8.5 WLAN positioning

38.3053GPPNG Radio Access Network (NG-RAN)Release 17Stage 2 functional specification of User Equipment (UE) positioning in NG-RANTS

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

8.5.1 General

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 receivers, and applying a location determination algorithm using databases of the estimated position’s references points.

The UE WLAN measurements may include:

– WLAN Received Signal Strength (RSSI);

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

Three positioning modes are supported:

– Standalone:
The UE performs WLAN position measurements and location computation, without network assistance.

– UE-assisted:
The UE provides WLAN position measurements with or without assistance from the network to the LMF for computation of a location estimate by the network.

– UE-based:
The UE performs WLAN position measurements and computation of a location estimate with network assistance.

8.5.2 Information to be transferred between NG-RAN/5GC Elements

This clause defines the information that may be transferred between LMF and UE.

8.5.2.1 Information that may be transferred from the LMF to UE

Table 8.5.2.1-1 lists assistance data for both UE-assisted and UE-based modes that may be sent from the LMF to the UE.

NOTE: The provision of these assistance data elements and the usage of these elements by the UE depend on the NG-RAN/5GC and UE capabilities, respectively.

Table 8.5.2.1-1: Information that may be transferred from the LMF to UE

Assistance Data

WLAN AP List

BSSID

SSID

AP Type Data⁽¹⁾

AP Location

NOTE 1: WLAN AP Type Data may include WLAN Type (e.g., 802.11a/b/g/n/ac/ad, etc.), transmit power, antenna gain, coverage area, etc.

8.5.2.1.1 WLAN AP BSSID

This assistance data provides the BSSID of the WLAN access point [21].

8.5.2.1.2 WLAN AP SSID

This assistance data provides the SSID of the WLAN access point [21].

8.5.2.1.3 WLAN AP Type Data

This assistance data provides additional information about the access point and may include WLAN Type (e.g., 802.11a/b/g/n/ac/ad, etc.), transmit power, antenna gain, coverage area, etc. [21]

8.5.2.1.4 WLAN AP Location

This assistance data provides the location (possibly including altitude information) of the access point [21].

8.5.2.2 Information that may be transferred from the UE to LMF

The information that may be signalled from the UE to the LMF is summarized in Table 8.5.2.2-1.

Table 8.5.2.2-1: Information that may be transferred from the UE to the LMF

Information	UE‑Assisted	UE-based/ Standalone
WLAN Location Information
BSSID	Yes	No
SSID	Yes	No
Received Signal Strength (RSSI)	Yes	No
Round Trip Time (RTT)	Yes	No
Time Stamp	Yes	No
Measurement characteristics	Yes	No
UE Location Information
UE position estimate with uncertainty shape	No	Yes
Position Time Stamp	No	Yes
Location Source (method(s) used to compute location)	No	Yes

8.5.2.2.1 Standalone mode

In Standalone mode, the UE reports the latitude, longitude and possibly altitude, together with an estimate of the location uncertainty, if available.

The UE should also report an indication of WLAN method and possibly other positioning methods used to calculate a fix.

8.5.2.2.2 UE-assisted mode

In UE-assisted mode, the UE should report:

– The BSSID/SSID of the measured WLAN access points, and associated RSSI or RTT.

8.5.2.2.3 UE-based mode

In UE-based mode, the UE reports the latitude, longitude, and possibly altitude, together with an estimate of the location uncertainty, if available.

The UE should also report an indication that WLAN method is used and possibly other positioning methods used to calculate the fix.

8.5.3 WLAN Positioning Procedures

8.5.3.1 Capability Transfer Procedure

The Capability Transfer procedure for WLAN positioning is described in clause 7.1.2.1.

8.5.3.2 Assistance Data Transfer Procedure

The purpose of this procedure is to enable the UE to request assistance data from the LMF (e.g., as part of a positioning procedure) and the LMF to provide assistance data to the UE (e.g., as part of a positioning procedure).

8.5.3.2.1 LMF initiated Assistance Data Delivery

Figure 8.5.3.2.1-1 shows the Assistance Data Delivery operations for the network-assisted WLAN method when the procedure is initiated by the LMF.

Figure 8.5.3.2.1: LMF-initiated Assistance Data Delivery Procedure

(1) The LMF determines that assistance data needs to be provided to the UE (e.g., as part of a positioning procedure) and sends an LPP Provide Assistance Data message to the UE. This message may include any of the WLAN assistance data defined in clause 8.5.2.1.

8.5.3.2.2 UE initiated Assistance Data Transfer

Figure 8.5.3.2.2-1 shows the Assistance Data Transfer operations for the network-assisted WLAN method when the procedure is initiated by the UE.

Figure 8.5.3.2.2-1: UE-initiated Assistance Data Transfer Procedure

(1) The UE determines that certain WLAN assistance data is desired (e.g., as part of a positioning procedure when the LMF provided assistance data are not sufficient for the UE to fulfil the request) and sends a LPP Request Assistance Data message to the LMF. This request includes an indication of which specific WLAN assistance data is requested.

(2) The LMF provides the requested assistance data in a LPP Provide Assistance Data message, if available at the LMF. The entire set of assistance data may be delivered in one or several LPP messages. In this case, this step may be repeated by the LMF several times. If any of the UE requested assistance data in step (1) are not provided in step 2, the UE shall assume that the requested assistance data are not supported, or currently not available at the LMF. If none of the UE requested assistance data in step (1) can be provided by the LMF, return any information that can be provided in an LPP message of type Provide Assistance Data which includes a cause indication for the not provided assistance data.

8.5.3.3 Location Information Transfer Procedure

The purpose of this procedure is to enable the LMF to request position measurements or location estimate from the UE, or to enable the UE to provide location measurements to the LMF for position calculation.

8.5.3.3.1 LMF initiated Location Information Transfer Procedure

Figure 8.5.3.3.1-1 shows the Location Information Transfer operations for the WLAN method when the procedure is initiated by the LMF.

Figure 8.5.3.3.1-1: LMF-initiated Location Information Transfer Procedure

(1) The LMF sends a LPP Request Location Information message to the UE for invocation of WLAN positioning. This request includes positioning instructions such as the positioning mode (UE-assisted, UE-based, Standalone), specific requested UE measurements if any, and quality of service parameters (accuracy, response time).

(2) The UE performs the requested measurements and possibly calculates its own location. The UE sends an LPP Provide Location Information message to the LMF before the Response Time provided in step (1) elapsed. If the UE is unable to perform the requested measurements, or if the Response Time provided in step 1 elapsed before any of the requested measurements have been obtained, the UE returns any information that can be provided in an LPP message of type Provide Location Information which includes a cause indication for the not provided location information.

8.5.3.3.2 UE-initiated Location Information Delivery Procedure

Figure 8.5.3.3.2-1 shows the Location Information delivery operations for the WLAN method when the procedure is initiated by the UE.

Figure 8.5.3.3.2-1: UE-initiated Location Information Delivery Procedure

(1) The UE sends an LPP Provide Location Information message to the LMF. The Provide Location Information message may include UE WLAN information or location estimate already available at the UE.