# Microwave Engineering Questions and Answers – Digital Modulation and Bit Error Rate

This set of Microwave Engineering Question Bank focuses on “Digital Modulation and Bit Error Rate”.

1. All modern wireless communication systems rely on digital modulation methods due to:
a) superior performance
b) low power requirements
c) sustainability
d) all of the mentioned

Explanation: Major advantages of digital modulation over analog modulation is that they have superior performance in the presence of noise and signal fading and the power requirement is very as compared to analog communication.

2. The probability of error depends on the ratio of bit energy to noise power density.
a) true
b) false

Explanation: If the noise power is higher than the energy transmitted per bit, then the probability of error is high. Suppose signal 0 is transmitted, if the noise level is greater than the threshold to detect signal 1, bit 0 is interpreted as 1.

3. Probability of bit error is greater for ASK as compared to FSK.
a) true
b) false

Explanation: Frequency shift keying method of modulation is more efficient than amplitude shift keying where the carrier is varied with respect to the amplitude of the message signal. Hence FSK has a lower bit error rate as compared to ASK.

4. Probability of bit error rate is greater for QPSK as compared to FSK.
a) true
b) false

Explanation: In QPSK (Quadrature phase shift keying), two data bits are used to select one of the four possible phase states of the received data sequence. Hence, this has a low error probability as compared to FSK.

5. Global positioning system uses _____ satellites in medium earth orbits to provide accurate position information.
a) 12
b) 24
c) 36
d) 48

Explanation: Global positioning system uses 24 satellites in medium earth orbits to provide accurate position information to users on land, air and sea. GPS has become one of the most pervasive applications of wireless technology to consumers throughout the world.
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6. GPS operates at a single frequency band.
a) true
b) false

Explanation: GPS operates at two frequency bands. L1 at 1575.42 MHz and L2 at 1227.60 MHz, transmitting spread spectrum signals with BPSK modulation.

7. WLAN is used for providing connection between a host computer and satellite for communication.
a) true
b) false

Explanation: WLANs are used to provide connections between a computer and peripherals over a short distance. These types of networks are used in airports, college campuses and many more.

8. There is no standard to be formed by commercial WLAN products.
a) true
b) false

Explanation: Most commercial WLANs follow IEEE 802.11 standards (Wi-Fi). They operate at either 2.4 or 5.7 GHz in the industrial, scientific and medical frequency bands and use either frequency hopping or direct sequence spread spectrum techniques.

9. Bluetooth devices operate at a frequency of :
a) 2.4 GHz
b) 4.5 GHz
c) 5.7 GHz
d) none of the mentioned

Explanation: Bluetooth operates at a frequency range of 2.4 GHz and RF power range of 1-100 mW and corresponding operating ranges of 1-100 m.

10. The modulation technique in which both amplitude and phase of the carrier are varied simultaneously is:
b) BPSK
c) QAM
d) QPSK