14. If bit rate is 10µsec then calculate the band width of ASK.
15. Which is the efficient modulation scheme among ASK and PSK give the reason.
16. Write the relation between complementary error function and Q-Function.
17. Write the Pe of ASK in terms of Q function.
18. What is meant by Signal space diagram?
19. A source generates three symbols with probability 0.25,0.25 and 0.5 at a rate of 3000 symbols/sec Assuming the symbols are generated independently from the source the most efficient source encoder would have average bit rate of——————————.

FSK Generation & Detection:

1. Define FSK. Write the practical applications of FSK.
2. Draw the waveforms of FSK scheme.
3. Draw the Phasor diagrams of FSK.
4. Write the equation of FSK wave.
5. What are the advantages and disadvantages of FSK?
6. Write the expression for Probability of error of FSK.
7. What is the BW of FSK?
8. List some applications of FSK.
9. Draw the block diagram of FSK generator and explain its working.
10. Draw the block diagram of coherent FSK demodulator and explain its working.
11. Draw the block diagram of non-coherent FSK demodulator and explain its working.
12. Show that FSK is inferior to PSK by 3dB for a given probability of error.
13. Define digital modulation schemes.
14. Identify the differences between Pass band and Base band Communication.
15. What is a matched filter?
16. What are the properties of matched filter?
17. What is MSK? What is the need for Minimum Shift Keying?
18. For the given 8 bit data 10111010 draw the FSK output waveform.
19. Draw the constellation diagram of FSK.
20. What will happen if the same frequency is used for both the carriers?
21. Draw FM signal and FSK signal differentiate those two signals.
22. What are the applications of FM?
23. How FSK is different from FM?
24. Write the probability of error expression of FSK in-terms of Q function.
25. Write the relation between complementary error function and Q-Function.
26. Among FSK and PSK which is the most efficient scheme and why?

PSK Generation & Detection:

1. Define PSK. Write the practical applications of PSK.
2. Draw the waveforms of PSK scheme.
3. Draw the signal space diagram of PSK.
4. Write the equation of PSK wave.
5. What are the applications of PSK?
6. What are the advantages and disadvantages of PSK?
7. Write the expression for Probability of error of PSK in terms of erfc()
8. Write the expression for Probability of error of PSK in terms Q().
9. Write the difference between erf(x) and erfc(x)..
10. What is the BW of PSK?
11. What are antipodal signals?
12. Give the equation for average probability of symbol error for coherent binary PSK.
13. Explain how QPSK differs from PSK in terms of transmission bandwidth and bit information it carries.
14. What are the advantages of M-ary modulation scheme?
15. Draw the constellation diagram for QPSK.
16. Compare FSK and PSK.
17. What do we infer from constellation diagrams of various modulation schemes?
18. Draw the block diagram of PSK generator. Explain its working.
19. Draw the block diagram of coherent PSK detector. Explain its working.
20. How non coherent PSK is advantageous over coherent PSK?
21. Other name of Non-coherent PSK is———–.
22. Write the expression for a Gaussian function———————.

DPSK Generation & Detection:

1. Define DPSK.
2. Draw the waveforms of DPSK scheme.
3. Write the equation of DPSK.
4. What are the applications of DPSK?
5. What are the advantages and disadvantages of DPSK?
6. Write the expression for Probability of error of DPSK.
7. What is the BW of DPSK?
8. What are the applications of DPSK?
9. Draw the DPSK system and explain its working.
10. If the input sequence to a DPSK modulator is 10011100 write the following sequences, Deferentially encoded sequence if previous bit is 0 And the phase of the encoded sequence.
11. The capacity of a band limited AWGN channel in terms of KBPS if the average received signal to noise power spectral density is 1000 and the BW is approximately infinite is…………..
12. For error free channel conditional probability is ————-.
13. The modulation technique that provides minimum probability of error is———-.

QPSK Generation & Detection:

1. Define QPSK.
2. Draw the waveforms of QPSK scheme.
3. Draw the Phasor diagrams of QPSK.
4. Write the equation of QPSK wave.
5. What are the applications of QPSK?
6. What are the advantages and disadvantages of QPSK?
7. Write the expression for Probability of error of QPSK.
8. Draw the block diagram of QPSK modulator. Explain its working.
9. Draw the block diagram of coherent QPSK de modulator. Explain its working.
10. Write the table for four di-bits with phases used in a QPSK modulation scheme.
11. Write the equation of QPSK wave.
12. What is the BW of QPSK?
13. What are the applications of QPSK?
14. Draw the constellation diagram for QPSK.
15. In Minimum Shift Keying the relation between the signal frequencies and bit rate are————.
16. A pulse for is passed through a matched filter then the impulse response of matched filter is—————————.
17. A lossless channel means—————–.
18. A distortion less channel means————————-.
19. Write the channel matrix for a Binary symmetric channel——————–.

Losses in fibre optics:

1. Define Transmission loss of Optical fibre?
2. What are various losses in fibre optics?
3. What are step index graded index optical fibers?

Data Formats:

1. Compare NRZ-I and NRZ- L.
2. What is the use of data formatting?
3. Compare NRZ and biphase encoding.
4. What is the relationship between quantization levels and number of bits in a code word?
5. Give the advantages of Manchester encoding.
6. Assume a data stream is made of ten 0s. Encode this stream using the following encoding schemes.
7. How much change can you find for each scheme? a)NRZ b)RZ c)Bi phase
1. List out the merits & demerits of each data formats.
2. Represent the given data 11010100 in Manchester encoding and NRZ –M scheme. ## Author: Lakshmi Prasanna Ponnala

Completed M.Tech in Digital Electronics and Communication Systems.

Posted on Categories Others
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