Advanced Communication, Digital Communication Viva Question-Answer for 6th Sem

Q1. What is multiplexing?


Ans: Multiplexing is method by which multiple analog message signals or digital data streams are combined into one signal over a shared mediuANSWER
Q2. What are different types of multiplexing?


Ans: i) Space-division multiplexing (SDM)
ii) Frequency-division multiplexing (FDM)
iii) Time-division multiplexing (TDM)
iv) Code-division multiplexing (CDM)ANSWER
Q3. What is TDM?

Ans: TDM is the process of dividing up one communication time slot into smaller time slots.
OR, It is the technique of separating the signal in time is called TDM.


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Q4. What do you mean by FDM?

Ans: Frequency division multiplexing is the technique of separating the signal in frequency is reffered as FDM.


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Q5. What is Amplitude shift Keying (ASK) ?

Ans: It is a type of digital modulation in which, the digital data modulates amplitude of the carrier.


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Q6. What are different types of digital modulation?

Ans: i) Phase shift keying (PSK)
ii) Frequency shift keying (FSK)
iii) Amplitude shift keying (ASK)


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Q7. What is Phase shift keying ( PSK)?

Ans: In this technique, the digital data modulates the phase of the carrier.


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Q8. What is Frequency shift keying (FSK) ?

Ans: In this technique, the digital data modulates the frequency of the carrier.


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Q9. What is Binary Phase shift Keying (BPSK) ?

Ans: In BPSK, binary symbol ‘1’ and ‘0’ modulate the phase of the carrier.


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Q10. What is bandwidth of BPSK signal?

Ans: BW=2fb. where fb=1/Tb.


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Q11. What do you mean by Differential Phase Shift Keying (DPSK)?

Ans: DPSK is differentially coherent modulation method. It does not need a coherent carrier at the demodulator. The input sequence of binary bits is modified such that the next bit depends upon the previous bit. In DPSK the phase of the carrier changes only on symbol ‘1’, while in BPSK, phase of the carrier get changes both at ‘1’ and at ‘0’. So this is the major difference between DPSK and BPSK.


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Q12. What is Bandwidth of DPSK?

Ans: BW= fb.

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Q13. Show the phase change in DPSK at the digital input 10111101.


Ans: Draw it by yourself with help of your textbook.ANSWER
Q14. What is QPSK?

Ans: Quadrature phase shift keying (QPSK) also known as 4-PSK, so the phase get changed at four different point or angle and that is at 45, 135,225 and 315O at the digital input 00,10,11,01 respectively.


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Q15. Why JK flip-flop is being used in this type if Keying?

Ans: JK flip-flop is used in this type of keying in order to separate the even an odd bits according to the digital inputs.


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Q16. What are the advantages over other types of keying?

Ans: i) The BW required by QPSK is just half of the BPSK.
ii) The information transmission rate is higher.
iii) Carrier power remains constant.


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Q17. What is a GUNN DIODE?

Ans: Gunn diode is a bulk semiconductor device, normally made up of N-type semiconductor.

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Q18. How would you find the propagation loss for two different known length and voltage of optical fiber.


Ans: Propagation loss= 10/(L1-L2) log V2/V1 .
Where L1,L2 are length of two different optical fiber and V2 and V1 are the voltages across it.

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Q19. What is the used formula to find out the bending loss for an optical fiber?


Ans: There is no any fixed formula to find so, bending loss is the relation between the voltages (V) to the diameter (d) of bended optical fiber.
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