# Wireless & Mobile Communications Questions & Answers – Multipath Shape Factors for Small – Scale Fading

This set of Wireless & Mobile Communications Assessment Questions and Answers focuses on “Multipath Shape Factors for Small – Scale Fading”.

1. The term small scale fading describes the slow fluctuations of received power level due to changes in receiver position.
a) True
b) False

Explanation: The term small scale fading describes the rapid fluctuations of received power level due to changes in receiver position. This effect is due to the constructive and destructive interference of the numerous multipath waves that impinge upon a wireless receiver.

2. The rapid fluctuations due to small scale fading affect the _________ design.
b) Transmitter
c) MSC
d) Base station

Explanation: The rapid fluctuation due to small scale fading affect every aspect of receiver design such as dynamic range, equalization, diversity, modulation scheme and channel error correction coding. These fluctuations are a function of direction of travel as related to the angle of arrival of multipath delay.

3. An approximately omnidirectional channel model accurately describes fading statistics if directional antennas are employed at the receiver.
a) True
b) False

Explanation: An approximately omnidirectional channel model accurately describes fading statistics if directional or smart antenna systems are employed at the receiver. Unfortunately, recent measurements and models have shown that the arriving multipath in a local area bears little resemblance to the omnidirectional propagation.

4. Which of the following is not a principle shape factor?
b) Angular constriction
c) Azimuthal direction of maximum fading
d) Angle of arrival

Explanation: Three principle shape factors are angular spread, angular constriction, and azimuthal direction of maximum fading. They are exactly related to the average rate at which a received signal fades.

5. Angular spread is a measure of how multipath concentrates about __________
a) Angle of arrival
b) Transmitted power
c) Single azimuthal direction of arrival

Explanation: The shape factor, angular spread is a measure of how multipath concentrates about a single azimuthal direction of arrival. It has several advantages like it is invariant under changes in transmitted power.
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6. Angular constriction is a measure of how multipath concentrates about ______ azimuthal direction.
a) Single
b) Two
c) Three
d) Four

Explanation: The shape factor, angular constriction is a measure of how multipath concentrates about two azimuthal directions. The measure for angular constriction is invariant under changes in transmitted power.

7. Shape factor, azimuthal direction of maximum fading is a directional parameter.
a) True
b) False

Explanation: Azimuthal direction of maximum fading is the third shape factor which is a directional or orientation parameter. Its value corresponds to the direction in which s mobile user would move in order to experience the maximum fading rate in the local area.

8. _______ of a stationary process is actually the variance of the rate of change.
a) Mean
b) Mean square
c) Mean squared derivative
d) Mean squared integral

Explanation: Mean squared derivative of a stationary process is actually the variance of the rate of change. The mean derivative of the stationary process is zero; the mean squared derivative is the simplest statistics that measures the fading rate of a channel.

9. Complex received voltage is a summation of __________ that have impinged upon receiver antenna.
a) Multipath waves
b) Waves
c) Power density
d) Single path waves

Explanation: Complex received voltage is a baseband representation. It us a summation of numerous multipath waves that have impinged upon the receiver antenna and have excited a complex voltage component at the input of a receiver.

10. Which of the following is equal to received power?
a) Square of complex voltage
b) Complex voltage
c) Magnitude of complex voltage
d) Magnitude squared of complex voltage

Explanation: The received power is equal to the magnitude squared of complex voltage. The mathematical operation of taking the squared magnitude of a complex quantity is a nonlinear operation.

11. Which of the following is equal to received envelope?
a) Square of complex voltage
b) Complex voltage
c) Magnitude of complex voltage
d) Magnitude squared of complex voltage

Explanation: The received envelope is equal to the magnitude of the complex voltage. The channel is assumed to be Rayleigh fading in order to calculate the mean squared fading rate.

12. Which of the following describes the average fading rate within a local area?
b) Angular constriction
c) Azimuthal direction of maximum fading
d) Angle of arrival

Explanation: Angular spread describes the average fading rate within a local area. The average of the two fading rate variances, regardless of the orientation of the measurement, is always given by averaging the variances observed over two perpendicular directions within the local area.

13. Angular constriction affects the average fading rate within local area.
a) True
b) False

Explanation: Angular constriction does not affect the average fading rate within local area. It describes the variability of fading rates taken along different azimuthal directions.

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