15 WLAN positioning method

25.3053GPPRelease 17Stage 2 functional specification of User Equipment (UE) positioning in UTRANTS

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

In the WLAN positioning method, the UE position is estimated with the knowledge of geographical coordinate of reference WLAN access points. This is accomplished by collecting a certain amount of measurements from UE’s WLAN receiver, and applying a location determination algorithm using databases of the estimated position’s references points.

The UE measurements can include:

– WLAN Received Signal Strength (RSSI);

– Round Trip Time (RTT) between WLAN Access Point and the UE.

Two modes are supported for WLAN positioning:

– Standalone: in this mode, the UE performs WLAN measurements and calculates its own location;

– UE-Assisted: The UE performs WLAN measurements without assistance from the network and sends these measurements to the SAS/RNC where the position calculation takes place using a database.

A UE with WLAN capability operates without assistance from the network.

15.1 Information to be transferred between UTRAN elements

The information that may be signalled from the UE to the network is listed in table 15.1-1.

Table 15.1-1: Information that may be transferred from the UE to the network

Information	UE‑assisted	Standalone
WLAN Location Information
BSSID	Yes	No
SSID	Yes	No
Received Signal Strength (RSSI)	Yes	No
Round Trip Time (RTT)	Yes	No
Measurement Time Stamp	Yes	No
Measurement Characteristics	Yes	No
UE Location Information
UE 3D Position estimate with uncertainty shape	No	Yes
Location Time Stamp	No	Yes
Location Source (method(s) used to compute location)	No	Yes

15.2 SAS initiated WLAN positioning procedure

The following describes the signalling for the optional initiation of the network WLAN positioning procedure by the SAS.

Figure 15.2-1: WLAN methods when initiated by the SAS

1. The operation begins with an authenticated request for positioning information about a UE from an application in the core network being received at the SRNC. The request from the CN may be a request for on-demand or periodic reporting. The SRNC acts as interface between the Core Network and the UE Positioning entities in the UTRAN.

2. The SRNC sends parameters received in the location request, including any periodic reporting information, together with the Cell ID and UE capability information to the SAS in a PCAP: Position Initiation Request message via the Iupc interface.

3. Depending on the UE capabilities, the SAS initiates a WLAN positioning procedure by sending a PCAP: Position Activation Request message that allows for the use of WLAN positioning (along with GPS or OTDOA, and optionally Barometric Pressure, Bluetooth or TBS positioning methods) via the Iupc interface. The PCAP Position Activation Request message may include periodic reporting information (number of reports and reporting interval).

4. The SRNC forwards to the UE the WLAN positioning request received from the SAS using RRC signalling. The SRNC also forwards in the RRC signalling message(s) the SAS request for either WLAN measurements, in the case of UE assisted, or a position coordinates, in the case of standalone. The RRC signalling may include a request for periodic reporting as described in subclause 6.6.4.1 if this was received in step 3. For a description of standalone WLAN, jump to step 9.

5. For UE assisted WLAN, the SRNC requests from the UE the measurement of WLAN RSSI and RTT. These measurements may be made while the UE is in RRC connected mode CELL_DCH state.

6. The UE returns to the SRNC the available WLAN measurements, together with a time stamp of when these values were obtained.

7. The information obtained in step 6 is sent from the SRNC to the SAS in a PCAP: Position Activation Response message.

8. The SAS calculates the UE position. If periodic reporting was not requested in step 2, the SAS returns the UE position to the SRNC in a PCAP: Position Initiation Response message. If periodic reporting was requested in step 2, the SAS forwards the position information to the SRNC in a PCAP Position Periodic Result message. The PCAP Position Initiation Response or PCAP Position Periodic Result message may include the positioning method(s) used and an indication of whether the position estimate satisfies the requested accuracy or not.

9. In case of standalone method, the UE returns the position estimate to the SRNC via RRC signalling. The SRNC forwards the position estimate to the SAS in a PCAP: Position Activation Response message. This estimate includes the position, the estimated accuracy of the results and the time of the estimate.

10. The SAS may verify the UE position estimate received in step 9 (e.g. using cell ID information). If periodic reporting was not requested in step 2, the SAS returns the resulting estimate to the SRNC in a PCAP: Position Initiation Response message. If periodic reporting was requested in step 2, the SAS forwards the position estimate to the SRNC in a PCAP Position Periodic Result message. The PCAP Position Initiation Response or PCAP Position Periodic Result message may include the positioning method(s) used and an indication of whether the position estimate satisfies the requested accuracy or not.

11. If there is insufficient information to yield a UE positioning estimate satisfying the requested accuracy, the SAS may start a new process from step 3.

12. The SRNC passes the position estimate received from the SAS to the CN including the positioning method (or the list of the methods) used to obtain the position estimate. If the CN has requested accuracy for the position estimate, the Location response shall include an indication whether the position estimate satisfies the requested accuracy or not.

13. If periodic UE reporting was requested in step 4, the UE continues to send WLAN measurement reports one reporting interval after the previous measurement report. The SRNC forward the WLAN measurement report information to the SAS in a PCAP Position Periodic Report message. The SAS may calculate the UE position and may verify the calculated UE position estimate or the received UE position estimate (e.g. using cell ID information) and sends the position information to the SRNC in a PCAP Position Periodic Result message. The SRNC passes the new position estimate to the CN including, if available, the positioning method (or the list of the methods) used to obtain the position estimate. If the CN has requested accuracy for the position estimate, the Location response shall include an indication whether the position estimate satisfies the requested accuracy or not. This step 13 is repeated until the desired amount of reports has been attained or the procedure is cancelled by the CN or UTRAN. The SAS may send the final location estimate in a PCAP Position Initiation Response message to the SRNC, and the SRNC forwards the final location information to the CN.

14. If periodic UE reporting was not requested in step 4, but was requested in step 2, the SAS may repeat the steps 3 to 12 as for the first request until the desired amount of reports has been attained or the procedure is cancelled by the CN or UTRAN. When repeating step 10 for the final request, the SAS returns the resulting final position estimate to the SRNC in a PCAP: Position Initiation Response message.