The first point is that cell phones and base stations transmit or communicate with each other on dedicated paired frequencies called channels.
Base stations use one frequency of that channel and mobiles use the other.
The second point is that a certain amount of bandwidth called an offset separates these frequencies. Now let's look at what these frequencies do, as we discuss how channels work and how they are used to pass information back and forth. Certain channels carry only cellular system data. We call these control channels . This control channel is usually the first channel in each cell.