Downlink WCDMA receivers based on combined chip and symbol level equalisation

Abstract

SUMMARYIn this paper, we consider iterative receiver techniques for the downlink in WCDMA systems (UMTS FDD mode). We start from the linear minimum mean square error (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 solution 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 filter by a channel equaliser within this PE to accelerate the convergence of the iterations. We also investigate various scenarios for the introduction of non-linearities 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 non-linearities in the PE scheme lead, in fact, to the parallel interference canceler (PIC).