# Linear Modulation Techniques

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

1. In linear modulation technique __________ of transmitted signal varies linearly with modulating digital signal.
a) Amplitude
b) Frequency
c) Phase
d) Angle

2. Linear modulation techniques are not bandwidth efficient.
a) True
b) False

3. Which of the following is not a linear modulation technique?
a) OQPSK
b) π/4 QPSK
c) FSK
d) BPSK

4. In BPSK, the ________ of constant amplitude carrier signal is switched between two values according to the two possible values.
a) Amplitude
b) Phase
c) Frequency
d) Angle

5. By applying cos(2πft), BPSK signal is equivalent to ________
a) Double sideband suppressed carrier amplitude modulated waveform
b) Single sideband suppressed carrier amplitude modulated waveform
c) Frequency modulated waveform
d) SSB amplitude waveform

6. BPSK uses non-coherent demodulator.
a) True
b) False

7. DPSK uses coherent form of PSK.
a) True
b) False

8. In DPSK system, input signal is differentially encoded and then modulated using a ________ modulator.
a) Amplitude
b) Frequency
c) BPSK
d) QPSK

9. The energy efficiency of DPSK is _________ to coherent PSK.
a) Superior
b) Same
c) Zero
d) Inferior

10. QPSK has ________ the bandwidth efficiency of BPSK.
a) Twice
b) Same
c) Half
d) Four times

11. QPSK provides twice the bandwidth efficiency and _______ energy efficiency as compared to BPSK.
a) Twice
b) Half
c) Same
d) Four times

12. What is the full form of OQPSK?
a) Optical Quadrature Phase Shift Keying
b) Orthogonal Quadrature Pulse Shift Keying
c) Orthogonal Quadrature Phase Shift Keying
d) Offset Quadrature Phase Shift Keying

13. The bandwidth of OQPSK is _______ to QPSK.
a) Identical
b) Twice
c) Half
d) Four times

14. QPSK signals perform better than OQPSK in the presence of phase jitter.
a) True
b) False

15. Which of the following is not a detection technique used for detection of π/4 QPSK signals?
a) Baseband differential detection
b) IF differential detection
c) FM discriminator detection
d) Envelope detection