__Digital Communications__

__Unit-4 (FAQ)__

**Short Answer Questions:-**

- What is meant by Probability of Error P
_{e}? - what is meant by Bit Error Rate BER? how BER and E
_{b}/N_{o}( approximately known as SNR) related to each other? - what is matched filter? give the impulse response of it.
- Differentiate the following. i. Base band transmission( or Communication) systems and Pass band Transmission systems. ii. coherent and Non-coherent systems.
- what is the need for MSK modulation?
- Draw the signal space diagrams of i. ASK ii. PSK iii. FSK iv. QPSK v. DPSK
- what is meant by gaussian error probability?
- write a short note on M-ary QPSK?
- Define error function, complementary error function and Q-function. Give the relation between Q- function and complementary error function.
- Compare digital modulation schemes in terms of Bandwidth and P
_{e}. - Give the meaning of QPSK. how it is different from PSK?
- write a short note about QPSK.
- what is meant by singal space or signal constellation diagram . give its significance
- draw the wave forms of ASK ,PSK and FSK when data input is 1100101.
- problems on the impulse response of matched filter.
- advantages of pass band over base band transmission?
- applications of ASK, PSK and FSK ,QPSK and DPSK.
- what are the advantages and disadvantages of all modulation schemes?
- advantages of QPSK.

**long Answer Questions:-**

- compare different digital modulation schemes.
- Draw the block diagram of Correlation receiver. Explain the working of it in detail.
- Draw the block diagram of integrate and dump receiver (base band Receiver). Explain the working of it in detail.
- Explain the working of DPSK system with an example.
- Derive the expression for P
_{e}of the following i. QPSK ii. PSK iii. matched filter iv. DPSK v. Optimum receiver vi. Integrate and dump receiver. - write a short note on synchronization methods.
- derive the transfer function of optimum receiver.
- derive the impulse response of matched filter.
- draw block diagrams of modulator and de-modulator for the following coherent modulation schemes and explain its working in detail i. FSK ii. QPSK iii. PSK iv.ASK
- draw block diagrams of modulator and de-modulator for the following non-coherent modulation schemes and explain its working in detail i. FSK ii. non coherent PSK or DPSK iii.ASK
- Derivations of P
_{e}of i. coherent ASK/BASK/ASK ii coherent PSK /BPSK/PSK iii.coherent FSK/BFSK/FSK. - Derivations of P
_{e}of i.Non- coherent ASK/Non- coherent BASK ii non-coherent PSK /Non- coherent BPSK iii.coherent FSK/ Non- coherentBFSK.

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