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EC2252 Communication Theory - Nov / Dec 2013 Important Questions

Anna University

Department of Electronics and Communication Engineering

Fourth Semester

EC2252 Communication Theory 

Nov / Dec 2013 Important Question

(Regulation 2008) 

Unit 1
1. (i)Compare the characteristics of DSBFC, DSBSC, SSBFC, SSBSC, VSB schemes.
(ii)Explain the concept of FDM with a suitable block diagram
2. With necessary diagrams and expressions explain the generation and demodulation of AM.
3.(i)Compare the various amplitude modulation schemes.(6)
(ii)With neat block diagram, explain the transmitter and receiver section ofFrequency Division Multiplexing.
4. (i)Draw an envelope detector circuit used for demodulation of Am and explain its operation
(ii)How SSB can be generating using Weaver’s method? Illustrate with a neat block diagram

Unit 2
1. Draw the circuit diagram of Foster Seeley discriminator and explain its working with relevant phasor diagram.
2.  (ii)With necessary diagrams explain the operation of slope detector for demodulating FM signal.
3. (i) Define frequency modulation. Draw the FM waveform. Derive an expres-sion for single tone frequency modulation.
(ii) Compare Narrowband and Wideband FM.
4. Write about the basic principle of FM detection and explain about radio detector

Unit 3
1. (ii)State any 5 properties of autocorrelation function             
(ii)When is a random process said to be strict stationary (SSS), wide sense stationary (WSS) and ergodicprocess
2.  (i)Explain Narrowband Noise. Show that a narrow band noise n(t) can be represented in terms of its in phase and qudrature phase components
(ii)Thermal noise from  a measured as 4*10^-17
 W at a temperature  of 20
 C for a given bandwidth. What will be the Noise power when temperature is changed to 50 degree.
3. (i)List the different type of random process and give the definitions
(ii)Write short notes on shot noise
 4. (i)Write the definition, power spectral density and autocorrelation function for white noise and narrow band noise(filtered white noise)
(ii)What causes thermal noise in a materiala? Write the expression for RMS values of the noise.

Unit 4
1. (i)Derive the figure of merit for FM Receiver.
(ii)What is the necessity of pre-emphasis and de-emphasis used in FM System? 
Explain pre-emphasis and de-emphasis with neat circuit. 
2. Sketch the block diagram of DSB-SC/AM system and derive the figure of merit. 
3. Using super heterodyne principle, draw the block diagram of AM radio
4. Discuss the effects of noise on the carrier in FM receiver with suitable mathematical 

Unit 5
1. Eight possible messages m1,m2,m3,m4,m5,m6,m7 and m8 from a source and their P(m1)=0.5,P(m2)=0.15,P(m3)=0.15,P(m4)=0.08,P(m5)=0.08,P(m6)=0.02,P(m7)=0.0
1,P(m8)=0.01.Construct the Shannon fano coding for each of these message in order to increase the average information per bit. Find the coding efficiency.
2. State and explain Shannon theorem on channel capacity and Define Mutual information. State any two properties
3. A Database Management System (DMS) has following alphabet with probability of occurrence as shown below 
4. Derive Shannon-Hartley theorem for the channel capacity of a continuous channel 
having an average limitation and perturbed by an additive band limited white Gaussian noise. Explain the bandwidth signal to noise radio trade off for this theorem  

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