Research On Multiuser Detection Algorithm Of LEO Satellite CDMA Uplink

Satellite communication has the unique characteristics of full coverage,all-time and all-weather,and LEO satellite has good development potential with its superior communication link.Spread spectrum technology is widely used in satellite communication system with its advantages of strong anti-interference ability,good secrecy and low power spectral density.However,with the increase of access users,the multiple access interference of LEO satellite uplink will increase continuously,restricting the communication performance of uplink.In addition,the multiuser signal in the high load scenario is becoming more and more serious in the synchronization session,which will further restrict the effective user capacity of the uplink.In order to solve the above problems,this paper studies the multiuser detection algorithm of LEO satellite CDMA uplink and the interference cancellation of synchronization in high-load scenarios.Multiuser detection algorithms vary from each other,and selecting a suitable one for LEO satellite uplink is quite significant.In this paper,four commonly used multiuser detection algorithms are compared by theoretical analysis and simulations in terms of bit error rate,stability and implementation complexity.The results show that the multi-level parallel interference canceling detection algorithm has the performance of approximate single user's bit error rate,and has a simple structure,which is applicable to the satellite-load receiver with limited power and limited processing capacity.According to the operational requirements of LEO satellite uplink,we designed the base band parameters and built up its multiple accesses interference models,and focused on establishing an asynchronous multiuser detection algorithm for this link.By introducing partial correlation function to asynchronous systems,we established a symbol level asynchronous parallel cancellation detection algorithm,which has a low computational complexity and simple structure.Furthermore,in order to effectively deal with the problem of error propagation caused by cascaded structure,a partial interference cancellation detection algorithm with offset weight factor is introduced.We built up an uplink multiuser simulation platform in order to verify the performance of asynchronous parallel interference cancellation detection algorithm and partial interference cancellation detection algorithm.In terms of bit error rate,we simulated uplinks' multiuser performance and obtained its performance gain after using multiuser detection algorithms,the results show that these two algorithms can effectively eliminate the multiple access interference and significantly improve the uplinks' bit error rate.By analyzing the problem of multiple access interference cancellation which occurs in the synchronization module under high load scenario,we break the strict front and back constraints of traditional receiver in synchronization and demodulation level,designed a hybrid algorithm which use parallel interference canceling to assist synchronization.Furthermore,the performance of this hybrid algorithm is simulated and verified in terms of envelope's peak-to-average ratio,detection probability and false alarm probability,the results show that this hybrid algorithm can approximate single user's acquisition performance under some certain degrees,and can effectively improve the user capacity of uplink.