This set of Wireless & Mobile Communications Multiple Choice Questions & Answers (MCQs) focuses on “Small- Scale Multipath Measurements”.
1. Which of the following is not a small scale multipath measurement technique?
a) Indirect pulse measurement
b) Direct pulse measurement
c) Spread spectrum sliding correlator measurement
d) Swept frequency measurement
View Answer
Explanation: Because of the importance of multipath structure in determining the small scale fading effects, a number of wideband channel sounding techniques have been developed. These are direct pulse measurement, spread spectrum sliding correlator and swept frequency measurement.
2. Direct RF pulse systems are complex.
a) True
b) False
View Answer
Explanation: Direct RF pulse systems have a very attractive system. They lack complexity because of the use of off the shelf equipment. This system can also provide a local average power delay profile.
3. What is the main disadvantage of RF pulse system?
a) Complexity
b) Not real time
c) Interference and noise
d) Simplicity
View Answer
Explanation: The main problem with RF pulse system is that it is subject to interference and noise. This is due to wide passband filter required for multipath time resolution.
4. Why is the phase of individual multipath components are not received in RF Pulse system?
a) Due to use of duplexer
b) Due to use of ADC
c) Due to use of flip flops
d) Due to use of envelope detector
View Answer
Explanation: Another disadvantage of RF pulse system is that phase of individual multipath components are not received due to use of an envelope detector. However, use of a coherent detector permits measurement of the multipath phase using this technique.
5. Spread spectrum sliding correlator has better ________ in comparison to RF pulse system.
a) Dynamic range
b) Frequency
c) Power density
d) Structure
View Answer
Explanation: While the probing signal may be wideband, it is possible to detect the transmitted signal using a narrowband receiver preceded by a wideband mixer. Thus, it improves the dynamic range of the system in comparison to RF pulse system.
6. If a PN sequence has chip duration of Tc, then chip rate is given by ___________
a) Tc
b) 1/Tc
c) 2 Tc
d) Tc2
View Answer
Explanation: In a spread spectrum channel sounder, a carrier signal is spread over a large bandwidth. It is done by mixing it with a binary pseudo number (PN) sequence having a chip duration of Tc and chip rate of 1/Tc.
7. The maximal length of PN sequence, the sequence length for n number of shift register is ______
a) 2n
b) 1/2n
c) 2n – 1
d) 2n + 1
View Answer
Explanation: For a maximal length pseudo number (PN) sequence, the sequence length is 2n – 1. Here, n is the number of shift registers in the sequence register.
8. The ratio between transmitter chip clock rate and the difference between the transmitter chip clock and difference between transmitter and receiver chip clock rates is called ___________
a) Slide factor
b) Chip factor
c) Reuse factor
d) Shape factor
View Answer
Explanation: The slide factor is defined as ratio between transmitter chip clock rate and the difference between the transmitter chip clock and difference between transmitter and receiver chip clock rates. It is unit less quantity.
9. Which of the following is not an advantage of spread spectrum channel sounding system?
a) Rejection of passband noise
b) Real time
c) Coverage range improvement
d) Less transmitter power required
View Answer
Explanation: One of the main advantage of spread spectrum channel sounding system is ability to reject passsband noise. Thus, it improves the coverage range for a given transmitter power. Also, required transmitter powers can be considerably lower compared to direct pulse systems due to inherent processing gain.
10. Which of the following is a disadvantage of spread spectrum channel sounding system?
a) Passband noise
b) Less coverage area
c) Large transmitter power required
d) Not in real time
View Answer
Explanation: A disadvantage of spread spectrum system as compared to direct RF pulse system, is that measurements are not made in real time. But they are compiled as the PN codes slide past one another.
11. There is no relationship between time domain and frequency domain techniques.
a) True
b) False
View Answer
Explanation: There is a dual relationship between time domain and frequency domain techniques. Therefore, it is possible to measure the channel impulse response in the frequency domain. Frequency domain channel sounder is used for measuring channel impulse response.
12. Transmissivity is a _________ domain response.
a) Time
b) Frequency
c) Time-frequency
d) Spatial
View Answer
Explanation: Transmissivity response is a frequency domain response. It is a frequency domain representation of channel impulse response. This response is then converted to the time domain using inverse discrete Fourier transform.
13. Frequency domain channel sounding technique do not require hard wired synchronization between transmitter and receiver.
a) True
b) False
View Answer
Explanation: Frequency domain channel sounding system requires careful calibration and hardwired synchronization between transmitter and receiver. However, this technique works well and indirectly provides amplitude and phase information in the time domain.
14. Frequency domain channel sounding system is _______ in nature.
a) Real time
b) Digital
c) Non real time
d) Analog
View Answer
Explanation: Frequency domain channel sounding system makes measurements of non real time nature. For time varying channels, the channel frequency response can change rapidly giving an erroneous impulse response measurement.
15. Faster sweep time can be accomplished by ________
a) Increasing frequency steps
b) Increasing time slots
c) Reducing time slots
d) Reducing frequency steps
View Answer
Explanation: A faster sweep time can be accomplished by reducing the number of frequency steps. But this sacrifices the time resolution and excess delay range in the time domain.
Sanfoundry Global Education & Learning Series – Wireless & Mobile Communications.
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