Question
What is Quadrature Amplitude Modulation or QAM?
Answer Options
- A) A technique for digital data compression used in digital television which removes redundancy in the data by comparing bit amplitudes
- B) Transmission of data by modulating the amplitude of two carriers of the same frequency but 90 degrees out of phase
- C) A method of performing single sideband modulation by shifting the phase of the carrier and modulation components of the signal
- D) A technique for analog modulation of television video signals using phase modulation and compression
Correct Answer: B
Explanation
Quadrature Amplitude Modulation (\text{QAM}) is a complex digital modulation scheme designed to achieve extremely high spectral efficiency by encoding multiple bits per symbol. It is a fundamental technique used in digital television, cable modems, and high-speed data links.
\text{QAM} achieves this efficiency by simultaneously modulating two carriers of the same frequency that are exactly 90^\circ out of phase (in quadrature), creating ‘I’ (In-phase) and ‘Q’ (Quadrature) components. \text{QAM} is thus the transmission of data by modulating the amplitude of two carriers of the same frequency but 90 \text{ degrees} out of phase. By varying the amplitude of both the I and Q components, the total signal can encode up to 10 bits per symbol (e.g., 1024-\text{QAM}), maximizing data rate within a fixed bandwidth.
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