OTDOA

OTDOA (Observed Time Difference Of Arrival) is a positioning feature introduced in rel9 E-UTRA (LTE radio). It's a multilateration method in which the User Equipment (UE) measures the time difference between some specific signals from several eNodeBs and reports these time differences to a specific device in the network (the ESMLC). The ESMLC based on these time differences and knowledge of the enodeBs locations calculates the UEs' position. OTDOA (Observed Time Difference Of Arrival) is a positioning feature introduced in rel9 E-UTRA (LTE radio). It's a multilateration method in which the User Equipment (UE) measures the time difference between some specific signals from several eNodeBs and reports these time differences to a specific device in the network (the ESMLC). The ESMLC based on these time differences and knowledge of the enodeBs locations calculates the UEs' position. In December 2008, due to regulatory requirements like the E911, which require that it should be possible to locate UEs with a certain accuracy, a work item was proposed in the 3GPP TSG-RAN42 meeting. This proposed between others the study of the feasibility of OTDOA. OTDOA was meant to work in a similar way as the 3G IPL feature. During the summer of 2009 the necessary changes to the RAN1 36.211, 36.212, 36.213 and 36.214 specifications were accepted. And a bit later the RAN4 requirements and RAN2 protocol related matters settled. A OTDOA procedure works as follows:The ESMLC requests through the LPP layer an OTDOA measurement: a set of RSTD (Reference Signal Time Difference) measurements from the UE. Together with this request the UE receives assistance data. This assistance data, provides a list of cells (enodeBs), with their PRS (Positioning Reference Signal) parameters, including BW, periodicity etc.