Virtual Labs

Study of effect of channel on system with various modulation

1. In a Rayleigh fading channel, which of the following strategies best mitigates deep fades without increasing transmit power?

a: Switching to high-order QAM. Explanation

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b: Implementing time diversity techniques. Explanation

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c: Reducing symbol rate. Explanation

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d: Using narrowband signals. Explanation

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2. Which mathematical distribution best models the amplitude of a received signal in a Rayleigh fading environment without a line-of-sight (LoS) path?

a: Gaussian distribution Explanation

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b: Rayleigh distribution Explanation

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c: Rician distribution Explanation

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d: Poisson distribution Explanation

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3. When AWGN is added to a Rayleigh fading channel, what combined impact does it have on BER performance?

a: It significantly improves BER performance. Explanation

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b: It results in a double-logarithmic BER increase. Explanation

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c: It causes a rapid BER degradation, especially at low SNR. Explanation

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d: It has negligible effect due to fading dominating. Explanation

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4. Which diversity technique specifically targets the frequency-selective nature of multipath fading?

a: Time diversity Explanation

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b: Spatial diversity Explanation

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c: Frequency diversity Explanation

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d: Polarization diversity Explanation

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5. In an OFDM system under Rayleigh fading and AWGN, which of the following improves robustness without bandwidth expansion?

a: Increasing subcarrier spacing Explanation

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b: Applying forward error correction and interleaving Explanation

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c: Using fewer subcarriers Explanation

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d: Lowering modulation order on each subcarrier Explanation

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6. Under a Rayleigh fading model, what is the expected value of the instantaneous SNR compared to the average SNR?

a: Always equal Explanation

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b: Greater than average Explanation

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c: Less than average Explanation

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d: It fluctuates around the average Explanation

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7. How does the Doppler shift influence Rayleigh fading in mobile scenarios?

a: It reduces the fading depth. Explanation

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b: It causes time-selective fading patterns. Explanation

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c: It increases the SNR consistently. Explanation

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d: It converts Rayleigh fading to Rician fading. Explanation

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8. In a system affected by both AWGN and Rayleigh fading, which decoding technique best improves BER without changing transmitter design?

a: Matched filtering Explanation

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b: Hard decision decoding Explanation

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c: Soft decision decoding with Viterbi algorithm Explanation

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d: Simple energy detection Explanation

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9. Why does Rayleigh fading typically result in higher BER compared to AWGN-only channels at the same SNR?

a: Because the channel bandwidth is lower. Explanation

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b: Because fading introduces deep nulls where signal strength drops drastically. Explanation

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c: Because Rayleigh fading channels are always non-linear. Explanation

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d: Because phase distortion is completely absent. Explanation

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10. Which metric best characterizes the severity of Rayleigh fading in a wireless channel?

a: Average received power Explanation

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b: Bit Error Rate Explanation

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c: Doppler spread Explanation

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d: Fading margin Explanation

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