CDMA Basics
Qualcomm
IS-95 Air Interface

American digital CDMA Standard

Since the beginning of broadcasting and especially in the first generations of mobile communications, different users where assigned to a dedicated radio channel. The channels differed in their carrier frequencies and were referred to Frequency Division Multiple Access (FDMA).

The digitization of radio signals made it possible to divide a radio channel into time slots. Each user was now not only assigned to a radio channel, but also a time slot. As described in great detail above, we speak of Time Division Multiple Access (TDMA).

There was another option in which all users could sent and received data on the same frequency. How could this work? That would be the maximum possible disruption, something you want to avoid using TDMA and FDMA. But with a trick it really works. A young American company called Qualcomm developed this trick. It is based on a technology called Code Division Multiple Access, CDMA.

How CDMA works and where it comes from is described here: CDMA Basics.

The air interface of this new CDMA based standard called IS-95 is described here IS-95 Air Interface.