# Digital Communications Questions and Answers – Evaluating Digital Communication System and Allocation of Communication Resources

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This set of Digital Communication online quiz focuses on “Evaluating Digital Communication System and Allocation of Communication Resources”.

1. Which refers to the presence of error correction coding scheme?
a) Coded
b) Uncoded
c) Coded & Uncoded
d) None of the mentioned

Explanation: The term coded refers to the presence of error correction coding scheme involving the use of redundant bits and expanded bandwidth.

2. The system will be more bandwidth efficient as WTb decreases.
a) True
b) False

Explanation: Any digital communication system will become more bandwidth efficient as its WTb product decreases.

3. In MPSK, R/W
a) Increases with increase in M
b) Increases with decrease in M
c) Decreases with increase in M
d) Is not dependent on M

Explanation: The bandwidth efficiency R/W increases as M increases in case of MPSK modulation.
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4. In MFSK, R/W
a) Increases with increase in M
b) Increases with decrease in M
c) Decreases with increase in M
d) Is not dependent on M

Explanation: In MFSK, the denominator increases faster as the numerator when M increases. Thus R/W decreases with increase in M.

5. Which modulation is selected for power limited system?
a) MPSK
b) MFSK
c) MPSK & MFSK
d) None of the mentioned

Explanation: For an uncoded system, if the channel is power limited MFSK is selected and if it is bandwidth limited MPSK is selected.

6. The transmission rate is given as
a) R/log2M
b) log2M/R
c) R/log10M
d) log10M/R

Explanation: The relationship between symbol transmission rate and data rate R is given by Rs= R/log2M.

7. Code’s redundancy is given as
a) n/k
b) k/n
c) nk
d) None of the mentioned

Explanation: The rate of code is given as k/n and its inverse n/k gives the redundancy of the code.

8. For more than two quantization level, _______ is used.
a) Hard decision
b) Soft decision
c) Hard & Soft decision
d) None of the mentioned

Explanation: When the output is quantized for more than two levels, soft decision is made.

9. How can the throughput of the system be increased?
a) Increasing EIRP
b) Increasing channel bandwidth
c) Decreasing system losses
d) All of the mentioned

Explanation: The basic ways to increase the throughput of the system is to increase the EIRP, by reducing the system losses, providing channel bandwidth, and efficient allocation of CR.

10. In which technique spot beam antennas are used to point the radio signals in different directions?
a) Code division
b) Space division
c) Frequency division
d) None of the mentioned

Explanation: In space division multiplexing, spot beam antennas are used to separate radio signals by pointing in different directions.

11. In polarization division technique ______ polarization is used.
a) Orthogonal
b) Non orthogonal
c) Orthogonal & Non orthogonal
d) None of the mentioned

Explanation: In polarization division technique orthogonal polarization is used to separate signals for reuse.

12. Channelization characterized by orthogonal spectra is called as
a) Time division multiplexing
b) Frequency division multiplexing
c) Time division & Frequency division multiplexing
d) None of the mentioned

Explanation: Channelization characterized by orthogonal wave-forms is called as time division multiplexing and those characterized by orthogonal spectra is called as frequency division multiplexing.

13. In double side band spectrum which side-band is called as inverted side-band?
a) LSB
b) USB
c) LSB & USB
d) None of the mentioned

Explanation: The double side band spectrum consists of two side bands. LSB is called as inverted side-band and the USB is called as erect side-band.

14. The mixing and filtering of DSB removes
a) LSB
b) USB
c) LSB & USB
d) None of the mentioned

Explanation: The mixing and filtering yields frequency shifted channels and it removes the USB.

15. The super group is made up of
a) Five groups
b) Sixty channels
c) Five groups & Sixty channels
d) None of the mentioned

Explanation: In FDM multiplex hierarchy, the first level is composed of five channels. The second level consists of five groups or 60 channels.

16. The orbital period of communication satellites is _______ as that of earth’s rotational period.
a) Same
b) Greater
c) Lesser
d) None of the mentioned

Explanation: The communication satellite is in circular orbit and has orbital period same as that of the earth’s rotational period.

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