4 General

25.1713GPPFrequency Division Duplex (FDD)Release 17Requirements for support of Assisted Global Positioning System (A-GPS)TS

4.1 Introduction

The present document defines the minimum performance requirements for both UE based and UE assisted FDD A‑GPS terminals.

4.2 Measurement parameters

4.2.1 UE based A-GPS measurement parameters

In case of UE-based A-GPS, the measurement parameters are contained in the RRC UE POSITIONING POSITION ESTIMATE INFO IE. The measurement parameter in case of UE-based A-GPS is the horizontal position estimate reported by the UE and expressed in latitude/longitude.

4.2.2 UE assisted A-GPS measurement parameters

In case of UE-assisted A-GPS, the measurement parameters are contained in the RRC UE POSITIONING GPS MEASURED RESULTS IE. The measurement parameters in case of UE-assisted A-GPS are the UE GPS Code Phase measurements, as specified in 3GPP TS 25.302 [5] and 3GPP TS 25.215 [6]. The UE GPS Code Phase measurements are converted into a horizontal position estimate using the procedure detailed in Annex F.

4.3 Response time

Max Response Time is defined as the time starting from the moment that the UE has received the final RRC measurement control message containing reporting criteria different from "No Reporting" sent before the UE sends the measurement report containing the position estimate or the GPS measured result, and ending when the UE starts sending the measurement report containing the position estimate or the GPS measured result on the Uu interface. The response times specified for all test cases are Time-to-First-Fix (TTFF) unless otherwise stated, i.e. the UE shall not re‑use any information on GPS time, location or other aiding data that was previously acquired or calculated and stored internally in the UE. A dedicated test message ‘RESET UE POSITIONING STORED INFORMATION’ has been defined in TS 34.109 [11] clause 5.4 for the purpose of deleting this information and is detailed in subclause B.1.10.

4.4 Time assistance

Time assistance is the provision of GPS time to the UE from the network via RRC messages. Currently two different GPS time assistance methods can be provided by the network.

a) Coarse time assistance is always provided by the network and provides current GPS time to the UE. The time provided is within 2 seconds of GPS system time. This allows the GPS time to be known within one GPS navigation data sub-frame. It is signalled to the UE by means of the GPS Week and GPS TOW msec fields in the Reference Time assistance data IE.

b) Fine time assistance is optionally provided by the network and adds the provision to the UE of the relationship between the GPS system time and the current UTRAN time. The accuracy of this relationship is 10 s of the actual relationship. This addresses the case when the network can provide an improved GPS time accuracy. It is signalled to the UE by means of the SFN and UTRAN GPS timing of cell frames fields in the Reference Time assistance data IE.

The time of applicability of time assistance is the beginning of the System Frame of the message containing the GPS Reference time.

4.4.1 Use of fine time assistance

The use of fine time assistance to improve the GPS performance of the UE is optional for the UE, even when fine time assistance is signalled by the network. Thus, there are a set minimum performance requirements defined for all UEs and additional minimum performance requirements that are valid for fine time assistance capable UEs only. These requirements are specified in subclause 5.1.2.

4.5 RRC states

The minimum A-GPS performance requirements are specified in clause 5 for different RRC states that include Cell_DCH and Cell_FACH. Cell_PCH and URA_PCH states are for further study. The test and verification procedures are separately defined in annex B.

4.6 2D position error

The 2D position error is defined by the horizontal difference in meters between the ellipsoid point reported or calculated from the UE Measurement Report and the actual position of the UE in the test case considered.