Inter-path interference suppression in WCDMA systems with low spreading factors

The 3rd generation mobile communications standard in Europe and Japan will be based on wideband code-division multiple-access (WCDMA). High data rate connections can be supported in WCDMA systems by employing low spreading factors while maintaining fixed bandwidth. Multiple access interference (MAI) that a high data rate user experiences can be considered low, and with lowest spreading factors inter-path interference (IPI) becomes the limiting factor for the performance of the conventional RAKE receiver. In this paper, linear receivers capable of suppressing inter-path interference in WCDMA downlink are discussed, and their performance is evaluated in a frequency-selective Rayleigh fading channel. The very promising chip equalizer receivers, which equalize the multipath channel prior to despreading, are included in the discussion with the RAKE and 'standard' LMMSE receivers.