This set of Wireless & Mobile Communications MCQs focuses on “Modulation Performance in Fading and Multipath Channels”.
1. Bit error rate provides the information about the type of error.
a) True
b) False
View Answer
Explanation: Bit error rate does not provide information about the type of error. However, bit error rate (BER) evaluation gives a good indication of the performance of a particular modulation scheme.
2. Which of the following is specified by a specific number of bit errors occurring in a given transmission?
a) Bit error rate
b) Equally likely event
c) Outage event
d) Exhaustive events
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Explanation: Outage event is specified by a specific number of bit errors occurring in a given transmission. Evaluating the probability of outage is one of the means to judge the effectiveness of the signalling scheme in a mobile radio channel.
3. Irreducible BER floor is created in frequency selective channels due to ____________
a) Intersymbol interference
b) Random spectral spreading
c) Time varying Doppler spread
d) Blind speed
View Answer
Explanation: Frequency selective fading is caused due to multipath delay spread which causes intersymbol interference. It results in an irreducible BER floor for mobile systems.
4. Irreducible BER floor is created in non frequency selective channels due to ____________
a) Intersymbol interference
b) Multipath time delay
c) Time varying Doppler spread
d) Blind speed
View Answer
Explanation: Even if a mobile channel is not frequency selective, the tie varying Doppler spread due to motion creates an irreducible BER floor. It is caused due random spectral spreading.
5. The performance of BPSK is best is term of BER because _______
a) Symbol offset interference does not exist
b) Existence of cross rail interference
c) No multipath delay
d) Doppler spread
View Answer
Explanation: BER performance of BPSK is best among all the modulation schemes compared. This is because symbol offset interference does not exist in BPSK. Symbol offset interference is also called cross rail interference due to the fact that the eye diagram has multiple rails.
6. High capacity mobile systems are interference limited.
a) True
b) False
View Answer
Explanation: High capacity mobile systems are interference limited, but they are not noise limited. It was clearly seen that when carrier to interference ratio (C/I) is large, the errors are primarily due to fading, and interference has very little effect. However, as C/I drops below a certain level, interference dominates the link performance.
7. Which of the following do not impact bit error rate in mobile communication systems?
a) Mobile velocity
b) Channel delay spread
c) Modulation format
d) Base station
View Answer
Explanation: The mobile velocity, channel delay spread, interference levels and modulation formats all independently impact the raw bit error rate in mobile communication systems. And simulation is a powerful way to design or predict the performance of wireless communication links.
8. Coherence time refers to ____________
a) Time required attaining a call with the busy base station
b) Time required for synchronization between the transmitter and the receiver
c) Minimum time for change in magnitude and phase of the channel
d) None of the mentioned
View Answer
Explanation: Coherence time is the time required for synchronization between the transmitter and receiver. It is the over which a propagating wave is said to be coherent.
9. Doppler spread refers to _________
a) Signal fading due to Doppler shift in the channel
b) Temporary failure of message transfer
c) Large coherence time of the channel as compared to the delay constraints
d) All of the mentioned
View Answer
Explanation: Doppler spread refers to signal fading due to Doppler shift in the channel. It is a measure of spectral broadening caused by time rate of change of the mobile radio channel.
10. A rake receiver uses multiple ______
a) Delay circuits
b) Correlators
c) Detectors
d) Flip flops
View Answer
Explanation: A rake receiver uses multiple correlators to separately detect multiple strongest components. It is designed to counter the effects of multipath fading.
Sanfoundry Global Education & Learning Series – Wireless & Mobile Communications.
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