# Wireless & Mobile Communications Questions & Answers – Practical Link Budget Design Using Path Loss Models

This set of Wireless & Mobile Communications Questions and Answers for Experienced people focuses on “Practical Link Budget Design Using Path Loss Models”.

1. Empirical approach is based on fitting curve or analytical expressions.
a) True
b) False

Explanation: The empirical approach is based on fitting curves or analytical expressions that recreate a set of measured data. This has the advantage of implicitly taking into account all propagation factors, both known and unknown through actual field measurements.

2. Which of the following is not a practical path loss estimation technique?
a) Log distance path loss model
c) Determination of percentage of coverage area
d) Hata model

Explanation: Log normal shadowing, log distance path loss model and determination of percentage of coverage area are practical pat loss estimation techniques. Hata model is only valid for exterior environment.

3. Average received signal power decreases __________ with distance.
a) Exponentially
b) Logarithmically
c) Two times
d) Four times

Explanation: Both theoretical and measurement based propagation models indicate that average received signal power decreases logarithmically with distance. It is valid for both outdoor and indoor channels.

4. What does path loss exponent indicates?
a) Rate at which path loss decreases with distance
b) Rate at which path loss increases with distance
c) Rate at which path loss decreases with power density
d) Rate at which path loss increases with power density

Explanation: The average large scale path loss for an arbitrary T-R separation is expressed as a function of distance by using a path loss exponent, n. It indicates the rate at which the path loss increases with distance.

5. The reference distance should not be in the far field of the antenna.
a) True
b) False

Explanation: It is important to select a free space reference distance that is appropriate for the propagation environment. The reference distance should always be in the far field of the antenna so that near field effects do not alter the reference path loss.
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6. Which distribution describes the shadowing effect?
a) Log normal distribution
b) Nakagami distribution
c) Cauchy distribution
d) Rayleigh distribution

Explanation: Log normal distribution describes the random shadowing effects. It occurs over a large number of measurement locations which have the same T-R separation, but have different clutter on the propagation path.

7. Log normal shadowing is a phenomenon that occurs with same T-R separation having same level clutter on the propagation path.
a) True
b) False

Explanation: Log normal shadowing occurs over a large number of measurement locations which have the same T-R separation, but have different levels of clutter on the propagation path. It follows log normal distribution.

8. Log normal shadowing implies that measured signal levels at specific T-R separation have ______ distribution when signal levels have values in dB units.
a) Rayleigh
b) Gamma
c) Gaussian
d) Nakagami

Explanation: Log normal shadowing implies that measured signal levels at a specific T-R separation have Gaussian (Normal) distribution. It is about the distance dependent mean of 4.68 where the signal levels have values in dB units.

9. A link budget is accounting of all __________
a) Gain and losses from the transmitter
b) Power transmitted by transmitter

Explanation: A link budget is accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, etc.) to the receiver in a telecommunication system. It accounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains and miscellaneous losses.

10. Antenna’s efficiency is given by the ratio of __________
a) Losses
b) Physical aperture to effective aperture
c) Signal power to noise power
d) Effective aperture to physical aperture

Explanation: The larger the antenna aperture the larger is the resulting signal power density in the desired direction. The ratio of effective aperture to the physical aperture is the antenna’s efficiency.

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