Improving receiver performance for pilot-aided frequency selective CDMA channels using a MMSE switch mechanism and multipath noise canceller

Abstract

The IS-95 downlink channel incorporates a pilot signal to aid the mobile receiver in obtaining coherent channel estimates for use in the RAKE receiver. We propose a simple, recursive multipath noise cancellation (MNC) detector which uses an on/off switch mechanism for controlling the noise cancellation for each RAKE finger. We derive the switch mechanism which minimizes the mean-squared error (MSE) at the RAKE output. This switched-MNC detector, when compared with the conventional RAKE receiver, demonstrates significant performance gains, increasing the downlink capacity of a typical IS-95 system by up to 10%, while requiring minimal additional complexity when implemented using a simple recursive structure for the MNC function. Furthermore, we observe that almost all of the performance gains of the MMSE switched-MNC detector can be achieved using the simpler, ad-hoc, "always-on" MNC detector, in which pilot multipath noise cancellation always occurs at each finger input without regard to minimizing the MSE.