Study Of Two-Way Satellite Time Transfer Modem

Time transfer methods are becoming increasingly important in the world of high-speed communication, global navigation and precision metrology. There are two primary methods of time dissemination around the world: two-way satellite time transfer_TWSTT and common-view Global Position System_GPS time transfer. There is a catch: GPS is a United States Department of Defense system, its applications are limited. TWSTT is often used as a secondary measurement to GPS or a sole means time recovery with performance that is superior to GPS time transfer, so it has been a hot topic in time community all the time.In this thesis, digital IF time transfer modem is mainly studied. In the second chapter, the principle of two-way time transfer with emphasis on its use with commercial communications satellites is firstly introduced in detail, then a new method of processing multi-stations data is presented; finally the signal flows and components are analyzed based on TWT-100. In the third chapter, some key technologies concerned with digital IF modem are introduced, such as PN sequence acquisition and tracking, carrier recovery and phase locked loop. In the fourth chapter, the IF modem implementation structure of two-way time transfer is presented. Frequency/time two dimension N channels acquisition is adopted in PN sequence acquisition, frequency locked loop and phase locked loop are used in carrier recovery, coordinated rotation digital computer is employed in phase computing. In the fifth chapter, hardware implementation of spread spectrum modulation module, sequence acquisition module, carrier NCO module and CORDIC module are given.