Downlink WCDMA receivers based on combined chip and symbol level equalizationchip and symbol level equalization

In this paper we consider iterative receiver techniques for the downlink in WCDMA systems (UMTS FDD mode). We start from the linear MMSE receiver (at symbol level), which is time-varying and hence too complex to implement. By applying polynomial expansion (PE) to the LMMSE receiver, an iterative soluton is obtained in which the complexity per iteration becomes comparable to twice that of the RAKE receiver. Our one contribution is to replace the channel matched lter by a channel equalizer within this PE to accelerate the convergence of the iterations. We also investigate various scenarios for the introduction of nonlinearities in the PE scheme that are particularly applicable to the multicode case of the High Speed Downlink Packet Access (HSDPA) mode since it is well known that nonlinearities in the PE scheme lead in fact to the Parallel Interference Canceler (PIC).