C.1 BTS frequency source stability and E-OTD LMU reporting periods

3GPP45.010GSM/EDGE Radio 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 43.059 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 43.059)). 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.