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Communications MCQ Set 1

1. Fading channel has memory.
a) True
b) False

View Answer

Answer: a [Reason:] Fading channel has memory and the received samples are correlated with each other in time.

2. How can frequency selective distortion be minimized?
a) By using pilot signal
b) By adaptive equalization
c) By spread spectrum
d) All of the mentioned

View Answer

Answer: d [Reason:] Frequency selective distortion can be minimized by using adaptive equalization, by using spread spectrum, by using pilot signal and also by using orthogonal FDM modulation.

3. How can slow fading be minimized?
a) By diversity technique
b) Error correcting codes
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] Slow fading can be minimized by using error correcting codes and also by using diversity technique to get additional uncorrelated estimates of a signal.

4. Fast fading can be minimized by
a) Robust modulation
b) Coding and interleaving
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] Fast fading can be minimized by using coding and interleaving, by using robust modulation and by introducing signal redundancy to increase signalling rate.

5. The decision feedback equalizer has a linear traversal filter which is
a) Feed forward section
b) Feedback section
c) Feed forward section & Feedback section
d) None of the mentioned

View Answer

Answer: a [Reason:] The decision feedback filter has a feed forward section which is a linear traversal filter.

6. The ISI and adjacent channel interference is removed by
a) Cancelling filter
b) Port processing equalizer
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] The known ISI which is introduced deliberately and the adjacent channel interference is removed by cancelling filter and post processing equalizer.

7. The inter-leaver is more effective if the vehicle is
a) Fast
b) Slow
c) Fast & Slow
d) None of the mentioned

View Answer

Answer: a [Reason;] The inter-leaver is more effective in fast running vehicles.

8. Channel noise is
a) Additive
b) White and stationary
c) Has infinite bandwidth
d) All of the mentioned

View Answer

Answer: d [Reason:] Channel noise is stationary, additive and white with infinite bandwidth.

9. Which noise component plays a role in decision making?
a) Relevant noise
b) Non relevant noise
c) Relevant & Non relevant noise
d) None of the mentioned

View Answer

Answer: a [Reason:] Only the relevant noise components play an important role in decision making. It does not depend on non relevant noise components.

10. Decision making needs
a) Priors
b) Likelihoods
c) Priors & Likelihoods
d) None of the mentioned

View Answer

Answer: c [Reason:] Decision making needs both priors and likelihoods and Bayes decision rule combines them to achieve minimum probability of error.

11. In matched filter _______ is performed.
a) Convolution
b) Correlation
c) Convolution & Correlation
d) None of the mentioned

View Answer

Answer: c [Reason:] In matched filter a known signal is correlated with an unknown signal. It is similar to convolving a unknown signal with time reversed version of it.

12. Which needs more signal power?
a) BPSK
b) 16-QAM
c) BPSK & 16-QAM
d) None of the mentioned

View Answer

Answer: b [Reason:] 16-QAM needs ten times more signal power than BPSK to attain the same probability of error.

13. Which has higher transmission rate?
a) BPSK
b) 16-QAM
c) BPSK & 16-QAM
d) None of the mentioned

View Answer

Answer: b [Reason:] The rate of transmission of bits in 16-QAM is four times that of BPSK.

14. Symbol error probability can also be determined using upper bound.
a) True
b) False

View Answer

Answer: a [Reason:] Certain signals lacks symmetry in representation. For those signals symbol error probability can be determined by using upper bound.

15. Which signal sets are called as equivalent signal sets?
a) Simplex
b) Bi-orthogonal
c) Simplex & Bi-orthogonal
d) None of the mentioned

View Answer

Answer: c [Reason:] Simplex signals and bi-orthogonal signals are examples of equivalent signal sets.

16. For neyman pearson decision criterion, which are important?
a) Probability of false alarm
b) Probability of miss
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] For neyman pearson decision criterion two probabilities are important – probability of false alarm and probability of miss.

17. What are the parameters calculated for an estimator?
a) Error
b) Mean square error
c) Variance
d) All of the mentioned

View Answer

Answer: d [Reason:] Some of the parameters calculated for an estimator are error, mean square error, variance, sampling deviation etc.

Communications MCQ Set 2

1. Channel’s phase response must be a linear function of
a) Time
b) Frequency
c) Time & Frequency
d) None of the mentioned

View Answer

Answer: b [Reason:] To achieve ideal transmission characteristics, the signal’s bandwidth must be constant and the channel’s phase response must be a linear function of frequency.

2. Amplitude distortion occurs when
a) Impulse response in not constant
b) Impulse response is constant
c) Frequency transfer function is constant
d) Frequency transfer function is not constant

View Answer

Answer: d [Reason:] When modulus of channel’s transfer function is not constant within W then amplitude distortion occurs.

3. Phase distortion occurs when
a) Phase response is function of frequency
b) Phase response is not a function of frequency
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: b [Reason:] When channels phase response is not a linear function of frequency within W then phase distortion occurs.

4. Equalization process includes
a) Maximum likelihood sequence estimation
b) Equalization with filters
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] Equalization process can be divided into two major categories called as maximum likelihood sequence estimator and equalizer with filter.

5. The maximum likelihood sequence estimator adjusts _______ according to _____ environment.
a) Receiver, transmitter
b) Transmitter, receiver
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: a [Reason:] In maximum likelihood sequence estimator it measures the impulse response value and adjusts the receiver environment according to that of the transmitter.

6. The filters used with equalizer is of ______ types.
a) Feed forward
b) Feed backward
c) Feed forward and feedback
d) None of the mentioned

View Answer

Answer: c [Reason:] The filters used with equalizers can be linear devices that contain only feed forward elements or non linear devices with both feed forward and feed back elements.

7. Transversal equalizers are ________ and decision feedback equalizers are ______
a) Feed forward , feed back
b) Feed back, feed forward
c) Feed forward, feed forward
d) Feedback, feedback

View Answer

Answer: a [Reason:] Linear devices with only feed forward elements are called as transversal equalizers and non linear devices with both feed forward and feed back elements are called as decision feedback equalizers.

8. Symbol spaced has ____ sample per symbol and fractionally spaced has ___ samples per symbol.
a) One, many
b) Many, one
c) One, one
d) Many, many

View Answer

Answer: a [Reason:] Predetection samples are provided only on symbol boundaries. A condition in which only one sample per symbol are provided is called as symbol spaced and the condition in which multiple samples are provided per symbol is called as fractionally spaced.

9. The _______ of the opening of eye pattern indicates the time over which the sampling for detection might be performed.
a) Length
b) Width
c) X-axis value
d) Y-axis value

View Answer

Answer: b [Reason:] An eye pattern is the display that results from measuring a system’s response to baseband signals in a prescribed way. The width of the opening gives the time over which the sampling for detection might be performed.

10. Range of time difference of the zero crossing gives the value of
a) Width
b) Distortion
c) Timing jitter
d) Noise margin

View Answer

Answer: c [Reason:] The time difference of the zero crossing in the eye pattern gives the value of timing jitter.

Communications MCQ Set 3

1. In layering, n layers provides service to
a) n layer
b) n-1 layer
c) n+1 layer
d) none of the mentioned

View Answer

Answer: c [Reason:] In layering n layer provides service to n+1 layer and use the service provided by n-1 layer.

2. Which can be used as an intermediate device in between transmitter entity and receiver entity?
a) IP router
b) Microwave router
c) Telephone switch
d) All of the mentioned

View Answer

Answer: d [Reason:] IP router, microwave router and telephone switch can be used as an intermediate device between communication of two entities.

3. Which has comparatively high frequency component?
a) Sine wave
b) Cosine wave
c) Square wave
d) None of the mentioned

View Answer

Answer: c [Reason:] Square wave has comparatively high frequency component in them.

4. Which has continuous transmission?
a) Asynchronous
b) Synchronous
c) Asynchronous & Synchronous
d) None of the mentioned

View Answer

Answer: b [Reason:] Synchronous has continuous transmission where as asynchronous have sporadic transmission.

5. Which requires bit transitions?
a) Asynchronous
b) Synchronous
c) Asynchronous & Synchronous
d) None of the mentioned

View Answer

Answer: b [Reason:] Synchronous transmission needs bit transition.

6. In synchronous transmission, receiver must stay synchronous for
a) 4 bits
b) 8 bits
c) 9 bits
d) 16 bits

View Answer

Answer: c [Reason:] In synchronous transmission, receiver must stay synchronous for 9 bits.

7. How error detection and correction is done?
a) By passing it through equalizer
b) By passing it through filter
c) By amplifying it
d) By adding redundancy bits

View Answer

Answer: d [Reason:] Error can be detected and corrected by adding additional information that is by adding redundancy bits.

8. Which is more efficient?
a) Parity check
b) Cyclic redundancy check
c) Parity & Cyclic redundancy check
d) None of the mentioned

View Answer

Answer: b [Reason:] Cyclic redundancy check is more efficient than parity check.

9. Which can detect two bit errors?
a) Parity check
b) Cyclic redundancy check
c) Parity & Cyclic redundancy check
d) None of the mentioned

View Answer

Answer: b [Reason:] CRC is more powerful and it can detect various kind of errors like 2 bit errors.

10. CRC uses
a) Multiplication
b) Binary division
c) Multiplication & Binary division
d) None of the mentioned

View Answer

Answer: c [Reason:] CRC uses more math like multiplication and binary division.

Communications MCQ Set 4

1. The sampling process include methods such as
a) Filtering
b) Sample and hold
c) Amplifying
d) None of the mentioned

View Answer

Answer: b [Reason:] The analog data is converted to digital data through sampling. Sampling is done using sample and hold mechanism which uses transistor, capacitor or shutter etc.

2. The output of sampling process are called as ________
a) Pulse code modulation
b) Pulse amplitude modulation
c) Frequency modulation
d) Amplitude modulation

View Answer

Answer: b [Reason:] In sampling process input data is split up into samples whose output samples are called as pulse amplitude modulation as the amplitude of the samples is derived from the input waveform.

3. According to Sampling theorem
a) Ts is greater than 1/2fm
b) Ts is lesser than 1/2fm
c) Ts is equal to 1/2fm
d) Ts is lesser than or equal to 1/2fm

View Answer

Answer: d [Reason:] By sampling theorem the input can be derived from the output samples if Ts is lesser than or equal to 1/2fm.

4. The fourier tranform of one impulse train is also another impulse train with period of the output equal to the
a) Period of the input
b) Reciprocal of the period of input signal
c) Half the period of input
d) Twice the period of the input

View Answer

Answer: b [Reason:] When we perform fourier tranform on one impulse train we will get another impulse train with its period reciprocally related to each other.

5. The process in which the top of each pulse in the output samples retains the shape of the analog segment is called as ________
a) Natural sampling
b) Ideal sampling
c) Aliasing
d) None of the mentioned

View Answer

Answer: a [Reason:] In the method of natural sampling, the top of each pulse in the sampled sequence retains the same shape of the analog input signal.

6. The effects of aliasing are ________
a) Attenuation of high frequency spectral replicates
b) Non uniform spectral gain applied to desired baseband spectrum
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] Aliasing is due to undersampling and its effects are attenuation and non uniform spectral gain.

7. Aliasing can be removed using
a) Prefiltering
b) Postfiltering
c) Prefiltering & Postfiltering
d) None of the mentioned

View Answer

Answer: c [Reason:] Aliasing can be removed using both prefiltering and postfiltering but prefiltering is most effective and preferred.

8. Which process is more economical?
a) Undersampling
b) Oversampling
c) Aliasing
d) None of the mentioned

View Answer

Answer: b [Reason:] Oversampling is most economic way of sampling or for converting analog information to digital as performing signal processing using digital system is less costlier than doing it with high performace analog system.

9. Flat top sampling or practical sampling has
a) Same frequency
b) Same amplitude
c) Same time difference
d) None of the mentioned

View Answer

Answer: b [Reason:] In flat top sampling the top of the pulses are flat which in turn means that they have same amplitude.

10. Multiplication of input signal with pulse train is done in ________ sampling.
a) Impulse sampling
b) Natural sampling
c) Flat top sampling
d) None of the mentioned

View Answer

Answer:b [Reason:] In impulse sampling the input signal is multiplied with impulse train and in natural sampling it is multiplied with pulse train.

Communications MCQ Set 5

1. Self information should be
a) Positive
b) Negative
c) Positive & Negative
d) None of the mentioned

View Answer

Answer: a [Reason:] Self information is always non negative.

2. The unit of average mutual information is
a) Bits
b) Bytes
c) Bits per symbol
d) Bytes per symbol

View Answer

Answer: a [Reason:] The unit of average mutual information is bits.

3. When probability of error during transmission is 0.5, it indicates that
a) Channel is very noisy
b) No information is received
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] When probability of error during transmission is 0.5 then the channel is very noisy and thus no information is received.

4. Binary Huffman coding is a
a) Prefix condition code
b) Suffix condition code
c) Prefix & Suffix condition code
d) None of the mentioned

View Answer

Answer: a [Reason:] Binary Huffman coding is a prefix condition code.

5. The event with minimum probability has least number of bits.
a) True
b) False

View Answer

Answer: b [Reason:] In binary Huffman coding the event with maximum probability has least number of bits.

6. The method of converting a word to stream of bits is called as
a) Binary coding
b) Source coding
c) Bit coding
d) Cipher coding

View Answer

Answer: b [Reason:] Source coding is the method of converting a word to stream of bits that is 0’s and 1’s.

7. When the base of the logarithm is 2, then the unit of measure of information is
a) Bits
b) Bytes
c) Nats
d) None of the mentioned

View Answer

Answer: a [Reason:] When the base of the logarithm is 2 then the unit of measure of information is bits.

8. When X and Y are statistically independent, then I (x,y) is
a) 1
b) 0
c) Ln 2
d) Cannot be determined

View Answer

Answer: b [Reason:] When X and Y are statistically independent the measure of information I (x,y) is 0.

9. The self information of random variable is
a) 0
b) 1
c) Infinite
d) Cannot be determined

View Answer

Answer: c [Reason:] The self information of a random variable is infinity.

10. Entropy of a random variable is
a) 0
b) 1
c) Infinite
d) Cannot be determined

View Answer

Answer: c [Reason:] Entropy of a random variable is also infinity.

11. Which is more efficient method?
a) Encoding each symbol of a block
b) Encoding block of symbols
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: b [Reason:] Encoding block of symbols is more efficient than encoding each symbol of a block.

12. Lempel-Ziv algorithm is
a) Variable to fixed length algorithm
b) Fixed to variable length algorithm
c) Fixed to fixed length algorithm
d) Variable to variable length algorithm

View Answer

Answer: a [Reason:] Lempel-Ziv algorithm is a variable to fixed length algorithm.

13. Coded system are inherently capable of better transmission efficiency than uncoded system.
a) True
b) False

View Answer

Answer: a [Reason:] Yes, the coded systems are capable of better transmission efficiency than uncoded system.