LATHA MATHAVAN ENGINEERING COLLEGE
KIDARIPATTI,MADURAI
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
SUBJECT CODE/NAME: EC6402 COMMUNICATION THEORY YEAR & SEC : II – “A” & “B”
NAME OF THE FACULTY: Mr.S.ANANTHAPANDI,AP/ECE
PART – A
1. / How many AM broadcast stations can be accommodated in a 100 kHz bandwidth if the highest frequency modulating a carrier is 5 kHz? / (NOV/DEC 2010)2. / State the applications of FDM / (APR/MAY 2010)
3. / What are the advantages of Vestigial side band / (APR/MAY 2011)
4. / What is meant by frequency translation / (NOV/DEC 2011)
5. / Compare the bandwidth and power requirements of AM, DSB-SC and SSB / (MAY/JUN 2013)
6. / State the differences between single side band and vestigial side band transmission system / (MAY/JUN 2014)
Unit – II
1. / Draw the block diagram of a method for generating a narrowband FM signal. / (APR/MAY 2010)
2. / Illustrate the relationship between FM and PM, with block diagrams. / (NOV/DEC 2010)
3. / Compare the transmission bandwidth required for Narrowband FM and Wide band FM. / (NOV/DEC 2010)
4. / Distinguish between narrowband FM and wideband FM / (APR/MAY 2011)
5. / How is the narrowband signal is converted into wideband FM / (NOV/DEC 2011)
6. / What is the modulation index of FM / (MAY/JUN 2013)
Unit –I
1. / (i) Draw an envelope detector circuit used for demodulation of AM and explain its operation.(10)(ii) How SSB can be generated using Weaver's method? Illustrate with a neat block diagram. (6) / (APR/MAY 2010)
2. / With a help of neat diagram, explain the operation of an envelope detector. Why does negative peak clipping takes place (16) / (APR/MAY 2011)
3. / With necessary diagram and expressions explain the generation and demodulation of AM(16) / (NOV/DEC 2011)
4. / Explain about VSB and its significance (4)
How do you demodulate AM signal? Explain about it (12) / (MAY/JUN 2013)
5. / With suitable block diagram and equation show how will you generate DBSSC and VSB signals (16)
/ (NOV/DEC 2013)
Unit – II
1. / (i)Explain Armstrong method to generate FM (12)
(ii)Differentiate Narrowband FM and Wideband FM (4) / (MAY/JUN 2013)
2. / Describe how FM wave is generated by the indirect method and give a suitable demodulating scheme for the same (16) / (NOV/DEC 2013)
3. / (i) Explain Armstrong method of FM generation (8)
(ii) Eplain the function of any FM detector circuit (8) / (NOV/DEC 2013)
4. / Draw the superheterodyne receiver and explain the operation of each block (16) / (MAY/JUN 2013)
PART – B
Unit - I
UNIT –III
Part- A
1.Define random variable .Specify the sample space and the random variable for a coin tossing experiment.
2. List the properties of the cumulative distributive function
3. When Random process is called as deterministic?
4. What is the classification of random process? give one example for each
5. Draw the auto correlation function and power spectral density of white noise
6. State central limit theorem.
7. Write the Rayleigh and Rician probability density functions.
8. What is covariance for a random process X(t)?
9. Define mean of a random process.
10. List the conditions to be satisfied for wide sense stationary.
11. What are the properties of a autocorrelation function ?
12. Define Ergodic processes.
13. What is cross correlation of random processes of X(t) and Y(t)?
14. Define autocorrelation.
15. Draw the input output relation for a power spectral density and cross spectral density.
16. Define Gaussian processes.
17. When do we say random processes X(t) as white process ?
18. What is powers spectral density of X(t)?
19. List the properties of Gaussian processes.
Part-B
1.(i)Write a note on stationary processes and its classifications. (6)
(ii)Derive the equation for finding the probability density function of a one to one differential function of a given random variable. (10)
2.(i)Explain about Transmission of random process through a Linear Time Invariant (LTI) filter. (8)
(ii)Find the autocorrelation of a sequence x(t) =Acos(2fc(t+θ)) where A and fc are constant and is a random variable that is uniformly distributed over the interval [-π π] . (8)
3. (i)Define autocorrelation. Discuss the properties of autocorrelation function. (10)
(ii)Consider the Random processes X(t) & Y(t) have zero mean and they are individually stationary. Consider the sum random process Z(t) = X(t) +Y(t). Determine the power spectral density of Z(t) . (6)
4. State and prove the properties of power spectral density .(16)
5. (i) Explain the following terms mean, correlation, covariance, ergodicity?(May/June 2013)(10)
(ii)X is uniformly disturbuted as given below: ?(May/June 2014)(16)
Find E(X), E(X2),E(cos X) &E [(X-mx)2]
UNIT IV
PART-A
1.Define white noise?(May/June 2013)
2.Define noise figure ?(May/June 2013)
3. State the need for pre-emphasis and de-emphasis circuits in the field of communication?(May/June 2014)
5. DC current of 2 mA flows through the semiconductor junction. Consider the effective noise bandwidth of 1 kHz and calculate the shot noise component.?(Nov/Dec 2014)
6. Define the term noise equivalent temperature?(Nov/Dec 2014)
7.Define noise figure?(May/June 2014)
PART-B
1.(i) write notes on shot noise and thermal noise?(May/June 2013) (8)
(ii)Derive the relationship between noise figure and equivalent noise temperature? (8)
2.Define and explain the followings (16) (May/June 2014)
(i)Gaussian noise and Gaussian distribution?
(ii)Thermal noise?
(iii) shot noise. What type of PDF does the Gaussian noise follow
3. (i) Three amplifiers 1,2,3 have the following characteristics:F1=9 dB, G 1 =50 dB; F2=6 DB, G2 =30dB; f3=4 dB,G3=20Db. The amplifiers are connected in tandem. Determine which combination gives the lowest noise figure. (10) (Nov/Dec 2014)
(ii) Discuss on thermal noise (6)
4. (i)What is meant by narrow band noise? Explain the characteristics of narrow band noise. (12) (Nov/Dec 2014)
(ii) An AWGN of power spectral density 1µW is fed through a filter with frequency response H(f)=1/2;|f|<40 kH =0 Elsewhere. Calculate the noise power at the output of the filter (4)
5. (i)Derive the figure of merit of a FM system ?(May/June 2013) (10)
(ii)Explain FM threshold effect.? (6)
UNIT - V
Part-A
1. Define entropy and its properties?(May/June 2013)
2. Define mutual information and channel capacity?(May/June 2013)
3..Define the sensitivity characteristics of a radio receiver?(May/June 2014)
4.Write the Shannon’s theorem for channel capacity?(Nov/Dec2014)
5. A source emits one of the four symbols A,B,C,D with probabilities 1/3,1/6,1/4 and 1/4 respectively. The emissions of symbols by the source are statistically independent. Calculate the entropy of the system?(Nov/Dec2014)
6. State Shannon’s theorem?(May/June 2014)
PART-B
1.(i) Find the Huffman coding for the probabilities P={0.0625,0.25,0.125,0.125,0.25,0.125,0.0625} and the efficiency of the code?(May/June 2013)(10)
(ii)State shannon’s theorems and explain ?(May/June 2013 (6)
2. (i)Consider the following binary sequence 11101001100010110100.... use the Lempel-Ziv algorithm to encode this sequence.Assume that the binary sysmbols 0 and 1 are already in the codebook(10) ?
(ii)A telephone network has a bandwidth of 3.4kHz .calculate the information capacity of the telephone channel for a signal-to-noise ratio of 30 db (3) ?(May/June 2013)
(iii)calculate the minimum signal-to-noise ratio required to support information transmission through the telephone channel at the rate of 9600 bits/sec with bandwidth of 9.6KHZ. (3)
3. (a) Explain Huffman coding system with an example(16)
(b) Explain how channel capacity could be improved be improved.Explain the S/N trade off in detail.(16)
4.(a) (i) Explain Huffman coding system with an example? (6) (Nov /Dec 2014)
(ii) Design a Huffman code for the source given in Q.9. Determine the average code length and codig efficiency (10)
5.(i) Briefy discuss about the lossy source coding schemes(6)
(ii) Design a Shannon fano code for the source given in Q.9. Determine the average code length and coding efficiency(10)