Research And Implementataion Of Synchronization Algorithms Based On Integrated Space-Air-Ground System

The rearch of Integrated Space-Air-Ground System has become hot all over the world, OFDM has been widely used because of the high frequency efficiency and high resistance to interference. However, it’s high sensitivety to frequency offset made synchronizing system important to OFDM system.This thesis analyze the characteristics of the Integrated Space-Air-Ground tt&c communication environment, the channel has the characteristics of multipath fading and dopple frequency shift, this thesis also discuss traditional classical algorithm jointing timing and frequency called SC and the improved algorithm about SC, summarize the factor which effect the performance of synchronization system, then, proposed the synchronization system of Integrated Space-Air-Ground tt&c communication system, the whole synchronization system can divided into five parts, adjustable correlation sequence of the preamble(ACSP), improved coarse timing synchronization, joint path timing and integer frequency offset synchronization, fractional frequency offset synchronization, fine-timing synchronization. This five parts in turn to perform. This synchronization system has no demand for the leader sequence, it’s suitable for any leader sequence, can be used in many systems. The length of cross-correlation can be adjust by the signal to noise ratio efficiently. Synchronization system has the same range with the bandwidth of system, so that the range of frequency estimation is large. The improved coarse timing synchronization solved the problem that the frequency offset has a big effect on the performance of frequency system, has a good performance with the big frequency offset. The improved fine timing synchronization can eliminate the interference of multipath, find the time of first arrived fath accurately, imporved the performance of synchronization system in multipath fading environment.Then, we verify the synchronization system in Matlab, analyze the performance of the synchronization system in different frequency offset, and different channel, and different signal to noise ratio. The simulation results shows that the timing synchronization and frequency synchronization both has a better performance than the classical algorithm. When the synchronization system is in the multipath fading chnnel,and the signal to noise ratio is 20 dB, normalizationed frequency offset is 2.58. The synchronization system can timing accurately and the error of normalizationed frequency offset is less than 0.004. Finally, utilized the HDL Coder to realized the synchronization system in FPGA without the heavy and complicated work.