# RGPV Question Papers – BE IV SEM – Analog and Digital Communication

B.E. (fourth semester) EXAMINATION, Dec, 2008

(Common for CS, EC, EE &EI, IT Engg.)

ANALOG AND DIGITAL COMMUNICATION

(404)

Note:   Attempt any five questions. All question carry equal marks. All parts of the question should be

Attempted at one place.

1. (a) Determine the Fourier transform of the damped sinusoidal wave form of frequency ω0  shown  in

fig: 1.

(b      Discuss sampling thermo. Explain the generation of sampled signal and how the original signal is

Recovered from a sampled signal. Also focus on aliasing effect.

2 (a) Explain filter method for generation of VSB signal. Show that the sum of the shifted spectrum of

The filter by  ωc should be constant over the frequency range |ω| < ωm..

(b)   An amplitude modulated wave 10 [1+ 0.6 cos 2π 103] cos 2π 106 t is to be detected by a linear diode

Detector. Find

(i)   The find constant ι

(ii)   The value of resistance R if the capacitor used is 10 pF.

Also drive the expression used.

3. (a) A carrier A cos ωct is frequency modulated by a single tone modulating signal, f(t) =Em cos ωntt.

Determine the expression FM and narrowband FM. How is the narrowband FM similar to AM/ also

draws the phasor diagram of NBFM and AM.

(b) A signal tone FM signal is given by :

EFM = 10SIN (16π 106 +20 SIN 2π  103t) volts

Find the modulation index, modulating frequency deviation, carrier frequency and the power of the FM signal.

4. (a)  What do you understand by quantization and what is its need in communication ? Determine the

Value of quantization noise introduce due to it full stop. also show that in PCM system an

Increased of one encoding bit increase the signal to quantization noise by 6 dB

(b )    Explain the working principle of the adaptive delta modulation system.

5. (a)  With the block diagram explain the generation of detection of DPSK signal .Also discuss why error

Rate in DPSK is greater than is PSK .

6. (a)  What is mutual information ? Determine the expression of mutual information in terms of

Different entropies.

(b)    Find the channel capacity of the channel shown in fig. 2.

7. (a) An analog signal having 4 kHz bandwidth is sampled at 1025 times the nyquist rate and each

Sample is quantized into one of 256 equally likely levels. Assume that the successive samples are

Statistically independent:

(i)   What is the information rate of this source?

(ii)  Can be output of this source be transmitted without error over an AGWN channel with a bandwidth

of 10 kHz and an SN ratio of 20 dB?

(iii)  Find the SN ratio required for error free transmission for part (ii).

(iv)  Find the bandwidth required for an AWGN channel for error free transmission of the output of this

source if the SN ratio of 20 dB?

(b)  What are the error controlling codes?

8. Write short notes on any two of the following:

(a)  Optimum filter