CS/EE/IT/BM -405 (N)
B.E.( 4th Semester) EXAM,June,2010
(Common for CS,EE,IT & BM Engg. Branch)
ANALOG & DIGITAL COMMUNICATION [CS-405]
Time :3 Hrs Max. Marks :100 Min. Marks:35
Notes :Attempt any five Questions taking one question from each unit.All question carry equal marks.
UNIT-I
Q.1 (a) Find the Fourier transform of a single-side exponential function (e)^-bt u(t) . Also draw the spectrum , where u(t) is unit step function ? 10
(b) State and Prove Parseval's theorem for energy signal and power signals ? 10
OR
Q.2 (a) Explain the following properties of Fourier transform : 10
(i) Time Scaling
(ii) Duality (symmetry)
(iii) Linearity (Superposition )
(iv) Frequency Shifting
(b) Calculate the signal energy for the signal expressed as under : 10
X(t) = (e)^-7t u(t)
where u(t) = 1 for t >0
= 0 for t< 0
UNIT-II
Q.3 (a) An amplitude modulated wave 10
10[ 1+ 0.6 Cos 2
is to be detected by a linear- diode detector . Then calculate :
(i) Time constant
(ii) The value of resistance R if the capacitor used is 100 micro F.
(b) How FM signal can be generated with PM signal ? Discuss in details ? 10OR
Q. 4 (a) When the modulating frequencies in an FM system is 400Hz and the modulating voltage is 2.4 V. the modulation index is 60, Then calculate : 10
(i) Maximum Deviation.
(ii) What is the modulating index when the modulating frequency is reduced to 250 Hz and modulating voltage is simultaneously raised to 3.2 V .
(b) Prove that after amplitude modulation the carrier power increases from Pc to Pc(1 +ma^2/2) where, Ma is the modulation Index ? 10
UNIT-III
Q.5 (a) State and explain the Sampling theorem whit Flat-top sampling Technique ? 10
(b) A PCM system uses a uniform quantizer followed by a V bit encoder . Show that r.m.s. signal to quantization noise ratio is approximately given as ( 1.8+ 6V) dB .? 10
OR
Q.6 (a) Write comparsion between PCM, delta modulation, Adaptive delta modulation and differential pulse code modulation ? 10
(b) A television signal having a bandwidth of 4.2 MHz is transmitted using binary PCM system, Given that the number of quantization levels is 512. Determine : 10
(i) Code word length
(ii) Transmission bandwidth
(iii) Final bit rate.
UNIT-IV
Q.7 (a) Explain the concept of BPSK in details ? 10 (b) Explain the ASK system and derive the relation for error probability of binary ASK ? 10
OR
Q.8 (a) In a digital CW communication system the bit rate of HRZ data stream is 1 Mbps and carrier frequency of transmission is 100 MHz. Determine the symbol rate of tranmission and bandwidth requirement of channel for different techniques : 10
(i) QPSK system
(ii) BPSK system
(iii) 16- Ary PSK system
(b) Compare the various digital modulation techniques ? 10
UNIT-V
Q.9 (a) Encode the following by Huffman coding method for M= 4. Calculate the coding efficiency ? 10
| X | X1 | X2 | X3 | X4 | X5 | X6 | X7 | X8 |
| P(X) | 0.2 | 0.2 | 0.15 | 0.15 | 0.1 | 0.1 | 0.05 | 0.05 |
(b) calculate the mutual information for the channel shown in fig. 10
OR
Q.10 (a) State Shannon - Hartley theorem for capacity of a Gaussian channel : 10
i.e. C= w log [ 1 + S/N] bits / sec
(b) Write short notes on any two of the following : 10
(i) Block Codes
(ii) Error- Control Codes
(iii) Cyclic codes
(iv) Line coding.
(i) Block Codes
(ii) Error- Control Codes
(iii) Cyclic codes
(iv) Line coding.
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