Virtual Labs

Amplitude shift keying, Frequency Shift Keying, Binary Phase Shift Keying: Generation and Detection

1. Why is coherent detection preferred over non-coherent detection in PSK systems under AWGN?

a: It simplifies the receiver design. Explanation

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b: It does not require carrier synchronization. Explanation

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c: It provides better bit error performance. Explanation

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d: It consumes less power. Explanation

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2. Which mathematical expression best represents the power spectral density (PSD) of a Binary FSK signal with non-coherent detection?

a: S(f) = sinc²(f) Explanation

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b: S(f) = 1/T * [δ(f - f1) + δ(f - f2)] Explanation

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c: S(f) = (A²/2) * [rect((f - f1)/B) + rect((f - f2)/B)] Explanation

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d: S(f) = A² * cos(2πft) Explanation

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3. Consider a 4-PSK system. What is the minimum Euclidean distance between symbols if the signal power is normalized to 1?

a: 2 Explanation

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b: 1 Explanation

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c: √2 Explanation

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d: √2/2 Explanation

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4. In digital modulation, what factor primarily determines the bandwidth efficiency of a scheme?

a: Symbol rate alone Explanation

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b: Modulation index Explanation

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c: Number of bits per symbol Explanation

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d: Carrier frequency Explanation

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5. In QPSK, what is the theoretical bit error rate (BER) under AWGN with coherent detection and Eb/N0 = 10 dB?

a: Q(√(2*10)) Explanation

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b: Q(√(20)) Explanation

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c: 0.5 * erfc(√(10)) Explanation

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d: Q(√(10)) Explanation

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6. In M-ary PSK, what is the primary trade-off when increasing the value of M?

a: Lower data rate but better noise immunity Explanation

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b: Higher bandwidth requirement and lower complexity Explanation

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c: Higher spectral efficiency but increased symbol error rate Explanation

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d: Increased power efficiency but reduced robustness Explanation

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7. Which modulation technique exhibits a constant envelope, making it suitable for nonlinear power amplifiers?

a: QAM Explanation

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b: ASK Explanation

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c: GMSK Explanation

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d: PSK Explanation

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8. A digital system transmits 16-QAM symbols at 1 Msymbol/s. What is the bit rate of the system?

a: 1 Mbps Explanation

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b: 2 Mbps Explanation

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c: 4 Mbps Explanation

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d: 16 Mbps Explanation

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9. How does Gray coding benefit digital modulation schemes like QAM?

a: Reduces signal power consumption Explanation

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b: Minimizes adjacent symbol errors Explanation

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c: Decreases required bandwidth Explanation

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d: Improves synchronization time Explanation

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10. For a signal with bit rate R and modulation with k bits per symbol, what is the symbol rate?

a: R + k Explanation

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b: R / k Explanation

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c: R × k Explanation

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d: R² / k Explanation

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