Research On Carrier Synchronization In CDMA LEO Satellite Communications

With the development of the wireless communication technology, CDMA LEO Micro-satellite Communication is becoming more and more important. The depplor frequency shift in the received signal is a typical character of the LEO satellite channel. This paper concerns relative technologies about carrier frequency synchronization and estimation in downlink signal in large doppler frequency shift condition. The characteristic of the wireless satellite channel is discussed firstly,especially the formation of the doppler shift and the effect of the doppler to received signal. Second, baced on the ML rule of the detection and estimation theory, we analysised the parameter estimation algorithms, and make the basement of the forward frequency estimation. Then, The CDMA theory and communication system is estabilished, especially the catching and tracking technology of the CDMA downlink signal in LEO satellite communication, which is very important and relative with the design of the carrier frequency synchronization. After this part, a time-frequency two dimension searching algorithm is discussed, alter the searching part, a frequency discriminater is used to enlarge the frequency cell and finished the exact frequency estimaton. System and the detailed algorithm is designed and simulated. It's proved that this design is effective. By using the serial-parallel searching structure, appropriate searching algorithm, and enlarged frequency cell, this design can reduce the frequency estimation time and error, also is not very complicated.