Virtual Labs

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

1. In a passband ASK system operating over an AWGN channel, which factor most significantly degrades its performance at low SNR?

a: Phase distortion Explanation

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b: Amplitude sensitivity to noise Explanation

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c: Bandwidth inefficiency Explanation

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d: Non-coherent demodulation Explanation

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2. In coherent passband FSK systems, how is intersymbol interference (ISI) minimized?

a: By increasing the frequency deviation Explanation

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b: By using orthogonal frequencies Explanation

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c: By applying raised cosine filtering Explanation

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d: By differential encoding Explanation

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3. Compared to passband PSK, passband FSK is generally more robust in which type of communication channel?

a: AWGN channels Explanation

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b: Frequency-selective fading channels Explanation

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c: Additive impulsive noise channels Explanation

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d: Flat-fading channels with strong phase jitter Explanation

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4. Why is coherent detection preferred over non-coherent detection in passband PSK systems?

a: It allows simpler hardware implementation. Explanation

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b: It improves BER performance by recovering phase information. Explanation

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c: It reduces bandwidth consumption. Explanation

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d: It makes the system more robust to frequency offset. Explanation

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5. What limits the minimum frequency separation in passband binary FSK for orthogonality?

a: Carrier phase offset Explanation

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b: Modulation index Explanation

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c: Symbol duration Explanation

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d: Signal power Explanation

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6. In passband ASK systems, what is the main reason it is rarely used in power-constrained wireless applications?

a: It requires excessive bandwidth. Explanation

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b: It suffers from poor spectral efficiency. Explanation

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c: It has high peak-to-average power ratio (PAPR). Explanation

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d: It is highly susceptible to amplitude variations from fading. Explanation

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7. For Binary PSK in a passband system, what is the theoretical BER expression over an AWGN channel with coherent detection?

a: Q(√(2Eb/N0)) Explanation

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b: Q(√(Eb/N0)) Explanation

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c: 1/2 × erfc(√(Eb/N0)) Explanation

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d: exp(−Eb/N0) Explanation

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8. What is the impact of Doppler spread on passband PSK systems in mobile channels?

a: Causes symbol timing offset Explanation

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b: Induces amplitude fading only Explanation

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c: Destroys carrier phase coherence Explanation

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d: Improves diversity performance Explanation

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9. In passband FSK systems, what is the role of the modulation index (h) in performance?

a: Controls symbol timing accuracy Explanation

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b: Determines orthogonality and bandwidth trade-off Explanation

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c: Reduces phase jitter Explanation

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d: Increases immunity to amplitude fading Explanation

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10. For a passband PSK system under ideal coherent detection, what characteristic of the constellation helps minimize BER?

a: Equal amplitude and orthogonal phase spacing Explanation

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b: Non-uniform amplitude levels Explanation

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c: Frequency separation between points Explanation

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d: Use of raised cosine pulses Explanation

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