Global System for Mobile Communications (GSM, around 80–85 % market share) and
IS-95 (around 10–15 % market share
[1]) are the
two most prevalent mobile communication technologies. Both technologies have to solve the same problem: to divide the finite
RF spectrum among multiple users.
TDMA (Time Division Multiple Access-underlying technology used in GSM's
2G) does it by chopping up the channel into sequential time slices. Each user of the channel takes turns to transmit and receive signals. In reality, only one person is actually using the channel at a specific moment. This is analogous to
time-sharing on a large computer server.
CDMA (Code Division Multiple Access-underlying technology used in GSM's
3G and IS-95's 2G) on the other hand, uses a special type of
digital modulation called
spread spectrum which spreads the voice data over a very wide channel in
pseudorandom fashion. The receiver undoes the randomization to collect the bits together and produce the sound.
For comparison, imagine a cocktail party, where couples are talking to each other in a single room. The room represents the available bandwidth. In GSM, a speaker takes turns talking to a listener. The speaker talks for a short time and then stops to let another pair talk. There is never more than one speaker talking in the room, no one has to worry about two conversations mixing. In CDMA, any speaker can talk at any time; however each uses a different language. Each listener can only understand the language of their partner. As more and more couples talk, the background noise (representing the
noise floor) gets louder, but because of the difference in languages, conversations do not mix. .....
Read more @http://en.wikipedia.org/wiki/Comparison_of_mobile_phone_standards