A user equipment (UE) periodically obtains its location using UE based Observed Time Difference of Arrival (OTDOA). The location is based on Reference Signal Time Differences (RSTDs) measured by the UE for downlink (DL) signals transmitted by each of a plurality of base stations, and the most current Real Time Differences (RTDs) for pairs of base stations. The RTDs may be determined by the UE using the RSTD measurements and Round Trip Time (RTT) measurements determined by a network entity or by the UE. The RTDs may be determined less frequently than the UE location to reduce network and UE load. Location of the UE may be improved based on testing a rate of change for each of the RTDs. The RTD determination may be improved using measurements from a plurality of UEs.