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Communications MCQ Set 1

1. In phase lock which parameter is synchronized
a) Frequency
b) Phase
c) Frequency & Phase
d) None of the mentioned

View Answer

Answer: c [Reason:] Being in phase lock means that the receiver’s local oscillator is synchronized in both frequency and phase with the received signal.

2. Coherent modulation requires ____ level of synchronization.
a) One
b) Two
c) Three
d) None of the mentioned

View Answer

Answer: c [Reason:] Coherent modulation requires three levels of synchronization – phase symbol and frame.

3. Non coherent system requires
a) Phase synchronization
b) Frequency synchronization
c) Phase & Frequency synchronization
d) None of the mentioned

View Answer

Answer: c [Reason:] Non coherent system requires frequency synchronization.

4. For block codes _____ is necessary.
a) Phase synchronization
b) Frequency synchronization
c) Frame synchronization
d) None of the mentioned

View Answer

Answer: c [Reason:] Frame synchronization is necessary when the information is organized in blocks or messages of some uniform number of symbols. Thus block code needs frame synchronization.

5. The synchronization necessary for BPSK is
a) Frequency tracking
b) Bit timing
c) Phase tracking
d) All of the mentioned

View Answer

Answer: d [Reason:] Non coherently detected BPSK is the simplest digital receiver and it requires frequency tracking, bit timing synchronizations and also phase synchronization.

6.Transmitter synchronization implies
a) One way communication
b) Two way communication
c) One & Two way communication
d) None of the mentioned

View Answer

Answer: b [Reason:] Transmitter plays a role in synchronization by varying the frequency and timing of its transmissions to correspond to expectation of receiver. This transmitter synchronization implies two way communication.

7. As the synchronization levels increases, cost
a) Decreases
b) Increases
c) Remains the same
d) None of the mentioned

View Answer

Answer: b [Reason:] For each level increase in synchronization levels, cost increases.

8. Synchronization is used in system which has
a) Non coherent modulation techniques
b) Many users accessing
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] For communication system using non coherent modulation techniques and many users accessing the central communication node, synchronization is necessary.

9. Which method has fast acquisition and can work without return link?
a) Open loop method
b) Closed loop method
c) Open & Closed loop method
d) None of the mentioned

View Answer

Answer: a [Reason:] The main advantage of open loop method is that acquisition is fast, the procedure can work without return link and the amount of real time computation that is required is small.

10. Which method has two way link?
a) Open loop method
b) Closed loop method
c) Open & Closed loop method
d) None of the mentioned

View Answer

Answer: b [Reason:] Closed loop method requires return link , large amount of real time processing and has two way link.

11. Which method requires external authority and is inflexible?
a) Open loop method
b) Closed loop method
c) Open & Closed loop method
d) None of the mentioned

View Answer

Answer: a [Reason:] Open loop method is inflexible, does not adjust quickly to unplanned changes and needs external authority that provides prior knowledge, where as closed loop method does not need all these.

12. Which method needs precorrect time ?
a) Open loop method
b) Closed loop method
c) Open & Closed loop method
d) None of the mentioned

View Answer

Answer: a [Reason:] In open loop method the frequency and time is precorrected.

13. In open loop method, the time reference error __________ with respect to time.
a) Increases exponentially
b) Decreases exponentially
c) Increases quadratically
d) Decreases quadratically

View Answer

Answer: a [Reason:] In open loop transmitter synchronization system, the time reference error increases quadratically with time.

14. When a terminal is able to utilize the measurements made on the return link it is called as
a) Open loop method
b) Closed loop method
c) Quasi close loop method
d) None of the mentioned

View Answer

Answer: c [Reason:] The case where a terminal is able to utilize the measurements made on a return link signal is called as quasi closed loop transmitter synchronization.

15. Which reduces the effective distance between signals in signal space?
a) Time error
b) Frequency offset
c) Time error & Frequency offset
d) None of the mentioned

View Answer

Answer: c [Reason:] Time error or frequency offset or combination of both will reduce the effective distance between signals in signal space and degrade error performance.

16. The system which has ______ signal to noise ratio can tolerate larger timing error.
a) Large
b) Small
c) Large & Small
d) None of the mentioned

View Answer

Answer: a [Reason:] The system with increased signal to noise ratio will allow it to tolerate larger timing error so the improvement is error performance is rapid.

Communications MCQ Set 2

1. Which waveforms are also called as line codes?
a) PCM
b) PAM
c) FM
d) AM

View Answer

Answer: a [Reason:] When pulse modulation is applied to binary symbol we obtain pulse code modulated waveforms. These waveforms are also called as line codes.

2. When pulse code modulation is applied to non binary symbols we obtain waveform called as
a) PCM
b) PAM
c) M-ary
d) line codes

View Answer

Answer: c [Reason:] When pulse code modulation is applied to binary symbols we get PCM waveforms and when it is applied to non binary symbols we obtain M-ary waveforms.

3. Examples of PCM waveforms are
a) Non return to zero
b) Phase encoded
c) Multilevel binary
d) All of the mentioned

View Answer

Answer: d [Reason:] Some of the examples or classification of pulse code modulated signals are non return to zero , return to zero, phase encoded, multilevel binary etc.

4. Which type is used and preferred in digital logic circuits?
a) NRZ-L
b) NRZ-M
c) NRZ-S
d) None of the mentioned

View Answer

Answer: a [Reason:] NRZ-L is extensively used in digital logic circuits. In this method, logic 1 is represented by one voltage level and logic 0 is represented by another voltage level.

5. Which method is called as differential encoding?
a) NRZ-L
b) NRZ-M
c) NRZ-S
d) None of the mentioned

View Answer

Answer: b [Reason:] In NRZ-M, logic 1 is represented by change in voltage level and logic 0 is represented by no change in level.This is called as differential encoding.

6. Which method is preferred in magnetic tape recording?
a) NRZ-L
b) NRZ-M
c) NRZ-S
d) None of the mentioned

View Answer

Answer: b [Reason:] NRZ-M is also called as differential encoding and it is most preferred in magentic tape recording.

7. NRZ-S is complement of _______
a) NRZ-L
b) NRZ-M
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: b [Reason:] NRZ-S is complement of NRZ-M. Logic 0 is represented by change in voltage level and logic 1 is represented as no change in voltage level.

8. The return to zero waveform consists of
a) Unipolar RZ
b) Bipolar RZ
c) RZ-AMI
d) All of the mentioned

View Answer

Answer: d [Reason:] Different types of return to zero waveforms are unipolar RZ, bipolar RZ, RZ-AMI. These are used in baseband transmission and in magnetic recording.

9. Phase encoded group consists of
a) Manchester coding
b) Bi-phase-mark
c) Miller coding
d) All of the mentioned

View Answer

Answer: d [Reason:] Different types of phase encoded waveform consists of manchester coding, bi-phase-mark, bi-phase-space, delay modulation.

10. In which waveform logic 1 is represented by half bit wide pulse and logic 0 is represented by absence of pulse?
a) Unipolar RZ
b) Bipolar RZ
c) RZ-AMI
d) Manchester coding

View Answer

Answer: a [Reason:] In unipolar RZ waveform, logic 1 is represented by half bit wide pulse and logic 0 is represented by absence of pulse.

11. In which waveform logic 1 and logic 0 are represented by opposite one half bit wide pulses?
a) Unipolar RZ
b) Bipolar RZ
c) RZ-AMI
d) Manchester coding

View Answer

Answer: b [Reason:] In bipolar return to zero waveform ones and zeroes are represented by opposite level pulses one half bit wide pulses.

12. In which waveform logic 1 is represented by equal amplitude alternating pulses?
a) Unipolar RZ
b) Bipolar RZ
c) RZ-AMI
d) Manchester coding

View Answer

Answer: c [Reason:] In RZ-AMI logic 1 is represented by equal amplitude alternating pulses and logic 0 is represented by absence of pulse.

Communications MCQ Set 3

1. In case of direct CDMA, interference will occur if the PN codes are
a) Orthogonal to each other
b) Non orthogonal to each other
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: b [Reason:] If the PN codes are not purely orthogonal in direct CDMA interference will occur.

2. If the active users using a cell doubles, the required Eb/I0
a) Doubles
b) Halves
c) Remains the same
d) None of the mentioned

View Answer

Answer: b [Reason:] If the active users were to double, then the received Eb/I0 would essentially be halved.

3. In CDMA ______ frequency reuse is possible.
a) No
b) 50%
c) 90%
d) 100%

View Answer

Answer: d [Reason:] In CDMA, 100% frequency reuse can be employed.

4. Bandwidth efficiency improvement involves
a) Dividing the geographical region into cells
b) Allowing frequency allocation
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] The idea of dividing the geographical region into cells and allowing frequency allocation of one cell can be reused represents bandwidth efficiency improvement methods.

5. Which has more user capacity?
a) CDMA
b) AMPS
c) TDMA
d) None of the mentioned

View Answer

Answer: a [Reason:] CDMA has more user capacity compared to AMPS and TDMA.

6. Which technique is interference limited?
a) TDMA
b) CDMA
c) AMPS
d) None of the mentioned

View Answer

Answer: b [Reason:] CDMA technique capacity is interference limited.

7. Which technique is dimension limited?
a) TDMA
b) FDMA
c) TDMA & FDMA
d) None of the mentioned

View Answer

Answer: c [Reason:] TDMA and FDMA capacity is dimension limited.

8. Which type of channel does the forward link contain?
a) Paging
b) Pilot
c) Traffic
d) All of the mentioned

View Answer

Answer: d [Reason:] The forward link contains different types of channels such as paging, pilot, synchronisation and traffic.

9. The types of channels that reverse channel contains are
a) Traffic
b) Access
c) Traffic & Access
d) None of the mentioned

View Answer

Answer: c [Reason:] The reverse channel contains two types of channels – traffic and access.

10. The steps followed in forward channel CDMA includes
a) Modulo 2 addition
b) Channelization
c) Modulo 2 addition & Channelization
d) None of the mentioned

View Answer

Answer: c [Reason:] Forward channel CDMA includes steps like modulo 2 addition, channelization, and base station identification.

11. Walsh cover technique is used for
a) Channelization
b) Spreading
c) Channelization & Spreading
d) None of the mentioned

View Answer

Answer: c [Reason:] Walsh cover is used for channelization plus spreading.

12. Short code is configured using ______ shift register.
a) 4-stage
b) 2-stage
c) 12-stage
d) 15-stage

View Answer

Answer: d [Reason:] The code in the forward direction, short code is designed using 15 stage shift register.

13. How many channels are transmitted in the forward and reverse direction?
a) 1,64
b) 64,1
c) 2,32
d) 32,2

View Answer

Answer: b [Reason:] In forward direction 64 channels are transmitter and in reverse direction only one channel is transmitted.

14. Which channel is more robust?
a) Forward channel
b) Reverse channel
c) Forward & Reverse channel
d) None of the mentioned

View Answer

Answer: a [Reason:] Forward channel is more robust than the reverse channel.

15. Which serves the hard hand-off process?
a) Base station
b) Mobile switching center
c) Mobile
d) None of the mentioned

View Answer

Answer: b [Reason:] Mobile unit continuously scans for stronger pilot and provides and serves hand off process.

16. Which serves the soft hand-off process?
a) Base station
b) Mobile switching center
c) Mobile
d) None of the mentioned

View Answer

Answer: c [Reason:] Soft hand off process is served by the mobile. It scans for stronger pilot and requests handoff to base station.

Communications MCQ Set 4

1. Cryptosystems are used for
a) Privacy
b) Authentication
c) Privacy & Authentication
d) None of the mentioned

View Answer

Answer: c [Reason:] Cryptosystems which includes the process of encryption and decryption is used for both privacy and authentication.

2. The key also contains a
a) Plaintext
b) Ciphertext
c) Plaintext & Ciphertext
d) None of the mentioned

View Answer

Answer: c [Reason:] The key is supplied along with a plaintext message for encryption and cipher text message for decryption.

3. The system which has insufficient information available to crypt-analyst is
a) One-time pad
b) Unconditionally secure
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] Unconditionally secure system is the one which has insufficient information available to crypt-analyst. One such system is one-time pad.

4. Caesar cipher was a mono alphabetic cipher.
a) True
b) False

View Answer

Answer: a [Reason:] An earliest example of a mono alphabetic cipher was the Caesar cipher.

5. In Caesar cipher, each plain text in replaced by
a) Alphabet shift
b) Numerals
c) Symbols
d) None of the mentioned

View Answer

Answer: a [Reason:] In Caesar cipher each plain text is replaced with new letter obtained by an alphabetic shift.

6. The trithemius cipher is a mono alphabetical cipher.
a) True
b) False

View Answer

Answer: b [Reason:] The Trithemius cipher is a poly alphabetical cipher.

7. In auto key method
a) Feedback is necessary
b) Feedback is not necessary
c) Can be either necessary or not
d) None of the mentioned

View Answer

Answer: a [Reason:] In auto key method feedback is necessary for encryption process.

8. In Vigenere method, ______ is provided.
a) Priming key
b) Feedback
c) Priming key & Feedback
d) None of the mentioned

View Answer

Answer: c [Reason:] Vigenere method which is also called as vigenere auto method priming key and feedback are used.

9. A cipher system is said to have perfect secrecy if
a) Posteriori probability is equal to priori probability
b) Posteriori probability is greater than priori probability
c) Posteriori probability is less than priori probability
d) None of the mentioned

View Answer

Answer: a [Reason:] A cipher system is said to have perfect secrecy if for every message and cipher text the posteriori probability is equal to priori probability.

10. The conditions for perfect secrecy are
a) Only one key transforming message should exist
b) All keys should be equally likely
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] The conditions for perfect secrecy are , there is only one key transforming message to each cipher text and all keys should be equally likely.

11. The _____ the uncertainty , the ______ is the information content.
a) Lesser, greater
b) Greater, lesser
c) Lesser, lesser
d) Greater, greater

View Answer

Answer: d [Reason:] The more uncertainty there is in predicting the occurrence of a message, the greater the information content.

12. Equivocation is the
a) Joint probability of X and Y
b) Conditional probability of X given Y
c) Conditional probability of Y given X
d) None of the mentioned

View Answer

Answer: b [Reason:] Equivocation is defined as the conditional probability of X given Y.

13. The maximum number of message bits contained in each character is called as
a) True rate
b) Absolute rate
c) Optimum rate
d) None of the mentioned

View Answer

Answer: b [Reason:] Absolute rate is the maximum number of message bits contained in each character.

14. When the key size is finite, equivocation approaches
a) Unity
b) Zero
c) Infinity
d) None of the mentioned

View Answer

Answer: b [Reason:] With a finite key size, equivocation approaches zero.

15. When a system is called as unbreakable?
a) When unique solution is available
b) When unique solution is not available
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: b [Reason:] A system is said to be unbreakable when unique solution is not available because of number of equations being smaller than the number of unknown key bits.

Communications MCQ Set 5

1. While recovering signal, which gets attenuated more?
a) Low frequency component
b) High frequency component
c) Low & High frequency component
d) None of the mentioned

View Answer

Answer: b [Reason:] High frequency components are attenuated more when compared to low frequency components while recovering the signals.

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

View Answer

Answer: c [Reason:] Mutual information can also be negative.

3. ASCII code is a
a) Fixed length code
b) Variable length code
c) Fixed & Variable length code
d) None of the mentioned

View Answer

Answer: a [Reason:] ASCII code is a fixed length code. It has a fixed length of 7 bits.

4. Which reduces the size of the data?
a) Source coding
b) Channel coding
c) Source & Channel coding
d) None of the mentioned

View Answer

Answer: a [Reason:] Source coding reduces the size of the data and channel coding increases the size of the data.

5. In digital image coding which image must be smaller in size?
a) Input image
b) Output image
c) Input & Output image
d) None of the mentioned

View Answer

Answer: b [Reason:] In digital image coding, output image must be smaller than the input image.

6. Which coding method uses entropy coding?
a) Lossless coding
b) Lossy coding
c) Lossless & Lossy coding
d) None of the mentioned

View Answer

Answer: b [Reason:] Lossy source coding uses entropy coding.

7. Which achieves greater compression?
a) Lossless coding
b) Lossy coding
c) Lossless & Lossy coding
d) None of the mentioned

View Answer

Answer: b [Reason:] Lossy coding achieves greater compression where as lossless coding achieves only moderate compression.

8. A code is a mapping from
a) Binary sequence to dicrete set of symbols
b) Discrete set of symbols to binary sequence
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: b [Reason:] A code is a mapping from discrete set of symbols to finite binary sequence.

9. Which are uniquely decodable codes?
a) Fixed length codes
b) Variable length codes
c) Fixed & Variable length codes
d) None of the mentioned

View Answer

Answer: a [Reason:] Fixed length codes are uniquely decodable codes where as variable length codes may or may not be uniquely decodable.

10. A rate distortion function is a
a) Concave function
b) Convex function
c) Increasing function
d) None of the mentioned

View Answer

Answer: b [Reason:] A rate distortion function is a monotone decreasing function and also a convex function.