One of the main problems with linear multiuser detectors for DS-CDMA systems with large spreading factors and time-varying multipath propagation is that typically not enough data is available to estimate the detector's parameters well. Pathwise processing is an approach that allows a separation between fastly varying and slowly varying parameters. In this approach, which was introduced by Matti Latva-aho, the scarce training data are used to estimate the few fastly varying parameters while the

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... hole received signal can be used to estimate the slowly varying parameters. We present some refinements to the original pathwise processing approach to avoid signal cancellation due to correlation between paths in slowly varying environments. We also consider the extension to spatio-temporal processing and propose the introduction of structural constraints in the detector filters to reduce complexity and facilitate the practical implementation. I. DATA MODEL For the received signal model, we assume the £ users to be transmitting linearly modulated signals over a linear, specular multipath channel with additive gaussian noise in an asynchronous fashion. Furthermore, we assume that the basestation receiver utilizes an antenna array with ¤ elements. A. Channel Model A specular model for the spatio-temporal channel is assumed. The channel impulse response is characterised for users