**DIGITAL COMMUNICATION UNIT WISE Important Questions and Answers :-**

**UNIT I**

1. Classify channel.Explain the mathematical models of any two communication channels.

2. Draw the block diagram of DPCM scheme and explain the principles in detail

3. Compare the bit error probability due to coherent ASK,PSK and FSK systems.Compare the performance of these systems

4. Explain the generation, detection , signal space diagram, bit error probability and power spectra of QPSK

**UNIT II**

1. Explain binary symmetric channel and additive noise channel with their mathematical models

2. Explain binary PSK and QPSK with corresponding equations and constellation diagrams.

3. Draw a neat block diagram of a typical digital communication system and explain the function of the key signal processing blocks .

4. Give the block diagram for the generation and detection of BFSK signal and give a brief explanation of the same.

**UNIT III**

1. Obtain the expression for Nyquist criteria for distortionless baseband transmission for zero ISI

2. What are called cyclic codes? Explain with merits and demerits?

3. Draw the block diagram and explain the process of a PCM system in detail.

4. Describe the DPCM transmitter and receiver scheme in detail

**UNIT IV**

1. Derive the expression for bit error probability due to a matched filter

2. Explain briefly about linear block codes

3. Explain about adaptive equalization

4. State and prove the properties of syndrome decoding

5. A rate 1/3 convolutional code has the following generators:

g1=[100], g2=[101] and g3=[111]

i)Draw the encoder circuit corresponding to this code.(21/2)

ii)Draw the state transition diagram for this code.(21/2)

iii)Draw the state diagram for this code.(21/2)

iv)Draw the trellis diagram for this code.(21/2)

v)This code is used for transmission over a AWGN channel with hard decision decoding.The output of the demodulation detector is (101001011110111..).Using viterbi decoding algorithm,find the transmitted sequence

**UNIT V**

1. Discuss the principle of adaptive delta modulation in detail

2. Explain spectral waveform encoding process

3. Give an account of the advantages and limitations of PCM

4. Explain binary symmetric channel and additive noise channel with their mathematical models.