A Study of the Technique of Linear Multiuser Detection in DS—CDMA Systems
WANGYi, ZHOUJiong-pan · 中国邮电高校学报：英文版 · 2001
The technique of linear multiuser detection in DS-CDMA systems is studied in this paper,The purpose is to find a receiver structure with good performance and moderate complexity,so that the receiver can efficiently suppress multiple-access interference(MAI)and multipath intererence and has good near-far resistant ability,which may improve the system's capability while reducing the requirement for power control.The main work of the dissertation can be summarized as follows:the performance of MMSE multiuser detector in synchronous/asynchronous DS-CDMA systems over different channels is analyzed in chapter 2 of the dissertation.Using matrix method,we analyze the relation between performance measurement and spreading code correlation matrix,Signal-Interference-Ration(SIR) and near-far factor,and prove that the performance of MMSE detector is better than that of the decorrelating detector.For fading channel,we analyze the performance of MMSE detector in DS-SS system firstly.Results show that the detector can efficiently suppress multipath interference,Extending to synchronous/asynchronous DS-CDMA systems over fading channels,we propose a simple linear detector structure that accomplishes despreading,detection and combining.Thus,the receiver is easy for implementation.Based on the proposed notion of combined spreading codes,we prove that the synchronous/asynchronous CDMA system is equivalent to the synchronous CDMA system over AWGN channel with double users.Therefore,the MMSE detector can efficiently suppress MAI and multipath interference in steady state,and has good near-far resistant ability.In chapter 3,we study the adaptive algorithm based on MMSE criterion.Firstly,the approach to the blind algorithm based on subspace is analyzed.We improve the algorithm in the part of channel estimation,which decreases the computational complexity while guaranteeing the performance.Meanwhile,we point out that CMOERLS algorithm is essentially an algorithm based on subspace approach.Also,it is shown from simulation that PASTd subsp