Asymptotic multiuser efficiency for decision-feedback multiuser detection

In this work, arbitrarily tight upper and lower bounds to the asymptotic multiuser efficiency (AME) are derived for K asynchronous users and decision-feedback multiuser detection. Because the multiple-access interference is noncausal, the precursor interference may be canceled out by making tentative decisions via conventional or decorrelated decisions, or by the zero-forcing feed-forward equalizer (ZF-DFE). We demonstrate that decision-feedback multiuser detection with conventional tentative decisions produces low near-far resistance and that with decorrelated tentative decisions uniformly improves performance at the expense of a long decoding delay. The ZF-DFE shows low AME compared to decision-feedback detection with decorrelated tentative decisions. In order to use all strong users´ final decisions, we propose a successively decorrelated decision-feedback technique for an asynchronous CDMA system. This detector is shown to uniformly outperform the decorrelated detector and stays close in performance to the optimum multiuser receiver