RGPV IV SEMESTER EXAMINATION (JULY 2010)
COMMON FOR CS, EE, IT & BM ENGG. BRANCH
ANALOG AND DIGITAL COMMUNICATION
Time: Three Hours Maximum Marks: 100
Min Marks: 35
Note : Attempt any five questions taking one question from each unit. All question Carry equal marks.
UNIT-I
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.
OR
2. (a) Explain the following properties of Fourier transform:
(i) Time Scaling
(ii) Duality (Symmetry)
(iii) Linearity (Superposition)
(iv) Frequency Shifting.
(b). calculate the signal energy for the signal expressed as under:
X (t) = e^(-7t) u(t)
where u(t) = 1 for t > 0
0 for t < 0
UNIT-II
3. (a) An amplitude modulation wave
10 [ 1+0.6 cos 2 π.10^3t].cos2π.10^6t
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 µ F.
(b). How FM signal can be generated with PM signal? Discuss in detail?
OR
4. (a) When the modulating frequencies in an FM system is 400 Hz and modulating voltage is 2.4 V, the modulation index is 60, then calculate:
(b) Prove that after amplitude modulation ,the carrier power increses from Pc to Pc(1+Ma^2/2) where, Ma is the modulation index?
UNIT-III
(b). calculate the signal energy for the signal expressed as under:
X (t) = e^(-7t) u(t)
where u(t) = 1 for t > 0
0 for t < 0
UNIT-II
3. (a) An amplitude modulation wave
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
(b). How FM signal can be generated with PM signal? Discuss in detail?
OR
4. (a) When the modulating frequencies in an FM system is 400 Hz and modulating voltage is 2.4 V, the modulation index is 60, then calculate:
(i) Maximum Deviation
(ii) What is the modulation index when the modulating frequency is deduced to 250 Hz and modulating voltage is simultaneously raised to 3.2 V.(b) Prove that after amplitude modulation ,the carrier power increses from Pc to Pc(1+Ma^2/2) where, Ma is the modulation index?
5. (a) State and explain Sampling theorem with Flat-Top sampling technique?
(b) A PCM system uses a uniform quanyizer followed by a V bit encoder.Show that r.m.s. signal to quantization noise ratio is approximately given as (1.8 +6 v) dB.
OR
6.(a) write comparison between PCM ,Delta modulation. Adaptive delta modulation and differential pulse code modulation?
(b) A television signal having a bandwideth of 4.2 MHz
is transmitted using binary PCM system. Given that the number of
quantizatuion level is 512.determine: (i) Code word length (ii) transmission bandwidth
(iii) Final bit rate.
UNIT-IV
7. (a) Explain the concept of BPSK in details?
(b) Explain the ASK system and derive the relation for error probability of binary ASK?
OR
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 transmission and bandwidth requirement of channel for different techniques:
(i) QPSK system
(ii) BPSK system
(iii) 16-Ary PSK system
(b) Compare the various digital modulation techniques?
UNIT-V 9 (a) Encode the following by Huffman coding method for M= 4. Calculate the coding efficency: [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..5]
(b) calculate the mutual information for the channel shown in fig. OR 10.(a) State Shannon Hartley theorem for capacity of a Gaussian channel :
i.e. C= w log[1+ S/N] bits/sec
(b) Write short notes on any two of the following:
(i) Block Codes
(ii) Error -control codes
(iii) Cyclic codes
(iv) Line codes
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