Research On Key Technologies Of Physical Layer Of High Frequency Space To Ground Communication Based On 5g NR

The integration of low orbit satellite communication and 5g mobile communication is one of the important directions of the future communication network development.Meanwhile,with the gradual depletion of available spectrum resources in low frequency,satellite communication is also gradually developing to high frequency millimeter wave band.Because of the high speed of low orbit satellite,the Doppler frequency bias will be as high as 700kHz in high frequency communication scene,which is dozens times of Doppler frequency deviation in the high-speed moving scene of 5 g ground with the same frequency.The high Doppler frequency offset will seriously destroy the orthogonality between the subcarriers of orthogonal frequency division multiplexing(OFDM)system,and produce inter carrier interference(ICI),which will affect the accuracy of channel estimation.At the same time,the high speed motion of low orbit satellite will cause serious time selective fading of the channel,which leads to the high pilot cost and high complexity of the algorithm.Therefore,how to compensate Doppler frequency offset and estimate the channel efficiently for this kind of high time-varying channel in the satellite to ground communication network has become a hot topic in the current research of the satellite to ground communication network.Firstly,the transmission characteristics of satellite channel are analyzed and the channel model is given.Then,the influence of Doppler frequency offset on the transmission performance of satellite to ground communication link is analyzed.A two-stage frequency offset compensation scheme is designed for the problem of high complexity of the method.Firstly,the Doppler frequency offset is estimated and pre compensated based on the satellite ephemeris information.The Doppler frequency offset is corrected to a small range with lower algorithm complexity.Furthermore,the residual Doppler frequency offset is compensated by the method of pilot correlation and autocorrelation.The results show that the proposed algorithm can ensure that the mean square error of the frequency offset estimation is about 1%when SNR=15dB,and the complexity of the algorithm is reduced to 1/4 of the same algorithm.Secondly,the estimation of high time-varying channel in satellite ground communication system is studied.Aiming at the low frequency selective and high time selective fading characteristics of high frequency LEO satellite channel,the channel estimation accuracy is improved by optimizing the time-frequency insertion density of pilot symbols.Furthermore,combined with the high time-varying of channel,a channel estimation algorithm based on pilot cluster and base extended mode is proposed,which can obtain better channel estimation results while keeping the pilot overhead unchanged good channel estimation performance.