The Research Of Key Technology For LEO Satellite Constellation Communication System Receiver

In recent years,the trend of satellite-ground integration in the telecommunication industry has injected new vitality into the construction of Low earth orbit(LEO)satellite constellation communication systems,and domestic and foreign LEO satellite constellation construction plans have emerged one after another.The primary challenge for LEO satellite communication is that the relative displacement between the satellite and terminal causes doppler frequency shift.If estimation and compensation of the doppler frequency shift are not well performed,it will seriously affect the performance of the communication system.In addition,with the development of the satellite Internet of things,the deployment of communication devices will be,for the foreseeable future,more and more intensive,which makes it increasingly shortage of spectrum resources.In this scenario,the ability of blind signal detection to perform signal collision detection and avoidance is a must for every equipment.Therefore,this paper mainly focuses on doppler frequency shift estimation and compensation and blind signal detection algorithms.Some research achievements have been obtained.In terms of doppler frequency shift estimation and compensation:(1)For the SC-FDMA communication system,the existing algorithms have been simulated and analyzed,and based on the analysis result,a doppler frequency shift estimation compensation scheme suitable for LEO satellite communication has been implemented.The scheme consists of two steps.First,estimating and compensating the fractional frequency offset in time domain to reduce inter carrier interference.Second,estimating and compensating the integer frequency offset in frequency domain to correct the data cyclicshift.The simulation result shows that the implemented scheme can effectively estimate and compensate the frequency offset,and is suitable for the LEO satellite communication system.(2)For the single carrier communication system,the existing decision-direct carrier recovery algorithm has been simulated and analyzed,and the problem of poor frequency offset estimation and compensation effect in the convergence process of this algorithm has been pointed out.To solve this problem,the reverse data combination decision-direct algorithm is proposed.In order to help the outputs of loop filter getting convergence,and improve the compensation effect of the output signal,the new algorithm uses the reverse combination of data and the inverted phase loop filter to extend the input data while ensuring the data phase is continuous.The simulation results show that the proposed algorithm is better than the traditional algorithm in regard to frequency offset estimation and compensation,whether the input data is a long or a short burst signal:In terms of blind signal detection algorithms:The simulation and analysis of the classic blind signal detection algorithms has been performed.Based on the diagram and formula derivation,the power spectral maximum minimum averaging ratio algorithm has been proved that it cannot work normally under the effect of large doppler frequency shift.To solve this problem,a spectral shift maximum minimum averaging ratio algorithm has been proposed.The proposed algorithm uses the frequency index corresponding to the maximum spectral modulus in the power spectral density to cyclically shift the power spectral density as a whole,so that the baseband signal shifted by the frequency offset could returns back to the vicinity of zero frequency.After the spectral shifting,the proposed algorithm calculates the detection variable and judges whether the signal is present.It is proved by the simulation result that the proposed algorithm can detect signals normally under the effect of large doppler frequency shift.This means the proposed algorithm has better ability than the original algorithm to anti frequency offset.