14. Which of the following algorithm uses simple programming?
a) LMS Gradient DFE
b) FTF algorithm
c) Fast Kalman DFE
d) Gradient Lattice DFE
View Answer
Answer: a
Explanation: Advantages of LMS gradient DFE algorithm are low computational
complexity and simple programming. While fast tranversal filter (FTF) algorithm,
Fast Kalman DFE and gradient lattice DFE uses complex programming.
13. Which of the following does not hold true for RLS algorithms?
a) Complex
b) Adaptive signal processing
c) Slow convergence rate
d) Powerful
View Answer
Answer: c
Explanation: Recursive least square (RLS) algorithm uses fast convergence rate as
opposed to LMS algorithms. They are powerful, albeit complex, adaptive signal
processing techniques which significantly improves the convergence of adaptive
equalizer.
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
View Answer
Answer: a
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.
6. Equalizer is usually implemented in __________
a) Transmitter
b) Baseband or at IF in a receiver
c) Radio channel
d) Modulator stage
View Answer
Answer: b
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.
2. Equalization is used to compensate __________
a) Peak signal to noise ratio
b) Intersymbol interference
c) Channel fading
d) Noises present in the signal
View Answer
Answer: b
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. 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
View Answer
Answer: c
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
View Answer
Answer: d
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
View Answer
Answer: a
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.
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
View Answer
Answer: c
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.
4. An equalizer is said to be converged when it is properly _______
a) Trained
b) Tracked
c) Installed
d) Used
View Answer
Answer: a
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
View Answer
Answer: d
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
View Answer
Answer: b
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
View Answer
Answer: c
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
View Answer
Answer: a
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
View Answer
Answer: b
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.
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
View Answer
Answer: d
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.
1. Which of the following factor could not determine the performance of algorithm?
a) Structural properties
b) Rate of convergence
c) Computational complexity
d) Numerical properties
View Answer
Answer: a
Explanation: The performance of an algorithm is determined by various factors.
These factors are rate of convergence, computational complexity and numerical
properties. The performance of algorithm does not depend on structural properties.
2. Rate of convergence is defined by __________ of algorithm.
a) Time span
b) Number of iterations
c) Accuracy
d) Complexity
View Answer
Answer: b
Explanation: Rate of convergence is required as number of iterations required for
the algorithm to converge close enough to the optimum solution. It enables the
algorithm to track statistical variations when operating in non stationary
environment.
3. Computational complexity is a measure of ________
a) Time
b) Number of iterations
c) Number of operations
d) Accuracy
View Answer
Answer: c
Explanation: Computational complexity is the number of operations required to make
one complete iteration of the algorithm. It helps in comparing the performance with
other algorithms.
Choice of equalizer structure and its algorithm is not dependent on ________
a) Cost of computing platform
b) Power budget
c) Radio propagation characteristics
d) Statistical distribution of transmitted power
View Answer
Answer: d
Explanation: The cost of the computing platform, the power budget and the radio
propagation characteristics dominate the choice of an equalizer structure and its
algorithm. Battery drain at the subscriber unit is also a paramount consideration.
6. Which of the following is not an algorithm for equalizer?
a) Zero forcing algorithm
b) Least mean square algorithm
c) Recursive least square algorithm
d) Mean square error algorithm
View Answer
Answer: d
Explanation: Three classic equalizer algorithm are zero forcing (ZF) algorithm,
least mean squares (LMS) algorithm and recursive least squares (RLS) algorithm.
They offer fundamental insight into algorithm design and operation
7. Which of the following is a drawback of zero forcing algorithm?
a) Long training sequence
b) Amplification of noise
c) Not suitable for static channels
d) Non zero ISI
View Answer
Answer: b
Explanation: The zero forcing algorithm has the disadvantage that the inverse
filter may excessively amplify noise at frequencies where the folded channel
spectrum has high attenuation
9. LMS equalizer minimizes __________
a) Computational complexity
b) Cost
c) Mean square error
d) Power density of output signal
View Answer
Answer: c
Explanation: LMS equalizer is a robust equalizer. It is used to minimize mean
square error (MSE) between the desired equalizer output and the actual equalizer
output.
11. Stochastic gradient algorithm is also called ________
a) Zero forcing algorithm
b) Least mean square algorithm
c) Recursive least square algorithm
d) Mean square error algorithm
View Answer
Answer: b
Explanation: The minimization of the MSE is carried out recursively, and it can be
performed by the use of stochastic gradient algorithm. This more commonly called
the least mean square (LMS) algorithm.
2. Diversity decisions are made by ____________
a) Receiver
b) Transmitter
c) Channel
d) Adaptive algorithms
View Answer
Answer: a
Explanation: In virtually all applications, diversity decisions are made by the
receiver and are unknown to the transmitter. Diversity exploits the random nature
of radio propagation by finding independent signal paths for communication.
4. ____________ is used to prevent deep fade for rapidly varying channel.
a) Modulation
b) Demodulation
c) Macroscopic diversity technique
d) Microscopic diversity technique
View Answer
Answer: c
Explanation: In order to prevent deep fades from occurring, macroscopic diversity
techniques can exploit the rapidly changing signal. By selecting the best signal at
all times, a receiver can mitigate small scale fading effects.
6. Space diversity s also known as ________
a) Antenna diversity
b) Time diversity
c) Frequency diversity
d) Polarization diversity
View Answer
Answer: a
Explanation: Space diversity is also known as antenna diversity. It is one of the
popular forms of diversity used in wireless communications. Signals received from
the spatially separated antenna on the mobile would have essentially uncorrelated
envelopes for antenna separation.
9. Polarization diversity uses the ________ as the diversity element.
a) Modulation index
b) Carrier frequency
c) Reflection coefficient
d) Coherence time
View Answer
Answer: c
Explanation: Decorrelation of the signal in each polarization is caused by multiple
reflections in the channel between mobile and base station antenna. Reflection
coefficient for each polarization is different, which results in different
amplitudes and phases for each reflection.
11. Frequency diversity is implemented by transmitting information on more than one
___________
a) Carrier frequency
b) Amplitude
c) Phase
d) Modulation scheme
View Answer
Answer: a
Explanation: Frequency diversity is implemented by transmitting information on more
than one carrier frequency. Frequency diversity is often employed in microwave line
of sight links which carry several channels in frequency division multiplex mode
12. Frequency diversity uses ________ as a diversity element.
a) Correlation coefficient
b) Coherence time
c) Coherence bandwidth
d) SNR
View Answer
Answer: c
Explanation: The rationale behind the frequency diversity is that frequencies
separated by more than the coherence bandwidth of the channel will be uncorrelated.
Thus, they will not experience the same fade.
14. Time diversity repeatedly transmits information at time spacings that exceed
___________
a) Coherence bandwidth
b) Dwell time
c) Run time
d) Coherence time
View Answer
Answer: d
Explanation: Time diversity repeatedly transmits information at time spacings that
exceed coherence time of the channel. Thus, multiple repetitions of the signal will
be received with independent fading conditions, thereby providing for diversity.
15. In maximal ratio combining, the output SNR is equal to __________
a) Mean of all individual SNRs
b) Maximum of all SNRs
c) Sum of individual SNR
d) Minimum of all SNRs
View Answer
Answer: c
Explanation: Maximal ratio combining produces an output SNR equal to the sum of the
individual SNRs. Thus, it has the advantage of producing an output with an
acceptable SNR even when none of the individual signals are themselves acceptable.
2. A RAKE receiver collects the __________ versions of the original signal.
a) Time shifted
b) Amplitude shifted
c) Frequency shifted
d) Phase shifted
View Answer
Answer: a
Explanation: RAKE receiver attempts to collect the time shifted versions of the
original signal. It is due to the fact that there is useful information present in
the multipath components.
10. Interleaving is used to obtain ___________ diversity.
a) Time
b) Frequency
c) Polarization
d) Antenna
View Answer
Answer: a
Explanation: Interleaving is used to obtain time diversity in a digital
communication system without adding any overhead. It provides rapid proliferation
of digital speech coders which transform analog voices into efficient digital
messages.
9. A RAKE receiver uses __________
a) Equalization
b) Channel coding
c) Diversity
d) Encryption
View Answer
Answer: c
Explanation: RAKE receiver is a diversity receiver. Diversity is provided by the
fact that the multipath components are practically uncorrelated from one another
when their relative propagation delays exceed chip period.
1. The technique for combining diversity signals are
a) Feedback
b) Maximal ratio
c) Equal gain
d) All of the mentioned
View Answer
Answer: d
Explanation: The most common techniques used for combining diversity signals are
selection, feedback, maximal ratio and equal gain.
2. Diversity technique is used for combating
a) Fading
b) Error bursts
c) Co-channel interference
d) All of the mentioned
View Answer
Answer: c
Explanation: Diversity technique is a common method used for combating fading,
co-channel interference and error bursts.
3. Diversity technique is applied at
a) Base station
b) Mobile receiver
c) Base station & Mobile receiver
d) None of the mentioned
View Answer
Answer: c
Explanation: Diversity technique can be applied at both base station and at mobile
receivers
4. Which is more effective and commonly preferred technique?
a) Time diversity
b) Spatial diversity
c) Frequency diversity
d) None of the mentioned
View Answer
Answer: b
Explanation: Most commonly used and more effective diversity technique is spatial
diversity technique.
5. Diversity technique
a) Provides significant link improvement
b) Needs training overhead
c) All of the mentioned
d) None of the mentioned
View Answer
Answer: a
Explanation: Diversity technique does not require training overhead at the
transmitter and also provides significant link performance.
7. Which signalling scheme is preferred for fading channel?
a) Frequency based modulation
b) Phase based modulation
c) Frequency & Phase based modulation
d) None of the mentioned
View Answer
Answer: c
Explanation: Frequency based modulation and phase based modulation is preferable
for fading channel than amplitude based modulation.
8. Uncorrelated fading occurs when
a) Time span is small
b) Time span is large
c) Does not depend on time span
d) None of the mentioned
View Answer
Answer: b
Explanation: As the time span increases, the fading is more uncorrelated and
effectiveness also increases.
13. Rake receivers are used in
a) Radio astronomy
b) CDMA
c) W-CDMA
d) All of the mentioned
View Answer
Answer: d
Explanation: Rake receivers are used in radio astronomy, CDMA, W-CDMA, wireless LAN
networks etc.
14. The rake receivers functions are similar to
a) Equalizer
b) Matched filter
c) Equalizer & Matched filter
d) None of the mentioned
View Answer
Answer: c
Explanation: The functionality of rake receiver resembles that of the equalizer and
matched filter.
7. A RAKE receiver uses __________ to separately detect the M strongest signals.
a) Single correlator
b) Multiple correlator
c) Single IF receiver
d) Multiple IF receivers
View Answer
Answer: b
Explanation: A RAKE receiver uses multiple correlators to separately detect the M
strongest multipath components. Demodulation and bit decisions are then based on
the weighted ouputs of the M correlators
