Department of Electronics and Communication Engineering 1

UNIT I SAMPLING AND QUANTIZATION Pulse Modulation 1. Explain in detail the generation of PWM and PPM signals (16) (M/J 2011) 2. Explain in detail the concept of PWM and PAM (16) (N/D 2012) 3. What is the classification of communication channels? Explain the mathematical model of any two communications channels. (16) (M/J 2011) 4. Draw a neat block diagram of a typical digital communication system and explain the functions of the key signal processing blocks.( 16) (N/D 2010) 5. Distinguish between base band signaling and band pass signaling. (6) (N/D 2010) Channel Classification 6. Explain Binary symmetric channel and Gaussian channel with supporting mathematical models. (10) (N/D 2010) 7. Explain in detail, the mathematical models of communication channel. (16) (N/D 2011) Geometric Representation of Signals 8. Derive an expression for geometrical representation of a signal. (8) (M/J2006) 9. Explain the Gram Schmidt Orthogonalisation Procedure for obtaining the basis set. (8) (M/J 2012) 10. Explain in detail the Gram Schmidt Orthogonalisation Procedure (16) (N/D 2011) 11. Determine the orthonormal basis set for the following set of signals using Gram- Schmidt orthogonalization procedure. (16) (N/D 2006) Spectral Waveform Coding 1. Explain in detail, the uniform quantization process. (8) (MAY 2011) 2. Explain in detail, the temporal waveform coding. (8) (MAY 2011) 3. Explain spectral waveform encoding process. (8) (MAY 2011) 4. Compare the various speech encoding techniques. (8) (MAY 2011) Sampling Department of Electronics and Communication Engineering 1

5. State Nyquist sampling theorem. What is the validity of an analog signal having Fourier transform X(f) that is zero outside the interval ( -fm < f < +fm)? (8) (DEC2010) 6. With necessary sketches and expressions, explain flat top sampling. (8) (APR/MAY2005) 7. With necessary derivation, prove that if a signal contains no frequencies higher than W hertz, it can be reconstructed from its samples at a sequence of points spaced 1/2W seconds apart. (8) (APR/MAY2005; MAY/JUN2006) 8. With neat diagram and necessary equations, explain the concept of sampling and reconstruction of signals. (8) (MAY/JUNE 2009) UNIT-II BASEBAND FORMATTING TECHNIQUES Encoding Techniques for analog sources 9. Draw the block diagram of differential PCM and explain the function of each block.(8) 10. Derive an expression for the quantization noise and Signal to Noise Ratio in a PCM system that uses uniform quantizer.(10) 11. A sinusoidal signal is transmitted using PCM. An output SNR of 55.8 db is required. Find the number of representation levels required to achieve this performance. (6) 12. Derive the expression for SNR in PCM system and compare it with delta modulation. Explain the process to improve SNR in PCM system. (10) (MAY/JUN2006) 13. Explain the process of quantization, encoding and decoding in PCM. How is DPCM better than PCM? (16) (MAY/JUN 2007) 14. Explain uniform and non uniform quantization. (4) (APR/MAY2008) 15. (a) Draw the block diagram of Differential Pulse Code Modulation scheme and explain the principle in detail.(10) (APR/MAY 2008) (b) Derive an expression for the processing gain of a DPCM system. (4) (APR/MAY 2008) (c) An existing standard PCM system for voice signal is replaced by a DPCM of processing gain 6dB, while maintaining the (SNR) Q. What is the reduction in the bit rate achieved by DPCM? (3) (APR/MAY 2008) 16. (a) Determine the number of quantization levels for an uniform quantizer (4) (b) What is the need of non-uniform quantization for speech signal (2) (APR/MAY 2008) (c) Write the principle of compander used for speech signal. (4) (APR/MAY 2008) (d) Calculate the bit rate of a delta modulator for a sampling rate of 40 ksamples/sec. (2) (APR/MAY 2008) (e) How does adaptive delta modulation alleviate the problems associated with delta modulation scheme? (4) (APR/MAY 2008) 17. Derive an expression for the processing gain of DPCM. (NOV/DEC2007) Department of Electronics and Communication Engineering 2

18. Draw the block diagram and explain in detail the process of PCM system. (10) (NOV/DEC 2008) 19. An analog voltage waveform with an absolute bandwidth of 100 Hz and an amplitude range of 10 V to +10 V is to be transmitted over a PCM system with 0.1% accuracy full scale. (a) Determine the minimum sampling rate needed.(4) (b) Determine the number of bits needed in each PCM word.(4) (c) Determine the minimum bit rate required in the PCM signal.(4) (d) Determine the minimum absolute channel bandwidth required for transmission of PCM signal. (4) 20. What is the need for companding in PCM? Draw the transfer characteristics of a companding system. (4) (MAY/JUNE 2009) Delta Modulation 21. Explain the principle of delta modulation. Also derive an expression for average output noise power. (8) MAY/JUN2006),(M/J 2009) 22. Explain in detail about delta modulation and the types of quantization errors with a neat block diagram. (12) (APR/MAY2005) 23. How does ADM elevate problems associated with DM? (NOV /DEC2007) 24. Explain the two types of quantization noise in delta modulation system.(8) (NOV /DEC2007) 25. Compare the principles of Delta Modulation with Adaptive Delta Modulation systems. (6) (NOV/DEC 2008) 26. What is meant by compander? Explain the two types of compression laws. (8) (APR/MAY2004) 27. Explain the frame format and signaling scheme used in T1 carrier system. (8) (APR/MAY2004) 28. What is meant by slope overload distortion in DM? Write the condition to be satisfied to avoid this distortion.(8) 29. (a) Explain in detail, the principle of Adaptive Delta Modulation. (10) (b) List out the advantages and limitations of PCM. (6) (N/D 2008) (M/J 2009) 30. (a) Explain in detail the concept of digital multiplexing and demultiplexing (8) (M/J 2009) (b) How is PCM influenced by noise sources? Explain in detail. (8) (M/J 2009) Department of Electronics and Communication Engineering 3

31. A PCM system uses a uniform quantizer followed by a 7 bit binary encoder. The bit rate of the system is equal to 50 10 6 bits per second. (a) What is the maximum bandwidth for the system to operate satisfactorily? (b) Determine the output Signal to Noise Ratio when a full load sinusoidal modulating wave of frequency 1 MHz is applied. (8) 32. Explain the principle of delta modulation and derive the expression for thermal noise in delta modulation. (8) (NOV /DEC2007) UNIT-III BASEBAND COMMUNICATION Receiving Filter 1. Derive the expression for bit error probability of a matched filter. (16) (MAY 2011) 2. Explain the signal design techniques to compensate ISI illumination. (16) (MAY 2011) 3. What is meant by matched filter? Compare its functioning with a correlator. (10) (NOV 2010) 4. How can a matched filter maximize the SNR for a given transmitted symbol? Explain in detail (6) 5. What is meant by Inter Symbol Interference (ISI)? Explain in detail, the Nyquist criterion for minimizing ISI. Explain the difficulties in implementing it, in a practical system. (16) 6. (a) What is meant by ISI? Explain the cause for ISI and Nyquist criteria for distortionless transmission. (10) (MAY/JUNE 2009) (b) Explain the base band M-ary PAM transmission. (6) (MAY/JUNE 2009) Equalizing Filter 7. What does the term equalization refer to? Explain the methods to implement equalization using transversal filters.(10) (NOV 2010) 8. Sketch the time response and frequency response of signal with raised cosine pulse spectrum.(8) (APR/MAY2004) 9. What is meant by ideal Nyquist channel? What are its merits and limitations? (8) 10. Derive the equation for the impulse response coefficients of the zero forcing equalizer. (8) 11. Explain the application of adaptive equalizers for telephone channel. (4) 12. Draw and explain the block diagram of adaptive equalization (8) (NOV /DEC2007) Department of Electronics and Communication Engineering 4

13. Design a 3-tap equalizer to reduce ISI due to P r (t). (APR/MAY2008) Detectors 14. Why is precoding used with duo binary signaling scheme? Draw the block diagram of precoder and explain its operation. (8) (APR/MAY2004) 15. Draw the block diagram of an adaptive filter and explain the LMS algorithm. (10)(A/M2004) 16. How is eye pattern used to study the performance of a data transmission system? (6) (APR/MAY2004) 17. Draw the block diagram of the duo binary signaling scheme and derive the overall frequency response of this scheme.(16) (NOV/DEC2004, NOV /DEC2007) 18. Derive an expression for Nyquist criterion for distortionless base band transmission for zero Inter Symbol Interference. (6) (APR/MAY2005) 19. Explain the eye pattern and adaptive equalization for data transmission. (10) (APR/MAY2005, MAY/JUN2006) 20. List out the merits and demerits of duo binary signaling. (6) 21. The binary data (0 1 1 1 0 0 1 0 1) are applied to the input of a duo binary encoder. Construct the duo binary encoder and the corresponding receiver output, without precoder. Due to error during transmission, the level produced by 3 rd digit is reduced to zero, construct the new receiver output. (10) (NOV/DEC2006) 22. Explain the following: (a) Adaptive equalization (b) Base band binary PAM system. (MAY/JUNE2007) 23. Compare base band binary PAM system with BFSK. (NOV /DEC2007) 24. Derive the expression for probability of error of a matched filter.(8) (NOV /DEC2007) 25. Explain correlative level coding and adaptive equalization of baseband transmission. (16) (NOV/DEC 2008) 26. (a) Explain duo binary encoding scheme and its error propagation. (10) (M/J 2009) (b)explain the two operating modes of adaptive equalizers (6) (MAY/JUNE 2009) 27. Explain the modified duo binary signaling scheme with neat sketches. (10) (MAY/JUNE 2009) Department of Electronics and Communication Engineering 5

28. Compare the power spectra of different binary formats. (6) (MAY/JUNE 2009) UNIT-IV BASEBAND SIGNAL TRANSMISSION AND RECEPTION Bandpass signal Transmission and Reception ASK, PSK, QPSK, MSK 1. Derive the bit error probability of coherent ASK, PSK and FSK systems. Compare their performances. ` (MAY 2011) 2. Explain in detail QPSK Signaling. (MAY 2011) 3. Derive bit error probability of QPSK receiver. Compare it with PSK receiver (MAY 2011) 4. Distinguish between coherent and non coherent scheme. (NOV 2010) 5. Explain non coherent detection method of BFSK Signaling. (NOV 2010) 6. Explain QPSK transmitter and coherent QPSK receiver with relevant diagram. (10) (APR/MAY2004,MAY/JUN2006, NOV/DEC2007) 7. Compare the performances of coherent PSK, coherent QPSK and coherent FSK.(6)(APR/MAY2004) 8. Draw the block diagram of MSK transmitter and explain the functions of each block. (8) 9. Explain the generations of MSK signal from CPSK signal. (8) 10. With necessary equations and signal space diagram, determine the probability of error for coherent binary FSK systems.(12) (APR/MAY2005) 11. Explain BPSK signal transmission and coherent BPSK reception with suitable diagrams. Derive an expression for the probability of symbol error.(16) 12. Explain in detail the FSK system with necessary equations and signal space diagram.(16) (MAY/JUN2006, NOV /DEC2007, APR/MAY2008) 13. Derive the probability of error in terms of E b /N 0 for QPSK.(8) (MAY/JUN2006, APR/MAY2008) 14. Draw the block diagram of MSK transmitter and explain the function of each block with the constellation diagram.(16) (MAY/JUNE,2007) 15. What are the advantages and disadvantages of MSK when compared with QPSK system? (6) 16. (a) Explain in detail carrier synchronization of QPSK signal.(6) (b) Explain the detection of binary FSK signal with block diagram. (7) (c) Explain binary PSK signal with geometrical representation. (3) (NOV /DEC2007) (NOV /DEC2007) 17. Draw the block diagrams of MSK transmitter and receiver and explain the functions of each block. Draw the constellation diagram. Derive the probability of error.(16) (NOV/DEC 2008) Department of Electronics and Communication Engineering 6

18. Distinguish between: (a) Coherent PSK and DPSK (4) (b) Coherent FSK and non-coherent FSK (4) (c) Coherent PSK and QPSK (4) (d) Coherent FSK and coherent MSK (4) (NOV/DEC 2008) 19. Explain the generation, detection, signal space diagram, bit error probability and power spectra of QPSK. (16) (MAY/JUNE 2009) 20. (a) Explain carrier and symbol synchronization. (10) (b) Compare the Digital modulation techniques in terms of bit error rate and bandwidth efficiency. (6) (MAY/JUNE 2009) 21. With necessary equations and signal space diagram, determine the probability of error for coherent binary PSK system. (16) (MAY/JUNE 2009) UNIT-V ERROR CONTROL CODING TECHNIQUES Convolutional Code 1. For a (2,1) convolution coder with constraint length 6, draw the tree diagram, state diagram and trellis diagram for the assumed coder. (MAY 2011) 2. Explain the encoding process of convolution codes with a suitable example. (16) (MAY2010) 3. Explain tree diagram, trellis diagram and state transition diagram of convolutional codes. (16) (A/M 2010) 4. (a)draw the block diagram of rate ½ convolutional encoder with constraint length 3. What is the generator polynomial of the encoder? Compute the encoded sequence you have drawn, corresponding to the message (10011). (12) (APR/MAY2004) (b) Draw the trellis diagram for the obtained encoded sequence. (4) (APR/MAY2005) 5. Draw the diagram of the ½ rate convolutional encoder for the generator polynomial g (1) (D) = 1+D and g (2) (D) = 1+D+D 2. Compute the encoder output for input sequence 101101. (10) 6. What is meant by free distance of a convolutional code? How does it affect the coding gain and the number of errors to be corrected? (6) 7. Explain in detail Viterbi-decoding algorithm.(12) (APR/MAY2005; MAY/JUN2005,(APR/MAY2008) 8. Consider a rate ½, non systematic convolutional code with, g (1) = {1,0,1} and g (2) ={1,1,1}. Department of Electronics and Communication Engineering 7

Determine the encoder output corresponding to the data sequence {1, 0, 1, 0, 1}. If the first and the fourth bit of the encoded sequence are affected during transmission, Explain the error correcting capability of the Viterbi algorithm. (16) 9. (a) For the (1/2) convolutional coder, draw the state and the trellis diagram for the input sequence 11010100. (8) (b) What are cyclic codes? List out the merits and demerits of cyclic codes. (8) (MAY/JUNE 2009) 10. Explain the convolutional decoder algorithm for the encoder of constraint length 3 and code rate ½. (16) (NOV /DEC2007) Classification of Line codes 11. Derive the power spectra of polar codes and on-off codes, and explain their characteristics. (16) (MAY 2011) Linear Block Codes 12. Determine the (7, 4) linear systematic block code word corresponding to 1101. Assume a suitable generator matrix. (MAY 2011) 13. For (6, 3) systematic linear block code, the codeword comprises I1, I2, I3, P1, P2, P3 where the 3 parity bits P1, P2, P3 are formed from the information bits as follows: a) P1 = I1 + I2 b)p2 = I1 + I3 c)p3 = I2 + I3 Determine the parity check matrix, generator matrix, all possible code words, minimum weight, minimum distance, the error correcting and detecting capability of the code.(16) (MAY/JUNE 2010) 14. Write the generator matrix and parity check matrix of (7, 4) Hamming code. (8) (APR/MAY2004) 15. Explain in detail decoding procedure for linear block code. (6) (APR/MAY2004) 16. Determine the code words for (7, 4) Hamming code. (8) (MAY/JUN2006) 17. State and prove the properties of syndrome decoding. (6) (APR/MAY2005, MAY/JUN2006) 18. Explain in detail the features of RS code. (4) (APR/MAY2004) 19. Explain any four characteristics of the following block codes a) BCH codes b) CRC codes c) Maximum length codes. (12) 20. Determine the generator and parity check matrix for (5, 1) repetition code. (4) 21. Determine the syndromes for all five probable signal error patterns in (5, 1) repetition code. (6) (MAY/JUN2006) Department of Electronics and Communication Engineering 8

22. Prove that the minimum distance of a linear block code is equal to the minimum weight of any non-zero word in the code. (4) (APR/MAY2008) 23. (a) The parity check matrix of a particular (7, 4) linear block code is given by 1 1 1 0 1 0 0 H = 1 1 0 1 0 1 0 1 0 1 1 0 0 1 Calculate the generator matrix. (6) (b) Explain the coding and decoding procedure of a linear block codes. (10) (MAY/JUNE 2009) Cyclic code 24. With necessary polynomial of a (7, 4) cyclic code is g(x) = 1 + x + x 3. Determine the systematic code word for the message vector M = 1011. (8) 25. A (15, 5) linear cyclic code has a generator polynomial, g(d) = 1+D+D 2 +D 4 +D 5 +D 8 +D 10. Draw the block diagrams of an encoder and syndrome calculator for the given code. Find the code polynomial in the systematic form, for the message polynomial m(d) = 1+D 2 +D 4. Is y (D) = 1+D 4 +D 6 +D 8 +D 14, a code polynomial? If not, calculate the syndrome of y (D). (16) 26. Explain the implementation of cyclic encoder and decoder based on linear feedback shift registers.(16) Department of Electronics and Communication Engineering 9