Blind Multi-user Detection Algorithm In The DS-UWB Communication System

UWB signal detection technologies are an important focus of the present study. In order to confront the spread of multi-path and fading, we can use the channel estimation, RAKE receiver, Multi-user detection, and other signal processing technologies. We can get the different path delay through channel estimation, fading amplitude, phase and other information. Rationally design the RAKE receiver and merger the multipath signals. However, in these technologies, the Multi-user detection has the optimal performance, but the complexity is too high, it is necessary to be further practical.In UWB communication systems, the multiple access interference is an important reason for limiting the system performance. In order to effectively suppress multiple access interference, we will use the multi-user detection technology into the ultra-wideband multi-user communication systems. At present, the majority of researches on ultra-wideband multiple access systems are based on the traditional single-user detector. So with the increase in the number of users, multiple access interference (MAI) becomes the essential factor which impacts the capacity and performance of the UWB system. Therefore, this paper discusses the multi-user detection technology in UWB system, in order to overcome the shortcomings of the traditional receiver, to effective suppress the multiple access interference, and to improve the capacity and performance of system.Nevertheless, there are some defects in traditional multi-user detector: it assumes that the receiver can acquire the signature waveform and timing of desired user and the interfering users. Based on the traditional multi-user detection, adaptive multi-user detector eliminates the need to know the signature waveforms and the timing of the interferers and has to need training data sequences for every active user. But the frequent use of training sequence is certainly a waste of channel bandwidth. The blind adaptation schemes (BMUD) does not require training sequences and the interference user's information, 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 mainly studied the blind multiuser detection algorithms of the DS-UWB system. First of all, it introduces the basic theory of the multi-user detection, that is the basic idea and basic structure of the multi-user detector. Then it makes the mathematical model of the blind multiuser detection in the DS-UWB system. It in-depth studied several classic algorithms of the blind multiuser detection and carried out a simulation. Constant Modulus algorithm (CMA) uses the priori knowledge for detecting. The performance of the improved algorithm (LS-CMA) is superior to CMA algorithm.The focus of the study in this article are the blind multiuser detection algorithms which are based on the subspace method. Based on the subspace method for blind multi-user detection algorithm's basic idea are using signal subspace parameters show a linear multi-user detector weight vector. Literature [58] thought to be sub-space for multi-user detection techniques, and proposed sub-space structure of multi-user detection. It also through adaptive subspace tracking algorithm to derive multi-user detector weight vector, and finally solved the expectations the user signal. In order to achieve blind detection, the classic sub-space tracking method used the received signal sample matrix to get the eigenvalue decomposition (EVD) or singular value decomposition (SVD). However, these two algorithms are highly complex. PASTd algorithm because of low complexity have been widely used in multi-user detection. However, PASTd algorithm to track the signal subspace is not orthogonal, resulting in very slow convergence rate. In response to this question, this paper Proposed an improved algorithm which is based on the prediction orthogonal approximation subspace tracking algorithm (OPAST)——positive definite matrix OPAST algorithm. And this new algorithm is applied to subspace blind MMSE multi-user detection. The simulation results prove that this improved positive definite matrix OPAST sub-space algorithm for multi-user detector has stable global convergence, and maintain much less computation complexity, so in the anti-MAI respect also has higher performance. This show that the positive definite matrix OPAST sub-space algorithm for multi-user detector is a better feasible solution.