A base transceiver station in a mobile communication system, includes a GPS time frequency unit for outputting a synchronized time which is received from at least one GPS satellite and frequency information; a BTS main processing unit for generating a control command to control one BTS; an ATM interface unit for interfacing with an asynchronous mode communication device; a packet routing unit for providing routing information used for setting path of packet data; a multi-rate channel unit for processing an inter-channel communication, each channel having a different data rate; a signal transformation unit for transforming and modulation/demodulation of an input signal; and a wireless unit for wireless communication with a mobile station.