As of today (September 9, 2002) there are three main cellular technologies: Older analog FDMA (Frequency Division Multiple Access), modern GSM TDMA (Time Division Multiple Access) and Newer CDMA (Code Division Multiple Access.) People mostly know of the latter two and the first one is almost wiped off from the history of Cellular Network technology.
I am not going too deep into the technical aspect of all the networks and am just giving an outline of FDMA.
Analog transmission is considered an “older” cellular phone technology. Back in the early 198o’s, it was the first network technology to be deployed successfully. FDMA is used exclusively for analog cellular systems, even though in theory FDMA can also be used with digital networks.
Essentially, FDMA splits the allocated spectrum into many ‘channels,’ each of approx 30 kHz bandwidth. During a data transfer, in form of audio or video, an FDMA networks allocates the entire channel to the phone and the data is modulated into this channel’s frequency band and sent over airwaves. At the receiver’s end, the information is recovered using a simple band-pass filter. The phone then uses common control-channel function to acquire channels during Handoffs ((Handoff is the term used for the broadcast site switching phenomena.)).
FDMA analog transmission is the least efficient due to its limitation of accommodating only one user per channel. Not only FDMA channels are larger and there is no data compression, but also there is a waste of bandwidth when there is any silence during a conversation. Analog signals are especially susceptible to noise and the extra noise cannot be filtered out. Furthermore, analog cell phones, due to the nature of the signal, must use higher power of one to three watts, to get acceptable call quality.
Thus, one can very well understand why FDMA networks failed to maintain its position. Digital technology has its advantages. Digital technology is much more efficient when using bandwidth. Due to digital compression, more data can flow over a network, efficiently. Digital is encrypted, difficult to decode, and is more secure than analog. It allows easy integration with personal communication systems such as hand held devices, palm pilots and hopefully in the future everything digital. Since Digital is so efficient, It can also lower average transmitter power as digital works ‘less harder’ as analog transmissions. Digital systems enable smaller and less expensive individual receivers and transmitters.
All these combined… FDMA is now phased out.