Some Dgital communication important MCQ's questions for university exams, Placements, companies exams, GATE and other exams preparations with answers.
1. Which noise is useful for dithering?
a) White noise
b) Pink noise
c) Brown noise
d) None of the mentioned
Answer: c
Explanation: Brown noise is sometimes useful for dithering.
2. Capacity of a channel can be increased by
a) Increasing channel bandwidth
b) Increasing signal power
c) Increasing channel bandwidth &signal power
d) None of the mentioned
Answer: c
Explanation: Capacity of a channel can be increased by increasing channel bandwidth and
also by increasing signal power.
3. Capacity of the channel can be increased by reducing in band noise power.
a) True
b) False
Answer: a
Explanation: Capacity of a channel can be increased by reducing the in band noise power.
4. Noise has
a) Infinite energy
b) Infinite power
c) Infinite energy & power
d) None of the mentioned
Answer: a
Explanation: Noise has infinite energy signal.
5. Thermal noise is
a) Energy signal
b) Power signal
c) Energy & Power signal
d) None of the mentioned
Answer: b
Explanation: Thermal noise is considered as power signal as it has infinite energy.
6. Thermal noise is a wide sense stationary process.
a) True
b) False
Answer: a
Explanation: Thermal noise is modeled as a wide sense stationary stochastic process.
7. The maximum likelihood function is
a) Positive
b) Negative
c) Any of the mentioned
d) None of the mentioned
Answer: a
Explanation: The maximum likelihood function is always positive.
8. Matched filtering operation includes
a) Spectral phase matching
b) Spectral amplitude matching
c) Spectral phase & amplitude matching
d) None of the mentioned
Answer: c
Explanation: Matched filtering includes two operations – spectral amplitude matching and
spectral phase matching.
9. Matched filter is
a) Linear
b) Non linear
c) Linear & Non linear
d) None of the mentioned
Answer: a
Explanation: Matched filter is a linear filter.
10. Which consists of less ISI?
a) Nyquist filter
b) Raised cosine filter
c) Nyquist & Raised cosine filter
d) None of the mentioned
Answer: b
Explanation: Raised cosine filter results in less ISI than Nyquist filter.
11. Digital communication is _______ to environmental changes?
a) Less sensitive
b) More sensitive
c) Does not depend
d) None of the mentioned
Answer: a
Explanation: Digital communication is less sensitive to environmental changes like
temperature etc.
12. Advantages of digital communication are
a) Easy multiplexing
b) Easy processing
c) Reliable
d) All of the mentioned
Answer: d
Explanation: Digital communication is a very reliable communication. It is easy for
multiplexing, easy for signalling and processing etc.
13. What is necessary for digital communication?
a) Precision timing
b) Frame synchronization
c) Character synchronization
d) All of the mentioned
Answer: d
Explanation: Bit, character, frame synchronization and precision timing is necessary for
digital communication. This is considered as a disadvantage of digital communication.
14. What are the disadvantages of digital communication?
a) Needs more bandwidth
b) Is more complex
c) Needs more bandwidth & Is more complex
d) None of the mentioned
Answer: c
Explanation: Digital communication needs more bandwidth, has higher complexity and little
performance degradation occurs during analog to digital conversion and vice versa.
15. Examples of digital communication are
a) ISDN
b) Modems
c) Classical telephony
d) All of the mentioned
Answer: d
Explanation: Some of the examples of digital communication systems are classical
telephony, ISDN, Modems, LANs, PCM TDM etc.
16. Which system uses digital transmission?
a) ISDN
b) LANs
c) ISDN & LANs
d) None of the mentioned
Answer: c
Explanation: Though the signal type is analog or digital, the transmission takes place in the
digital domain in ISDN and LANs.
17. 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
Explanation: The measure of frequencies outside which spectrum is zero is called as
absolute bandwidth. It is usually infinite.
18. The attenuation level in bounded power spectral density is
a) 35
b) 50
c) 35 & 50
d) none of the mentioned
Answer: c
Explanation: 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.
19. Synchronization available in digital communication are
a) Symbol synchronization
b) Frame synchronization
c) Carrier synchronization
d) All of the mentioned
Answer: d
Explanation: The synchronization techniques available in digital communication are symbol
synchronization, frame synchronization and carrier synchronization.
20. Digital system includes
a) Better encryption algorithm
b) Difficult data multiplexing
c) All of the mentioned
d) None of the mentioned
Answer: a
Explanation: Digital system has an advantage of better encryption algorithm, easier data
multiplexing and more reliability.
21. Analog to digital conversion includes
a) Sampling
b) Quantization
c) Sampling & Quantization
d) None of the mentioned
Answer: C
23. What are the main features of a receiver?
a) Synchronization
b) Multiple parallel receiver chain
c) Synchronization & Multiple parallel receiver chain
d) None of the mentioned
Answer: c
Explanation: The main features of a receiver which increases its complexity are
synchronization of carrier, phase, and timing and multiple parallel receiver chain.
24. 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
Explanation: 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.
25. Wired channels are
a) Lossy
b) Lossless
c) Lossy & Lossless
d) None of the mentioned
Answer: a
Explanation: Wired channels are lossy channels.
26. 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
Explanation: The equivalent temperature is the function of the receiver design and it must
be always kept low.
27. Which corrects the sampling time problem in a digital system?
a) Interpolator
b) Decimator
c) Equalizer
d) Filter
Answer: a
Explanation: Interpolator corrects the sampling time problem using discrete time
processing.
28. 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
Explanation: Some of the main features which make the transmitter complex are higher
clock speed, higher transmit power, directional antennas and need for a linear amplifier.
29. Transmission media used in low frequency band are
a) Air
b) Water
c) Copper cable
d) All of the mentioned
Answer: d
Explanation: Air, water and copper cable can be used as transmission media in low
frequency band communication.
30. Transmission media used for medium frequency band are
a) Coaxial cable
b) Copper cable
c) Optical fiber
d) All of the mentioned
Answer: b
Explanation: For medium frequency band communication air and copper cable can only be
used as a transmission medium.
