- PDF Free Download

Size: px

Start display at page:

Download ""

Harold Nathaniel Sparks
5 years ago
Views:

VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur 603 203.

1 VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING QUESTION BANK EC6402 COMMUNICATION THEORY III YEAR / VI SEMESTER ACADEMIC YEAR (EVEN)

2 EC6402 COMMUNICATION THEORY L T P C OBJECTIVES: To introduce the concepts of various analog modulations and their spectral characteristics. To understand the properties of random process. To know the effect of noise on communication systems. To study the limits set by Information Theory. UNIT I AMPLITUDE MODULATION 9 Generation and detection of AM wave-spectra-dsbsc, Hilbert Transform, Pre-envelope & complex envelope - SSB and VSB comparison -Superheterodyne Receiver. UNIT II ANGLE MODULATION 9 Phase and frequency modulation-narrow Band and Wind band FM - Spectrum - FM modulation and demodulation FM Discriminator- PLL as FM Demodulator - Transmission bandwidth. UNIT III RANDOM PROCESS 9 Random variables, Central limit Theorem, Random Process, Stationary Processes, Mean, Correlation & Covariance functions, Power Spectral Density, Ergodic Processes, Gaussian Process,Transmission of a Random Process Through a LTI filter. UNIT IV NOISE CHARACTERIZATION 9 Noise sources and types Noise figure and noise temperature Noise in cascaded systems. Narrow band noise PSD of in-phase and quadrature noise Noise performance in AM systems Noise performance in FM systems Pre-emphasis and de-emphasis Capture effect, threshold effect. UNIT V INFORMATION THEORY 9 Entropy - Discrete Memoryless channels - Channel Capacity -Hartley - Shannon law - Source coding theorem - Huffman & Shannon - Fano codes. TOTAL: 45 PERIODS OUTCOMES: At the end of the course, the students would Design AM communication systems. Design Angle modulated communication systems Apply the concepts of Random Process to the design of Communication systems Analyze the noise performance of AM and FM systems TEXT BOOKS: 1. J.G.Proakis, M.Salehi, Fundamentals of Communication Systems, Pearson Education S. Haykin, Digital Communications, John Wiley, REFERENCES: 1. B.P.Lathi, Modern Digital and Analog Communication Systems, 3rd Edition, Oxford University Press, B.Sklar, Digital Communications Fundamentals and Applications, 2nd Edition Pearson Education H P Hsu, Schaum Outline Series - Analog and Digital Communications TMH Couch.L., "Modern Communication Systems", Pearson, 2001.

3 DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING QUESTION BANK SUBJECT : EC6402 COMMUNICATION THEORY SEM / YEAR: IV / II year B.E. UNIT I AMPLITUDE MODULATION Generation and detection of AM wave-spectra-dsbsc, Hilbert Transform, Pre-envelope & complex envelope - SSB and VSB comparison -Super heterodyne Receiver. PART A Q.No Questions BT Level Domain 1. What are the advantages of VSB-AM? 2. State heterodyning principle. 3. What are the advantages of modulating low frequency signal into high frequency signal? 4. List the types of AM modulators? 5. Define Coherent Detection. 6. Why do you need modulation in communication systems? 7. Identify the differences between single side band and vestigial side band systems. 8. Write about diagonal clipping and negative peak clipping? 9. Suggest a modulation scheme for broadcast video transmission. 10. Apply the concepts of sensitivity and selectivity in AM receiver Draw the AM modulated wave for modulation index=0.5 and its spectra. 12. Illustrate the applications of Hilbert transform.

4 13. Apply the concepts of power relations and find the total power in a modulated wave if the carrier is 10 watts and amplitude modulated to a depth of 80%. 14. Compare AM with DSB-SC and SSB-SC. 15. Distinguish between high level and low level modulation? 16. Differentiate between linear and nonlinear modulation 17. A transmitter radiates 9kW without modulation and kW after modulation. Determine depth of modulation. 18. When a signal m(t)=3cos(2 x10 3 t) modulates a carrier c(t)=5cos(πx10 6 t), determine the modulation index and transmission bandwidth if the modulation is AM. 19. Summarize the methods for generating SSB-SC signal. 20. Can you formulate the theory for modulation index of an AM signal and write its classification. PART B 1. What is the need for carrier suppression in AM system? Draw and explain the functioning of such system. (16) 2. (i)explain the generation of SSBSC signal using phase shift method. (8) (ii)suggest a scheme for recovering the message signal from the signal s(t)=2m(t)cos2πfct. Explain the same. (8) 3. (i) An AM signal is generated by modulating the carrier fc=800mhz by the signal m(t)=sin3000πt+0.5cos5000πt. The AM signal s(t)=100[1+m(t)] cos2πf c t is fed to a 50ohm load. (8) a) Determine the average power in the carrier and in the sidebands. b) Find the modulation index and peak power delivered to the load. (ii)explain the function of switching modulator in the generation of AM signal. (8) 4. (i)analyze the concepts of AM modulation and derive the equation of an AM wave. Also draw the modulated AM wave for various modulation index. (8) (ii) Summarize the methods of demodulation of DSBSC and explain briefly about costas loop. (8) 5

5 5. (i)draw the VSB spectrum and explain the significance. (8) (ii)how do you demodulate AM signal? Explain. (8) 6. (i)compare the characteristics of DSBFC, DSBSC, SSBFC, SSBSC, SB schemes. (8) (ii)what is heterodyning and explain the operation of Superheterodyne Receiver with a suitable block diagram. (8) 7. (i)what is Hilbert transform? And how it can be used for various applications. (8) (ii)analyze the frequency components present in the output when the 1000kHz carrier is simultaneously AM modulated with 300Hz, 800Hz and 1.5kHz audio sine waves. (8) 8. (i) Apply the concepts of envelope detection for demodulation of AM and explain its operation. (8) (ii)how would you generate SSB using Weavers method? Illustrate with a neat block diagram. (8) 9. (i)construct the balanced modulator circuit for the generation of DSB-SC-AM and explain its operation. (8) (ii)develop the coherent detection method in detail for the detection of DSB-SC and SSB-SC. What happens when there is phase mismatch? (8) 10. (i) How do you apply ring modulator for the generation of DSB-SC signal? (8) (ii) For an AM DSBFC wave with peak unmodulated carrier voltage V c =10V, a load resistance R L =10Ω and a modulation coefficient m a =1,determine (8) a) Powers of the carrier and the upper sidebands b) Total sideband power c) Total power of the modulated wave d) Draw the power spectrum BTL3

6 UNIT II ANGLE MODULATION Phase and frequency modulation-narrow Band and Wind band FM - Spectrum - FM modulation and demodulation FM Discriminator- PLL as FM Demodulator - Transmission bandwidth. PART A Q. No Questions BT Level Domain 1. Compare WBFM and NBFM. 2. State the Carson s rule to determine the bandwidth of FM. 3. Why frequency modulation is more preferred for voice transmission? 4. List the advantages of AM and FM. 5. Apply the concepts of detection for detecting FM signals. 6. Analyze the bandwidth of FM when the carrier is modulated by a sinusoidal modulating frequency of 2kHz resulting in a frequency deviation of 5kHZ. 7. Formulate the difference between the direct method and indirect method of FM. 8. What is the need for pre-emphasis? 9. List the applications of phase locked loop? 10. Draw the block diagram of a method for generating a narrow band FM? 11. Give the mathematical expression for FM and PM. 12. Describe the limitations of slope detector? 13. Summarize the merits and demerits of balanced slope detector. 14. Point out the advantages and disadvantages of Foster-Seely discrimination method? 15. Define modulation index of FM and PM. 16. Differentiate between phase and frequency modulation.

7 17. A carrier of frequency 100MHz is frequency modulated by a signal x(t)=20sin(200πx10 3 t). What is the bandwidth of the FM signal if the frequency sensitivity of the modulator is 25kHz per volt? 18. What is the bandwidth required for an FM wave in which the modulating frequency signal is 2kHz and the maximum frequency deviation is 12kHz? 19. Show that Armstrong method is superior to reactance modulator? 20. Outline the concepts of lock in range and dynamic range of PLL. PART B 1. (i)explain the operation of ratio detector for FM detection. (8) (ii)explain the operation of PLL as a FM demodulator. (8) 2. (i) Explain how FM is achieved using Varactor diodes. (8) (ii)make at least five comparisons of AM and FM systems. (8) 3. Apply the concepts of FM and PM with an angle modulated wave which is described by 10 cos 2 10 ) 0.1sin 10 ) t] a) Considering as PM signal with Kp= 10, find m(t). (8) b) Considering as FM signal with Kp= 10 π, find m(t). (8) 4. A carrier frequency of 80MHz is frequency modulated by a sine wave amplitude of 20volts and frequency of 80MHz and the frequency sensitivity of the modulator is 20KHz/v. (16) a) Determine the appropriate bandwidth of the FM wave by using Carson s Rule b) Determine the bandwidth by transmitting only those frequencies whose amplitude exceed 1% of the unmodulated carrier amplitude. 5. (i)how do you obtain the expression for the single tone frequency modulated signal and hence prove that is the constant envelope modulation requiring infinite bandwidth. (12) (ii)list the components present in the spectrum of the FM. (4) 6. (i)explain the FM discriminator with a suitable diagram. (8) (ii)how FM can be derived from PM and vice versa. (8)

8 7. (i)obtain the mathematical representation of FM and PM waves. (8) (ii) With a neat diagram, analyze the concepts of FM with direct method of generation. (8) 8. (i)define FM and derive the expression for wideband FM in terms of Bessel functions. (10) (ii)how do you obtain FM from PM and vice versa? Explain. (6) 9. (i) What are the methods of FM generation and explain the Armstrong method to generate FM signal. (10) (ii) How do you relate the phase modulation with frequency modulation? (6) 10. (i)when the modulating frequency in an FM system is 400Hz and the modulating voltage is 2.4V and the modulation index is 60.Calculate the maximum deviation. Apply the concepts of modulation index and calculate the modulating index when the modulating frequency is reduced to 250Hz and the modulating voltage is simultaneously raised to 3.2V. (8) (ii)with necessary diagrams, develop the operation of slope detector for demodulating FM signal. (8)

9 UNIT III RANDOM PROCESS Random variables, Central limit Theorem, Random Process, Stationary Processes, Mean, Correlation & Covariance functions, Power Spectral Density, Ergodic Processes, Gaussian Process, Transmission of a Random Process Through a LTI filter. PART A Q.No Questions BT Level Domain 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. Demonstrate when random process is called deterministic? 4. Classify random process? Give one example for each. 5. Express 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. Describe mean, autocorrelation and covariance of a random process. 9. Give the conditions to be satisfied for wide sense stationary. 10. What are the properties of an autocorrelation function? 11. Quote Ergodic processes and Gaussian processes. 12. Infer the cross correlation of random processes of X(t) and Y(t)? 13. Show the input output relation for a power spectral density and cross spectral density. 14. Investigate when random processes X(t) is called white process? 15. Summarise an expression for noise equivalent bandwidth. 16. Generalize the power spectral density of X(t). 17. Pointout the properties of Gaussian process. 18. The pdf of a random variable is given as f X (x) =k for a x b and 0 otherwise where k is a constant. Calculate the value of k.

10 19. Evaluate when a random process is called as stationary, deterministic and ergodic. 20. Distinguish between random variable and random process. PART B 1. Explain the following, (i) Random variable (5) (ii) Gaussian process (5) (iii) Central limit theorem (6) 2. (i) Describe and prove the properties of Gaussian Process. (8) (ii) Differentiate the strict-sense stationary with that of wide sense stationary process. (8) 3. (i) Analyze the following terms mean, correlation, covariance, and ergodicity. (8) (ii) Quote the properties of the auto correlation function. (8) 4. (i) An AWGN of power spectral density 1µW is fed through a filter with frequency response H(f) = 1/2 ; f < 40 khz 0 ; elsewhere Calculate the noise power at the output of the filter. (8) (ii)describe about stationary processes and its classifications. (8) 5. Generalize the equation for finding the probability density function of a one to one differential function of a given random variable. (16) 6. (i) Examine about Transmission of random process through a Linear Time Invariant (LTI) filter. (8) (ii) Find the autocorrelation of a sequence x(t) =A cos(2πfc(t+θ)) where A and fc are constant and θ is a random variable that is uniformly distributed over the interval [-π π]. (8) 7. (i) Define autocorrelation. Discuss the properties of autocorrelation function. (8) (ii) Let X(t) and Y(t) be both zero-mean and WSS random processes. Consider the random process z(t) = X(t) + Y(t). Determine the auto correlation and power spectrum of z(t) if X(t) and Y(t) are jointly WSS. (8)

11 8. Discuss and prove the properties of power spectral density. (16) 9. (i) Let X have the uniform distribution given by 12π 0 x 2π f X (x) = 0 Otherwise Calculate mean, mean square value and variance. (8) (ii) Let X(t) = A cos (ωt+φ) and Y(t) = A sin (ωt+φ), where A and ω are constants and Φ is a uniform random variables [0, 2π]. Discover the cross correlation of x(t) and y(t). (8) 10. Given a random process X(t)=A Cos(ωt+θ), where A and ω are constants and θ is a uniform random variable. Judge that X(t) is Ergodic. (16)

12 UNIT IV NOISE CHARACTERIZATION Noise sources and types Noise figure and noise temperature Noise in cascaded systems. Narrow band noise PSD of in-phase and quadrature noise Noise performance in AM systems Noise performance in FM systems Pre-emphasis and de-emphasis Capture effect, threshold effect. PART A Q.No Questions BT Level Domain 1. Describe white noise? Give its Characteristics. 2. Define noise figure and SNR. 3. A Receiver is connected to an antenna of resistance of 50Ω has an equivalent noise resistance of 30Ω. Invent the receiver noise figure. 4. When carrier to noise ratio is high, how will you get figure of merit of FM systems? 5. Formulate the narrow-band noise m(t) at the IF filter output in terms of its in-phase and quadrature components. 6. Discuss the need for pre-emphasis and de-emphasis. 7. Quote threshold effect in AM receiver and Q factor of a receiver. 8. What is FM threshold effect? 9. Distinguish the noise performance of DSBSC receiver using coherent detection with AM receiver using envelope detection. 10. Illustrate coherent system? 11. Classify the methods are to improve FM threshold reduction? 12. The figure of merit of AM system is 1/3 when the modulation is 100 percent and that of FM is (3/2) m f 2.The use of FM offers improved noise performance over AM when (3/2)m f 2 > 1/3. Where m f modulation index in FM. Solve the characteristics of super heterodyne receivers. 13. Name what is capture effect? What do you understand by capture effect in FM? 14. Discuss threshold effect with respect to noise? 15. Label noise equivalent bandwidth. 16. Calculate noise figure and equivalent noise temperature for a receiver connected to an antenna whose resistance is 100Ω and equivalent noise resistance is 50Ω.

13 17. Pointout the characteristic of shot noise. 18. Two resistors of 20 kω, 50 kω are at room temperature (290 o K). For a bandwidth of 100 KHz, Evaluate the thermal noise voltage generated by the two resistors in series. 19. DC current of 2 ma flows through the semiconductor junction. Consider the effective noise bandwidth of 1 khz and Infer the shot noise component. 20. Evaluate thermal noise voltage across the simple parallel RC circuit shown with R =1kΩ and C=1µF at T = 270 o C. PART B 1. (i) Write a short note on shot noise and also explain about power spectral density of shot noise. (8) (ii) Show and discuss the causes and effects of various forms of noise created within a receiver? (8) 2. (i) Describe the following (a) White noise (b) Noise temperature. (8) (ii) Illustrate how to represent narrowband noise. (8) 3. What is coherent detector? Derive an expression for SNR at input (SNRc) and output of (SNRo) of a coherent detector. (16) 4. (i) Express and derive the output SNR for FM reception. (8) (ii) Explain the significance of pre-emphasis and de-emphasis in FM system. (8) 5. (i) Describe and derive the figure of merit of a FM system. (12) (ii) Infer FM threshold effect. (4) 6. (i) Formulate the figure of merit for AM system for noncoherent system, with suitable assumptions. (12) (ii) Formulate the relationship between noise figure and equivalent noise temperature. (4) 7. (i) The three amplifiers 1, 2 and 3 have the following characteristics: F 1 =9dB, G 1 =50dB, F 2 =6dB, G 2 =30dB, F 3 =4db, G 3 =20dB. The amplifiers are connected in tandem. Discover which combination gives the lowest noise figure. (8) (ii) Analyze in detail about narrow band noise and the properties of in-phase and quadrature components of narrow band noise. (8) 8. (i) Solve the expression for figure of merit of DSB-SC receiver using coherent detection. (8) (ii) Define and explain the following: Gaussian noise and Gaussian

14 distribution and thermal noise. What type of PDF does the Gaussian noise follow? (8) 9. (i) Discuss how sine wave plus noise is represented. Obtain the joint PDF of such noise component. (8) (ii) Consider two amplifiers are connected in cascade. First stage amplifier has gain and noise figure as 10 db and 2 db. Second stage has noise figure of 3 db. Estimate the total noise figure. (8) 10. Evaluate the effective noise temperature of a cascade amplifier. Assess how the various noises are generated in the method of representing them. (16)

15 UNIT V INFORMATION THEORY Entropy - Discrete Memoryless channels - Channel Capacity -Hartley - Shannon law - Source coding theorem - Huffman & Shannon - Fano codes PART A Q. No Questions BT Level Domain 1. Define Shannon s channel coding theorem 2. Demonstrate entropy for a discrete memory less source. 3. State channel coding theorem 4. Point out the source coding techniques 5. Give the expression for code efficiency in terms of entropy. 6. Test whether the information of a continuous system is non negative? Give reason? 7. What is prefix code? 8. Calculate the channel capacity of binary synchronous channel with error probability of Define channel redundancy? 10. A telephone network has a bandwidth of 3.4 khz, Solve for the information capacity of the telephone channel for a signal-to-noise ratio of 30dB. 11. Explain the significance of the entropy H(X/Y) of a communication system where X is the transmitter and Y is the receiver. 12. Quote information rate? 13. Identify Shannon s Channel capacity theorem. 14. Summarize the properties of Entropy? 15. An event has six possible outcomes with probabilities 1/2, 1/4, 1/8, 1/16, 1/32, 1/32. Interpret the entropy of the system. 16. Formulate the equation for finding the entropy of a binary source. 17. Generalize the Shannon channel capacity for a discrete memory less channel

16 18. Differentiate between lossless and lossy coding. 19. A source emits one of the four symbols A, B, C and D with probabilities 1/3, 1/6, 1/4, 1/4 respectively the emissions of symbols by the source are statistically independent. Measure the entropy of the system 20. Recognize entropy and find the entropy of a DMS with probability s1=1/4, s2=1/4, and s3=1/4. PART B 1. Discuss Source coding theorem, give the advantage and disadvantage of channel coding in detail, and Summarize the data compaction. (16) 2. (i) Explain in detail Huffman coding algorithm and compare this with the other types of coding. (12) (ii) Describe S/N trade off. (4) 3. (i) Explain how channel capacity could be improved. Demonstrate the S/N trade off in detail. (10) (ii) List out the need for source coding and channel coding. (6) 4. (i) Identify about the lossy source coding schemes. (8) (ii) Source emits one of the five symbols A, B, C, D, E with probabilities 0.4, 0.19, 0.16, 0.15, 0.1 respectively the emissions of symbols by the source are statistically independent. Design a Shannon Fano code for the source. Discover the average code length and efficiency. (8) 5. Explain the properties of entropy and with suitable example, point out the entropy of binary memory less source. (16) 6. (i) What is Entropy? Explain the important properties of entropy. (8) (ii) Show that how will you use the source coding to increase average information per bit. (8) 7. Develop binary optical code for the following probability symbols using Huffman procedure and calculate entropy of the source, average code Length, efficiency, redundancy and variance 0.2, 0.18, 0.12, 0.1, 0.1, 0.08, 0.06, 0.06, 0.06, (16)

17 8. Write short notes on Differential entropy, derive the channel capacity theorem and discuss the implications of the information capacity theorem. (16) 9. Deduce the expression for channel capacity of a continuous channel. Find also the expression for channel capacity of continuous channel of an infinite bandwidth. Comment on the results. (16) 10. Describe binary symmetric channel? Derive channel capacity formula for symmetric Channel. (16)

VALLIAMMAI ENGINEERING COLLEGE

VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur 603 203. DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING QUESTION BANK SUBJECT : EC6402 COMMUNICATION THEORY SEM / YEAR: IV / II year B.E.