Anna University Chennai 2006-1st Sem B.E Electronics & Tele-Communication Engineering VESTER of EC341 – DIGITAL COMMUNICATION - Question Paper

ANNA UNIVERSITY :: CHENNAI – 600 025
MODEL ques. PAPER
VI SEMESTER
B.E. ELECTRONICS AND COMMUNICATION ENGINEERING
EC341 – DIGITAL COMMUNICATION
Time: 3 Hours Maximum : 100 Marks
ans All ques.
PART – A (10 x two = 20 Marks)
1. If x(t) = cos (2pt / T) sin (4 pt / T) is to be sampled, what is the maximum
sampling interval?
2. obtain the step size S when a signal m(t) = five sin(2pft) is quantized using uniform
quantizer to achieve an SNR= 1536.
3. What is inter symbol interference? discuss.
4. What is raised cosine pulse? discuss.
5. find the signal constellation of a QPSK signal.
6. Compare the bandwidth efficiency of the M-ary FSK and M-ary PSK modulation
schemes.
7. find the parity cheque matrix of a (5,1) repetition code whose generator matrix
is G = [11111]
8. provide the Hamming bound of (n,k) linear block code and hence discuss perfect
code.
9. List the applications of spread spectrum systems.
10. List the properties of PN sequence and discuss.
PART – B (5 x 16 = 80 Marks)
11. It is needed to transmit data at the rate of 2Mbps through a channel whose
bandwidth is 2MHz and No = 10-14 W/Hz.
i) Suggest a suitable modulation scheme and obtain out the amplitude of the
transmitted carrier to achieve a BER of 10-5 at the receiver and the bandwidth
efficiency ? of the system and
ii) If the needed ? is 0.5, what modulation scheme would you select for
transmission and draw the block diagram of the modulator and demodulator for
the identical.
12.a) With the help of a neat block diagram, discuss the encoder and decoder of
differential PCM system. Also find an expression for prediction coefficient of
first order predictor.
(OR)
12.b)i) discuss the encoder and decoder for Delta Modulation.
ii) elaborate slope overload and granular noise? How to overcome them.
13.a) Derive and plot the power spectra of NRZ unipolar and bipolar format signals.
(OR)
13.b) Draw the block diagram of duobinary encoder and decoder and discuss. elaborate
the draw backs of this scheme? Suggest a method to overcome the identical.
14.a) For(7,4) Hamming code with the generator binomial g(D) = 1+D2 + D3
(i) Form the generator matrix in systematic form.
(ii) find the code word polynomial for a message polynomial m(D) =
1+D+D3.
(iii) Design the encoder for the above code.
(OR)
14.b) For a (2,1,3) convolution code with g1 = ( one 0 one 1) and g2 = ( one 1 one 1), design the
encoder and obtain the subsequent.
(i) Generator matrix
(ii) Transfer function matrix calculate the coded output using both the
methods assuming the input u = (101101).
15.a) discuss with the help of block diagrams and waveforms, the subsequent techniques
of spread spectrum communication.
(i) Direct sequence
(ii) Frequency hopping
(OR)
15.b)i) Derive an expression for Jamming margin for direct sequence spread spectrum
system with BPSK modulation.
ii) An PN sequence is generated using a feed back register of length m = 4. The chip
rate is 107 chips per sec. obtain the length, chip duration and the period of the PN
sequence.
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Earning:   Approval pending.