Applied Research Of The Optimum Spatial Filtering In Multiuser Detection

At present, Direct Sequence-Code Division Multiple Access(DS-CDMA) technology is a way that widely using in the CDMA mobile communication system. Its performance is confined by two factors, one is the multiple access interference ( MAI ) , another is the near-far problem. And the multiuser detection technology is a key technology to overcome the multiple access interference ( MAI ).By research and analysis on the existence multiuser detection technology, the combination of the spatial filtering and the multiuser detection technology, also namely the combinative space-time multiuser detection technology, which is an effective way to solve the problem of the multiple access interference(MAI). This way uses spatial filtering to eliminate the multiple access interference(MAI) from different space directions, then it uses the time domain multiuser detection technology to eliminate the multiple access interference(MAI) from beam directions.At first, the paper makes research and analysis on spatial filtering technology. Especially on the ground of simulation research of the DOA estimating MUSIC method, the paper starts with the array covariance matrix, that makes the noise subspace algorithm be fully orthogonal with direction vector after preprocessing. With the result, the original MUSIC algorithm's shortcomings can be resolved, and correlation,coherent or closed Space position Angle of Arrival is correctly estimated. Following, the performances of the MUSIC algorithm and the improved MUSIC algorithm are compared, that is for gainning an effective way of the DOA direction estimate.Secondly, the paper makes research on two-dimensional space-time processing technology. By simulation and analysis on the combination of the Spatial MMSE Filter and the Decorrelation Multiuser Detector, and the combination of the Spatial MLSE Filter and the Decision-Feedback Detector, the results show that the combinative space-time multiuser detection technology can effectively improve the detection performance by comparing with the time domain multiuser detection technology.