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## Communications MCQ Set 1

1. Which circuit is called as regenerative repeaters?
a) Analog circuits
b) Digital circuits
c) Amplifiers
d) A/D converters

Answer: b [Reason:] The main advantage of digital communication is that the signals can be reproduced easily. Thus digital circuits are called as regenerative repeaters.

2. What are the advantages of digital circuits?
a) Less noise
b) Less interference
c) More flexible
d) All of the mentioned

Answer: d [Reason:] Digital circuits are less subject to noise, distortion and interference as it works on digital pulses and also the pulses can be regenerated.

3. How many different combinations can be made from a n bit value?
a) 2(n+1)
b) 2(n)
c) 2(n)+1
d) None of the mentioned

Answer: b [Reason:] 2(n) different combinations can be made from n bit value. For example, from 2 bit value 22 different combinations-00,01,10,11 can be made.

4. How many bytes does a gigabyte have?
a) 1 million bytes
b) 10 million bytes
c) 1 billion bytes
d) 10 billion bytes

Answer: c [Reason:] One gigabyte has 1 billion bytes.

5. What is the ASCII value of space?
a) 32
b) 48
c) 96
d) 65

Answer: a [Reason:] The ASCII value of space is 32 and ASCII value of 0 is 48.

6. Which block or device does the data compression?
a) Channel encoder
b) Source encoder
c) Modulator
d) None of the mentioned

Answer: b [Reason:] Source encoder converts the digital or analog signal to a sequence of binary digits. This process is called as source encoding or compression.

7. What is code rate?
a) k/n
b) n/k
c) All of the mentioned
d) None of the mentioned

Answer: a [Reason:] Here n is the total bits of sequence and k bits are mapped.Amount of redundancy introduced is given by n/k and its reciprocal is code rate.

8. Pulse shaping is done by which block or system?
a) Encoder
b) Baseband modulator
c) Pulse code modulator
d) Demodulator

Answer: c [Reason:] Pulse code modulator does filtering process to build pulses that occupy more than one-bit time.

9. Equalizer is used for ?
a) Filtering
b) Diminish distortion
c) All of the mentioned
d) None of the mentioned

Answer: c [Reason:] Equalizer is used as a filtering option and also diminishes or reduces the distortion.

10. Source coding block is used for?
a) Compressing
b) Digitizing
c) A/D conversion
d) All of the mentioned

Answer: d [Reason:] Source encoding does all these processes-compression , digitizing the signal and performs analog to digital conversion.

11. Which measurement considers phase as an important parameter?
a) Coherent
b) Non-coherent
c) All of the mentioned
d) None of the mentioned

Answer: a [Reason:] Coherent measurement considers phase as the important parameter.

12. The size of the alphabet M in symbol is calculated as?
a) 2(k+1)
b) 2k
c) 2(k-1)
d) 1+2k

Answer: b [Reason:] The size of the alphabet is calculated using 2^k where k is the number of bits in the symbol.

## Communications MCQ Set 2

1. Power spectral density function is a ?
a) Real and even function
b) Non negative function
c) Periodic
d) All of the mentioned

Answer: d [Reason:] A power signal is periodic signal and its function is a real even and non negative function as per the definition.

2. Energy spectral density defines
a) Signal energy per unit area
b) Signal energy per unit bandwidth
c) Signal power per unit area
d) Signal power per unit bandwidth

Answer: b [Reason:] Energy spectral density gives the signal energy equal to the area under the waveform energy spectral density versus frequency curve.

3. Power spectrum describes distribution of _________ under frequency domain.
a) Mean
b) Variance
c) Gaussian
d) None of the mentioned

Answer: b [Reason:] Power spectrum gives the distribution of variance of a signal in the frequency domain, sampled into spectral components.

4. How can power spectral density of non periodic signal be calculated?
a) By integrating
b) By truncating
c) By converting to periodic
d) None of the mentioned

Answer: b [Reason:] A power signal usually is a periodic signal. But power spectral density of non periodic signal can be calculated by truncating it and observing it in the range of (-T/2,T/2).

5. What is Wiener-Khinchin theorem?
a) Spectral density and auto-covariance makes a fourier transform pair
b) Spectral density and auto-correlatioon makes a fourier tranform pair
c) Spectral density and variance makes a fourier tranform pair
d) None of the mentioned

Answer: b [Reason:] According to the theorem spectral density of a signal x(t) and auto correlation function makes a fourier tranform pair.

6. According to Parseval’s theorem the energy spectral density curve is equal to?
a) Area under magnitude of the signal
b) Area under square of the magnitude of the signal
c) Area under square root of magnitude of the signal
d) None of the mentioned

Answer: b [Reason:] According to Parseval/s theorem the energy spectral density function can be given as equal to the square of the magnitude of the signal x(t).

7. Spectogram is the graph plotted against ?
a) Frequency domain
b) Time domain
c) Both of the mentioned
d) None of the mentioned

Answer: b [Reason:] Spectral density function is plotted against frequency domain and spectogram is a graph which is plotted against time domain.

8. Autocorrelation is a function which matches –
a) Two same signals
b) Two different signal
c) One signal with its delayed version
d) None of the mentioned

Answer: c [Reason:] Autocorrelation is a function that matches a signal with its delayed version.

9. Autocorrelation is a function of
a) Time
b) Frequency
c) Time difference
d) Frequency difference

Answer: c [Reason:] Autocorrelation is a function of time difference as it matches the signal with its delayed version.

10. Autocorrelation is maximum at _______
a) Unity
b) Origin
c) Infinite point
d) None of the mentioned

Answer: b [Reason:] According to its properties autocorrelation is maximum at origin.

11. Autocorrelation function of periodic signal is equal to _______
a) Energy of the signal
b) Power of the signal
c) Its area in frequency domain
d) None of the mentioned

Answer: b [Reason:] Autocorrelation function of a real valued signal is equal to energy of the signal and auto-correlatioon function of periodic signal is equal to the average power of the signal.

12. Autocorrelation is a _______ function.
a) Real and even
b) Real and odd
c) Complex and even
d) Complex and odd

Answer: a [Reason:] According to properties of autocorrelation function it a even function when the frequency value f is real.

13. Autocorrelation function of white noise will have ?
a) Strong peak
b) Infinite peak
c) Weak peak
d) None of the mentioned

Answer: a [Reason:] Autocorrelation function curve of continuous time white noise signal has strong peak.

## Communications MCQ Set 3

1. Which method is much better and efficient?
a) Vector quantization
b) Scalar quantization
c) Vector & Scalar quantization
d) None of the mentioned

Answer: a [Reason:] Vector quantization will always equal or exceed the performance of scalar quantization.

2. Analog source coding method are
a) Temporal waveform coding
b) Spectral waveform coding
c) Model based coding
d) All of the mentioned

Answer: d [Reason:] Three types of analog source coding methods are temporal waveform coding, spectral waveform coding and model based coding.

3. The source output in PCM and DPCM is quasi stationary.
a) True
b) False

Answer: b [Reason:] The source output of PCM and DPCM and stationary in nature.

4. Which reduces the dynamic range of quantization noise in PCM ?
a) Non uniform quantizer
b) Uniform quantizer
d) None of the mentioned

Answer: c [Reason:] Adaptive quantizer reduces the dynamic range of quantization noise in PCM and DPCM.

5. The type of distortion which occurs in delta modulation are
b) Granular noise
c) Slope overload distortion & Granular noise
d) None of the mentioned

Answer: c [Reason:] The two types of distortion that occurs in delta modulation are slope overload distortion and granular noise.

6. Binomial distribution deals with
a) Continuous random variable
b) Discrete random variable
c) Continuous & Discrete random variable
d) None of the mentioned

Answer: b [Reason:] Binomial distribution deals with discrete random variable.

7. In poisson distribution mean is ______ variance.
a) Greater than
b) Lesser than
c) Equal to
d) Does not depend on

Answer: c [Reason:] In poisson distribution, variance is nearly same or equal to mean of the distribution.

8. Stochastic process are
a) Random in nature
b) Are function of time
c) Both of the mentioned
d) None of the mentioned

Answer: c [Reason:] Stochastic process are random in nature and are function of time.

9. Stochastic processes are
a) Strict sense stationary process
b) Wide sense stationary process
c) All of the mentioned
d) None of the mentioned

Answer: b [Reason:] Stochastic process is a wide sense stationary process.

10. Gaussian process is a
a) Wide sense stationary process
b) Strict sense stationary process
c) All of the mentioned
d) None of the mentioned

Answer: c [Reason:] If Gaussian process is a wide sense stationary process then it will also be strict sense stationary process.

## Communications MCQ Set 4

1. Top layer is
a) Physical media
b) Application
c) Design
d) None of the mentioned

Answer: b [Reason:] Top layer is application where as bottom layer is physical media.

2. Entities also does
a) Error correction
b) A/D
c) D/A
d) All of the mentioned

Answer: d [Reason:] Entities also does A/D, D/A, encryption and error correction.

3. In channel, delay is
a) Fixed
b) Variable
c) Fixed & Variable
d) None of the mentioned

Answer: c [Reason:] In channel, delay can be either fixed or variable.

4. Channel can provide connectivity to
a) Point to point
b) 1 to many
c) Many to many
d) All of the mentioned

Answer: d [Reason:] Channel can provide connectivity between point to point, 1 to many and also many to many.

5. Embedding is a form of
a) Abstraction
b) Layering
c) Entity sharing
d) None of the mentioned

Answer: b [Reason:] Embedding is a form of layering.

6. Transmission media is
a) Acoustic
b) Guided
c) Optical
d) All of the mentioned

Answer: d [Reason:] Transmission media can be acoustic, electronic or optical form.

7. In transmission media, the symbol type is generally
a) Analog
b) Digital
c) Analog & Digital
d) None of the mentioned

Answer: a [Reason:] In transmission media, the symbol type is generally analog signals.

8. Noise is _____ in nature.
a) Random
b) Systematic
c) Random or Systematic
d) None of the mentioned

Answer: c [Reason:] Noise can be random or systematic.

9. The radiation loss increases as
a) Frequency increases
b) Frequency decreases
c) Does not depend on frequency
d) None of the mentioned

10. Attenuation is a function of
a) Channel length
b) Transmission media
c) Signal frequencies
d) All of the mentioned

Answer: d [Reason:] Attenuation is a function of channel length, transmission media and signal frequencies.

## Communications MCQ Set 5

1. Acquisition is a process of bringing two spreading signals into _______ alignment.
a) Fine
b) Coarse
c) Fine & Coarse
d) None of the mentioned

Answer: b [Reason:] Acquisition is a process of bringing two spreading signals into coarse alignment with one another.

2. Tracking maintains the possible waveform ______ alignment using feedback loop.
a) Fine
b) Coarse
c) Fine & Coarse
d) None of the mentioned

Answer: a [Reason:] Tracking continuously maintains the best possible waveform fine alignment by means of a feedback loop.

3. Acquisition can be of ______ type.
a) Coherent
b) Non coherent
c) Coherent & Non coherent
d) None of the mentioned

Answer: c [Reason:] Acquisition can be categorized as two types coherent and non coherent.

4. Uncertainty in the distance between transmitter and receiver translates into uncertainty in
a) Frequency
b) Propagation delay
c) Efficiency
d) None of the mentioned

Answer: b [Reason:] uncertainty in the distance between the transmitter and the receiver translates into uncertainty in the propagation delay.

5. Acquisition uses ______ likelihood algorithm for acquiring the code.
a) Minimum
b) Maximum
c) Minimum & Maximum
d) None of the mentioned

Answer: b [Reason:] It considers all possible code positions in parallel and maximum likelihood algorithm is used to acquire the code.

6. Acquisition can be accomplished ________ as all possible codes are examined ______
a) Slowly, one by one
b) Rapidly, simultaneously
c) Slowly, simultaneously
d) Rapidly, one by one

Answer: b [Reason:] Acquisition can be accomplished rapidly as all possible codes are examined simultaneously.

7. Matched filter does ______ search.
a) Serial
b) Parallel
c) Serial & Parallel
d) None of the mentioned

Answer: a [Reason:] A single correlator or matched filter does serial search.

8. How many correlators are used for despreading and code tracking function?
a) One
b) Two
c) Three
d) None of the mentioned