The Research On Inter-cell Interference Suppression Of CDMA System

CDMA technology has large capacity, wide coverage, low power consumption, and other prominent advantages. Because of using the non-strictly orthogonal spreading codes, the existence of non-zero cross correlation coefficient can lead to the interference of users, which can be divided into intra-cell interference and inter-cell interference. The multiuser detection technology, as a superior performance against the multiple access interference, has become the key technology of the third generation mobile communications. Most of multiuser detection techniques only consider the intra-cell interference, ignoring the inter-cell interference, and inter-cell interference has the significant impact on the system capacity of CDMA, so studying the multiuser detection algorithm which can eliminate inter-cell interference has the great significance. By analyzing the advantages and disadvantages of the non-blind algorithm and blind algorithm, the semi-blind multiuser detection algorithm, which suppress the inter-cell interference, is proposed in this dissertation focusing on the Base Station of the uplink. In this paper, the main works are as follows:Firstly, the principle and classification of the multiuser detection, and the traditional multiuser detection algorithms are introduced. From the number of users, bit error rate and performance aspects of anti-Near-Far effect of the several traditional linear and nonlinear multi-user detection algorithms are studied.Secondly, the rank estimation module and the subspace tracking module of the Subspace blind multiuser detection algorithm are researched through simulation and performance analysis, such as PAST algorithm, PASTd algorithm and OP AST algorithm. In addition to this, the fast estimation subspace tracking algorithm is studied. Compared with the projection approximation on subspace tracking algorithm with deflation, the simulation results show that the fast subspace tracking algorithm has the faster convergence and smaller error rates, which are prepared for the proposal of new algorithms.Thirdly, based on the traditional non-blind multiuser detection algorithm and the subspace blind multiuser detection algorithm, the Hebb-PPIC semi-blind multiuser detection algorithm is proposed in order to suppress the inter-cell interference. This approach fully utilizes all known users'information, performs Hebb-PPIC detector to suppress the interference within the cell, and exploits the linear blind MMSE detector to suppress the inter-cell interference. This method not only has the fast computing speed, but also reduces the computational complexity of the blind multiuser detection algorithm. Simulation results show that compared with the non-blind multiuser detection algorithm and pure blind multiuser detection algorithm, the proposed algorithm has the better detection performance. Fourthly, the blind LMS algorithm, RLS algorithm and Kalman filter algorithm are researched. Their performance analysis and simulation were performed in the static environment and dynamic environment of the additive white Gaussian noise channel and the slow time-varying Rayleigh fading channel. Based on this, the linear semi-blind multiuser detection algorithm is proposed for the inter-cell interference suppression on the CDMA uplink, which is called the based subspace LMS semi-blind multiuser detection algorithm. By exploiting the spreading sequences of all known users, and the PASTd algorithm applied to the LMS algorithm, this algorithm can obtain the weight vector adaptively. The simulation results show that the output SIR performance of the linear semi-blind algorithm is better than the blind LMS algorithm.