What is the principle of quadrature amplitude modulation (QAM) in digital communication systems, and how does it improve the spectral efficiency of transmitted signals?
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Principle of QAM:
Quadrature Amplitude Modulation (QAM) in digital communication systems involves modulating two carrier signals, which are 90 degrees out of phase (in-phase (I) and quadrature (Q)). The data is split into two streams to modulate the amplitude of each carrier. These modulated carriers are combined, forming a signal with varying amplitude and phase, represented on a constellation diagram.
QAM improves spectral efficiency by:
1. Increasing Data Rates: By modulating both amplitude and phase, QAM transmits multiple bits per symbol (e.g., 16-QAM transmits 4 bits per symbol).2. Using Both Dimensions: It utilizes both in-phase and quadrature components, making efficient use of available bandwidth.
3. Higher Bandwidth Efficiency: Transmitting more bits per symbol allows for higher data rates within the same bandwidth, making QAM highly efficient for high-speed digital communications.