Research On Same-frequency Interference Cancellation Algorithm For WCDMA Satellite Signals

Satellite communication has many excellent features such as long communication distance,large coverage area,large system capacity,and convenience.It has become an important communication method in the world,especially in the military field.With the apparent increase in the application of satellite communications in the military field,satellite communications links have been increasingly disrupted by hostile forces.Therefore,it has great significance to study the interference and anti-jamming technologies of satellite communication systems.In order to resist the same-frequency strong interference in the WCDMA satellite signals downlink,this thesis proposes an interference processing scheme based on the reconstruction and cancellation of strong interference signals,mainly research the parameter estimation algorithms for strong interference WCDMA satellite signals and weak target WCDMA satellite signals.And designs a synchronization detection algorithm based on the traversal related process of scrambling code,the algorithm can detect multiple WCDMA signals simultaneously.Firstly,this thesis analyzes serial interference cancellation(SIC)methods for multiaccess interference in WCDMA systems.Based on the disadvantages of the SIC method,a new interference cancellation scheme for WCDMA satellite signals is proposed in this thesis,and the workflow of this scheme is designed in detail.Secondly,the parameters estimation algorithm of WCDMA satellite signals is studied,including frequency offset estimation algorithm and amplitude estimation algorithm.Considering the characteristics of strong interference signal,a tracking loop combining the FLL and the PLL is designed in order to estimate the frequency offset accurately.In order to estimate the amplitude of strong interference signal,an amplitude estimation algorithm based on linear interpolation of channel estimation is designed.In addition,in order to improve accuracy of frequency offset estimation algorithm for the weak target WCDMA satellite signal,a double frequency offset estimation algorithm based on Kalman filter is designed.Compared with the traditional WCDMA frequency offset estimation algorithm,the double frequency offset estimation algorithm based on Kalman filter can estimate frequency offset more accurately under low SNR conditions.Then,considering the shortcomings of traditional synchronization algorithm in WCDMA system,a synchronization detection algorithm based on scrambling code traversal related is designed,which can detect the synchronization peaks of multiple WCDMA signals simultaneously.In order to reduce the computational complexity of the correlation calculation process,this thesis further proposes a fast correlation algorithm based on segmentation and overlap.The scrambling code traversal correlation algorithm based on segmentation and overlap designed in this thesis has higher detection success rate for WCDMA signals with low SNR.Finally,the improved frequency offset estimation algorithm,amplitude estimation algorithm and the scrambling code traversal correlation algorithm based on segmentation and overlap are tested on MATLAB simulation platform.The test results show that the frequency offset estimation algorithm designed in this thesis is more accurate than the traditional frequency offset estimation algorithm.Then verify the whole interference cancellation scheme and test the cancellation effect.The test results show that the samefrequency interference cancellation algorithm designed in this thesis can effectively reduce the interference and decode the weak target signal when the power difference between strong interference and the target signal is within 20 dB.This verifies the validity of the parameter estimation algorithm designed in this thesis and the correctness of the same-frequency interference cancellation scheme.