• In FDMA, the available bandwidth is divided into various frequency bands.
• Each station is allocated a band to send its data. This band is reserved for that station for all the time.
• The frequency bands of different stations are separated by small bands of unused frequency. These unused frequency bands are called guard bands that prevent station interferences.
• FDMA is different from frequency division multiplying (FDM).
• FDM is a physical layer technique whereas FDMA is an access method in the data link layer.
• FDM combines loads from different low bandwidth channels and transmit them using a high bandwidth channel. The channels that are combined are low-pass. The multiplexer modulates the signal, combines them and creates a band pass signal. The bandwidth of each channel is shifted by the multiplexer.
• In FDMA, data link layer in each station tells its physical layer to make a band pass signal from the data passed to it. The signal must be created in the allocated band. There is no physical multiplexer at the physical layer.