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 of 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 of 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.