A Study On Blind Multi-user Detection Algorithms In DS-CDMA Communication Systems

Code Division Multiple Access is self-interfered system,where multi-access interference(MAI) and Near-far effect are existing as the main factors restricting CDMA system capacity.Over the past decade,a significant amount of research has addressed various multiuser detection(MUD) techiniques.MUD is an efficient techinique for interference suppression that reduces the multi-access interference(MAI) and that solves the Near-far problem and improves system capacity.The blind adaptation schemes(BMUD) does not require training sequences and the interference user's information.It is an especially attractive research hotpot to the downlinks of CDMA lately because it only needs the prior knowledge of the signature waveform and the timing of the desired user,that is, the same knowledge as the conventional receiver.This paper has summarized the recent multiuser detection algorithm, and further studied blind adaptive multiuser detection. The main work is showed as follows:1. Based on the study of adaptive quasi-Newton subspace eigen-estimation algorithm,the paper has applied an improved adaptive quasi-Newton subspace eigen-estimation method to blind multiuser detection. Theoretical analysis shows the novel algorithm offers the faster and the better tracking performance.When compared with the PASTd algorithm,its computer simulation results show the proposed approach has a relatively faster convergence rate and rank tracking capability.Meanwhile,the improved blind multiuser detector can adapt fairly rapidly to the dynamic channel traffic, which may pose a problem for a time-varying mobile communication channel.2. This paper has systematically studied the convergent performance of the standard linearly constrained CM algorithm and non-standard linearly constrained CM algorithm in the AWGN channel and verified the conclusions through the computer simulation. From the simulation results,we will see the slow-convergence disadvantage of the LCMA.Therefore,two variable step methods are applied to LCMA in this paper.Theoretical analysis and computer simulation show the variable step LCMA has been improved in both aspects of convergence performance and stability performance.3. This paper has extended the variable step LCMA into the multipath fading...