Virtual Labs

Study of effect of channel on system with various modulation

Question 1: In a Rayleigh fading channel, what statistical property of the envelope causes deep signal fades?

a: High average power of multipath components. Explanation

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b: Zero mean of the in-phase and quadrature components. Explanation

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c: Exponential decay of the amplitude envelope. Explanation

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d: Constant phase rotation across paths. Explanation

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Question 2: Why does higher-order modulation (like 64-QAM) suffer more in Rayleigh fading than lower-order schemes (like BPSK)?

a: Because higher-order schemes require narrower bandwidths. Explanation

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b: Because symbol spacing is smaller, making them more error-prone during fades. Explanation

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c: Because they have lower average power. Explanation

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d: Because they introduce non-linearity into the channel. Explanation

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Question 3: How does a frequency-selective Rayleigh fading channel affect an OFDM system compared to a flat-fading channel?

a: All subcarriers experience equal gain and phase shifts. Explanation

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b: Some subcarriers are severely attenuated while others are not. Explanation

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c: It has no significant impact because OFDM uses cyclic prefixes. Explanation

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d: It affects the bit duration rather than the frequency response. Explanation

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Question 4: In a high-mobility environment with severe Doppler spread, which design aspect is most affected?

a: The peak-to-average power ratio (PAPR). Explanation

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b: The carrier frequency selection. Explanation

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c: The coherence time of the channel. Explanation

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d: The baseband signal bandwidth. Explanation

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Question 5: How does increasing diversity order affect the cumulative distribution function (CDF) of received SNR in Rayleigh fading?

a: The CDF shifts left, indicating more outage probability. Explanation

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b: The CDF becomes more linear. Explanation

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c: The tail of the CDF becomes steeper, reducing probability of deep fades. Explanation

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d: The CDF becomes uniform. Explanation

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Question 6: In a Rayleigh fading channel with AWGN, which metric most accurately predicts system reliability?

a: Instantaneous received power. Explanation

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b: Symbol energy to noise power spectral density ratio (Es/N0). Explanation

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c: Average signal-to-noise ratio (SNR). Explanation

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d: Outage probability at a target SNR threshold. Explanation

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Question 7: When modeling a multipath Rayleigh fading channel, the autocorrelation function of the fading envelope depends on:

a: Modulation index and bit rate. Explanation

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b: Doppler spread and time separation. Explanation

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c: SNR and carrier-to-noise ratio. Explanation

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d: Delay spread and antenna gain. Explanation

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Question 8: In an AWGN channel, which of the following pairs offers the best tradeoff between spectral efficiency and BER?

a: BPSK with repetition coding. Explanation

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b: 64-QAM with no coding. Explanation

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c: 16-QAM with convolutional coding. Explanation

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d: QPSK with zero padding. Explanation

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Question 9: Which assumption is violated when Rayleigh fading is modeled as stationary over long intervals?

a: The in-phase and quadrature components are Gaussian. Explanation

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b: The fading process has a constant Doppler spectrum. Explanation

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c: The signal experiences independent fading at each instant. Explanation

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d: The channel autocorrelation depends only on time difference. Explanation

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Question 10: Which method enables coherent detection in Rayleigh fading when the channel state is not known at the receiver?

a: Minimum Euclidean distance decoding. Explanation

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b: Differential modulation (e.g., DPSK). Explanation

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c: Matched filtering. Explanation

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d: Zero-forcing equalization. Explanation

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