Equalization Techniques for Direct Sequence Code-Division Multiple Access Systems in Multipath Channels

We address the problem of Code-Division Multiple Access (CDMA) systems in a multipath environment where a high data rate introduces intersymbol interference as well as inter-user interference. We discuss a linear equalizer as well as a reduced-state-sequence estimation (RSSE) scheme for CDMA channels with intersymbol interference. The linear equalizer is a modification of the decorrelating detector proposed by Lupas and Verdu. The RSSE collapses 2/sup K/ states into 2 states where K is the number of users. Both techniques are superior to a traditional matched filter detector (RAKE) when the interuser interference and/or the intersymbol interference is relatively strong. In a severe near-far environment, the RSSE can show significant (2 -3 dB) improvement over the linear equalizer in terms of receiver signal-to-noise ratio.