Detection Of Asynchronous NOMA In Interference Environment

Compared with OMA(Orthogonal Multiple Access),NOMA(Non-Orthogonal Multiple Access)can significantly improve system capacity,spectrum efficiency,transmission capacity,etc.,and has become an important candidate technology for the fifth generation communication system.NOMA technology has developed rapidly in recent years,but most of the existing research work is carried out under ideal conditions,without considering NOMA signal detection in asynchronous systems,carrier frequency offsets,and interference environments.This thesis considers these issues and mainly studies the signal detection technology of A-NOMA(Asynchronous NOMA)based on OFDM(Orthogonal Frequency Division Multiplexing)in the interference environment.The specific research work is as follows:First,aiming at the asynchronous problem,the impact of asynchrony on user detec tion is firstly analyzed,and a signal detection algorithm using cyclic prefix for phase com pensation is studied.Then,an asynchronous timing synchronization scheme is designed.This scheme can make the interference between users small enough,and obtain the timing position of each user more accurately,and obtain the specific phase compensation value.In addition,this thesis analyzes the effects of CFO(Carrier Frequency Offset)on the detection of A-NOMA user signal based on formula derivation and simulation results.The power difference can alleviate the effect of frequent Offset.Second,aiming at improving the anti-jamming capability of the system,the influence of single-tone and narrow-band jamming on system synchronization and user detection is firstly analyzed.Then,CME(Consecutive Mean Excision)and FCME(Forward Consecutive Mean Excision),two classic frequency-domain detection methods and preprocessing methods before detection are studied,and the data of the interfered subcarrier is zeroed to suppress the influence of interference.Third,the useful signal on the interfered sub-carrier is also suppressed when the receiver suppresses the signal,so that the signal after interference suppression has the problem of time domain data distortion affecting the synchronization of the system.To solve this problem,a frequency offset estimation algorithm based on linear fitting is proposed,and the effectiveness of the algorithm is verified by simulation.In addition,it is necessary to design the interleaving depth.Fourth,after the signal is interference suppressed,using serial interference cancellation when detecting low-power users will introduce IUI on the interfered sub-carriers.To solve this problem,a method of secondary suppression is proposed,that is,the data on the interfered sub-carrier is zeroed out before decoding the low-power users to eliminate the interference between users.Simulation results show that the bit error rate of low-power users is significantly improved after secondary suppression.Finally,the whole link simulation analysis of the A-NOMA link structure studied in this thesis verifies that the link structure has good anti-interference performance.