Excellent writing on this transition period from 2G to 3G and beyond is in this printable .pdf file, a chapter from The Essential Guide to Wireless Communications Applications by Andy Dornan. Many good charts. Back to code division multiple access. A CDMA system assigns a specific digital code to each user or mobile on the system. It then encodes each bit of information transmitted from each user.
Every cell site can transmit on every frequency available to the wireline or non-wireline carrier.
That's because the specificity of the coded signals helps a CDMA system treat other radio signals and interference as irrelevant noise. Some of the details of CDMA are also interesting. Before we get to them, let's stop here and review, because it is hard to think of the big picture, the overall subject of cellular radio, when we get involved in details. We've discussed, at least in passing, five different cellular radio systems. We looked in particular at AMPS, the mostly analog, original cellular radio scheme.