The article describes a principle of 3D-positioning by pseudo-ranges using ultrashort laser pulses. It can be used as an local optical positioning system (LOPS). Laser pulses are sent out highly divergent to four detectors with known positions. The goal is to determine the 3D position of the laser pulser. A TSCPC system is used to measure differential time of flight between the four detectors. The main problem of differential TCSPC is the small probability to detect each two photons of the same pulse at different positions. It therefore takes the highest possible laser power to measure pseudo-ranges this way over a distance of 30 m and more. A second requirement for such a system is mobility. This is why we tried to realize the laser subystem with a diode laser and subsequent beam shaping using axicon optics. Investigations with different ps-laser pulsers and different detector types are shown. An important investigation concerning the ranging accuracy was the comparison of two TCSPC systems, one with TAC and ADC and the other with TDC. Furthermore the development of an elastic lens for variable defocussing of the laser is shown.