What does FDM mean?
In FDM, signals of different frequencies are combined for concurrent transmission. Frequency division multiplexing (FDM) is a technique of multiplexing which means combining more than one signal over a shared medium.The frequency division multiplexing suffers from the problem of crosstalk. When FDM is used to allow multiple users to share a single physical communications medium (i.e. not broadcast through the air), the technology is called frequency-division multiple access (FDMA).