stations each of which is located in one cell of a larger service region each base station in the service region is connected by a group of communication links to the mobile switching center with the communication link being either direct or indirect through a controller that may span a plurality of base stations a communication link transports user data which may be a digital representation of voice between the base station and the mobile switching center each base station contains a group of radio transmitters and receivers with each transmitter receiver pair being connected to one communication link each transmitter receiver pair operates on a pair of radio frequencies one frequency to transmit radio signals to the mobile subscriber unit and the other frequency to receive radio signals from the mobile subscriber unit with cdma systems a plurality of transmitter receiver pairs share a common frequency pair this is made possible by the orthogonal coding that is inherent with cdma the first stage of a cellular communications connection is executed when a transmitter receiver pair at the base station operating on a predetermined pair of radio frequencies is activated and a mobile subscriber unit is tuned to the same pair of radio frequencies the second stage of the communication connection is.