Spread Spectrum, TDMA and FDMA

Digital Communications Systems

This set of Digital Communication Questions for entrance exams focuses on “Spread Spectrum, TDMA and FDMA”.

1. In which modulation schemes, the spreading of spectrum occurs?
a) Frequency modulation
b) Amplitude modulation
c) Frequency & Amplitude modulation
d) None of the mentioned

2. Gaussian noise has _____ power spread _____ over all frequencies.
a) Zero, uniformly
b) Zero, non uniformly
c) Infinite, uniformly
d) Infinite, non uniformly

3. Jamming is caused by
a) Multipath
b) Natural phenomena
c) Multipath & Natural phenomena
d) None of the mentioned

4. Which system makes the detection difficult for all users other than the intended users?
a) Low probability of intercept
b) Low probability of detection
c) Low probability of intercept & detection
d) None of the mentioned

5. The radio meter consists of
a) Low pass filter
b) High pass filter
c) Band pass filter
d) Band reject filter

6. Spread spectrum signals are used for
a) Ranging
b) Determination of position
c) Ranging & Determination of position
d) None of the mentioned

7. Uncertainty in the delay measurement is _________ to the bandwidth of signal pulse.
a) Directly proportional
b) Inversely proportional
c) Not related
d) None of the mentioned

8. Uncertainty in the delay measurement is _______ to rise time of the pulse.
a) Directly proportional
b) Inversely proportional
c) Not related
d) None of the mentioned

9. In spread spectrum technique, the desired signal is multiplied _____ and interference signal is multiplied _____
a) Once, twice
b) Twice, once
c) Twice, thrice
d) Thrice, twice

10. Each satellite has ______ transponders.
a) 10
b) 12
c) 15
d) 18

11. The preamble consists of
a) Synchronization
b) Addressing
c) Error control sequence
d) All of the mentioned

12. Which method is efficient?
a) Fixed assignment
b) Dynamic allocation
c) Fixed assignment & Dynamic allocation
d) None of the mentioned

13. Which has a lesser average packet delay?
a) FDMA
b) TDMA
c) Dynamic FDMA
d) None of the mentioned

14. The maximum waiting time before transmission of a packet is
a) (M-1)T/M
b) (M-1)M/T
c) (M+1)T/M
d) (M+1)M/T

15. CDMA is
a) Similar to FDMA
b) Similar to TDMA
c) Combination of both
d) None of the mentioned

16. Frequency modulation technique involves
a) Data modulation
b) Frequency hopping modulation
c) Data & Frequency hopping modulation
d) None of the mentioned

17. Which needs precise time coordination?
a) CDMA
b) TDMA
c) CDMA & TDMA
d) None of the mentioned

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