  In this paper we present decision-feedback differential detection (DF-DD)
schemes for autocorrelation-based detection in impulse-radio ultra-wideband
(IR-UWB) systems, a signaling scheme regarded as a promising candidate in
particular for low-complexity wireless sensor networks. To this end, we first
discuss ideal noncoherent sequence estimation and approximations thereof based
on block-wise multiple-symbol differential detection (MSDD) and the Viterbi
algorithm (VA) from the perspective of tree-search/trellis decoding. Exploiting
relations well-known from tree-search decoding, we are able to derive the novel
decision-feedback differential detection (DF-DD) schemes. A comprehensive
comparison with respect to performance and complexity of the presented schemes
in a typical IR-UWB scenario reveals---along with novel insights in techniques
for complexity reduction of the sphere decoder applied for MSDD---that sorted
DF-DD achieves close-to-optimum performance at very low, and in particular
constant receiver complexity.
