  Power efficiency of noncoherent receivers for impulse-radio ultra-wideband
(IR-UWB) transmission systems can significantly be improved, on the one hand,
by employing multiple-symbol differential detection (MSDD), and, on the other
hand, by providing reliability information to the subsequent channel decoder.
In this paper, we combine these two techniques. Incorporating the computation
of the soft information into a single-tree-search sphere decoder (SD), the
application of this soft-output MSDD in a typical IR-UWB system imposes only a
moderate complexity increase at, however, improved performance over hard-output
MSDD, and in particular, over conventional symbol-by-symbol noncoherent
differential detection.
