Quadrature Amplitude Modulation

What Does Quadrature Amplitude Modulation Mean?

Quadrature amplitude modulation (QAM) is a modulation scheme used for both digital and analog signals. QAM doubles the effective bandwidth by combining two amplitude-modulated signals into a single channel. This allows multiple analog signals to be placed on a single carrier, for example, in television signals, which contain both color signals and sound. The two channels required for stereo sound signals can be carried by a single QAM. Digital QAM or quantized QAM is often used for radio communication systems from regular cellular to LTE including WiMAX and Wi-Fi.

Advertisements

Techopedia Explains Quadrature Amplitude Modulation

Quadrature amplitude modulation (QAM) is a technique used to transmit two digital bit streams or two analog signals by modulating or changing the amplitudes of two carrier waves so that they differ in phase by 90 degrees, a quarter of a cycle, hence the name quadrature. One signal is called the "I" signal and the other is the "Q" signal, which can be mathematically represented by a cosine and a sine wave, respectively.

QAM combines the two carriers and sends the combined signals in a single transmission to be separated and extracted at the destination. The signals are demodulated, and the data are then extracted from each and recombined to form the original modulating information. Examples of technologies using QAM are the PAL and NTSC television systems, where the different channels, which are provided by QAM, enable the transmission of the components of chroma or color information to TV sets.

Advertisements

Related Terms

Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.