A MIMO RAKE receiver with enhanced interference cancellation

We investigate the design of a RAKE receiver for application in the downlink of a wideband code-division multiple access (WCDMA) system in which multiple transmit and multiple receive antennas as well as multiple spreading codes are used. In order to precisely model the space-, code- and intersymbol interference after the RAKE, we derive an equivalent channel model in the space-code domain with two paths corresponding to the current and previous symbol periods. We propose to cancel all interference jointly with a suitable Wiener filter operating after the RAKE. The filter works fine already with a small number of taps and the receiver performs similar to the well-known chip-level equalizer, provided that both receivers operate over the same time window. An advantage of the RAKE is that the effort scales more directly with the resources used in the space-code domain. On the other hand, short scrambling sequences are needed to enable an efficient implementation of the enhanced interference cancellation.