9.1 Positioning Procedure Initiation

3GPP43.059Functional stage 2 description of Location Services (LCS) in GERANRelease 16TS

9.1.1 Core Network Position Procedure Initiation over the A interface

This procedure is used by the Core Network to start the positioning procedure in GERAN over the A interface.

Figure 26: Positioning Procedure Initiation Over A Interface

1) The MSC sends the BSSAP Perform Location Request message on the existing SCCP connection for the target MS to request the BSC to start the positioning procedure. The Location Type is always included. Depending on the type of location request, additional parameters may be included to provide the Cell Identifier, Classmark Information Type 3, LCS Client Type, Chosen Channel, LCS Priority, Quality of service, A-GNSS Assistance Data, and APDU. In addition, the IMSI and / or the IMEI of the mobile station involved in the positioning procedure may be provided by the MSC in order, if forwarded by the BSC, to allow the SMLC to maintain a context between subsequent requests for a mobile station, to tune positioning for each mobile station and to add more options for SMLC diagnostics.

2) The common positioning procedures for CS domain are executed (see below).

3) The BSC sends the BSSAP Perform Location Response message to the MSC. A location estimate, velocity estimate, positioning data, deciphering keys, or LCS Cause may be included.

9.1.2 Positioning Procedure Initiation from an Internal LCS Client for the CS Domain (A/Gb mode)

Figure 27 illustrates how a serving BSC may obtain the location of a target MS that is already in dedicated mode on behalf of some PLMN operator LCS client in GERAN – e.g. to support handover. The procedure is valid when local regulatory requirements do not require privacy checking for PLMN operator initiated location.

Figure 27: Positioning Procedure Initiation from an Internal LCS Client

1) An LCS client within the GERAN requests the current location of a target MS from the serving BSC

2) The common positioning procedures for CS domain are executed see Figure 28. The BSC returns the MS location estimate to the requesting LCS client.

9.1.3 Core Network Position Procedure Initiation over the Gb interface

This procedure is used by the Core Network to start the positioning procedure in GERAN over the Gb interface except for the Multilateration positioning methods (i.e. MTA and MOTD, treated in subclause 9.1.3a and is shown in Figure 27a-1).

Figure 27a: Positioning Procedure Initiation over Gb Interface

1) The SGSN sends the BSSGP Perform Location Request message to request the BSS to start the positioning procedure. The TLLI, IMSI, DRX Parameters or eDRX Parameters, Current BVCI for the MS, Current NSEI for the MS, Location Type, Current Cell Identifier, and LCS Capability IEs are always included. The SGSN may also include the Coverage Class and MS Radio Access Capability IEs for a MS that supports EC-GSM-IoT (see 3GPP TS 43.064). The IMSI, DRX Parameters or eDRX Parameters, Current BVCI for the MS, Current NSEI for the MS and optionally the Coverage Class and MS Radio Access Capability shall be stored in the SCCP signalling context towards the SMLC for potential use in a TA Request procedure later on. Depending on the type of location request, additional parameters may be included in the BSSGP Perform Location Request message to provide LCS Client Type, LCS Priority, LCS Quality of Service, and A-GNSS Assistance Data. In addition, the IMEI of the mobile station involved in the positioning procedure may be provided by the SGSN. The IMSI and, if forwarded by the BSS, the IMEI, would allow the SMLC to maintain a context between subsequent requests for a mobile station, to tune positioning for each mobile station and to add more options for SMLC diagnostics.

2) The common positioning procedures for PS domain are executed (see clause 9.2a).

3) The BSS sends the BSSGP Perform Location Response message to the SGSN. The TLLI and the BVCI identifying the cell from which the last LLC PDU was received from the MS are always included. A location estimate, velocity estimate, positioning data, deciphering keys, or LCS Cause may be included.

9.1.3a Core Network Position Procedure Initiation over the Gb interface for Multilateration Positioning methods

This procedure is used by the Core Network to start the Multilateration positioning methods in GERAN over the Gb interface (i.e. MTA and MOTD). The signalling flow applies for an MS in Packet Idle mode only and is shown in Figure 27a-1. When the serving cell of an MS is known the Multilateration positioning method in GERAN is triggered by the Perform Location Request message sent from SGSN to BSS as depicted in clause 9.6.

Figure 27a-1: Positioning Procedure Initiation over Gb Interface for Multilateration Positioning

If the MS is in Packet Idle mode (i.e. Ready timer is not running) the following procedure is executed.

1) Upon receiving a position request from a GMLC, the SGSN sends a paging request message to each BSS supporting paging for positioning in the set of BSS managing cells in the paging area corresponding to the target MS and indicates in the paging request that a positioning event has triggered the paging, i.e. it sends a paging request for positioning.

2) This triggers the MS to start the cell re-selection procedure unless a cell re-selection has been performed up to [60] seconds prior to receiving the paging request message indicating that the paging is triggered by a positioning event. The MS then reselects to the “best” cell.

3) The MS sends a paging response to the SGSN, which may occur in the serving cell or in the new cell in case of cell reselection. Due to the interim cell reselection procedure the paging response may be received from another BSS (i.e. BSS 2) than the BSS (i.e. BSS 1) the paging request indicating the positioning cause was sent to.

a) In the paging response the MS includes MS accuracy related information (“MS Sync Accuracy”, “MS Transmission Offset”) on the RR layer (see 3GPP TS 44.060 [28]).

b) The BSS estimates the timing advance (i.e. a value used as the “Multilateration Timing Advance”), including a compensation using the reported “MS Transmission Offset”, as well as calculates the BTS Reception Accuracy Level (see 3GPP TS 45.010 [42]), applicable to the serving cell when the MS sends the paging response.

c) The BSS sends the paging response including “Multilateration Timing Advance”, “MS Sync Accuracy” and “BTS Reception Accuracy Level”” in an UL-UNITDATA PDU to the SGSN.

Upon receiving the paging response from the BSS, the SGSN, includes the “Multilateration Timing Advance”, “MS Sync Accuracy” and “BTS Reception Accuracy Level” sends a BSSGP PERFORM-LOCATION-REQUEST to the BSS, managing the serving cell and follows the MTA or MOTD method related procedure as described in sub-clause 9.6.

9.1.4 Positioning Procedure Initiation from Core Network (Iu mode)

This procedure is used by the Core Network to start the positioning procedure in GERAN Iu mode. This procedure is used when the source node in the Core Network is the 3G-MSC (Iu-cs interface) or when the source node in the Core Network is the 3G-SGSN (Iu-ps interface).

Figure 27b: Positioning Procedure Initiation from Core Network (Iu mode)

1) The MSC/SGSN sends the Location Reporting Control message on the existing SCCP connection for the target MS to request the BSC to start the positioning procedure. The Location Type is always included. Depending on the type of location request, additional parameters may be included to provide LCS Client Type, LCS Priority, Quality of service, and A-GNSS Assistance Data.

2) The Positioning Procedure for Iu mode is executed (see below).

3) The BSC sends the Location Report message to the MSC/SGSN. A location estimate (with optional velocity estimate), or LCS Cause may be included.

9.1.5 Positioning Procedure Initiation from Internal LCS Client (Iu mode)

FFS.