This set of Wireless & Mobile Communications Multiple Choice Questions & Answers (MCQs) focuses on “Fundamentals of Equalization”.
1. Which of the following is not used to improve received signal quality over small scale times and distance?
a) Modulation
b) Equalization
c) Diversity
d) Channel coding
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Explanation: Equalization, diversity and channel coding are the three techniques which are used to improve received signal quality and link performance over small scale times and distance. But, the approach, cost, complexity and effectiveness varies in wireless communication system.
2. Equalization is used to compensate __________
a) Peak signal to noise ratio
b) Intersymbol interference
c) Channel fading
d) Noises present in the signal
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Explanation: Equalization compensate the intersymbol interference (ISI) created by multipath within time dispersive channels. An equalizer within a receiver compensates for the average range of the expected channel amplitude and delay characteristics.
3. Training and tracking are the operating modes of _________
a) Diversity techniques
b) Channel coding techniques
c) Equalization techniques
d) Demodulation techniques
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Explanation: General operating modes of an adaptive equalizer includes training and tracking. A known fixed length training sequence is sent by the transmitter so that the receiver’s equalizer may adapt to a proper setting for minimum bit error rate detection.
4. An equalizer is said to be converged when it is properly _______
a) Trained
b) Tracked
c) Installed
d) Used
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Explanation: When an equalizer has been properly trained, it is said to have converged. Equalizers are commonly used in digital communication systems where user data is segmented into short time blocks or time slots.
5. Time for convergence of an equalizer is not a function of _______
a) Equalizer algorithm
b) Equalizer structure
c) Time rate of change of multipath radio channel
d) Transmitter characteristics
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Explanation: The timespan over which an equalizer converges is a function of the equalizer algorithm, the equalizer structure and the time rate of change of the multipath radio channel. Equalizers require proper retraining in order to maintain effective ISI cancellation.
6. Equalizer is usually implemented in __________
a) Transmitter
b) Baseband or at IF in a receiver
c) Radio channel
d) Modulator stage
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Explanation: An equalizer is implemented at baseband or at IF in a receiver. Since the baseband complex envelope expression can be used to represent bandpass waveform, the channel response, the demodulated signal and adaptive equalizer algorithm are usually simulated and implemented at baseband.
7. Equalizer is ________ of the channel.
a) Opposite
b) Same characteristics
c) Inverse filter
d) Add on
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Explanation: An equalizer is actually an inverse filter of the channel. The goal of equalization is to satisfy that the combination of the transmitter, channel and receiver be an all pass channel.
8. ______ controls the adaptive algorithm in an equalizer.
a) Error signal
b) Transmitted signal
c) Received signal
d) Channel impulse response
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Explanation: The adaptive algorithm is controlled by the error signal. The error signal is derived by comparing the output of the equalizer and some signal which is either an exact scaled replica of the transmitted signal or represents a property of transmitted signal.
9. The adaptive algorithms in equalizer that do not require training sequence are called ________
a) Linear adaptive algorithms
b) Blind algorithms
c) Non-linear adaptive algorithms
d) Spatially adaptive algorithms
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Explanation: Blind algorithms exploit the characteristics of the transmitted signal and do not require training sequence. These type of algorithm are able to acquire equalization through property restoral techniques of transmitted signal.
10. Which of the following is a blind algorithm?
a) Linear adaptive algorithms
b) Constant modulus algorithm
c) Non-linear adaptive algorithms
d) Spatially adaptive algorithms
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Explanation: Blind algorithm technique uses algorithms such as the constant modulus algorithm (CMA) and the spectral coherence restoral algorithm (SCORE). CMA is used for constant envelope modulation and forces the equalizer weights to maintain a constant envelope on the received signal.
Sanfoundry Global Education & Learning Series – Wireless & Mobile Communications.
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