On sphere detection and minimum-phase prefiltered reduced-state sequence estimation

In this paper, prefiltering techniques for Sphere Detection (SD) in frequency-selective channels are examined. It is shown that a link between QL-factorization of the channel matrix and minimum-phase prefiltering exists. As a result, it is possible to regard SD as a generalization or traditional reduced-state sequence estimation, providing a unifying framework for the two detection methods. It is illustrated how minimum-phase prefiltering or the Linear Minimum Mean-Square Error Decision Feedback Equalization (LMMSE-DFE) forward filter is capable or reducing the complexity of sphere detectors significantly, while still obtaining near-optimal performance. The significant reduction in complexity is obtained as prefiltering enables earlier decision making in SD. Simulations carried out in an EDGE system confirm that prefiltering leads to a considerable complexity reduction for sphere detectors.