Wireless & Mobile Communications Questions & Answers – Constant Envelope Modulation

This set of Wireless & Mobile Communications Multiple Choice Questions & Answers (MCQs) focuses on “Constant Envelope Modulation”.

1. In non-linear modulation, the amplitude of the carrier varies with the variation of modulating signal.
a) True
b) False

Explanation: In non-linear modulation, the amplitude of the carrier is constant regardless of the variation in the modulating signal. Many practical mobile radio communication systems use these types of nonlinear modulation methods.

2. In constant envelope family of modulation, class C amplifiers introduces degradation in spectrum occupancy.
a) True
b) False

Explanation: The constant envelope family of modulation has an advantage of satisfying various conditions. In this, power efficient Class C amplifiers can be used without introducing degradation in the spectrum occupancy of the transmitted signal.

3. Constant envelope modulation techniques occupy ______ bandwidth than linear modulation schemes.
a) Larger
b) Smaller
c) Same
d) Twice

Explanation: Constant envelope modulation technique occupies a larger bandwidth than linear modulation technique. It is one of the disadvantage of constant envelope modulation. It is not well suited where bandwidth efficiency is more important than power efficiency.

4. In BFSK __________ of constant amplitude carrier signal is switched between two values.
a) Phase
b) Angle
c) Frequency
d) Amplitude

Explanation: In BFSK, the frequency of a constant amplitude carrier signal is switched between two values according to the two possible message states. These states are called high and low tunes, which corresponds to binary 1 or 0.

5. MSK stands for ________
a) Maximum shift keying
b) Minimum shift keying
c) Minimum space keying
d) Maximum space keying

Explanation: MSK stands for minimum shift keying. It is a special type of continuous phase shift keying. It is form of digital modulation technique that was developed in 1950s.

6. What is the modulation index of MSK?
a) 0.1
b) 1
c) 0.5
d) 0

Explanation: Minimum shift keying is a special type of CPFSK. Its peak frequency deviation is equal to ¼ the bit rate. In other words, MSK is continuous phase FSK with a modulation index of 0.5.

7. The modulation index of an FSK signal is similar to modulation index of ________
a) Amplitude modulation
b) Phase modulation
c) QPSK
d) Frequency modulation

Explanation: The modulation index of an FSK signal is similar to FM modulation index. It is defined by (2∆F)/Rb. Here ∆F is the peak RF frequency and Rb is the bit rate.

8. The name minimum phase shift keying implies minimum _________
a) Frequency separation
b) Amplitude separation
c) Phase change
d) Amplitude deviation

Explanation: The name minimum phase shift keying implies minimum frequency separation, i.e. the bandwidth that allows orthogonal detection. A modulation index of 0.5 corresponds to the minimum frequency spacing that allows two FSK signals to be coherently orthogonal.

9. MSK is sometimes also referred as _________
a) Slow FSK
b) Fast FSK
c) Slow PSK
d) Fast PSK

Explanation: Minimum shift keying is sometimes also referred as fast FSK. It is so called because frequency spacing used is only half as much as that used in conventional noncoherent frequency shift keying.

10. Which of the following is not a property of MSK?
a) Variable envelope
b) Spectral efficiency
c) Good BER performance
d) Self synchronizing capability

Explanation: MSK has a constant envelope. It is a spectrally efficient scheme. It possesses properties such as constant envelope, spectral efficiency, good BER performance and self-synchronizing capability.

11. MSK is a special form of OQPSK.
a) True
b) False

Explanation: Yes, MSK can be thought of as a special form of offset quadrature phase shift keying. The condition is that baseband rectangular pulses are replaced with half sinusoidal pulses.

12. GMSK is a ________ of MSK.
a) Integral
b) Opposite
c) Derivative
d) Similar

Explanation: Gaussian minimum phase shift keying is a simple binary modulation scheme. It is viewed as a derivative of MSK. GMSK considerably reduces the sidelobe levels in the transmitted spectrum.

13. Which of the following holds true for GMSK?
a) Minimum ISI
b) Minimum error rate
c) Good spectral efficiency
d) Variable envelope property

Explanation: GMSK sacrifices the irreducible error rate caused by partial response signalling in exchange for extremely good spectral efficiency and constant envelope properties. And the premodulation Gaussian filtering introduces ISI in the transmitted signal.

14. MSK has complex demodulation and synchronization circuits.
a) True
b) False

Explanation: MSK has simple demodulation and synchronization circuits. It has various other advantages like continuous phase property makes it highly desirable for highly reactive loads. Due to these advantages, MSK is a popular modulation scheme for mobile radio communication.

Sanfoundry Global Education & Learning Series – Wireless & Mobile Communications.

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