The Research Of Multiuser Detection Based On Improved EM Algorithms

It’s evident that the3rd Generation (3G) and beyond3G mobile communication will bring greater convenience to our work and daily life, with the rapid development of mobile communication technologies. Due to the rapid growth of the amount of user, the power of multiple access interference (MAI) increases accordingly, which results in higher BER and lower performance. The capacity as well as the performance is affected by the existence of inter-symbol interference (ISI) and MAI in the system. Thus, how to efficiently suppress multiple access interference and improve system performance has become one of the hotspots of the mobile communication technology research.Multi-user detection (MUD) is one of the key techniques for Code Division Multiple Access (CDMA) system.It can be effectively solve the above problem. It applies the user’s PN sequence, delay, amplitude and phase information to make combined detection in order to cope with the MAI and near-far effect, reduce the inter-symbol interference, increase the communication user number, improve the system performance and capacity.In this thesis such models of detectors as the traditional multi-user detector, decorrelating detector, optimal multi-user detector, MMSE detector, SIC detector and PIC detector are analyzed and compared. The simulations of these algorithms were carried out in this thesis. It was difficulty to implement the optimum algorithm in the actual project as result of the high computational complexity. Therefore, the EM algorithm was applied to the field of MUD. The fundamental of the EM algorithm is analyzed in this thesis.The thesis gives the derivations of the MUD algorithm based on the EM method in the DS-CDMA system. The simulation results show that:it has a lower computational complexity while it achieved near-optimal detection performance. In order to simplify the mathematical analysis chosen on the assumption noise is Gaussian while we analyze the system. However, the slow convergence was a critical factor which restricted the application of the EM algorithm. In this thesis, in order to accelerate the convergence speed of the EM algorithm, several improved EM algorithm are proposed and applied in the field of MUD. Such as ECM algorithm, Aitken ECM algorithm, Aitken-delta ECM algorithm, ECME algorithm, Cascade EM algorithm, Monte Carlo EM algorithm, EM Gradient algorithm are analyzed. The simulation results show that the proposed algorithm achieved well performance while it has a faster convergence speed.