05.103GPPRadio subsystem synchronizationTS
E-OTD location systems require measurements of OTDs made at both the LMUs and MS. It is by comparing the two sets of OTDs that a location estimate can be determined (see 3GPP TS 03.71 Annex C). In order to reduce signalling requirements each LMU’s measurements of OTDs are only reported at intervals by the LMU to the SMLC. (For MS-assisted E-OTD the LMU’s OTDs are retained by an SMLC whereas for MS-based E-OTD the OTD’s are further reported to the MS periodically (see 3GPP TS 03.71)). The maximum allowable interval between LMU reports depends on both the predictability of the BTS frequency source and the level of accuracy required of the location estimate.