1. Power delay profile and magnitude frequency response of a mobile radio channel are related through _______
a) Laplace Transform
b) Fourier Transform
c) S Transform
d) Wavelet Transform
Explanation: Power delay profile and magnitude frequency response of a mobile radio channel are related through the Fourier transform. Therefore, it is possible to obtain an equivalent description of the channel in the frequency domain using its frequency response characteristics.
2. ______ and coherence bandwidth are inversely proportional to one another.
a) Rms delay spread
b) Mean excess delay
c) Excess delay spread
d) Doppler spread
Explanation: The rms delay spread and coherence bandwidth are inversely proportional to one another. However, their exact relationship is a function of the exact multipath structure.
3. Coherence bandwidth is a statistical measure of range of frequencies over which channel is considered _______
a) Time dispersive
b) Frequency selective
c) Time variant
d) Flat
Explanation: Coherence bandwidth is a statistical measure of range of frequencies over which channel is considered flat. A flat channel is a channel which passes all spectral components with approximately equal gain and linear phase.
4. Which of the following describes time varying nature of the channel in a small scale region?
a) Delay spread and coherence time
b) Coherence bandwidth and delay spread
c) Doppler spread and coherence time
d) Delay spread and doppler spread
Explanation: Delay spread and coherence bandwidth describes the time dispersive nature of the channel in a local area. They do not give information about the time varying nature of the channel caused by either relative motion between the mobile and base station, or by movement of objects in the channel
5. Doppler spread is a range of frequencies over which received Doppler spread is _______
a) Zero
b) Non zero
c) Infinite
d) One
Explanation: Doppler spread is a range of frequencies over which received Doppler spectrum is essentially non-zero. It is a measure of spectral broadening caused by time rate of change of mobile radio channel.
6. _______ is a statistical measure of time duration over which channel impulse response is invariant.
a) Coherence time
b) Doppler spread
c) Mean excess delay
d) Rms delay spread
Explanation: Coherence time is actually a statistical measure of the time duration over which the channel impulse response is essentially invariant. It quantifies the similarity of the channel response at varying times.
7. Which of the following is not a channel parameter?
a) Bandwidth
b) Coherence time
c) Rms delay spread
d) Doppler spread
Explanation: Channel parameters are coherence bandwidth, rms delay spread and Doppler spread. Signal parameters are bandwidth and symbol period. Different types of fading occur depending on the relation between channel and signal parameters.
8. ______ leads to time dispersion and frequency selective fading.
a) Doppler spread
b) Multipath delay spread
c) Time dispersive parameters
d) Frequency delay spread
Explanation: Multipath delay spread leads to time dispersion and frequency selective fading. Doppler spread leads to frequency dispersion and time selective fading. These two propagation mechanism are independent of each other.
9. Which of the following s not a characteristic of flat fading?
a) Mobile radio channel has constant gain
b) Linear phase response
c) Non linear phase response
d) Bandwidth is greater than the bandwidth of transmitted signal
Explanation: The received signal will undergo flat fading if mobile radio channel has a constant gain and linear phase response over a bandwidth which is greater than the bandwidth of transmitted signal. It is the most common type of fading
10. Spectral characteristics of the channel changes with time in flat fading.
a) True
b) False
Explanation: In flat fading, the multipath structure of the channel is such that spectral characteristics of the transmitted signal are preserved at the receiver. But, the strength of the received signal changes with time due to fluctuations in the gain of channel caused by multipath