Virtual Labs

Study of effect of channel on system with various modulation

In a digital communication system affected by Rayleigh fading and AWGN, which of the following statements correctly describes the impact on the received signal?

a: Rayleigh fading only affects the phase of the signal, while AWGN only affects its amplitude. Explanation

Explanation

b: Rayleigh fading causes rapid amplitude and phase fluctuations, and AWGN adds constant background noise. Explanation

Explanation

c: AWGN causes deep fades in the signal, while Rayleigh fading adds predictable noise. Explanation

Explanation

d: Both Rayleigh fading and AWGN only delay the signal without altering its amplitude or phase. Explanation

Explanation

In a Rayleigh fading channel, which underlying statistical condition is the primary cause for the high probability of 'deep fades'?

a: The presence of a dominant Line-of-Sight (LoS) signal path. Explanation

Explanation

b: The zero-mean Gaussian nature of the in-phase and quadrature components. Explanation

Explanation

c: The linear decay of signal power as a function of distance. Explanation

Explanation

d: The constant phase relationship between all received multipath components. Explanation

Explanation

For coherent BPSK over a Rayleigh fading channel with AWGN, which technique at the receiver helps most to combat the effects of fading before demodulation?

a: Using a matched filter without channel knowledge Explanation

Explanation

b: Applying an adaptive equalizer to reverse channel distortions Explanation

Explanation

c: Increasing the carrier frequency Explanation

Explanation

d: Adding a cyclic prefix Explanation

Explanation

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

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

Explanation

b: The carrier frequency selection. Explanation

Explanation

c: The coherence time of the channel. Explanation

Explanation

d: The baseband signal bandwidth. Explanation

Explanation

In a BPSK system over a Rayleigh fading channel with AWGN, what happens to the average Bit Error Rate (BER) when the average SNR increases?

a: The average BER decreases but remains higher than in an AWGN-only channel. Explanation

Explanation

b: The average BER increases due to stronger fading effects. Explanation

Explanation

c: The average BER stays constant regardless of SNR. Explanation

Explanation

d: The average BER drops to zero immediately after a certain SNR threshold. Explanation

Explanation

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

Explanation

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

Explanation

c: Because they have lower average power. Explanation

Explanation

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

Explanation

In a BPSK system over a Rayleigh fading channel with AWGN, why is the BER higher than in an AWGN-only channel for the same average SNR?

a: Because fading causes random fluctuations in amplitude, sometimes producing deep fades where the signal is very weak. Explanation

Explanation

b: Because the transmitted signal power is lower in Rayleigh fading channels. Explanation

Explanation

c: Because BPSK cannot be demodulated in the presence of noise. Explanation

Explanation

d: Because the AWGN is multiplied by the fading coefficient, increasing its variance. Explanation

Explanation

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

a: Instantaneous received power. Explanation

Explanation

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

Explanation

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

Explanation

d: Outage probability at a target SNR threshold. Explanation

Explanation

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

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

Explanation

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

Explanation

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

Explanation

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

Explanation

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

a: Minimum Euclidean distance decoding. Explanation

Explanation

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

Explanation

c: Matched filtering. Explanation

Explanation

d: Zero-forcing equalization. Explanation

Explanation