9.3a TA Based Positioning in PS Domain for A/Gb-mode

3GPP43.059Functional stage 2 description of Location Services (LCS) in GERANRelease 17TS

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

The TA is based on the existing Timing Advance (TA) parameter. The TA value is known for the serving BTS. To obtain TA values in case the MS is in packet idle mode and the value is not available in the BTS signalling is used to retrieve it. The cell-ID of the serving cell and the TA is returned as the result of the TA procedure.

If available, the TA value shall be provided to the SMLC by the requesting BSS in the BSSAP-LE Perform Location request. This enables TA based positioning in the SMLC without any further interactions. The current serving cell ID shall always be provided by the BSS to the SMLC.

9.3a.1 Definition of PS Domain TA Modes

9.3a.1.1 MS in Packet Idle Mode

When the BSS receives a TA Request message and the MS is in Packet Idle Mode and the TA value is not available in the BSS, the MS may be paged or may be sent a Packet Polling Request message. If there is a PBCCH allocated in the current cell, the BSS will send a Packet Polling Request message to the MS. If there is no PBCCH allocated in the current cell, the BSS will perform packet paging (sends a Paging Request Type 1, 2, or 3 message) for the MS.

The paging response message or Packet Control Acknowledgement message will provide the TA value to the BSS and this will be provided to the SMLC, possibly together with other radio measurements from the MS, in the TA Response message. The associated procedure is described below.

For an MS in EC operation the BSS will send an EC Paging Request message to the MS.

9.3a.1.2 MS in Packet Transfer Mode

When the BSS receives a TA Request message and the MS is in Packet Transfer Mode and the TA value is not available in the BSS the MS shall be sent a Packet Polling Request message.

The Packet Control Acknowledgement message will provide the TA value to the BSS and it will be provided to the SMLC, possibly together with other radio measurements from the MS, in the TA Response message. The associated procedure is described in the next clause.

For an MS in EC operation the BSS shall send an EC Packet Polling Request message instead of a Packet Polling Request message to the MS. The EC Packet Control Acknowledgement message will provide the TA value to the BSS.

9.3a.2 TA Positioning Procedure

This TA positioning procedure is generic for a standalone SMLC or integrate SMLC in the BSS.

For a TA positioning procedure when the MS is in EC operation see sub-clause 9.3a.2a.

Figure 29a: TA Positioning Procedure for the SMLC in the PS Domain

1) If the SMLC has not already received the TA Value in the BSSAP-LE Perform Location Request message, the SMLC sends a BSSAP-LE Connection Oriented Information message to the BSS serving a particular target MS. The APDU parameter in this message contains a BSSLAP TA Request.

2) If the TA value is available in the BSS, the BSS immediately returns it in step 4, otherwise the BSS either performs a packet paging procedure or sends a Packet Polling Request message (for details, see clause 9.5.2).

2a) If there is no PBCCH allocated in the current cell and the MS is in Packet Idle Mode, the BSS will perform packet paging (sends a Paging Request Type 1, 2, or 3 message) for the MS.

2b) If there is a PBCCH allocated in the current cell or the MS is in Packet Transfer Mode, the BSS will send a Packet Polling Request message to the MS.

3) The MS responds to the BSS.

3a) If the MS receives the packet paging it will send a page response.

3b) If the MS receives a Packet Polling Request message it will return a Packet Control Acknowledgement message.

4) The BSS returns the current TA value and current serving cell for the target MS to the SMLC in a BSSLAP TA response contained within a BSSAP-LE Connection Oriented Information message. The TA response may also include the latest measurement results received from the target MS for the serving and neighbouring cells. The SMLC then derives a location estimate for the target MS based on the received serving cell ID, TA value and other measurement results if included.

9.3a.2a TA Positioning Procedure for an MS in EC operation

This TA positioning procedure is generic for a standalone SMLC or an integrated SMLC in the BSS.

Figure 29b: TA Positioning Procedure for the SMLC when the MS is in EC operation

2) If the TA value is available in the BSS, the BSS immediately returns it in step 4, otherwise the BSS either performs a paging procedure or sends an EC Packet Polling Request message to the MS.

2a) If the MS is in Packet Idle Mode, the BSS will send an EC-Paging Request message to the MS.

2b) If the MS is in Packet Transfer Mode, the BSS will send an EC Packet Polling Request message to the MS.

3) The MS responds to the BSS.

3a) If the MS receives the paging it will send a page response.

3b) If the MS receives an EC Packet Polling Request message it will return an EC Packet Control Acknowledgement message.

9.3a.3 Unsuccessful TA positioning procedure in BSS

There are three messages defined to handle error scenarios during positioning procedure in BSS. The messages are 1) Reject, 2) Abort and 3) Reset. Refer to 3GPP TS 48.071 [21] for details. The Reset message does not apply for PS domain.

After receiving the BSSLAP TA Request in BSS, a Reject will be sent with proper cause value from BSS to SMLC in "BSSAP-LE Connection Oriented Information Message" if TA positioning cannot be performed in BSS at that time for reasons other than handover or another ongoing RR management procedure.

An Abort is possible if the TA positioning cannot be done in the BSS during that time. Abort is used to indicate to SMLC the failure of the current TA positioning attempt (e.g. due to reception of an BSSGP_Perform_Location_Abort from the SGSN) and allowing a new one from application level.