Research On Multipleuser Detection In Asynchronous CDMA Communication System

Multi-user detection technology is an important technology in CDMA communication system,it can effectively eliminate the MAI to ensure system performance.An ideal multi-user detection techniques is a simple in complexity and can achieve a particular performance.With the spread spectrum communication technology become the most widely used communication system currently,transformation of the multi-user detection technology from theory to achieve become the focus of research nowadays.The asynchronous spreading use long-code is studied in this article:(1)Analysis of the basic causes of multiple access interference in the spread spectrum communication system and discussion the shortcomings of traditional receiver in dealing with the existence of other user information,shows that we need to introduce multi-user detection technology to achieve a good performance in CDMA communication system.For all kinds of interference canceller applicable in different environments,the parallel interference canceller has a simple structure,good performance and guaranteed real-time characteristics,and it is chosen in this research to solve the undesirable phenomenon in asynchronous long code spread spectrum communication system.(2)We introduce the traditional asynchronous parallel interference cancellation scheme and find the existence of some shortcomings in the system.There is a gap between the performance of the synchronous system in and the asynchronous one in capability.The decision feedback process thinking is used between bits of information andbetween different levels of parallel interference cancellation scheme,we proposed an improved asynchronous strategies,computer simulation shows the difference performance in improving the overall BER.(3)In multi-rate CDMA communication systems,the traditional parallel interference cancellation does not work.We propose a virtual-user based way allows users to eliminate the low-speed users' MAI by increasing the complexity,which can effectively improve the performance of high-speed users.(4)The proposed improved asynchronous strategy applied in parallel interference elimination algorithm is rewrited in hardware description language.Modelsim simulation result is given,and the logic analyzer is also used to achieve this paper.Hardware simulation gives the resource algorithm's structure need to achieve.With all the work above,the theory is changed into practice,and this project still has a certain practical significance.