MCQOPTIONS
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MCQOPTIONS
This section includes 46 Mcqs, each offering curated multiple-choice questions to sharpen your Digital Communications knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Which are called as substitution encryption techniques? |
| A. | Caesar cipher |
| B. | Trithemius cipher |
| C. | Caesar & Trithemius cipher |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 2. |
The transmitter of frequency hopping system is fed with encoding scheme such as |
| A. | Frequency shift keying |
| B. | Binary phase shift keying |
| C. | Frequency & Binary phase shift keying |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 3. |
Spread spectrum can be used to transmit |
| A. | Analog data |
| B. | Digital data |
| C. | Analog & Digital data |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 4. |
The segment of the key-stream of plaintext is obtained by _____ of two sequences together. |
| A. | ANDing |
| B. | ORing |
| C. | Addition |
| D. | Modulo 2 addition |
| Answer» E. | |
| 5. |
In which method cipher feedback is used? |
| A. | Synchronous encryption method |
| B. | Self synchronous encryption method |
| C. | All of the mentioned |
| D. | None of the mentioned |
| Answer» C. All of the mentioned | |
| 6. |
In CDMA the incoming signal is _____ with the spreading code. |
| A. | Added |
| B. | Multiplied |
| C. | XOR-ed |
| D. | None of the mentioned |
| Answer» C. XOR-ed | |
| 7. |
The ratio (J/S)reqd gives the measure of |
| A. | Vulnerability to interference |
| B. | Invulnerability to interference |
| C. | All of the mentioned |
| D. | None of the mentioned |
| Answer» C. All of the mentioned | |
| 8. |
Short code is configured using ______ shift register. |
| A. | 4-stage |
| B. | 2-stage |
| C. | 12-stage |
| D. | 15-stage |
| Answer» E. | |
| 9. |
Which type of demodulator is used in the frequency hopping technique? |
| A. | Coherent |
| B. | Non coherent |
| C. | Coherent & Non coherent |
| D. | None of the mentioned |
| Answer» C. Coherent & Non coherent | |
| 10. |
Walsh cover technique is used for |
| A. | Channelization |
| B. | Spreading |
| C. | Channelization & Spreading |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 11. |
In CDMA, the users share the bandwidth |
| A. | Synchronously |
| B. | Asynchronously |
| C. | Synchronously & Asynchronously |
| D. | None of the mentioned |
| Answer» C. Synchronously & Asynchronously | |
| 12. |
Processing gain is given as |
| A. | Wss/R |
| B. | Rch/R |
| C. | Wss/R & Rch/R |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 13. |
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» B. Maximum number of chips necessary | |
| 14. |
The conditions for perfect secrecy are |
| A. | Only one key transforming message should exist |
| B. | All keys should be equally likely |
| C. | One key transforming message to each cipher text & all keys should be equally likely |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 15. |
The types of channels that reverse channel contains are |
| A. | Traffic |
| B. | Access |
| C. | Traffic & Access |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 16. |
The standard building block uses _______ of a key to transform 64-bit input into 64-bit output. |
| A. | 32 bit |
| B. | 48 bit |
| C. | 64 bit |
| D. | 128 bit |
| Answer» C. 64 bit | |
| 17. |
The steps followed in forward channel CDMA includes |
| A. | Modulo 2 addition |
| B. | Channelization |
| C. | Modulo 2 addition & Channelization |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 18. |
In which method the key-stream is generated independently of the message? |
| A. | Synchronous encryption method |
| B. | Self synchronous encryption method |
| C. | All of the mentioned |
| D. | None of the mentioned |
| Answer» B. Self synchronous encryption method | |
| 19. |
The jammer which monitors a communicator's signal is known as |
| A. | Frequency follower jammers |
| B. | Repeat back jammers |
| C. | Frequency follower & Repeat back jammers |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 20. |
Spread spectrum multiple access techniques allows the multiple signal to be transmitted |
| A. | One after the other |
| B. | Simultaneously |
| C. | All of the mentioned |
| D. | None of the mentioned |
| Answer» C. All of the mentioned | |
| 21. |
Which has worse signal to noise performance? |
| A. | Delay locked loop |
| B. | Tau-dither loop |
| C. | Delay locked & Tau-dither loop |
| D. | None of the mentioned |
| Answer» C. Delay locked & Tau-dither loop | |
| 22. |
Spread spectrum is a ______ technique. |
| A. | Encoding |
| B. | Decoding |
| C. | Encoding & Decoding |
| D. | None of the mentioned |
| Answer» B. Decoding | |
| 23. |
Frequency hopping system can provide reliable mitigation only if |
| A. | Hopping rate is greater than the symbol rate |
| B. | Hopping bandwidth is large |
| C. | Hopping rate is greater than the symbol rate & its bandwidth is large |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 24. |
The original bandwidth of the unspread signal in spread spectrum is ____ to data rate. |
| A. | Proportional |
| B. | Inversely proportional |
| C. | Not related |
| D. | None of the mentioned |
| Answer» B. Inversely proportional | |
| 25. |
Pulse jammer consists of |
| A. | Pulse modulated excess band noise |
| B. | Pulse modulated band-limited noise |
| C. | Pulse width modulated excess band noise |
| D. | Pulse width modulated band-limited noise |
| Answer» C. Pulse width modulated excess band noise | |
| 26. |
For hybrid systems the minimum required processing gain is |
| A. | 5db |
| B. | 10db |
| C. | 17db |
| D. | 25db |
| Answer» D. 25db | |
| 27. |
Which method is better? |
| A. | To share same bandwidth |
| B. | To share different bandwidth |
| C. | To share same & different bandwidth |
| D. | None of the mentioned |
| Answer» C. To share same & different bandwidth | |
| 28. |
Spread spectrum has immunity from |
| A. | Noise |
| B. | Multi-path distortion |
| C. | Noise & Multi-path distortion |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 29. |
In substitution technique encryption protection is more. |
| A. | True |
| B. | False |
| Answer» C. | |
| 30. |
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 |
| Answer» B. Posteriori probability is greater than priori probability | |
| 31. |
Which system allows larger processing gain? |
| A. | Direct sequence |
| B. | Frequency hopping |
| C. | Direct sequence & Frequency hopping |
| D. | None of the mentioned |
| Answer» C. Direct sequence & Frequency hopping | |
| 32. |
Spread spectrum makes ______ difficult. |
| A. | Jamming |
| B. | Interception |
| C. | Jamming & Interception |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 33. |
Multi paths may be because of |
| A. | Reflections from buildings |
| B. | Refraction |
| C. | Atmospheric reflections |
| D. | All of the mentioned |
| Answer» E. | |
| 34. |
In DSSS the signal is recovered using |
| A. | Low pass filter |
| B. | High pass filter |
| C. | Band pass filter |
| D. | Band stop filter |
| Answer» D. Band stop filter | |
| 35. |
Which filter is used to get the final FHSS signal? |
| A. | Low pass filter |
| B. | High pass filter |
| C. | Band pass filter |
| D. | Band stop filter |
| Answer» D. Band stop filter | |
| 36. |
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» C. Direct sequence & Frequency hopping | |
| 37. |
Perfect secrecy can be achieved for |
| A. | Finite number of messages |
| B. | Infinite number of messages |
| C. | Finite & Infinite number of messages |
| D. | None of the mentioned |
| Answer» C. Finite & Infinite number of messages | |
| 38. |
The 64 bit block input key has _____ number of parity bits. |
| A. | 4 |
| B. | 6 |
| C. | 8 |
| D. | 16 |
| Answer» D. 16 | |
| 39. |
One-time pad has |
| A. | Random key |
| B. | Unconditional security |
| C. | Can be used only once |
| D. | All of the mentioned |
| Answer» E. | |
| 40. |
For any cyclic shift, the auto-correlation function is equal to |
| A. | 1/p |
| B. | -1/p |
| C. | -p |
| D. | p |
| Answer» C. -p | |
| 41. |
Direct system allows detection of signals whose psd level is |
| A. | Below noise level |
| B. | Above noise level |
| C. | All of the mentioned |
| D. | None of the mentioned |
| Answer» B. Above noise level | |
| 42. |
Which are the design options for anti jam communicator? |
| A. | Time diversity |
| B. | Frequency diversity |
| C. | Special discrimination |
| D. | All of the mentioned |
| Answer» E. | |
| 43. |
In Vigenere method ______ is provided. |
| A. | Priming key |
| B. | Feedback |
| C. | Priming key & Feedback |
| D. | None of the mentioned |
| Answer» D. None of the mentioned | |
| 44. |
The width of each channel in frequency hopping spread spectrum corresponds to |
| A. | Bandwidth of input signal |
| B. | Pseudorandom sequence used |
| C. | Carrier frequency |
| D. | None of the mentioned |
| Answer» B. Pseudorandom sequence used | |
| 45. |
For direct sequence systems what is the minimum required processing gain? |
| A. | 3db |
| B. | 10db |
| C. | 12db |
| D. | 20db |
| Answer» C. 12db | |
| 46. |
The _____ the uncertainty, the ______ is the information content. |
| A. | Lesser, greater |
| B. | Greater, lesser |
| C. | Lesser, lesser |
| D. | Greater, greater |
| Answer» E. | |