Within a cell, mobile operators want to allow as many customers as possible to use the network. They achieve this by using multiple access technology, which allows the available spectrum to be shared between several users. Analog systems usually separate conversations by subdividing the spectrum into narrow frequency bands and by using directional transceivers at the base station. Digital systems also divide each frequency into time slots, or encode transmissions so that more than one can use the same airwaves at the same time.
All radio systems use some kind of frequency division—they partition their available spectrum into sub-bands, each of which can be tuned into by one or more users. A system that gives each communication ...