Estimation of Composite Spatial Signatures for DS/CDMA Multipath Signals Using Space-time Processing
Wei‐Chiang Wu, Hui-Feng Hung, Yi-Wen Jeng · 2004
In an uplink DS/CDMA cellular system with antenna arrays equipped with a basestation, the channel can be modeled as a multiple single-input-multiple-output (SIMO) system. As multipath fading is considered, all multipath components associated with a single mobile can be grouped as a single signal. Hence, the composite steering vector (spatial signature) is a linear combination of steering vectors corresponding to distinct direction-of-arrivals (DOAs) for each path. The basestation relies on accurate information from all the users' composite spatial signatures to exploit multiuser detection techniques to extract each user's data. A conventional multiple-signal classification (MUSIC) algorithm cannot be applied to estimate the DOAs in a coherent signal environment, and the multidimensional MUSIC (MD-MUSIC) method is computationally prohibitive. This study proposes a blind algorithm to estimate the composite spatial signatures in a multiuser DS/CDMA communication system. By making use of the space-time characteristics of an antenna-array DS/CDMA model, the multiuser multidimensional parameter estimation problem is converted into a set of single-user optimization problems. Each user's composite spatial signature is then determined by exploiting the subspace concept. The proposed algorithm is computationally efficient, and no training sequences are required. More specifically, the simulation result demonstrates that the algorithm is near-far resistant.