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## Communications MCQ Set 1

1. Wavelength and antenna size are related as
a) λ/2
b) λ/4
c) 2λ
d) 4λ

Answer: b [Reason:] The transmission of Em field in space is done with the help of antennas. Antenna size depends of the wavelength. The length of the antenna is equal to λ/4.

2. The detection method where carrier’s phase is given importance is called as
a) Coherent detection
b) Non coherent detection
c) Coherent detection & Non coherent detection
d) None of the mentioned

Answer: a [Reason:] When the receiver uses carrier’s phase as major factor for detection then it is called as coherent detection and when carrier is not given importance it is called as non coherent detection.

3. The coherent modulation techniques are
a) PSK
b) FSK
d) All of the mentioned

Answer: d [Reason:] Some of the examples of coherent modulation techniques are phase shift keying, amplitude shift keying, frequency shift keying and continuous phase modulation.

4. The real part of sinusoid carrier wave is called as
a) Inphase
c) Inphase & Quadrature
d) None of the mentioned

Answer: a [Reason:] The two main parts of sinusoid carrier wave – real part is called as inphase and the imaginary part is called as quadrature.

5. Antipodal signal sets are those vectors that can be illustrated as
a) Two 180 opposing vector
b) Two 90 opposing vector
c) Two 360 opposing vector
d) None of the mentioned

Answer: a [Reason:] In BPSK the two vectors, the signal set can be illustrated as two 180 opposing vector which is called as antipodal signal sets.

6. The FSK signal which has gentle shift from one frequency level to another is called as
a) Differential PSK
b) Continuous PSK
c) Differential & Continuous PSK
d) None of the mentioned

Answer: b [Reason:] In general FSK the signal change from one frequency to another will be abrupt but in continuous FSK the signal change from one frequency to another will be gentle and gradual.

7. Which modulation scheme is also called as on-off keying method?
b) FSK
c) PSK
d) GMSK

Answer: a [Reason:] In ASK modulation scheme the signal attains either maximum amplitude or zero point. Thus it is also called as on-off keying.

8. In amplitude phase keying each phase vector is separated by
a) 90
b) 0
c) 45
d) 180

Answer: c [Reason:] The combination of ASK and PSK is called as APK. In APK each vector is separated by 45.

9. The term heterodyning refers to
a) Frequency conversion
b) Frequency mixing
c) Frequency conversion & mixing
d) None of the mentioned

Answer: c [Reason:] The term heterodyning means frequency conversion and frequency mixing that yields a spectral shift in the signal.

10. The transformation of waveform into a single point in signal space is called as
a) Vector point
b) Predetection point
c) Preamplification point
d) Transformation point

Answer: b [Reason:] The first step of detection process is to reduce waveform into a single or group of random variable. This first step in the transformation of waveform into a point in signal space. This point is called as predetection point.

## Communications MCQ Set 2

1. Digital communication is _______ to environmental changes?
a) Less sensitive
b) More sensitive
c) Does not depend
d) None of the mentioned

Answer: a [Reason:] Digital communication is less sensitive to the environmental changes like temperature etc.

2. Advantages of digital communication are
a) Easy multiplexing
b) Easy processing
c) Reliable
d) All of the mentioned

Answer: d [Reason:] Digital communication is a very reliable communication. It is easy for multiplexing, easy for signalling and processing etc.

3. What is necessary for digital communication?
a) Precision timing
b) Frame synchronization
c) Character synchronization
d) All of the mentioned

Answer: d [Reason:] Bit, character, frame synchronization and precision timing is necessary for digital communication. This is considered as disadvantage of digital communication.

4. What are the disadvantages of digital communication?
a) Needs more bandwidth
b) Is more complex
c) Both of the mentioned
d) None of the mentioned

Answer: c [Reason:] Digital communication needs more bandwidth, has higher complexity and little performance degradation occurs during analog to digital conversion and vice versa.

5. Examples of digital communication are
a) ISDN
b) Modems
c) Classical telephony
d) All of the mentioned

Answer: d [Reason:] Some of the examples of digital communication systems are classical telephony, ISDN, Modems, LANs, PCM TDM etc.

6. Which system uses digital transmission?
a) ISDN
b) LANs
c) ISDN & LANs
d) None of the mentioned

Answer: c [Reason:] Though the signal type is analor or digital, the transmission takes place in digital domain in ISDN and LANs.

7. The interval of frequencies outside which the spectrum is zero is called as ________
a) null to null bandwidth
b) normalized bandwidth
c) absolute bandwidth
d) none of the mentioned

Answer:c [Reason:] The measure of frequencies outside which spectrum is zero is called as absolute bandwidth. It is usually infinite.

8. The attenuation level in bounded power spectral density is
a) 35
b) 50
c) 35 & 50
d) none of the mentioned

Answer: c [Reason:] Bounded power spectral density is the bandwidth outside which the spectrum must have fallen to a stated level below that found at the band center.

9. Synchronization available in digital communication are
a) Symbol synchronization
b) Frame synchronization
c) Carrier synchronization
d) All of the mentioned

Answer: d [Reason:] The synchronization techniques available in digital communication are symbol synchronization, frame synchronization and carrier synchronization.

10. Digital system includes
a) Better encryption algorithm
b) Difficult data multiplexing
c) Both of the mentioned
d) None of the mentioned

Answer: a [Reason:] Digital system has advantage of better encryption algorithm, easier data multiplexing and more reliability.

11. Analog to digital conversion includes
a) Sampling
b) Quantization
c) Sampling & Quantization
d) None of the mentioned

Answer: c [Reason:] Analog to digital conversion is a two step process which includes sampling and quantization.

## Communications MCQ Set 3

1. What are the main features of receiver?
a) Synchronization
b) Multiple parallel receiver chain
c) Both of the mentioned
d) None of the mentioned

Answer: c [Reason:] The main features of receiver which increases its complexity are synchronization of carrier, phase, and timing and multiple parallel receiver chain.

2. What conditions must be fulfilled in a good digital communication system?
a) High data rate
b) High fidelity
c) Low transmit power
d) All of the mentioned

Answer: d [Reason:] Some of the conditions which must be satisfied in a digital communication system are high data rate, high fidelity, low bandwidth, low transmit power and low transmitter and receiver complexity.

3. Wired channels are
a) Lossy
b) Lossless
c) Lossy & Lossless
d) None of the mentioned

Answer: a [Reason:] Wired channels are lossy channels.

4. The equivalent temperature in a receiver design must be kept
a) Low
b) High
c) Does not affect the receiver
d) None of the mentioned

Answer: a [Reason:] The equivalent temperature is the function of the receiver design and it must be always kept low.

5. Which corrects the sampling time problem in a digital system?
a) Interpolator
b) Decimator
c) Equalizer
d) Filter

Answer: a [Reason:] Interpolator corrects the sampling time problem using discrete time processing.

6. What are the main features of a transmitter?
a) Higher clock speed
b) Linear power amplifier
c) Directional antennas
d) All of the mentioned

Answer: d [Reason:] Some of the main features which makes the transmitter complex are higher clock speed, higher transmit power, directional antennas and need for linear amplifier.

7. Transmission media used in low frequency band are
a) Air
b) Water
c) Copper cable
d) All of the mentioned

Answer: d [Reason:] Air, water and copper cable can be used as transmission media in low frequency band communication.

8. Transmission media used for medium frequency band are
a) Coaxial cable
b) Copper cable
c) Optical fiber
d) All of the mentioned

Answer: b [Reason:] For medium frequency band communication air and copper cable can only be used as transmission medium.

9. Matched filter technique is used to
a) Increase SNR
b) Decrease SNR
c) SNR is not affected
d) None of the mentioned

Answer: a [Reason:] Matched filter technique is a demodulation process used to increase SNR.

10. Matched filter can also be used as least squares estimator.
a) True
b) False

Answer: a [Reason:] A matched filter can also be used as a least squares estimator.

11. Digital communication system can handle
a) Analog signals
b) 1D signals
c) 2D signals
d) All of the mentioned

Answer: d [Reason:] Digital communication system can handle signals that are analog or those that are already digital. It can also handle 1D and 2D signals.

12. The information source of digital communication system can be
a) Packetized
b) Continuous
c) Packetized & Continuous
d) None of the mentioned

Answer: c [Reason:] Information source comes from a higher networking layer. It can be continuous or packetized.

## Communications MCQ Set 4

1. DS/BPSK includes
b) Demodulation
c) Despreading & Demodulation
d) None of the mentioned

Answer: c [Reason:] DS/BPSK is a two step precess which includes despreading and demodulation.

2. In direct sequence process which step is performed first?
b) Demodulation
c) Despreading & Demodulation
d) None of the mentioned

Answer: a [Reason:] In direct sequence process , De-spreading correlator is followed by a modulator.

3. The processing gain is given as
a) Wss/R
b) R/Wss
c) Wss/2R
d) R/2Wss

Answer: a [Reason:] The processing gain is given by the ratio of minimum bandwidth of the data to data rate.

4. Chip is defined as
a) Shortest uninterrupted waveform
b) Largest uninterrupted waveform
c) Shortest diversion
d) None of the mentioned

Answer: a [Reason:] A chip is defined as the shortest uninterrupted waveform in the system.

5. Processing gain is given as
a) Wss/R
b) Rch/R
c) Wss/R & Rch/R
d) None of the mentioned

Answer; c [Reason:] Processing gain is given as both as the ratio of minimum bandwidth of the data to data rate and also the by the ratio of code chip rate and data rate as minimum bandwidth is approximately equal to code chip rate.

6. Which modulation scheme is preferred for direct sequence spread spectrum process?
a) BPSK
b) QPSK
c) BPSK & QPSK
d) None of the mentioned

Answer: c [Reason:] Both the modulation scheme BPSK and QPSK can be used for direct sequence spread spectrum process.

7. The frequency hopping system uses ______ modulation scheme.
a) FSK
b) BPSK
c) MFSK
d) MPSK

Answer: c [Reason:] The frequency hopping spread spectrum system uses M-ary frequency shift keying modulation scheme.

8. The minimum spacing between consecutive hop positions gives the
a) Minimum number of chips necessary
b) Maximum number of chips necessary
c) Chip rate
d) None of the mentioned

Answer: a [Reason:] The minimum spacing between consecutive hop positions given the minimum number of chips necessary in the frequency word.

9. Which system allows larger processing gain?
a) Direct sequence
b) Frequency hopping
c) Direct sequence & Frequency hopping
d) None of the mentioned

Answer: b [Reason:] Frequency hopping spread spectrum system allows greater processing gain than direct sequence spread spectrum technique.

10. In which technique is phase coherence hard to maintain?
a) Direct sequence
b) Frequency hopping
c) Direct sequence & Frequency hopping
d) None of the mentioned

Answer: b [Reason:] In frequency hopping spread spectrum phase coherence is hard to maintain from hop to hop.

11. Which type of demodulator is used in frequency hopping technique?
a) Coherent
b) Non coherent
c) Coherent & Non coherent
d) None of the mentioned

Answer: b [Reason:] As it is difficult to maintain phase coherence, non coherent demodulator is used.

12. Robustness gives the inability of a signal to withstand the impairments.
a) True
b) False

Answer: b [Reason:] Robustness gives the ability of a signal to withstand the impairments such as noise, jamming etc.

13. Chips are the
a) Repeated symbols
b) Non repeated symbols
c) Smallest length symbols
d) None of the mentioned

Answer: a [Reason:] The repeated symbols are called as chips.

14. Slow frequency hopping is
a) Several hops per modulation
b) Several modulations per hop
c) Several symbols per modulation
d) None of the mentioned

Answer: b [Reason:] Slow frequency hopping is several modulation per frequency hop.

15. Fast frequency hopping is
a) Several modulations per hop
b) Several modulations per symbol
c) Several symbols per modulation
d) None of the mentioned

Answer: d [Reason:] Fast frequency hopping is several frequency hops per modulation.

16. Which duration is shorter?
a) Hop duration
b) Symbol duration
c) Chip duration
d) None of the mentioned

Answer: a [Reason:] In frequency hopping technique hop duration is shorter than the symbol duration.

## Communications MCQ Set 5

1. The technique for combining diversity signals are
a) Feedback
b) Maximal ratio
c) Equal gain
d) All of the mentioned

Answer: d [Reason:] The most common techniques used for combining diversity signals are selection, feedback, maximal ratio and equal gain.

2. Diversity technique is used for combating
b) Error bursts
c) Co-channel interference
d) All of the mentioned

Answer: d [Reason:] 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
c) Base station & Mobile receiver
d) None of the mentioned

Answer: c [Reason:] 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

Answer: b [Reason:] 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) Both of the mentioned
d) None of the mentioned

Answer: a [Reason:] Diversity technique does not require training overhead at the transmitter and also provides significant link performance.

6. What are the modes of adaptive equalizer?
a) Training mode
b) Tracking mode
c) Training & Tracking mode
d) None of the mentioned

Answer: c [Reason:] Adaptive equalizer operates on two modes – training mode and tracking mode.

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

Answer: c [Reason:] 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

Answer: b [Reason:] As the time span increases, the fading is more uncorrelated and effectiveness also increases.

9. Interleaving does
a) Forward error correction
b) Backward error correction
c) Forward & Backward error correction
d) None of the mentioned

Answer: a [Reason:] Inter leaver does forward error correction.

10. Rake receiver does
a) Counter effects multi-path fading
b) Resembles equalizer
c) Both of the mentioned
d) None of the mentioned

Answer: c [Reason:] Rake receiver resembles equalizers and it is used to counter the effects of multipath fading and is also used to exploit the path diversity.

11. Information reliability depends on
a) Magnitude of each component
b) Time of arrival of each component
c) Both of the mentioned
d) None of the mentioned

Answer: c [Reason:] The information reliability can be improved by computing the amplitude and time of arrival of each component.

12. A rake receiver uses multiple
a) Delay circuits
b) Correlators
c) Detectors
d) None of the mentioned

Answer: b [Reason:] A rake receiver uses multiple correlators to separately detect multiple strongest components.

13. Rake receivers are used in
b) CDMA
c) W-CDMA
d) All of the mentioned

Answer: d [Reason:] 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