Research On Baseband Sampling And Carrier Frequency Offset Estimation And Compensation Algorithm Of Broadband LEO Satellite

LEO satellite network makes use of its low cost,wide coverage and convenient deployment to realize the seamless link service of the global Internet.The integration of terrestrial cellular network and satellite network has become an important development trend.Therefore,3GPP standard represented by 5G new radio needs to be used on satellites,including orthogonal frequency division multiplexing.However,due to the high dynamic characteristics of LEO satellites,the carrier frequency offset and sampling frequency offset between the receiver and the signal will interfere with the signal,resulting in constellation rotation and even cyclic shift,which can not be ignored.Firstly,this paper introduces the LEO satellite mobile communication system based on OFDM,derives the relationship between normalized Doppler and sampling frequency offset,and further introduces the method of calculating normalized Doppler with ephemeris.To solve the above problems,it is feasible to estimate and compensate the carrier frequency offset and sampling frequency offset by using ephemeris.In this paper,the expression of received signal is deduced for the cumulative effect of sampling frequency offset,and based on this,the compensation algorithm of carrier frequency offset and sampling frequency offset is proposed.Finally,it is verified by experiments in the actual satellite communication scene.The main contributions and innovations of this paper are as follows:1.This paper introduces the influence of sampling window offset caused by the cumulative effect of sampling frequency offset,and deduces the expression of OFDM system affected by sampling frequency offset and carrier frequency offset,and obtains the closed expression of interference,which is consistent with the actual situation.2.By analyzing the interference expression,two main influencing factors are obtained,and a new compensation algorithm is designed according to this.The proposed compensation algorithm combines the compensation methods of time domain and frequency domain,and reduces the interference power on the basis of correcting the phase rotation.3.Because the compensation algorithm depends on the main influencing factors,this paper proposes a normalized Doppler estimation algorithm based on ephemeris and Kalman filter.For the fixed receiver,the ephemeris is directly used for normalized Doppler estimation and carrier and sampling frequency offset compensation;For the mobile receiver,the normalized Doppler estimation is combined with Kalman filter.4.In this paper,the real satellite is used to carry out the actual measurement experiment of LEO satellite communication scene,which verifies the effectiveness of the proposed scheme,and the results show that the method has good performance.