Virtual Labs

Pass band implementation of Amplitude shift keying, Frequency Shift Keying, Binary Phase Shift Keying: Generation and Detection

1. In coherent passband FSK systems, what is the most significant technical challenge that must be addressed in high-mobility wireless environments?

a: Maintaining precise carrier phase alignment over fast fading channels Explanation

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b: Achieving orthogonal frequency separation under limited bandwidth Explanation

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c: Maintaining constant envelope amplitude Explanation

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d: Minimizing group delay distortion Explanation

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2. Why does passband ASK perform poorly in environments with multipath fading and Doppler effects?

a: The receiver cannot distinguish closely spaced frequencies Explanation

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b: Amplitude information is highly susceptible to deep fades and phase distortion Explanation

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c: Carrier frequency cannot be synchronized without Doppler tracking Explanation

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d: ASK requires adaptive filtering to decode phase transitions Explanation

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3. Among passband ASK, FSK, and PSK, which is the most bandwidth-efficient under ideal channel conditions and why?

a: ASK, because it encodes directly in amplitude Explanation

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b: FSK, due to orthogonal frequency spacing Explanation

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c: PSK, due to the possibility of higher-order phase states with minimal bandwidth expansion Explanation

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d: All are equally efficient when error-correcting codes are used Explanation

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4. What is the practical limitation of increasing the number of phase states in a passband PSK system?

a: It increases spectral efficiency linearly with no trade-offs Explanation

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b: It decreases SNR requirement per bit Explanation

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c: It reduces symbol duration significantly Explanation

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d: It reduces phase separation, increasing symbol error probability Explanation

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5. Why is non-coherent FSK preferred in low-complexity wireless sensor nodes despite slightly worse BER than coherent FSK?

a: It enables higher bandwidth efficiency Explanation

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b: It simplifies receiver design by removing the need for carrier phase tracking Explanation

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c: It uses constant power transmission, unlike coherent FSK Explanation

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d: It is more robust to Doppler spread in fast fading channels Explanation

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6. Why is PSK considered more power-efficient than FSK or ASK under the same bandwidth constraints in a passband system?

a: PSK transmits using multiple carriers simultaneously Explanation

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b: PSK uses phase transitions that are less affected by amplitude noise Explanation

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c: PSK occupies wider bandwidth, allowing better energy spread Explanation

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d: FSK and ASK require frequent carrier synchronization Explanation

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7. In which scenario would passband FSK be preferred over PSK for digital communication?

a: When maximizing bandwidth efficiency is the top priority Explanation

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b: When constant-envelope modulation is needed for nonlinear RF amplifiers Explanation

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c: When precise carrier phase synchronization is available Explanation

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d: When high-order modulation is required for very high data rates Explanation

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8. Why is ASK rarely used in modern passband wireless systems, even though it’s simple to implement?

a: It requires complex carrier tracking algorithms Explanation

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b: It performs poorly under amplitude fading and interference Explanation

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c: It cannot be demodulated with envelope detectors Explanation

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d: It is illegal for use in licensed RF bands Explanation

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9. Why does the BER increase in higher-order passband PSK systems such as 8-PSK or 16-PSK?

a: They require greater frequency spacing between symbols Explanation

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b: The symbols become closer in phase, making them harder to distinguish under noise Explanation

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c: They introduce amplitude modulation into the signal Explanation

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d: They require non-constant envelope detectors Explanation

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10. Which of the following will **most effectively** improve the performance of a passband PSK system in a fading channel?

a: Increasing carrier frequency Explanation

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b: Using Gray coding Explanation

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c: Employing diversity techniques such as MIMO or time diversity Explanation

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d: Switching to ASK modulation Explanation

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