R05321002-principles-of-communication-

Set No. 1

Code No: R05321002

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF COMMUNICATION ( Common to Electronics & Instrumentation Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) What are the types of communications? Explain. (b) Define noise. Where is it most likely to affect the signal?

[8+8]

2. The rms voltage of a carrier wave is 5 volts before modulation and 5.9 volts after modulation. What is the percentage of modulation? Calculate the modulated power if the unmodulated power is 2kw. [16] 3. Derive the spectrum of narrowband angle modulation(NBFM).

[16]

4. Explain the cross-talk in PAM due to the HF and LF limitations of the channel. Which one of two affects more than one channel and why? [16] 5. With reference to PCM system explain the following: (a) Sampling (b) Companding (c) Mid-riser quantizer (d) Mid-Tread quantizer.

[16]

6. (a) Differentiate BPSK & QPSK (b) Define i. ii. iii. iv.

Baud Rate Matched Filter Band width efficiency. SNR.

[8+8]

7. (a) Show that, using sampling, that the total information in binary units that can be in a communication channel in time T is given by WT log2   transmitted PS 1 + PN Where W is the channel bandwidth PS is the signal power and PN is the noise power in the channel. (b) What conditions have to be satisfied by K and the code length for the coding efficiency to be 100 percent, if a discrete memoryless source whose alphabet consists of K equiprobable symbols? [8+8] 1 of 2

Set No. 1

Code No: R05321002

8. (a) Construct the standard array for a (6, 3) linear block code whose generator 1 0 0 1 1 0 matrix is given below. G = 0 1 0 0 1 1 0 0 1 1 0 1

(b) Write the advantages of table lookup decoding scheme in linear block codes. [10+6] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: R05321002

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF COMMUNICATION ( Common to Electronics & Instrumentation Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Ignoring the constant relative amplitude component, plot and add the appropriate sine waves graphically, in each case using the first four components, so as to synthesize (a) a square wave (b) a sawtooth wave.

[8+8]

2. Explain the detection of SSB-SC signals and explain the effect of phase and frequency error. [16] 3. Show that a low pass filter can be used as a discriminator.

[16]

4. Draw and explain the PWM modulator.

[16]

5. With reference to PCM system explain the following: (a) Sampling (b) Companding (c) Mid-riser quantizer (d) Mid-Tread quantizer.

[16]

6. (a) Draw the modulation waveforms for transmitting binary information over bandpass channels, for the following modulation schemes. ASK FSK PSK and Baseband pulse shaping followed by DSB modulation. (b) What are the advantages and disadvantages of digital modulation schemes over analog modulation methods? [8+8] 7. (a) Consider a telegraph source having two symbols, dot and dash. The dot duration is 0.2s. The dash duration is 3 times the dot duration. The probability of the dot’s occurring is twice that of the dash, and the time between symbols is 0.2s. Calculate the information rate of the telegraph source. (b) A system has band width of 4Khz and SNR of 28 db at the input of the receiver. Calculate i. It’s information carrying capacity 1 of 2

Set No. 2

Code No: R05321002

ii. The capacity of channel if it’s bandwidth is double while the transmitted signal power remains constant. [10+6] 8. (a) What do you understand by error control coding? Explain the various methods briefly. (b) What are cyclic codes? Explain the algebraic structure of cyclic codes. [8+8] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: R05321002

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF COMMUNICATION ( Common to Electronics & Instrumentation Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Derive the proprieties of Fourier transform. (a) Differentiation (b) Integration.

[8+8]

2. Explain the Synchronous Detection in DSB-SC demodulation process with block diagram. [16] 3. A carrier which attains a peak voltage of 5 volts has a frequency of 100 MHz. This carrier is frequency-modulated by a sinusoidal waveform of frequency 2 kHz to such extent that the frequency deviation from the carrier frequency is 75 kHz. The modulated waveform passes through zero and is increasing at time t = 0. Write an expression for the modulated carrier waveform. [16] 4. Explain Natural sampling with circuit.

[16]

5. (a) Explain µ-law and A-law for compression. (b) In what way PCM is different from other analog pulse modulations? What makes it a digital system. [10+6] 6. (a) Compare ASK, FSK and PSK systems with respect to bandwidth, power used, and equipment complexity. (b) Draw the block diagram of FSK transmitter and explain.

[9+7]

7. (a) A DMS X has four symbols x1 , x2 , x3 , and x4 with P (x1 ) = 1/2, P (x2 ) = 1/4, and P (x3 ) = P (x4 ) = 1/8. Construct a Shannon-fano code for X, and show that this code has the optimum property that ni =I(xi ) and that the code efficiency is 100 percent. (b) If a discrete memoryless source whose alphabet consists of K equiprobable symbols. Explain why the use of a fixed-length code for the representation of such a source is about as efficient as any code can be. [12+4] 8. Write explaining notes on: (a) BCH codes (b) Golay codes (c) R S codes 1 of 2

Set No. 3

Code No: R05321002 (d) Trellie’s codes.

[16] ⋆⋆⋆⋆⋆

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Set No. 4

Code No: R05321002

III B.Tech Supplimentary Examinations, Aug/Sep 2008 PRINCIPLES OF COMMUNICATION ( Common to Electronics & Instrumentation Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) What are the types of communications? Explain. (b) Define noise. Where is it most likely to affect the signal?

[8+8]

2. In a linear collector-modulated amplifier, the plate supply is 300 volts, and the dc collector current under an unmodulated amplitude is 20 amperes. The sinusoidal modulating voltage appearing in the collector circuit of the modulate amplifier has an amploitude of 150 volts. The unmodulated carrier power is 5 kw. Calculate (a) the modulation index; (b) the carrier power after modulation (c) the collector circuit efficiency, and (d) the collector dissipation under modulated as well as unmodulated condition. [16] 3. The linear characteristic deviation in a balanced-slope detector is 3B/2, where 2B is the 3 dB bandwidth of each resonant circuit. Justify. [16] 4. Draw and explain the PAM modulator.

[16]

5. (a) What do you understand by PCM? How quantizing and coding are done? (b) What is aliasing effect and aperture effect. How these effects can be overcome. [8+8] 6. (a) Compare ASK, FSK and PSK systems with respect to bandwidth, power used, and equipment complexity. (b) Draw the block diagram of FSK transmitter and explain.

[9+7]

7. (a) Define and discuss i. Mutual information ii. Average information. iii. Channel matrix (b) What are the characteristic features of Shannon?s theorem and ShannonHartley law? [9+7]

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Set No. 4

Code No: R05321002 8. (a) Find the generator matrix of the H matrix given  1 1 1 1 1 1 1 0 0 0 0 1 0 0  1 1 1 1 0 0 0 1 0 1 0 0 1 0 H=  1 1 0 0 1 1 0 1 1 0 1 0 0 1 1 0 1 0 1 0 1 1 1 1 1 0 0 0 And first 5 code words

 0 0   0  1

(b) If the information words is A=00101100111, find the code word T. ⋆⋆⋆⋆⋆

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[12+4]