Mobile communication base transceiver stations enable multiple users to be connected simultaneously within a limited radio-frequency spectrum. This method is called Multiple Access Technology. This technology can be divided into two types: analogue and digital. FDMA (Frequency Division Multiple Access) is a leading analogue type, while TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access) are leading technologies in digital type Multiple Access Technologies.
FDMA divides allocated frequency into multiple channels to provide multiple connections. Each divided frequency is occupied for each connection until it serves another connection. This method is easy to realize but the loss of frequency is bigger than other systems. To improve its frequency usage, TDMA was suggested which added time division concept to FDMA.
TDMA technology divides specified frequency using time information to send and restore the communication data using the information. A leading TDMA is European GSM. CDMA applied Spread-Spectrum Technology to mobile communication. It expands communication data to a much broader frequency band before transmission.
These three systems can be easily explained by supposing a big conference hall full of people. In FDMA system, people using same language go into multiple small meeting rooms in their turns.
In TDMA system, everyone, using same language, in the conference hall agrees to speak only during an allocated time for each person. It sounds that their conversations would be fragmented, but this presents no problem.
Compared to TDMA and FDMA, CDMA is like people talk at once in a same place. However, each conversation couple uses their own language not to interfere other people in the room.