Virtual Labs

Study of Modulation schemes with Memory, like MSK, GMSK etc.

1. How does the Gaussian filter bandwidth-time product (BT) in GMSK affect the system’s trade-off between spectral efficiency and inter-symbol interference (ISI)?

a: A higher BT value increases ISI but improves bandwidth efficiency Explanation

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b: A lower BT value reduces bandwidth but increases ISI Explanation

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c: A higher BT value reduces ISI but reduces bandwidth efficiency Explanation

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d: BT has no significant impact on ISI or spectral efficiency Explanation

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2. In GMSK, how does the presence of memory due to Gaussian filtering affect maximum likelihood sequence estimation (MLSE)?

a: It simplifies MLSE by reducing symbol dependencies Explanation

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b: It makes MLSE unnecessary since phase transitions are smooth Explanation

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c: It increases MLSE complexity due to inter-symbol correlation Explanation

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d: It has no effect because MLSE assumes memoryless input Explanation

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3. Why is MSK considered a special case of continuous phase frequency shift keying (CPFSK)?

a: Because it uses rectangular pulse shaping for frequency changes Explanation

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b: Because its modulation index is exactly 0.5 leading to phase continuity Explanation

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c: Because it allows abrupt phase changes at symbol boundaries Explanation

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d: Because it uses a variable frequency deviation per bit Explanation

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4. In the context of GMSK, which factor most directly determines the extent of inter-symbol interference (ISI)?

a: Phase offset of the carrier Explanation

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b: Shape and duration of the Gaussian filter Explanation

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c: Bit error rate of the demodulator Explanation

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d: Carrier-to-noise ratio (CNR) Explanation

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5. How does the minimum frequency spacing in MSK ensure orthogonality between symbols?

a: By keeping symbol energy below a defined threshold Explanation

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b: By ensuring the integral of cross-product between basis functions is zero Explanation

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c: By enforcing amplitude normalization over the bit duration Explanation

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d: By using Gaussian filtering to shape transitions Explanation

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6. Why is non-coherent detection more challenging in GMSK compared to MSK?

a: Because GMSK has higher peak-to-average power ratio Explanation

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b: Because GMSK introduces memory through pulse shaping Explanation

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c: Because GMSK uses multi-level amplitude shifts Explanation

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d: Because GMSK requires IQ demodulation Explanation

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7. How does continuous phase modulation in MSK help in reducing spectral side lobes?

a: By eliminating the need for guard intervals Explanation

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b: By spreading the signal energy evenly across the spectrum Explanation

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c: By smoothing phase transitions, reducing abrupt changes in the waveform Explanation

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d: By ensuring orthogonality among all possible symbol pairs Explanation

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8. In terms of power spectral density (PSD), which statement best describes GMSK?

a: It exhibits nulls at integer multiples of the symbol rate Explanation

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b: Its PSD is sharply bounded due to abrupt phase changes Explanation

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c: It has a smoother PSD roll-off than MSK due to pulse shaping Explanation

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d: Its PSD contains impulses due to phase discontinuities Explanation

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9. What is the role of coherent demodulation in improving BER performance for GMSK signals?

a: It suppresses adjacent channel interference Explanation

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b: It enables maximum phase deviation for better noise immunity Explanation

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c: It provides optimal symbol decisions by tracking phase accurately Explanation

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d: It filters out Gaussian noise before detection Explanation

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10. Why is GMSK preferred in GSM systems over QPSK or MSK?

a: Because it has a lower implementation cost Explanation

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b: Because it avoids amplitude fluctuations and has spectral compactness Explanation

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c: Because it requires fewer synchronization bits Explanation

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d: Because it can be demodulated using envelope detection Explanation

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