Wireless & Mobile Communications Questions & Answers – Impulse Response Model of a Multipath Channel

This set of Wireless & Mobile Communications Interview Questions and Answers for Experienced people focuses on “Impulse Response Model of a Multipath Channel”.

1. Small scale variations of a mobile radio signal are directly related to _______
a) Impulse response of mobile radio channel
b) Impulse response of base station
c) Frequency response of antenna
d) Frequency response of base station

Explanation: The small scale variations of a mobile radio signal can be directly related to the impulse response of mobile radio channel. he impulse response is a wideband channel characterization and contains all information necessary to simulate or analyze any type of radio transmission through the channel.

2. Impulse response is a narrowband characterization.
a) True
b) False

Explanation: Impulse response is a wideband channel characterization. It contains all information necessary to simulate or analyse any type of radio transmission through the channel.

3. Mobile radio channel can be modelled as a ______ filter.
a) Non-linear
b) Low-pass
c) Linear
d) Bandpass

Explanation: Mobile radio channel may be modelled as a linear filter with a time varying impulse response. The time variation is due to receiver motion in space. The filtering nature is caused by summation of amplitudes and delays of multiple arriving waves at any instant of time.

4. Impulse response does not play any role in characterization of the channel.
a) True
b) False

Explanation: Impulse response is a useful characterization of channel. It may be used to predict and compare the performance of different mobile communication systems and transmission bandwidth for a particular mobile channel condition.

5. Received signal can be expressed as ______ of transmitted signal with channel impulse response.
b) Subtraction
c) Division
d) Convolution

Explanation: The received signal y(t) can be expressed as a convolution of transmitted signal x(t) with impulse response of mobile radio channel. The variable t represents the time variations due to motion and the channel impulse multipath delay for fixed value of t.
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6. Discretization of multipath delay axis of impulse response into equal time delay segments is called __________
a) Excess delay bins
b) Delay bins
c) Discrete bins
d) Digital bins

Explanation: It is useful to discretize the multipath delay axis of the impulse response into equal time delay segments called excess delay bins. The technique of quantizing the delay bins determines the time delay resolution of the channel model.

7. Small scale received power is ________ of average powers received in each multipath component.
a) Log
b) Exponential
c) Multiplication
d) Sum

Explanation: The average small received power is the sum of the average powers received in each multipath component. This is the case if transmitted signal is able to resolve the multipath.

8. The received power of a wideband signal fluctuates significantly when a receiver is moved about a local area.
a) True
b) False

Explanation: Amplitude of individual multipath components does not fluctuate widely in local area. Therefore, the received power of a wideband signal does not fluctuate significantly when a receiver is moved about a local area.

9. Average power for a CW signal is _______ to average received power for a wideband signal in small scale region.
a) Equivalent
b) Two times
c) Four times
d) Ten times

Explanation: Average power for a CW signal is equivalent to average received power for a wideband signal in small scale region. This can occur when either the multipath phases are identically and independently distributed or when path amplitudes are uncorrelated.

10. The received local ensemble average power of wideband and narrowband signals are ________
a) Different
b) Equivalent
c) Not dependent
d) Double

Explanation: The received local ensemble average power of wideband and narrowband signals is equivalent. When the transmitted signal has bandwidth greater than bandwidth of the channel, the received power varies very little. However, if transmitted signal has very narrow bandwidth, large fluctuation occurs at receiver.

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