Under what condition do we have a slow fading channel?
a. Signal Bandwidth > Coherence Bandwidth
b. Signal Bandwidth < Coherence Bandwidth
c. Coherence Time > Symbol Period
d. Coherence Time < Symbol Period
Explanation: Slow fading occurs when the coherence time (duration over which the channel is stable) is larger than the symbol period. This means the channel conditions do not vary significantly during the transmission of a symbol.
Question 2:
The model represented by the formula c(τ,t)= ∑(n=0 to N(t)) αn(t)e^(jφn(t))δ(τ−τn(t)) is called:
a. Frequency Response
b. Flat Fading Response
c. Slow Fading Response
d. Time-Varying Impulse Response
Explanation: This formula represents a time-varying impulse response, which describes how the multipath channel affects transmitted signals over time.
Question 3:
Central Limit Theorem (CLT) in wireless signal propagation states that the summation of a large number of random multipath signals results in a distribution called:
a. Rayleigh
b. Nakagami
c. Rician
d. Gaussian
Explanation: According to the CLT, the sum of many independent random processes tends to follow a Gaussian distribution, which applies to multipath signals in wireless communication.
Question 4:
Under what condition do we have a flat fading channel?
a. Signal Bandwidth < Coherence Bandwidth or Delay Spread < Symbol Period
b. Signal Bandwidth > Coherence Bandwidth or Delay Spread > Symbol Period
c. Signal Bandwidth > Coherence Bandwidth or Delay Spread < Symbol Period
d. Signal Bandwidth < Coherence Bandwidth or Delay Spread > Symbol Period
Explanation: Flat fading occurs when the coherence bandwidth is larger than the signal bandwidth, or when the delay spread is smaller than the symbol period.
Question 5:
Under what condition do we have a fast fading channel?
a. Signal Bandwidth > Coherence Bandwidth
b. Coherence Time < Symbol Period
c. Coherence Time > Symbol Period
d. Signal Bandwidth < Coherence Bandwidth
Explanation: Fast fading occurs when the coherence time is smaller than the symbol period, meaning channel variations happen rapidly within a single symbol duration.
Question 6:
Which distribution is used when the Line of Sight (LOS) component is present in the received signal?
a. Gaussian
b. Nakagami
c. Rician
d. Rayleigh
Explanation: Rician distribution models scenarios with a dominant LOS component alongside multipath components, unlike Rayleigh which assumes no LOS.
Question 7:
The key difference between wideband and narrowband channels is:
a. Time difference between multipath components in wideband exceeds 1/signal bandwidth, while narrowband doesn't
b. Time difference between multipath components in wideband exceeds signal period, while narrowband doesn't
c. The ratio of the time difference between multipath components to the signal period is much greater than unity in wideband, while narrowband isn't
d. All of the above
Explanation: These conditions collectively define the key differences between wideband and narrowband channels.
Question 8:
Statistical scattering function can be found by:
a. Calculating the Fourier transform of the cross-correlation function between time-varying impulse response and frequency response
b. Calculating the inverse Fourier transform of the cross-correlation function for time-varying impulse response and frequency response
c. Calculating the inverse Fourier transform of the autocorrelation function for the time-varying impulse response
d. Calculating the Fourier transform of the autocorrelation function for the time-varying impulse response
Explanation: The scattering function is derived from the Fourier transform of the autocorrelation function.
Question 9:
Under what condition do we have a frequency-selective fading channel (time dispersion)?
a. Signal Bandwidth < Coherence Bandwidth or Delay Spread > Symbol Period
b. Signal Bandwidth > Coherence Bandwidth or Delay Spread > Symbol Period
c. Signal Bandwidth > Coherence Bandwidth or Delay Spread < Symbol Period
d. Signal Bandwidth < Coherence Bandwidth or Delay Spread < Symbol Period
Explanation: Frequency-selective fading occurs when the signal bandwidth exceeds the coherence bandwidth, or when delay spread exceeds the symbol period.
Question 10:
The channel with the largest time dispersion is:
a. Red curve
b. Green curve
c. Blue curve
d. All of the above
Explanation: The red curve shows the largest delay spread, indicating the largest time dispersion.
Question 11:
The channel with the largest coherence bandwidth is:
a. Red curve
b. Green curve
c. Blue curve
d. All of the above
Explanation: Smaller delay spread implies a larger coherence bandwidth. The green curve has the smallest delay spread.
Question 12:
The channel with the largest Doppler spread is:
a. Red curve
b. Blue curve
c. Both blue and red curves
d. None of the above
Explanation: Doppler spread is highest for the red curve, indicating faster relative motion.
Question 13:
The channel with the highest selectivity in the frequency domain is:
a. Red curve
b. Green curve
c. Blue curve
d. All of the above
Explanation: Frequency selectivity is highest for channels with the smallest coherence bandwidth. Blue curve exhibits this characteristic.
Question 14:
The channel with the highest mobility is:
a. Red curve
b. Blue curve
c. Both red and blue curves
d. None of the above
Explanation: High mobility leads to higher Doppler spread, as shown by the red curve.
Question 15:
The channel with the lowest inter-symbol interference is:
a. Red curve
b. Green curve
c. Blue curve
d. All of the above
Explanation: Channels with smaller delay spreads, such as the green curve, have less inter-symbol interference.
Question 16:
The channel with the largest coherence time is:
a. Red curve
b. Blue curve
c. Both red and blue curves
d. None of the above
Explanation: Coherence time is inversely proportional to Doppler spread. Blue curve shows the largest coherence time.
Question 17:
The channel that causes the lowest inter-carrier interference is:
a. Red curve
b. Green curve
c. Blue curve
d. All of the above
Explanation: Channels with moderate delay spreads, like the red curve, reduce inter-carrier interference.
Question 18:
The channel with the highest selectivity in the time domain is:
a. Red curve
b. Blue curve
c. Both red and blue curves
d. None of the above
Explanation: Time-domain selectivity is related to coherence time. Channels with larger coherence times are more selective in the time domain. The blue curve has the largest coherence time.
Question 19:
The channel with the highest overall fading impact is:
a. Red curve
b. Blue curve
c. Green curve
d. Cannot be determined from given information
Explanation: The red curve shows both high Doppler spread and significant delay spread, indicating the most severe fading effects overall.
Question 20:
Which type of fading is most affected by the speed of the mobile station?
a. Flat fading
b. Frequency-selective fading
c. Fast fading
d. Slow fading
Explanation: Fast fading is most directly affected by mobile station speed as it relates to the Doppler spread, which increases with velocity.