Userwise distortionless pathwise interference cancellation for the DS-CDMA uplink

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 rapidly varying and slowly varying parameters. In this approach, which was introduced by Matti Latva-aho (see PhD thesis, Oulu University, Finland, 1998), the scarce training data are used to estimate the few rapidly varying parameters while the whole 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