4 General

38.1713GPPNRRelease 17Requirements for Support of Assisted Global Navigation Satellite System (A-GNSS)TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.1 Introduction

The present document defines the minimum requirements for both UE based and UE assisted FDD or TDD A-GNSS terminals which have NG-RAN access via gNB (in SA NR, NR-DC or NE-DC operation mode [2]) or via ng-eNB (in EN-DC operation mode [2]) and which are supporting A-GNSS in 5GS via LPP [3] between UE and LMF as described in TS 38.305 [17].

4.2 Measurement parameters

4.2.1 UE based A-GNSS measurement parameters

In case of UE-based A-GNSS, the measurement parameters are contained in the GNSS‑LocationInformation IE which is included in the A‑GNSS‑ProvideLocationInformation IE provided in the LPP message of type PROVIDE LOCATION INFORMATION. The measurement parameter in case of UE-based A-GNSS is the horizontal position estimate reported by the UE and expressed in latitude/longitude.

4.2.2 UE assisted A-GNSS measurement parameters

In case of UE-assisted A-GNSS, the measurement parameters are contained in the GNSS‑SignalMeasurementInformation IE which is included in the A‑GNSS‑ProvideLocationInformation IE provided in the LPP message of type PROVIDE LOCATION INFORMATION. The measurement parameters in case of UE-assisted A-GNSS are the UE GNSS code phase measurements, as specified in TS 38.215 [4]. The UE GNSS 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 receives the LPP message of type REQUEST LOCATION INFORMATION, and ending when the UE starts sending the LPP message of type PROVIDE LOCATION INFORMATION. The response times specified for all test cases are TTFF unless otherwise stated, i.e. the UE shall not re‑use any information on GNSS 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’ is defined in TS 38.509 [9] clause 5.6 for the purpose of deleting this information and is detailed in clause B.1.10.

4.4 Time assistance

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

a) Coarse time assistance is always provided by the network and provides current GNSS time to the UE. The time provided is within ±2 seconds of GNSS system time. It is signalled to the UE by means of the gnss‑DayNumber and gnss‑TimeOfDay fields in the gnss-SystemTime IE.

b) Fine time assistance is optionally provided by the network and adds the provision to the UE of the relationship between the GNSS system time and the current E-UTRAN or NR time. The accuracy of this relationship is ±10 μs of the actual relationship. This addresses the case when the network can provide an improved GNSS time accuracy. It is signalled to the UE by means of the gnss-SystemTime IE and the gnss‑ReferenceTimeForCells IE.

The specific GNSS system time is identified through the gnss‑TimeID field of the GNSS‑SystemTime IE. In case where several GNSSs are used in the tests, only one gnss‑TimeID is used to determine the Time of Day. For all the constellations, the gnss‑TimeModels IE shall be available at the SS, as specified in Annex E.

4.4.1 Use of fine time assistance

The use of fine time assistance to improve the GNSS 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 clause 5.1.2 for UEs that support A-GPS L1 C/A only and in clause 6.1.2 for UEs that support other GNSSs.

4.5 RRC states

The minimum A-GNSS performance requirements are specified in clauses 5 and 6 for RRC_CONNECTED state. The test and verification procedures are separately defined in annex B.

4.6 Error definitions

The 2D position error is defined by the horizontal difference in meters between the ellipsoid point reported or calculated from the LPP message of type PROVIDE LOCATION INFORMATION and the actual position of the UE in the test case considered.

4.7 UEs supporting multiple constellations

Minimum performance requirements are defined for each global GNSS constellation (BDS, Galileo, GLONASS, GPS/Modernized GPS). UEs supporting multiple global constellations shall meet the minimum performance requirements for a combined scenario where each UE supported constellation is simulated.

NOTE: For test cases where signals from “GPS” and “Modernized GPS” are included, “GPS” and “Modernized GPS” are considered as a single constellation, unless otherwise specified.

4.8 UEs supporting multiple signals

For UEs supporting multiple signals, different minimum performance requirements may be associated with different signals. The satellite simulator shall generate all signals supported by the UE. Signals not supported by the UE do not need to be simulated. The relative power levels of each signal type for each GNSS are defined in Table 4.1. The individual test scenarios in clause 6 define the reference signal power level for each satellite. The power level of each simulated satellite signal type shall be set to the reference signal power level defined in each test scenario in clause 6 plus the relative power level defined in Table 4.1.

Table 4.1: Relative signal power levels for each signal type for each GNSS

BDS

Galileo

GLONASS

GPS/Modernized GPS

QZSS

SBAS

Signal power levels relative to reference power levels

B1I

0 dB

L1 C/A

0 dB

L1 C/A

0 dB

+5 dB

B1C

0 dB

+2 dB

-6 dB

L1C

+1.5 dB

L1C

+1.5 dB

B2a

0 dB

+2 dB

L2C

-1.5 dB

L2C

-1.5 dB

B3I

0 dB

+3.6 dB

+5 dB

NOTE 1: For test cases which involve “Modernized GPS”, the satellite simulator shall also generate the GPS L1 C/A signal if the UE supports “GPS” in addition to “Modernized GPS”.

NOTE 2: The signal power levels in the Test Parameter Tables represent the total signal power of the satellite per channel not e.g. pilot and data channels separately.

NOTE 3: For test cases which involve "BDS", D1 represents MEO/IGSO satellites for B1I and B1C signal types and D2 represents GEO satellites for B1I signal type.