The multiple access techniques used in different cellular systems are different. The AMPS, which is the now classical analogue cellular mobile system, namely the advanced mobile phone system, that uses frequency divisions multiple access. Now duplexing require two channels one for transmission from the base to the mobile, and another from the mobile to the base: this is what we call duplexing. Therefore one has to also consider the appropriate duplexing scheme for having two-way conversation.
The AMPS system uses frequency division multiple access for the accessing and it is also used for duplexing frequency division, whereas you have the improved system, the digital system, which is a second generation system, known as the global system of mobiles, GSM, which uses instead of frequency division multiple access, time division multiple access, and the duplexing is still in the frequency domain, that is separate frequencies are used for the uplink and the donwlink or the forward and the reversing communication.
US Digital Cellular communications, similarly, that is second generation system, like the GSM, also uses the time division multiple access for multiple accessing and the frequency division duplex, namely the different frequencies for the two directions.
And so is the case with the Japanese digital cellular systems, which is again the second generation system, they also use the time division multiple access for accessing and frequency division duplexing for the two directions.
On the other hand, you have got the cordless system, which is CT2 and DECT this is the second generation cordless systems. They use both frequency division multiple access so far as the accessing is concerned, but unlike the cellular systems, they do not use FDD, they use time division duplexing for the two directions of use.
You have in the second generation another system, which is the IS-95, which is code division multiple access based and the uses the code division multiple access for the accessing part, but for the duplexing, that is both directions they use a frequency division duplexing. We call this as N-CDMA, because in the beginning it was only 1.25 MHz bandwidth it was taken. The third generation systems will have about 5 MHz bandwidth, and they are known as wide-band CDMA techniques, and they are going to use of course multiple accesses, code division multiple access, obviously, and the both FDD, namely the frequency division duplexing as well as the time division duplexing are being proposed to be used for the third generation CDMA systems.