What is QAM (Quadrature Amplitude Modulation)?
Quadrature Amplitude Modulation (QAM): What is it?
Contents
- QAM Definitio: QAM (Quadrature Amplitude Modulation) is defined as a modulation technique that combines phase and amplitude modulation to transmit information.
- Working Principle: QAM changes both the amplitude and phase of a carrier wave to double the effective bandwidth.
- Analog vs Digital QAM: Analog QAM is used in traditional TV systems, while Digital QAM, known as Quantized QAM, is used in modern digital communications like Wi-Fi and cellular networks.
- QAM Formats: Different QAM formats, such as 16-QAM, 32-QAM, and 64-QAM, vary in the number of bits they can transmit per symbol, represented in constellation diagrams.
- Applications of QAM: QAM is used in many communication systems, including radio, microwave, optical fiber, and digital cable television, enhancing data rates and bandwidth efficiency.
What is QAM (Quadrature Amplitude Modulation)?
QAM (Quadrature Amplitude Modulation) is defined as a modulation technique that combines phase and amplitude modulation in a single channel. It transmits information by changing both the amplitude and phase of a carrier wave, doubling the effective bandwidth. QAM is also known as quadrature carrier multiplexing.
A QAM signal involves direct modulation of a carrier wave in quadrature. The term “quadrature” means the phase difference between the two carriers is 90 degrees, but both have the same frequency.
One signal is called the in-phase “I” signal, and the other is called the quadrature “Q” signal. Mathematically, one of the carrier signals can be represented by a sine wave (i.e. 
) and the other can be represented by a cosine wave (i.e. 
).
The two modulated carrier signals are transmitted together at the source and at the destination, these two carrier signals are demodulated (i.e. separated) independently. To demodulate the signal coherent detection method is used.
The waveform of the QAM technique is shown below.
