# Mumbai University Previous year question papers

## Digital Communication and Coding Techniques

N.B. :

(1) Question No. 1 is compulsory.

(2) Answer any four of the remaining questions.

(3) Draw diagram wherever necessary.

(4) Assume suitable data, if necessary.

1.(a) Differentiate between –

(i) QASK and QPSK (ii) Systematic and Non Systematic Codes

(b) What is duo Binary encoding,? Explain with neat diagram. How does duobinary encoding reduce BW requirement.

2. (a) A DMS has five symbols with probabilities 0.2,0.2, OJ, 0.35 and 0.15 respectively. Co~ct H~ code and calculatecode efficiency.Repeat for ShannonFano code.

(b) Explain with neat-block diagram- the principle of working of non-coherent FSK. receiver. – ,

3. (a)’ Derive expres~ion for SNR of a Integrate- and dump filter. –

(b) Given. Parity check matrix for (7,4) Hamming code –

4(a)  Calculate syndrome vector for single errors. Draw block diagram of encoder and syndrome decoder and explain. With a neat block diagram explain DSSS technique. What is processing gain and jamming margin.

(b) The generator polynomial for a (7, 4) cyclic code is G(D)= 1 +D + D3. Compute systematic and non-systematic code for data IIP 1010. Find generator matrix.

5. (a) For a ~ rate, K = 3 convolutional code, the impulse response is given as g 1 = [1, I, 1] and g2 = [1 0 1] Draw ~lock diagam of encoder and.obtain encoded output for data 1110110. Also sketch code tree and trace path cOITesponding to above message ~ata.·

(b) Why is MSK called shaped QPSK ? Justify with relevant expressions or waveforms. 10

6. (a) Describe briefly tapped delay line equalizes. 10

(b) What is ISI ? Derive expression for ISI and explain methods to overcome ISI. 10

7. (a) Draw block diagram of BPSK Transmitter and receiver and explain,sketch signal 10

space diagram and PSD of BPSK.

(b) Write note on :-

(i) Viterbi Algorithm