Research On The Synchronization Of Low Earth Orbit Satellite Communication Based On MF-TDMA

The low-orbit satellite communication system based on MF-TDMA?Multi-Frequency Time Division Multiple Access?has the advantages of flexible networking and dynamic allocation of channel resources,which has been one of the most hot research field in the future.Low-orbit satellites are faced with low signal-to-noise ratio and significant doppler shift.In this case,synchronization technology is a key issue for low-orbit satellite communication system,whose performance directly affects the receiver performance.This thesis focuses on the advanced synchronization technology based on MF-TDMA low-orbit satellite communication system.First of all,this thesis models the received signal,and deduces the signal-to-noise ratio of the tree structure multicarrier de-multiplexer method and the multi-phase FFT multicarrier de-multiplexer method.On this basis,the influence of narrowband Gaussian white noise,frequency offset and phase noise on bit error rate are further deduced.The simulation results verify the accuracy of the results,and pave the way for the following synchronization techniques.Secondly,we study two different frame capture algorithms.A preamble sequence can be used for peak platform acquisition and correlation peak capture,and then a concrete flow diagram of two acquisition algorithms is proposed.It is found that under the condition of low SNR,the acquisition performance of the correlation peak is about 1dB better than that of using the peak platform when the probability of the failure capture is about 10^-5.In addition,for the complexity of the existing sampling clock offset estimation algorithm,this thesis presents a low complexity sampling clock phase estimation algorithm suitable for hardware implementation.The algorithm is improved on the basis of the absolute value transformation,and the computational complexity is reduced from O?LM?to O?L+M?.Morever,the performance loss is small.On the basis of this,aiming at the problem that the receiver needs fast capture and continuous sampling recovery of short frames,this thesis presents a general scheme of data frame header recognition combined with continuous timing recovery.Using this scheme,we can not only reduce the hardware implementation complexity,but also can estimate the short burst data continuously and quickly restore the best sampling decision.Finally,aiming at the problem that the existing carrier synchronization technology can not balance the frequency offset estimation range and the estimation accuracy under the condition of low SNR,this thesis firstly proposes a double symmetric pilot pattern.Using this symmetric pilot pattern,this thesis presents a two-stage carrier synchronization scheme combining the frequency domain coarse estimation and time domain fine estimation.By adjusting the parameters of symmetric pilot parameters,the scheme can flexibly adjust the range and accuracy.It is worth noting that the normalized frequency offset estimation variance is still close to CRLB?Cramer-Rao Lower Bound?when SNR is-7dB,which is very suitable for the low-orbit satellite communication system with low signal-to-noise ratio and large frequency offset characteristics.