| With the gradual popularization of mobile internet and intelligent terminals in our daily life,people show increasing demand for high speed and quality data transmission.As an important part of seamless network,satellite communication requires the capability to transmit data at a high speed.In order to improve the transmission capability of the satellite system,orthogonal frequency division multiplexing(OFDM)is proposed to use in the satellite.The OFDM can not only effectively improve the utilization efficiency of frequency resources for the satellite,but also provide convenience for the satellite to integrate with the ground mobile Internet.However,OFDM has strict requirements of synchronization performance.Therefore,it has become fairly important to solve the problems of terminal synchronization when OFDM is applied to satellite system.That will be deeply studied in this thesis.Firstly,the problems of the synchronous acquisition of low orbit satellite system based on OFDM technology is studied.After analyzed the existing synchronization technologies,it is found that the method of useing training sequence can achieve good performance when the signal is subjected to large frequency offset.Based on this,a new acquisition algorithm is proposed.The proposed algorithm uses the Chu sequence to design the training sequence,and gives the synchronization acquisition scheme.Because of the symbol timing estimation curve is sharp,there is no timing fuzzy problem.Besides,the integer frequency offset estimation is completed in the time domain,so it can more conducive to rapid capture.Secondly,the OFDM frequency offset tracking algorithm is studied,and a new residual frequency offset(RFO)tracking algorithm is proposed.Based on the idea of decision feedback,the algorithm uses the phase rotation of the demodulated data caused by RFO to estimate the frequency offset value,and compensates the RFO in the time domain.The tracking performance of the proposed algorithm is better than the method of traditional decision feedback,without assistance of pilot,and the algorithm does not consume additional frequency resources.The computational complexity is not high.Meanwhile,the tracking range of the proposed algorithm may be affect by the noise,modulation and other aspects.For example,if signal noise ratio(SNR)is 15 dB,when using QPSK modulation mode,the tracking range will be 8.5% of the subcarrier spacing,when using 16 QAM modulation modem,the tracking range will be 4.5% of the subcarrier spacing.Although the tracking range is not large,it is enough to complete the tracking task based on the good acquisition algorithm.Finally,the total synchronization solution has been provided and simulated on the computer. |
