TDMA

TDMA stands for Time Division Multiple Access.  It is a system that is used for digital cellular.  To understand it, let us take apart the letters.  "MA" means multiple access, which just means a system that can handle many phone conversations or other wireless conversations.  "D", division, asks the question "how do we keep these different conversations separate from each other?"  And the answer to that question is the first letter "T" for time.  The different conversations are separated in time.

There are several TDMA type systems for Cellular.  GSM mostly in Europe and Asia and some in the Americas is mostly a TDMA system.  iDEN for Nextel in the Americas is mostly a TDMA system.  PDC in Japan is also mostly a TDMA system.

Let us look at GSM as an example.  In GSM, 8 different cellular phone conversations, each called a "channel", share a single frequency.  They do that since the data is only allowed a time slot that is one eighth of the time.  So, every complete interval of time would contain 8 different phone conversations, digitally coded, end to end.  At the receiving end, the digital coding is separated for each of the 8 conversations.  The electronics also converts the signal from digital back to audio, and again spreads it out in time such that it seems a continuous audio signal and not a signal just there 1/8th of the time.

PDC is a TDMA, time division multiple access system.  However in its case, each frequency is shared by 3 channels or 3 customer conversations.