My question concerns on the accuracy of the localization system which relies on measuring the TDoA of the signal using 4 beacons spaced between 20 m (SBL for underwater acoustic) and USBL system where the transducers are spaced 10 cm (in total in 3). In this case the angle of arrival is measured and converted in bearing using couple of anchors. Knowing the distance between sender and receiver the position is found. The method used is phase-difference. 

My question is about the accuracy of such system and why for example the USBL moslty  uses the phase difference and does not perform the hyperbolic localization but relies on bearing and range. Is there any theoretical limit which constrains to perform this way. The frequency is about 40khz.

Thanks in advance