Turbo equalisation based detectors in wideband synchronous multiuser CDMA networks

Multipoint-to-point CDMA networks have been the primary focus in multiuser interference suppression research, where the recent development of the turbo MMSE detector promises near interference-free performance at an acceptable complexity. The complementary case, namely point-to-multipoint transmission, is increasingly becoming more important since traffic on the forward link is likely to be substantially higher, particularly for data. The paper presents the notion of mitigating multiuser interference in the forward link - where under orthogonal spreading, multiuser interference arises only due to the frequency selectivity of the medium - via equalisation. MMSE and turbo-MMSE equalisation-based receivers are developed. They are observed to mitigate significantly multiuser interference in the forward link of a wireless LAN. A turbo configuration, where the front-end equaliser is a linear MMSE equaliser in the earlier passes and a decision-feedback MMSE equaliser in later passes, is found to deliver especially good results. The relevance of such approaches to the multicell CDMA forward link is also discussed in relation to recent trends that tie pricing to the quality of service provided.