Quadrature Amplitude Modulation (QAM) is a modulation scheme used in digital communication to transmit data by varying both the amplitude and phase of a carrier signal. QAM allows for the transmission of multiple bits of information per symbol, making it a more bandwidth-efficient modulation scheme.
In QAM, the amplitude and phase of the carrier signal are simultaneously modulated to represent different combinations of amplitude and phase levels. The most common form is Quadrature Amplitude Modulation, where both amplitude and phase are modulated. The term “quadrature” refers to the use of two carriers that are 90 degrees out of phase with each other.
The number of amplitude and phase combinations determines the order of the QAM modulation. For example, in 16-QAM, there are 16 different possible combinations, allowing the transmission of 4 bits per symbol. Higher-order QAM, such as 64-QAM or 256-QAM, can transmit even more bits per symbol, but they are more susceptible to noise and interference.
QAM is widely used in digital communication systems, including cable modems, digital television broadcasting, and some wireless communication standards like Wi-Fi and 4G LTE. It strikes a balance between spectral efficiency and susceptibility to noise, making it suitable for various applications.