LMMSE chip equalisation for 3GPP WCDMA downlink receivers with channel coding

The downlink capacity of WCDMA systems is highly important due to the expected asymmetrical nature of the traffic. It is thus of paramount importance that highly efficient downlink receivers are implemented. The conventional RAKE receivers, as are likely to be initially implemented in UMTS networks, suffer significant performance degradation under high traffic loads. A candidate receiver for the downlink of such networks is the LMMSE chip level equaliser. The principal of such receivers is to restore the orthogonality of users from one cell by equalising the received signal from that cell at chip level before despreading. This technique is not only able to suppress the intra-cell multiple access interference (MAI) but may also be used to reduce the inter-cell MAI. This paper addresses the use of the minimum mean-squared error (MMSE) criteria for the construction of a linear MMSE chip equaliser for a WCDMA downlink receiver. Channel coding, as specified in the 3GPP technical specifications, is employed in both single and multi-cell scenarios. Simulation demonstrate such receivers are able to achieve considerable performance gains when compared to the conventional RAKE receiver