DIGITAL COMMUNICATION SYSTEM PAPER 1

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COMMUNICATION SYSTEM II EC 304 6th Sem May 2k5

Note: Section A is compulsory. Attempt any Four questions from Section B and any Two questions from section C. Give examples wherever possible. Define explicitly the notations used.

Section A Marks: 2 each

1.
(a) Differentiate with the help of neat diagram between sampling and quantization.
(b) What is a band limited signal?
(c) Explain the term ‘Nyquist interval’.
(d) If the amplitudes of a signal m(t) is confined to the range of (-mp, mp) and the range is divided into L zones, each of step size ?, find out the expression for quantization noise.
(e) Draw the waveforms of an unmodulated carrier, data, ASK, PSK and FSK.
(f) State the advantages of DPSK and PSK.
(g) Sketch the QPSK waveform for the sequences 1101010010 assuming the carrier frequency to be equal to the bit rate.
(h) What is a spread spectrum modulation? Discuss briefly.
(i) What do you understand by paging? What are the different components of a paging system?
(j) List the different error control and detection techniques in a computer network. What do you understand by ARQ?

Section B Marks: 5 each

2. Explain the receiver for the detection of DPSK signals.

3. Illustrate with the help of a neat diagram the phase relationship between symbols intervals of two users of a CDMA system.

4. Given the signal m(t)= 10* cos 200* ?* t cos* 800* ?* t. What is the minimum sampling rate based on:

(a) The low pass uniform sampling theorem.
(b) Band pass sampling theorem.

5. In a binary PCM system, the output signal-to-quantizing-noise ratio is to be held to a minimum of 40 dB. Determine the number of required levels and find the corresponding output signal-to-quantizing-noise ratio.

6. What are the different elements of switching? Discuss cellular digital switching requirement.

Section C Marks: 10 each

7. Explain the following types of computer communication networks with proper diagram wherever applicable:
I. TYMNET
II. ARPANET
III. ISDN
IV. LAN

8. (a) Consider an audio signal comprised of the sinusoidal term

s(t) = 3* cos* 500* ?* t
(i) Find the signal to quantization noise ratio when this is quantized using 10-bit PCM.
(ii) How many bits of quantization are needed to achieve a signal to quantization noise ratio at least 40 dB?
(b) Discuss the advantages and disadvantages of the following signaling formats:
(i) Unipolar NRZ
(ii) Bipolar RZ
(iii) Alternate mask inversion RZ

9 (a) Find the bit error probability for a BPSK system with a bit rate fo 1 Mbit/s. The received waveforms s1(t) = A cos wot are coherently detected with a matched filter. The value of a is 10 mV. Assume that the single-sided noise power spectral density is No= 10-11 W/Hz and that signal power and energy per bit are normalized relative to a 1 ohm load.
(b) Derive the expression for the throughput of Carrier Sense Multiple Access (CSMA)