The Research Of Multiple Access Interference Cancellation In CDMA Communication System

CDMA technology plays an important role in satellite communications, although the CDMA technology has the advantages in capacity, security and spectrum utilization, the user’s random access and spread spectrum code is not strictly orthogonal to the user’s signal will generate multiple access interference (MAI) problem. MAI carries the spread spectrum code related information, which is different from the general noise, and the multi-user detection technology has been used to effectively eliminate MAI and improve the performance and capacity of the system. In this dissertation, study the low spread spectrum ratio CDMA communication system,and explore the multiple access interference cancellation detection algorithm with low computational complexity and easy implementation.Firstly, to solve the problem of the signal is easy to break and the robustness of the estimation is poor in traditional estimation method the iterative method is proposed to improve the stability of the bit rate. To solve the problem of the loss of useful information in traditional asynchronous interference cancellation policy,an improved asynchronous enhancement strategy is proposed, which is used to compensate the loss of the information of the missing part and the delay information. The simulation results show that the improved method is better.Secondly,to solve the problems of high delay of SIC detection algorithm and the structure complexity of PIC detection algorithm, the detection algorithm (T-PSIC) based on user delay packet and string interference cancellation for asynchronous CDMA systems is proposed. The improved algorithm is based on the principle of delay close to the user,PIC detection was used in the group,and SIC was used to detect the group. The simulation results show that the improved algorithm overcomes the problem of the SIC algorithm, which makes the PIC detection algorithm simple, and improves the performance of the non-ideal power control.Finally, to solve the problem of error detection in parallel interference cancellation detection, a partial parallel interference cancellation detection algorithm (R-PPIC) based on user power ratio is proposed, the fundamental idea is that the first level PIC does not deal with the user when a user power is very small,which reduce the interference caused by strong users, and the probability of the first error estimates. The simulation results show that the new algorithm can achieve better error performance when the user’s power control is not ideal or there is near and far effect.