Researches On A Satellite Communication System Based On Onboard FDMA-CWTDM Conversion

FDMA/CWTDM (Frequency Division Multiple Access/Continuous Wave Time Division Multiplex) multi-access/multiplexing system is believed to be an excellent new system for satellite communications, which can be derived from modifying the system based on onboard FDMA-TDM conversion by using CWTDM instead of TDM. This thesis deals with developing a prototype of satellite communication system, which is composed of an onboard FDMA-CWTDM conversion transponder of 36MHz band width and a simulator of emitters and receivers of multiple earth stations, combined with some comprehensive anti-jamming processes. The thesis researches on the related onboard processing techniques including FDMA de-multiplexing, adaptive excision of narrowband jamming, CWTDM and digital AGC techniques, as well as a simulator to generate FDMA direct sequence spreading spectrum signal. We have succeeded in developing the system, including a lot of simulation experiments, hardware realization, system debugging and its performance test. Test results have validated that the system has excellent performance and extremely strong ability of anti-jamming. The author’s main contributions are as follows.1. Based on the idea of software radio, an emitter model with good performance and of compact structure is proposed, and a simulator to generate FDMA direct sequence spreading spectrum signals is developed by using an FPGA chip and the related circuit board.2. Through deep researches on digital AGC, a proper scheme is proposed and implemented by using FPGA. Practical running and testing results show that the AGC behaves very well, which can guarantee the processing transponder within linear dynamic range under very strong jamming.3. Based on the previous development of the process transponder, the frequency division de-multiplexer, the IIR notch filter for excising narrowband jamming and the CWTDM module are remarkably improved by optimizing the algorithm, debugging the parameters and making the hardware compact. For example, the IIR notch filter can effectively excise narrowband jamming to make the jamming tolerance of the system greatly enhanced. In order to conveniently debug this complex system, a segment-wise debugging scheme is designed and realized by modifying the FPGA module and comparing their outputs with the simulation results, which guarantees the whole system to reach the best performance. 4. The system is successfully debugged by means of base band connection and intermediate frequency connection. The developed system has passed comprehensive test, and the results demonstrate that it behaves quite well, and all the specifications have exceeded the previous expectation.