# Wireless & Mobile Communications Questions & Answers – Equalization Techniques

This set of Wireless & Mobile Communications Multiple Choice Questions & Answers (MCQs) focuses on “Equalization Techniques”.

1. Equalization techniques can be categorised into _______ and ______ techniques.
a) Linear, non linear
b) Active, passive
c) Direct, indirect
d) Slow, fast

Explanation: Equalization techniques can be classified into linear and non linear techniques. These categories are determined from how the output of an adaptive equalizer is used for subsequent control of the equalizer.

2. Equalization is linear if an analog signal is fed back to change the subsequent outputs of the equalizer.
a) True
b) False

Explanation: If the analog signal is not used in the feedback path to adapt the equalizer, the equalization is linear. On the other hand, if it is fed back to change the subsequent outputs of the equalizer, the equalization is non-linear.

3. In the context of equalizers, LTE stands for ________
a) Long transversal equalizer
b) Least time-varying equalizer
c) Linear transversal equalizer
d) Linear time-varying equalizer

Explanation: The most common equalizer structure used for equalization is linear transveral equalizer (LTE). It is made up of tapped delay lines, with the tappings speed a symbol period apart.

4. Which of the following is not a characteristic of FIR filter?
a) Many zeroes
b) Poles only at z=0
c) Transfer function is a polynomial of z-1
d) Many poles

Explanation: Finite impulse response filter (FIR) has many zeroes but poles only at z=0. The transfer function of the filter is a polynomial of z-1. It is also referred to as transversal filter.

5. Which of the following is not an advantage of lattice equalizer?
a) Simple structure
b) Numerical stability
c) Faster convergence
d) Dynamic assignment

Explanation: The structure of lattice equalizer is more complicated than a linear transversal equalizer. But, numerical stability and faster convergence are two advantage of laatic equalizer. Also, its unique structure allows dynamic assignment of the most effective length of lattice equalizer.
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6. Non-linear equalizers are used in applications where channel distortion is not severe.
a) True
b) False

Explanation: Non-linear equalizers are used in applications where the channel distortion is too severe for a linear equalizer to handle. They are most commonly used in practical wireless communication.

7. Which of the following is not a non-linear equalization technique?
a) Decision feedback equalization
b) Maximum likelihood symbol detection
c) Minimum square error detection
d) Maximum likelihood sequence detection

Explanation: Decision feedback equalization, maximum likelihood symbol detection and maximum likelihood sequence detection offers non-linear equalization. They offer improvements over linear equalization techniques and are used in most 2G and 3G systems.

8. For a distorted channel, LTE performance is superior to DFE.
a) True
b) False

Explanation: LTE is well behaved when the channel spectrum is comparatively flat. But if the channel is severely distorted or exhibits null in the spectrum, the performance of LTE deteriorates and MSE of DFE is better than LTE.

9. Which of the following does not hold true for MLSE?
a) Minimizes probability of sequence error
b) Require knowledge of channel characteristics
c) Requires the statistical distribution of noise
d) Operates on continuous time signal

Explanation: Matched filter operates on the continuous time signal, whereas maximum likelihood sequence estimation (MLSE) equalizer and channel estimator rely on discretized samples. MLSE is optimal in the sense that it minimizes the probability of sequence error.

10. MLSE decodes each received signal by itself.
a) True
b) False

Explanation: Rather than decoding each received signal by itself, MLSE tests all possible data sequences by using a channel impulse response simulator within the algorithm. It chooses the data sequence with maximum probability as the output.

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