FDM - definition

FDM (Frequency Division Multiplexing) is a transmission channel multiplexing technique involving the simultaneous transmission of multiple information signals over a common transmission medium, with each signal occupying a different, mutually non-overlapping frequency band. This allows multiple independent data streams to be transmitted in parallel over a single cable, optical link or radio band, without interference between them.

In an FDM system, each information channel modulates its own carrier wave, whose central frequency differs from the others. The signals thus obtained are summed up and transmitted over a common medium, and finally received and separated by means of frequency filters or demultiplexers. Adequate spacing between channels, called a frequency guard, prevents inter-signal interference.

FDM is used in many analogue and digital transmission technologies, including classical telephone systems, radio and television broadcasting, fibre-optic links (in the WDM version - Wavelength Division Multiplexing), satellite transmission and radio communications. In telecommunications networks, it enables efficient use of the available bandwidth and simultaneous service of multiple users without the need for time division of the transmission.

From a technical point of view, the effectiveness of FDM depends on the precision of filtering, stability of carrier frequencies and resistance to inter-channel interference. Compared to time-division multiplexing (TDM), FDM allows continuous data transmission without the need for synchronisation time, which is particularly important in applications requiring a constant stream of information, such as voice or video transmission. Today's FDM systems are increasingly being realised digitally using DSP techniques, which increases their flexibility, quality and robustness to noise.

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