A digital mobile communication system wherein a master clock of a mobile communication system for offering audio or data service using a code division multiple access (CDMA) is set as a global positioning system (GPS) clock provided in a GPS and the interface and timing between various subsystems using the GPS clock and an exchanger are redesigned to achieve an exact timing schedule, and a timing design method between various subsystems. In order to maintain frequency and time synchronization between various subsystems in a CDMA system using an exchanger therefor, the respective subsystems are designed based on the clock supplied from a GPS, a hardware interconnection between the systems is designed based on the GPS clock to attain an exact timing, thereby achieving a fast and exact frame transmission.