Frequency division multiplexing( FDM) is a multiplexing method in which a wide frequency band is divided into several narrower frequency bands. Each of these frequency bands corresponds to a separate transmission channel. This multi- carrier modulation works with several independent carrier frequencies, whereby each individual carrier signal is modulated and transmitted completely independently of other carrier frequencies with different data streams.
In frequency division multiplexing, several modulated frequencies are transmitted simultaneously over the transmission channel. Depending on the concept, the bandwidth of the transmission channels can be the same or different.
A variant of frequency division multiplex is frequency division duplex( FDD), in which the uplink and downlink radio channels between the receiving and base stations are separated and transmitted on different frequencies. An extremely bandwidth-efficient variant of frequency division multiplex is orthogonal frequency division multiplex( OFDM), which uses a much smaller frequency band for the same transmission rate.