Frequency Division Multiple Access (FDMA): One of several technologies used to separate multiple transmissions over a finite frequency allocation. FDMA refers to the method of allocating a discrete amount of frequency bandwidth to each user to permit many simultaneous conversations. In cellular telephony, for example, each caller occupies approximately 25kHz of frequency spectrum. The cellular telephony frequency band, allocated from 824 MHz to 840 MHz and 869 MHz, consists of 416 total channels, or frequency slots, available for conversations. Within each cell, approximately 48 channels are available for mobile users. Different channels are allocated for neighboring cell sites, allowing for re-use of frequencies with a minimum of interference. This technique of assigning individual frequency slots, and re-using these frequency slots throughout the system, is known as FDMA.


The below picture depicts a visual comparison of how FDMA, TDMA, and CDMA allocate bandwidth.

*Note how FDMA follows the “Frequency” axis, TDMA the “Time” axis, and CDMA the “Code” axis.

Source: http://www.ce-mag.com/archive/2000/sepoct/0009c30a.jpg