In this paper, a 3D indoor localization demonstrator on the basis of impulse-radio ultrawideband (UWB) technology and time-difference-of-arrival (TDOA) principle is developed and analyzed. The parameters of the transmitter and receiver hardware components are investigated to determine their influence on the localization performance. The signal detection method based on a comparator and the precise time measurement unit was examined. Two effects, namely the threshold-trigger offset and the TDOA variance errors, were quantified. Corrections methods of both these phenomena have been proposed, which delivered very good results in the experiments. With the identified and modeled inaccuracies, the Cramer-Rao lower bound for a 3D TDOA localization system is derived for the first time and verified by measurements, performed in a large-scale industrial environment. The results obtained from measurements follow closely the variance predicted by the CRLB. Moreover, the comparison with the literature published up to date proves the excellent performance of the system presented here.