SP103 Digital Communication Techniques

Model question paper time : 3 hrs marks : 50

Module I

I a) Define and explain the characteristic function of a random variable. (4)

b) Show how can the statistical averages be derived from the characteristic function. (2)

c) Explain a Rayleigh random variable. Specify its application. (4)

OR

II a) Explain the terms

(i) Autocorrelation and (ii) power density spectrum of a random process (5)

b) Derive the response of an LTI system to a random input signal. (2)

c) The power density spectrum of a random signal is x(t) is given by

XX(f)= ½ N0 for all f

Find the power density spectrum of the output y(t) of the circuit given below for the above

input.

(3)

Module II

III a) Explain how a band pass signal could be characterized with quadrature components?

(4)

b) Give the response of a B P system to a B P signal. (3)

c) Explain (i) pre-envelope and (ii) complex envelope (1+2)

OR

IV a) Explain Gram Schmidtt procedure for orthogonalisation of signals. (4)

b) Describe the representation of a PAM in the signal space (4)

c) Give the representation of a BP white noise. (2)

Module III

V a) What is a correlation receiver? (5)

b) Explain an optimum demodulator for binary signals in AWGN channel. (5)

OR

VI a) Explain a matched filter receiver. (5)

b) Derive the probability of error for envelope detection of M-ary orthogonal signals. (5)

Module IV

VII a) Describe Rayleigh and Ricean fading channels. (6)

b) Explain how a statistical model is developed for fading channels. (4)

OR

VIII a) What is a channel correlation function? (5)

b) Explain a tapped delay line channel model for a frequency selective fading channel.

(5)

Module V

IX a) State and explain Nyquist criteria for Zero Inter Symbol Interference. (5)

b) Characterize a partial response signal for a Band Limited Channel. (5)

OR

X a) Explain coefficient optimization in the context of a Decision Feedback Equalization. (5)

b) What is linear equalization and peak distortion criteria? (3)

c) What is a Zero Forcing Filter? (2)

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