Mid Sem Examinations-I, February 2017
JAIPUR NATIONAL UNIVERSITY, JAIPUR
School of Engineering & Technology
Subject: Digital Communication Subject
Code: 6EC1
Time: 2 Hrs Total Marks:
20
1. Attempt any eight questions. Each carries one mark.
.... 1x8
i. An analog signal f ( t )=10 sint is passed through 4 bit PCM system. Find the step
size of PCM system.
ii. Draw the quantization and sampling of any analog signal and show your number of
quantization level and sampling.
iii. Draw the block diagram Differential PCM.
iv. Write the quantization noise occur in the delta modulation.
v. How the adaptive delta modulation will reduce these noise.
vi. What is the practical value A and in the A-law and law compandor?
vii. Write the mathematical expression for Gaussian probability density function for
random variable X , mean and variance is ( , 2 ).
viii. In PCM system as the number of bits per sample increase by n to n+K then
calculate change in S/Nq (db).
ix. Draw the AMI, Manchestor line code for 1 1 0 1 0 0 1 0 1 0.
x. Draw the match filter output for the rectangular input function
{
x ( t )= A 0<t T
0 t> T
xi. Draw the waveform Binary ASK and FSK.
xii. Write the probability of error comparison of ASK, FSK and PSK.
2. i. Drive the expression for Signal to noise ratio (S/N) db in PCM system. .. 3x2
ii. The information in an analog waveform with peak to peak to value is 10 volt and frequency
3KHz. If the sampling frequency is 60% higher than the natural sampling frequency of analog
signal, when it passes through the 4-bit PCM. Then calculate
a) Number of quantization level.
b) Step size
c) Bandwidth
d) S/N in db
iii. Explain the Matched filter. Drive the expression for probability of error in the matched filter.
iv. Explain the Non- Uniform Quantization method for waveform coding with example.
OR
i. Explain the modulation and demodulation of delta modulator using block diagram.
f Am
ii. A sine wave of frequency m and amplitude is applied to delta modulator having
step size . Show that the overload distortion will occur if
Am>
2 f mT s
iii. Compute the matched filter output response over (0, T) to the pulse waveform
{
t
x ( t )= e 0 t T
0 otherwise
iv. Draw the HDB3 and B8ZS line coding for 10000110000000011.
s 1 ( t ) , s 2 ( t ) , s3 ( t ) s 4 (t ) . Use the Gram-Schmidt orthogonalization
3. i. For the given signals
procedure to find an orthonormal basis for the set of signals. .. 3x2
ii. Draw the constellation diagram of the binary ASK, FSK and PSK. Find signaling distance.
iii. Calculate probability of error for Binary ASK.
iv. A binary ASK system for equally probable messages having peak amplitude is 0.2 volt
uses 2 sec bits and channel has N 0 1015 W /H z . Determine the probability of error.
OR
i. Draw the constellation diagram with signaling point of QPSK signal.
ii. Sketch the QPSK waveform for the sequence 1101010010.
iii.Drive the expression for probability of error binary PSK.
iv. Determine the bit error probability for a BPSK system having a bit rate of 1 Mbit/sec. The
receiver receives the waveforms s1(t)=Acos t and s2(t)= --Acos t . The received signals
are coherently detected using a matched filter. If A=10mv and single sided noise power spectral
N0
density is =10 -11W/Hz. Assume that the signal power and energy per bit are normalized.
