Frequency-division multiplexing

In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separate signal.

This allows a single transmission medium such as a microwave radio link, cable or optical fiber to be shared by multiple independent signals.

Another use is to carry separate serial bits or segments of a higher rate signal in parallel.

Similarly, additional baseband signals are used to modulate carriers at other frequencies, creating other channels of information.

All the channels are sent through the transmission medium, such as a coaxial cable, optical fiber, or through the air using a radio transmitter.

Modern telephone systems employ digital transmission, in which time-division multiplexing (TDM) is used instead of FDM.

Since the late 20th century, digital subscriber lines (DSL) have used a Discrete multitone (DMT) system to divide their spectrum into frequency channels.

An analog NTSC television channel is divided into subcarrier frequencies for video, color, and audio.

Meanwhile, their efforts led to an elementary understanding of electroacoustic technology, resulting in the invention of the telephone.