laboursonline – MCQs, Mock Tests | Electrical measurements Digital Communications MCQs set-15

Which should be used first to decrypt?

1. Public key
2. Private key
3. Public & Private key
4. None of the mentioned

✅ Correct Answer: 2

The digital signature provides authentication to the

1. Sender
2. Message
3. Sender & Message
4. None of the mentioned

✅ Correct Answer: 3

In hash function output length is fixed.

1. True
2. False
3.
4.

✅ Correct Answer: 1

The hash function

1. Is collision free
2. Has manageable collision
3. Has high unmanageable level of collision
4. None of the mentioned

✅ Correct Answer: 1

DSA protocol is based on

1. Discrete logarithm problem
2. Continuous logarithm problem
3. Discrete & Continuous logarithm problem
4. None of the mentioned

✅ Correct Answer: 1

What is the source for performance degradation?

1. Thermal noise
2. Man made noise
3. Natural noise
4. All of the mentioned

✅ Correct Answer: 4

The received power is attenuated by a factor called

1. Path loss
2. Free space loss
3. Path & Free space loss
4. None of the mentioned

✅ Correct Answer: 3

Scintillation describes the fading caused by

1. Atmospheric changes
2. Physical changes
3. Thermal noise
4. Propagating effects

✅ Correct Answer: 2

Large scale fading refers the attenuation in

1. Amplitude
2. Phase
3. Signal power
4. None of the mentioned

✅ Correct Answer: 3

Small scale refers to changes in

1. Amplitude
2. Phase
3. Amplitude & Phase
4. None of the mentioned

✅ Correct Answer: 3

Small scale fading manifests due to

1. Signal dispersion
2. Time variant behavior
3. Signal dispersion & Time variant behavior
4. None of the mentioned

✅ Correct Answer: 3

The parameters used to describe large scale fading are

1. Reference distance
2. Path loss exponent
3. Standard deviation of random variable
4. All of the mentioned

✅ Correct Answer: 4

Small scale fading occurs due to

1. Doppler shift
2. Time delay
3. Doppler shift & Time delay
4. None of the mentioned

✅ Correct Answer: 3

What are the types of small scale fading that occurs due to Doppler shift?

1. Slow fading
2. Fast fading
3. Slow & Fast fading
4. None of the mentioned

✅ Correct Answer: 3

Multiple isolated peaks in multipath components is called as

1. Fingers
2. Returns
3. Fingers & Returns
4. None of the mentioned

✅ Correct Answer: 3

If delay time is greater than symbol time, _______ fading occurs.

1. Frequency selective
2. Time selective
3. Frequency non selective
4. None of the mentioned

✅ Correct Answer: 1

If delay time is lesser than symbol time, ______ fading occurs.

1. Frequency non selective
2. Flat
3. Frequency non selective & Flat
4. None of the mentioned

✅ Correct Answer: 3

When channel coherence bandwidth is greater than the transmitted signal bandwidth ______ occurs.

1. Time selective
2. Frequency selective
3. Frequency non selective
4. None of the mentioned

✅ Correct Answer: 3

Channel’s time spreading properties are

1. Coherence bandwidth
2. Signal dispersion
3. Coherence bandwidth & Signal dispersion
4. None of the mentioned

✅ Correct Answer: 3

When channel coherence time is less than the time duration of a transmission symbol, then ______ fading occurs.

1. Fast
2. Slow
3. Time selective
4. None of the mentioned

✅ Correct Answer: 1

Minimum time required for magnitude change or phase change is called as

1. Shift time
2. Coherence time
3. Delay time
4. None of the mentioned

✅ Correct Answer: 2

When a user’s moving, the user’s velocity causes shift in frequency. This is called as

1. Doppler shift
2. Frequency shift
3. Velocity shift
4. None of the mentioned

✅ Correct Answer: 1

Coherence time is _______ to Doppler spread.

1. Directly proportional
2. Inversely proportional
3. Not dependent
4. None of the mentioned

✅ Correct Answer: 2

Block fading occurs in

1. Frequency domain
2. Time domain
3. Frequency & Time domain
4. None of the mentioned

✅ Correct Answer: 3

If coherence bandwidth is smaller than the bandwidth of the signal, _____ fading occurs.

1. Flat
2. Frequency selective
3. Fast fading
4. Time selective

✅ Correct Answer: 2

Flat fading can be avoided or stopped by

1. Error coding
2. Equalization
3. Adaptive bit loading
4. All of the mentioned

✅ Correct Answer: 4

The effect of Doppler shift can be counterattacked by

1. OFDM
2. By using two receivers with separate antennas
3. By using diversity receiver
4. All of the mentioned

✅ Correct Answer: 4

When transmitter and receiver moves towards each other, the magnitude of frequency shift is

1. Positive
2. Negative
3. Zero
4. Infinity

✅ Correct Answer: 1

If signalling rate is less than fading rate, _____ fading occurs.

1. Slow
2. Fast
3. Time selective
4. None of the mentioned

✅ Correct Answer: 2

Frequency tracking loop can minimize irreducible error rate by using

1. GMSK
2. DMSK
3. MSK
4. QAM

✅ Correct Answer: 2

The technique for combining diversity signals are

1. Feedback
2. Maximal ratio
3. Equal gain
4. All of the mentioned

✅ Correct Answer: 4

Diversity technique is used for combating

1. Fading
2. Error bursts
3. Co-channel interference
4. All of the mentioned

✅ Correct Answer: 4

Diversity technique is applied at

1. Base station
2. Mobile receiver
3. Base station & Mobile receiver
4. None of the mentioned

✅ Correct Answer: 3

Which is more effective and commonly preferred technique?

1. Time diversity
2. Spatial diversity
3. Frequency diversity
4. None of the mentioned

✅ Correct Answer: 2

What are the modes of adaptive equalizer?

1. Training mode
2. Tracking mode
3. Training & Tracking mode
4. None of the mentioned

✅ Correct Answer: 3

Which signalling scheme is preferred for fading channel?

1. Frequency based modulation
2. Phase based modulation
3. Frequency & Phase based modulation
4. None of the mentioned

✅ Correct Answer: 3

Uncorrelated fading occurs when

1. Time span is small
2. Time span is large
3. Does not depend on time span
4. None of the mentioned

✅ Correct Answer: 2

Interleaving does

1. Forward error correction
2. Backward error correction
3. Forward & Backward error correction
4. None of the mentioned

✅ Correct Answer: 1

Rake receiver does

1. Counter effects multi-path fading
2. Resembles equalizer
3. Resembles equalizer & Counter effects multi-path fading
4. None of the mentioned

✅ Correct Answer: 3

Information reliability depends on

1. Magnitude of each component
2. Time of arrival of each component
3. Magnitude & Time of arrival of each component
4. None of the mentioned

✅ Correct Answer: 3

A rake receiver uses multiple

1. Delay circuits
2. Correlators
3. Detectors
4. None of the mentioned

✅ Correct Answer: 2

Rake receivers are used in

1. Radio astronomy
2. CDMA
3. W-CDMA
4. All of the mentioned

✅ Correct Answer: 4

The rake receivers functions are similar to

1. Equalizer
2. Matched filter
3. Equalizer & Matched filter
4. None of the mentioned

✅ Correct Answer: 3

Fading channel has memory.

1. True
2. False
3.
4.

✅ Correct Answer: 1

How can frequency selective distortion be minimized?

1. By using pilot signal
2. By adaptive equalization
3. By spread spectrum
4. All of the mentioned

✅ Correct Answer: 4

How can slow fading be minimized?

1. By diversity technique
2. Error correcting codes
3. By diversity technique & Error correcting codes
4. None of the mentioned

✅ Correct Answer: 3

Fast fading can be minimized by

1. Robust modulation
2. Coding and interleaving
3. Robust modulation, Coding and interleaving
4. None of the mentioned

✅ Correct Answer: 3

The decision feedback equalizer has a linear traversal filter which is

1. Feed forward section
2. Feedback section
3. Feed forward section & Feedback section
4. None of the mentioned

✅ Correct Answer: 1

The ISI and adjacent channel interference is removed by

1. Cancelling filter
2. Port processing equalizer
3. Cancelling filter & Port processing equalizer
4. None of the mentioned

✅ Correct Answer: 3

The inter-leaver is more effective if the vehicle is

1. Fast
2. Slow
3. Fast & Slow
4. None of the mentioned

✅ Correct Answer: 1