# Mumbai University Previous year question papers

## Digital Communication

N. no’: Q.l is compulsory and attempt any four questions from Q.2 to Q.7

1. (n) Derive the trnnsfer function H (f) for an optimum filter.conditiona optimumfiltercanbe calledas a matched  filter?

b) Compare

(i) BPSK and QPSK

(ii) Block codes and Convolution codes Under which

2.(a) Draw and explain decision feedback equalizer. Show how it  overcomes drawbacksof transversalequalizer. 10

(b)Drawblock diagram of BFSK Tx and Rx. The bit stream 001010011010is tq be transmittedusingBFSK.SketchtransmittedwavefOIDl. 10

3. (a) How duobiruuy signa1iD.gtechnique introduces controlled IS! in data stream?

(b) Define’ amount of information’ .Discuss the different properties of information.Also define Entropy? 10

4 (a) For the biruuy bit stream 11011010 0010, draw the following waveforms

(i) UnipolarNRZ’ (ii)PolarRZ (iiilBipolarNRZ

(iv) Polar quaternary NRZ (Gray coding) (v/Mary system (M=8)

(b) Consider a (7A) code whose generator matrix is 10

1 1 1 10 0 0

G= 1010100

0110010

1100001

(i) Find all the codewords of the code.

(ii) Find H, the parity- check matrix of the code.

(iii)Compute the syndrome for the received vector 1101101. Is this a valid codevector?

(iv) What is the euor-correcting capability of the code?

(v) What is the error-detecting capability of the code?

5.(a) Define the following:

(i) Systematic and non-systematic code

(ii) Hamming weight’ (iii) Fnmming distanCe

(iv) Rate of code (v) Properties ofh!1mmingcode

(b) Encode the message 101 in systematic form using polynomial division Ipld the generator g(X)'” 1+ X + X2+ x’. 10

6.(a) In relation to spread spectrwn explain the following terms: 10

(i) slow frequenCyhopping (ii) fast frequency hopping

(b) Draw block diagram of a generator of DPSK. Also show how data is recovered from DPSK signal. 10

7.Write short note on any 1WO.

(a) Intersymbol interference and Interchannel interference

b) Eye Diagram

(c) Viterbidecoding.