Modulation And Demodulation Technologies Practice MCQs

Questions: 15 | Attempted: 0

1. In 64-QAM modulation, how many bits are transmitted per symbol?

A) 4 bitsB) 6 bitsC) 8 bitsD) 64 bits

2. In a digital communication system, what is the fundamental difference between 'Bit Rate' and 'Baud Rate'?

A) Bit rate is the number of signal units per second, while Baud rate is the number of bits per second.B) Bit rate and Baud rate are identical in all modulation schemes.C) Bit rate is the number of bits transmitted per second, while Baud rate is the number of signal state changes (symbols) per second.D) Bit rate measures analog frequency, while Baud rate measures digital bandwidth.

3. Which modulation technique shifts the phase of the carrier wave by 90 degrees for each state, allowing it to mathematically transmit 2 bits per symbol?

A) BPSK (Binary Phase Shift Keying)B) QPSK (Quadrature Phase Shift Keying)C) 16-QAMD) FSK (Frequency Shift Keying)

4. What is the primary advantage of utilizing Frequency Modulation (FM) over Amplitude Modulation (AM) for analog voice and radio broadcast?

A) FM requires significantly less bandwidth than AM.B) FM transmitters are much cheaper to build.C) FM is highly resilient to amplitude noise and electrical interference, resulting in clearer audio.D) FM can bounce off the ionosphere for global communication.

5. In Quadrature Amplitude Modulation (QAM), which two characteristics of the carrier wave are varied simultaneously to represent digital data?

A) Frequency and PhaseB) Amplitude and PhaseC) Amplitude and FrequencyD) Wavelength and Speed

6. What physical limitation does 'Slope Overload' describe in a Delta Modulation (DM) system?

A) The inability of the digital signal to catch up with an analog input signal that is changing amplitude too rapidly.B) The distortion caused by transmitting over long distances.C) The loss of high-frequency components due to aliasing.D) The saturation of the amplifier output stage.

7. If a microwave backhaul link upgrades its modulation scheme from QPSK to 256-QAM while maintaining the exact same symbol rate (Baud rate), what happens to the raw data bit rate?

A) It remains the same.B) It doubles.C) It quadruples.D) It increases by a factor of 8.

8. What is the primary purpose of plotting a 'Constellation Diagram' in digital modulation analysis?

A) To map the geographical coverage area of a cell tower.B) To visually display the amplitude and phase of all possible signal states (symbols) in a complex I/Q plane, aiding in the analysis of noise and distortion.C) To show the frequency spectrum of an optical signal.D) To trace the IP routing path through a network.

9. During the Pulse Code Modulation (PCM) process, what is the correct chronological sequence of the three primary operations used to convert analog voice into digital data?

A) Quantization, Sampling, EncodingB) Sampling, Quantization, EncodingC) Encoding, Sampling, QuantizationD) Sampling, Encoding, Quantization

10. Why is Differential Phase Shift Keying (DPSK) often preferred over standard Phase Shift Keying (PSK) in certain practical receiver designs?

A) DPSK doubles the data speed compared to PSK.B) DPSK does not require a complex, phase-coherent local oscillator at the receiver because the data is encoded in the phase difference between successive symbols.C) DPSK is an analog modulation scheme, making it compatible with legacy equipment.D) DPSK requires half the bandwidth of PSK.

11. In mobile networks (such as LTE and 5G), what is the vital function of 'Adaptive Modulation and Coding (AMC)'?

A) It encrypts the signal based on the user's password.B) It dynamically changes the modulation scheme (e.g., from 256-QAM down to QPSK) based on real-time radio channel quality to maintain connection stability.C) It translates analog voice into VoIP packets.D) It switches the phone's frequency band to save battery.

12. Continuous Phase Frequency Shift Keying (CPFSK), specifically Minimum Shift Keying (MSK) and Gaussian MSK (GMSK) used in GSM, offers what primary spectral advantage?

A) It completely eliminates the need for an antenna.B) It avoids sudden, sharp phase changes, which drastically reduces out-of-band spectral leakage and prevents interference with adjacent channels.C) It allows unlimited data capacity in a 200 kHz channel.D) It uses amplitude variation to increase data rates.

13. In Orthogonal Frequency Division Multiplexing (OFDM), what ensures that the closely packed subcarriers do not interfere with each other (Inter-Carrier Interference)?

A) Large physical guard bands of empty spectrum are placed between each subcarrier.B) The peak of each subcarrier's frequency aligns exactly with the mathematical 'zero' crossing point of all other adjacent subcarriers.C) They are transmitted at entirely different times using TDMA.D) They are encrypted using different public keys.

14. Which fundamental technique multiplies the digital baseband signal with a high-frequency, pseudo-random 'chipping code' to distribute the signal energy across a much wider frequency band?

A) Amplitude Shift Keying (ASK)B) Quadrature Amplitude Modulation (QAM)C) Direct Sequence Spread Spectrum (DSSS)D) Pulse Position Modulation (PPM)

15. What happens to a digital signal's robustness against noise when the modulation scheme scales to higher orders (e.g., from 16-QAM to 64-QAM to 256-QAM) without increasing the total transmit power?

A) The signal becomes much more resilient to noise.B) The robustness remains exactly the same.C) The signal becomes highly susceptible to noise and phase jitter because the constellation points are packed much closer together.D) The noise is mathematically cancelled out by the higher bit rate.