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Reg No.:_ Name:

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
SIXTH SEMESTER B.TECH DEGREE EXAMINATION(S), DECEMBER 2019
Course Code: EC302
Course Name:Digital Communication
Max. Marks: 100 Duration: 3 Hours
PARTA
Answer any two full questions, each carries 15 marks Marks

1 a) Derive the expression for the normalised power of quantization error ina PCM (8)
system with uniform quantization.
b) Explain how eye pattern is used to study the performance of a data transmission (7)
system?
2 a) The signal x(t) = cos(200zxt) + 0.25cos(700zt) is sampled at a rate of 400 samples (7)
per second. The sampled waveform is then passed through an ideal low pass filter
with 200Hz bandwidth. Write the expression for the filter output. Sketch the
frequency spectrum of the sampled waveform.
b) Evaluate the power spectral density of unipolar NRZ code. Plot the spectrum. (8)
3 a) Explain the need for a pre-coder in a duo-binary signalling system. For the given (8)
input binary data 1011101, obtain the output of the duobinary encoder. Explain
how the data can be detected at the receiver.
b) With necessary expressions, explain the practical difficulties encountered in ideal (7)

Nyquist channel & how they are overcome by raised cosine filters.

PART छ
Answer any two full questions, each carries 15 marks
4 a) Explain in detail, the principle of correlation receiver. (7)
b) With the help of diagrams, explain the working of BPSK transmitter &receiver. (8)
5 Consider the signals y)(t),y2(t),v3(t)&y4(t) given below. (15)
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Find the orthonormal basis for these set of signals using Gram-Schmidt
orthogonization procedure.

6 Derive the expression for probability of error in BFSK. (15)

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