EC-502 Digital Communication - May 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWrite sampling theorem for low pass and band pass signals. Also explain time division multiplexing in brief.
   How to answer

   • Statement of low-pass sampling theorem with Nyquist rate
   • Statement of band-pass sampling theorem
   • Block / concept of TDM transmitter and receiver
   • Multiplexing / demultiplexing operation in brief
2. 7 Marks
   bCompare PAM, PWM, PPM and describe generation and detection of any one.
   How to answer

   • Comparison of PAM, PWM, PPM on amplitude, width, position and noise
   • Generation method block diagram
   • Detection method block diagram
   • Detailed description of generation and detection of any one
3. 7 Marks
   aDiscuss following in brief:

   1. i)Quantization and quantization noise
   2. ii)Delta and adaptive modulation
   3. iii)RZ signaling and bipolar signaling
   How to answer

   • Definition of quantization and types
   • Quantization noise derivation / expression
   • Delta modulation and adaptive delta modulation principle
   • RZ signaling vs bipolar signaling waveforms
4. 7 Marks
   bExplain companding and inter symbol interference.
   How to answer

   • Companding definition and need - A-law / mu-law
   • Compander characteristics diagram
   • Inter symbol interference causes
   • Methods to reduce ISI
5. 7 Marks
   aDifferentiate following with neat diagram.

   1. i)ASK and BPSK
   2. ii)QPSK and DPSK
   3. iii)Coherent and non coherent BFSK
   How to answer

   • Principle and waveform / block diagram of each scheme
   • Comparison table of ASK vs BPSK, QPSK vs DPSK, coherent vs non-coherent BFSK
   • Neat diagrams for each pair
6. 7 Marks
   bDiscuss spectral properties of QPSK and MSK.
   How to answer

   • Power spectral density expression of QPSK
   • Power spectral density expression of MSK
   • Bandwidth and sidelobe comparison
   • Conclusion on spectral efficiency
7. 7 Marks
   aWhat is Grain Schmidt orthogonalization procedure? Explain the concept of signal space for the computation of probability of error.
   How to answer

   • Gram-Schmidt orthogonalization steps and formulas
   • Orthonormal basis construction
   • Signal space / constellation representation
   • Use of signal space for error probability calculation
8. 7 Marks
   bCalculate error probability for BPSK, QPSK and QAM systems.
   How to answer

   • Signal space and decision regions for BPSK
   • Error probability derivation $P_e = Q\left(\sqrt{2E_b/N_0}\right)$
   • Extension to QPSK and QAM expressions
   • Comparison of results
9. 7 Marks
   aDescribe following in brief:

   1. i)Entropy and information rate
   2. ii)BW and signal to noise ratio trade off
   3. iii)Linear block codes and cyclic codes
   How to answer

   • Entropy and information rate definitions and formulas
   • Bandwidth vs SNR trade-off from Shannon-Hartley
   • Linear block codes principle
   • Cyclic codes principle
10. 7 Marks
    bState Shannon's theorem and Shannon Hartley theorem. Also describe concept of convolution codes.
    How to answer

    • Shannon's channel coding theorem statement
    • Shannon-Hartley theorem $C = B \log_2(1+S/N)$
    • Convolution codes concept - encoder, constraint length
    • Trellis / Viterbi decoding idea
11. 7 Marks
    aHow differential encoding is achieved? Write advantages and disadvantages of differential encoding.
    How to answer

    • Differential encoding rule and circuit
    • Advantages such as phase ambiguity resolution
    • Disadvantages such as error propagation
    • Example waveform
12. 7 Marks
    bExplain following in detail:

    1. i)Natural sampling and flat top sampling
    2. ii)Manchester code
    3. iii)Polar signaling
    How to answer

    • Natural vs flat-top sampling operation and spectra
    • Manchester code rules and waveform
    • Polar signaling types and waveforms
    • Advantages / applications
13. 7 Marks
    aDescribe eye pattern and on-off signaling.
    How to answer

    • Eye pattern formation and interpretation
    • ON-OFF signaling waveform
    • Effect of ISI and noise on eye opening
    • Applications
14. 7 Marks
    bDiscuss following in brief with suitable examples.

    1. i)Concept of M-ary PSK and M-ary FSK
    2. ii)Matched filter and correlator detector
    How to answer

    • M-ary PSK / FSK signal representation and examples
    • Matched filter principle and impulse response
    • Correlator detector operation
    • Comparison with examples
15. 7 Marks
    aDraw encoder and decoder circuits and describe burst error correcting codes.
    How to answer

    • Encoder circuit diagram for burst error correcting code
    • Decoder circuit diagram
    • Burst error correction principle e.g. Fire / interleaved codes
    • Example of correction capability
16. 7 Marks
    bWrite technical short note on following:

    1. i)Crosstalk and aliasing
    2. ii)Encoding techniques
    3. iii)Minimum shift keying
    4. iv)Comparison of different modulation techniques.
    How to answer

    • Crosstalk and aliasing causes and effects
    • Encoding techniques overview
    • Minimum shift keying principle and spectrum
    • Comparison table of modulation techniques