In RF Hopping mode, each route of service information is processed by fixed base band unit and and carrier frequency processing unit, while the working frequency carrier of carrier frequency processing unit is provided by frequency synthesizer.
Under the control of the control unit, frequency carrier can be changed according to certain rules. This mode is called “carrier frequency hopping” or “RF hopping”. In RF hopping, one transmitter processes the frequency carriers used by all bursts of one communication, which is realized through the change of synthesizer frequency instead of the switching of base band signal. The number of TRX depends on cell traffic instead of restricted by carrier.
Because of the change of synthesizer, the combiner should be changes, only broadband combiner can be used. This kind of synthesizer has a insertion loss of about 3db. The cascade connection of multiple combiners has large insertion loss, so the actual application is restricted. But once fault occurs to certain TRX, the troubleshooting function of the system will shut down this TRX.
GSM specifications do not specify that GSM BTS must use “base band hopping” or “band hopping”, while the hopping mode used by BTS equipment is specified by the equipment supplier. As to mobile terminals, since each terminal has only one carrier unit, it’s bound to use carrier frequency hopping.