CDMA

CDMA stands for Code Division Multiple Access.  If this seems confusing, let us break it down.

• Multiple Access implies a means where many people can be talking at once - many conversations at one time
• D = Division asks the question how to keep all of those conversations separate
• C stands for code.  This means that the method we will use to allow many conversations in cellular at once, yet keep them separate, is to assign each a code.

So, CDMA is a form of digital cellular where each cellular conversation is given a digital code that is combined with that conversation.  And at the receive end, the receiver - likely a base station - will use the same code in order to retrieve the conversation from that same person and only that person without interference.

CDMA was really not a new invention, but the adaptation of an electronics military usage that once was called "spread spectrum" technology.  Combining a code with voice tends to not only make the voice hard to retrieve - and hence make it very private, it also tends to make the transmitter seem odd since the frequencies are so spread out.  Therefore, if one were to look for the transmitter electronically, it would be hard to find.  It is perhaps with all of this stealth that it is not surprising that the first application of "spread specturm"  was for Military applications. 

However, CDMA also has capabilities for (a) putting many customers on the air at one time without interference and (b) capabilities for very high data transfer.  For this reason, Qualcomm Corporation in San Diego California developed patents for using spread spectrum technology within Cellular service - calling it CDMA.