EC3491 Communication Systems Important Questions

EC3491 Communication Systems Important Questions

Unit 1

1. Draw and explain the working of a square law modulator and square law detector.
2. Explain super heterodyne receiver and its advantages over Tuned Radio-Frequency receivers.
3. State and illustrate Hilbert transform.
4. State and prove any three properties of Hilbert transform.
5. Elaborate on pre-envelope and complex envelope amplitude modulation techniques.
6. Derive the mathematical expressions for DSB-SC and SSB-SC modulated signals.

Unit 2

1. Derive the output signal-to-noise ratio for an AM receiver using envelope detection and hence obtain the figure of merit, assuming that the noise is additive, white and Gaussian. Compare the results with that of SSB and DSB-SC receivers.
2. Draw and explain PPM and PWM signal generation circuit for PAM signal.
3. Compare PAM, PPM and PWM.
4. If the analog signal to be quantized (unipolar quantization with 4 bits) has a range from 0 V to 10 V, determine number of quantization level, quantization step (resolution), quantization error when the analog input is 7.4 V, quantization level when the analog voltage is 7.4 V, and its binary code.
5. Differentiate between TDM and FDM. Give one application for each.
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Unit 3

1. Derive the expressions for quantization noise, receiver noise and overall signal-to-noise ratio of a DM system.
2. Explain the operation of a cyclic code (7,3) with a suitable generator polynomial.
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Unit 4

1. Derive the probability of error for Binary FSK modulation scheme and compare its BER performance with that of BPSK modulation scheme.
2. Derive the expression for the bit error probability of a QPSK system.
3. Compare the merits and demerits of BPSK and QPSK w.r.t power spectral density (PSD) and bit error rate (BER) with essential illustration.
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Unit 5

1. Discuss the different modulation schemes in digital communication and derive the probability of error for any bandwidth efficient modulation technique.
2. State and prove Nyquist first criterion for zero ISI.
3. Explain in detail about Channel Equalizer by focusing more on zero forcing equalizer (ZFE) and minimum mean-square error equalizer (MMSEE) with necessary figures, block diagrams and mathematical expressions.
4. Illustrate and elaborate the following concepts with mathematical expressions.
   (i) Receiver Noise.
   (ii) Probability of False Alarm.
   (iii) The Matched Filter.