KIIT University 2007 B.Tech Electronics and Tele-Communication Engineering DIGITAL COMMUNICATION TECHNIQUE - Question Paper
DIGITAL COMMUNICATION TECHNIQUE
---- fifth SEMESTER---------
DCT EC 501 (E&TC, IT)
FIFTH SEMESTER EXAMINATION-2007 DIGITAL COMMUNICATION TECHNIQUE [ EC 501 ]
Full Marks: 70 Time: 3 Hours
Answer any SIX questions including Question No.l which is compulsory.
The figures in ihe margin indicate full marks.
Candidates are required to give their answers in their own words as far as
practicable and of all parts of a question should be answered at one place only.
1. a) Mention four advantages of digital communication. [2x10
b) What is bit rate and how it is related to bandwidth in PCM system?
c) What do you mean by White Gaussian Noise?
d) An analog signal is band limited to BHz, sampled at Nyquist rate and the samples are quantized into four levels. The quantization levels Q2, Q3 and Q4 are assumed to be independent of each other and occur with probabilities P1=P2=1/8 and P2=P3=3/8. Find the information rate of the source.
e) Define Guard band.
f) What do you mean by orthonormal function?
(i)
KIIT-U/2007/Autumn End Semester Examination-2007
g) What is the significance of signal space diagram?
h) What is the function of repeater in PCM system?
i) What are the advantages of MSK over QPSK modulation technique?
j) The bit stream 01001 is differentially encoded using delay and EX-OR scheme for DPSK transmission. Assuming the reference bit b(0)=1 and assigning phases of 0 and n for symbol Oand 1 respectively, find the transmitted phase sequence for this.
2. a) Show that the signal to quantization noise ratio for a message signal m(t) with peak amplitude mp is given by
SNR = 3M1M = No. of quantization levels . mp
Also show that for sinusoidal modulation SNR/dB = 6n +1.76 dB n=no. of bits required for coding
b) The speech signal is to be PCM encoded and transmitted. If the maximum quantization error is 0.5% of the peak amplitude, find
(i) Minimum transmission bandwidth and bit rate.
(ii) Minimum transmission bandwidth for transmitting 24 identical signals using TDM. Assume sampling frequency f =8 KHz.
Explain with neat diagram of transmitter and receiver of QPSK modulation scheme. Also draw the signal space diagram for it.
a) Derive an expression for probability of bit error of a binary coherrent FSK receiver.
b) Binary data is transmitted in PSK at a rate of 1 Mb/s, over RF link having band width of 3 MHz. Assume that the noise power spectral density at the coherrent receiver is 10-10 watts/Hz. Find the signal power per bit required at the receiver input to maintain the probability of error less than or equal to 1 0-6.
5. a) Describe Shannon-Hartley theorem of channel capacity.
What do you mean by bandwidth - S/N trade off?
b) A Gaussian channel has 1 MHz bandwidth. Calculate the channel capacity if the signal power to noise power spectral density=104. Also find the maximum information rate.
6. A signal is either s,(t)=A cos 2 n f0t or s2(t)=0, for an [10 interval T=n/f0 with n as an integer. The signal is corrupted by white noise. Find the transfer function of
the matched filter for the signal.
Also find the expression for the probability of error.
7. a) With neat diagram explain Adaptive Delta Modulation. (5 How it is more advantageous than Delta Modulation?
(?)
KIir-U/2007/Autumn End Semester hjtamin,Ui<m-2007
b) In a delta modulation system, the voice signal js sampled at a rate of 64 KHz. If the maximum signal amplitude is 1V, determine the minimum value of the step size of the modulator to avoid slope overload error. (Assume Nyquist criteria is maintained)
8. Write short notes on any two.
a) Optimum filter
b) Companding in PCM system
c) ,T1 digital communication system
KlIT-U/2007/Autumn End Semester Examination-2007
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