6.5.6 WLAN-based Positioning

37.3553GPPLTE Positioning Protocol (LPP)Release 17TS

This clause defines support for positioning using measurements related to WLAN access points.

6.5.6.1 WLAN Location Information

WLAN-ProvideLocationInformation

The IE WLAN-ProvideLocationInformation is used by the target device to provide measurements for one or more WLANs to the location server. It may also be used to provide WLAN positioning specific error reason.

— ASN1START

WLAN-ProvideLocationInformation-r13 ::= SEQUENCE {

wlan-MeasurementInformation-r13 WLAN-MeasurementInformation-r13 OPTIONAL,

wlan-Error-r13 WLAN-Error-r13 OPTIONAL,

}

— ASN1STOP

6.5.6.2 WLAN Location Information Elements

WLAN-MeasurementInformation

— ASN1START

WLAN-MeasurementInformation-r13 ::= SEQUENCE {

measurementReferenceTime-r13 UTCTime OPTIONAL,

wlan-MeasurementList-r13 WLAN-MeasurementList-r13 OPTIONAL,

}

WLAN-MeasurementList-r13 ::= SEQUENCE (SIZE(1..maxWLAN-AP-r13)) OF WLAN-MeasurementElement-r13

WLAN-MeasurementElement-r13 ::= SEQUENCE {

wlan-AP-Identifier-r13 WLAN-AP-Identifier-r13,

rssi-r13 INTEGER (-127..128) OPTIONAL,

rtt-r13 WLAN-RTT-r13 OPTIONAL,

apChannelFrequency-r13 INTEGER (0..256) OPTIONAL,

servingFlag-r13 BOOLEAN OPTIONAL,

}

WLAN-AP-Identifier-r13 ::= SEQUENCE {

bssid-r13 OCTET STRING (SIZE (6)),

ssid-r13 OCTET STRING (SIZE (1..32)) OPTIONAL,

}

WLAN-RTT-r13 ::= SEQUENCE {

rttValue-r13 INTEGER (0..16777215),

rttUnits-r13 ENUMERATED { microseconds,

hundredsofnanoseconds,

tensofnanoseconds,

nanoseconds,

tenthsofnanoseconds,

… },

rttAccuracy-r13 INTEGER (0..255) OPTIONAL,

}

— ASN1STOP

WLAN-MeasurementInformation field descriptions

measurementReferenceTime

This field provides the UTC time when the WLAN measurements are performed and should take the form of YYMMDDhhmmssZ.

wlan-MeasurementList

This field provides the WLAN measurements for up to 64 WLAN APs.

wlan-AP-Identifier

This field provides the BSSID and optionally the SSID of the wireless network served by the WLAN AP [26].

rssi

This field provides the AP signal strength (RSSI) of a beacon frame, probe response frame or measurement pilot frame measured at the target in dBm as defined in Table 6-7 of [26].

rtt

This field provides the measured round trip time between the target device and WLAN AP and optionally the accuracy expressed as the standard deviation of the delay. Units for each of these are 1000ns, 100ns, 10ns, 1ns, and 0.1ns.

apChannelFrequency

This field provides the AP channel number identification of the reported WLAN AP.

servingFlag

This parameter indicates whether a set of WLAN AP measurements were obtained for a serving WLAN AP (TRUE) or a non-serving WLAN AP (FALSE). A target device with multiple radio support may indicate more than one type of serving access for the same time instant.

rttValue

This field specifies the Round Trip Time (RTT) measurement between the target device and WLAN AP in units given by the field rttUnits.

rttUnits

This field specifies the Units for the fields rttValue and rttAccuracy. The available Units are 1000ns, 100ns, 10ns, 1ns, and 0.1ns.

rttAccuracy

This field provides the estimated accuracy of the provided rttValue expressed as the standard deviation in units given by the field rttUnits.

6.5.6.3 WLAN Location Information Request

WLAN-RequestLocationInformation

The IE WLAN-RequestLocationInformation is used by the location server to request WLAN measurements from a target device.

— ASN1START

WLAN-RequestLocationInformation-r13 ::= SEQUENCE {

requestedMeasurements-r13 BIT STRING {

rssi (0),

rtt (1)} (SIZE(1..8)),

…,

[[ assistanceAvailability-r14 BOOLEAN OPTIONAL — Need ON

]]

}

— ASN1STOP

WLAN-RequestLocationInformation field descriptions

requestedMeasurements

This field specifies the WLAN measurements requested. This is represented by a bit string, with a one‑value at the bit position means the particular measurement is requested; a zero‑value means not requested. The following measurement requests can be included.

rssi: AP signal strength at the target

rtt: Round Trip Time between target and AP

assistanceAvailability

This field indicates whether the target device may request additional WLAN assistance data from the server. TRUE means allowed and FALSE means not allowed.

6.5.6.4 WLAN Capability Information

WLAN-ProvideCapabilities

The IE WLAN-ProvideCapabilites is used by the target device to provide its capabilities for WLAN positioning to the location server.

— ASN1START

WLAN-ProvideCapabilities-r13 ::= SEQUENCE {

wlan-Modes-r13 BIT STRING { standalone (0),

ue-assisted (1),

ue-based (2)} (SIZE (1..8)),

wlan-MeasSupported-r13 BIT STRING {

rssi-r13 (0),

rtt-r13 (1)} (SIZE(1..8)),

… ,

[[ wlan-AP-AD-Supported-r14

BIT STRING { ap-identifier (0),

ap-location (1)} (SIZE (1..8))

OPTIONAL,

periodicalReportingSupported-r14 PositioningModes OPTIONAL,

idleStateForMeasurements-r14

ENUMERATED { required } OPTIONAL

]],

[[ scheduledLocationRequestSupported-r17 ScheduledLocationTimeSupportPerMode-r17 OPTIONAL

]]

}

— ASN1STOP

WLAN-ProvideCapabilities field descriptions

wlan-Modes

This field specifies the WLAN mode(s) supported by the target device. This is represented by a bit string, with a one value at the bit position means the WLAN mode is supported; a zero value means not supported.

wlan-MeasSupported

This field specifies the measurements supported by the target device when accessing a WLAN. This is represented by a bit string, with a one‑value at the bit position means the particular measurement is supported; a zero‑value means not supported. A zero-value in all bit positions in the bit string means only the basic WLAN positioning method is supported by the target device which is reporting of the WLAN identity. The following bits are assigned for the indicated measurements.

rssi: AP signal strength at the target

rtt: Round Trip Time between target and AP

wlan-AP-AD-Supported
This field specifies the WLAN AP assistance data supported by the target device. This is represented by a bit string, with a
one-value at the bit position means the particular assistance data is supported; a zero-value means not supported. A zero-value in all bit positions or absence of this field means no assistance data is supported. The following bits are assigned for the indicated assistance data.

ap-identifier: WLAN AP identity information

ap-location: WLAN AP location information

periodicalReportingSupported

This field, if present, specifies the positioning modes for which the target device supports periodicalReporting. This is represented by a bit string, with a one value at the bit position means periodicalReporting for the positioning mode is supported; a zero value means not supported. If this field is absent, the location server may assume that the target device does not support periodicalReporting in CommonIEsRequestLocationInformation.

idleStateForMeasurements

This field, if present, indicates that the target device requires idle state to perform WLAN measurements.

scheduledLocationRequestSupported

This field, if present, specifies the positioning modes for which the target device supports scheduled location requests – i.e., supports the IE ScheduledLocationTime in IE CommonIEsRequestLocationInformation – and the time base(s) supported for the scheduled location time for each positioning mode. If this field is absent, the target device does not support scheduled location requests.

6.5.6.5 WLAN Capability Information Request

WLAN-RequestCapabilities

The IE WLAN-RequestCapabilities is used by the location server to request WLAN positioning capabilities information from a target device.

— ASN1START

WLAN-RequestCapabilities-r13 ::= SEQUENCE {

}

— ASN1STOP

6.5.6.6 WLAN Error Elements

WLAN-Error

The IE WLAN-Error is used by the location server or target device to provide error reasons for WLAN positioning to the target device or location server, respectively.

— ASN1START

WLAN-Error-r13 ::= CHOICE {

locationServerErrorCauses-r13 WLAN-LocationServerErrorCauses-r13,

targetDeviceErrorCauses-r13 WLAN-TargetDeviceErrorCauses-r13,

}

— ASN1STOP

WLAN-LocationServerErrorCauses

The IE WLAN-LocationServerErrorCauses is used by the location server to provide error reasons for WLAN positioning to the target device.

— ASN1START

WLAN-LocationServerErrorCauses-r13 ::= SEQUENCE {

cause-r13 ENUMERATED {undefined,

…,

requestedADNotAvailable-v1420,

notAllrequestedADAvailable-v1420

},

…,

[[ apLocationDataUnavailable-r14 NULL OPTIONAL — Need ON

]]

}

— ASN1STOP

WLAN-LocationServerErrorCauses field descriptions

cause

This field provides a WLAN AP specific error cause for the server applicable to provision of assistance data. If the cause value is ‘requestedADNotAvailable‘, none of the requested assistance data could be provided and no further information needs to be included. If the cause value is ‘notAllRequestedADAvailable‘, the server was able to provide some but not all requested WLAN AP assistance data. In this case, the server should include any of the specific error indications as applicable. Note that inclusion of these fields is applicable when some of the associated information can be provided for some WLAN APs but not for all WLAN APs.

WLAN-TargetDeviceErrorCauses

The IE WLAN-TargetDeviceErrorCauses is used by the target device to provide error reasons for WLAN positioning to the location server.

— ASN1START

WLAN-TargetDeviceErrorCauses-r13 ::= SEQUENCE {

cause-r13 ENUMERATED {undefined,

requestedMeasurementsNotAvailable,

notAllrequestedMeasurementsPossible,

},

wlan-AP-RSSI-MeasurementNotPossible-r13 NULL OPTIONAL,

wlan-AP-RTT-MeasurementNotPossible-r13 NULL OPTIONAL,

}

— ASN1STOP

WLAN-TargetDeviceErrorCauses field descriptions

cause

This field provides a WLAN specific error cause. If the cause value is ‘notAllRequestedMeasurementsPossible’, the target device was not able to provide all requested WLAN measurements (but may be able to provide some measurements). In this case, the target device should include any of the wlan‑AP‑RSSI‑MeasurementNotPossible, or wlan‑AP‑RTT‑MeasurementNotPossible fields, as applicable.

6.5.6.7 WLAN Assistance Data

WLAN-ProvideAssistanceData

The IE WLAN-ProvideAssistanceData is used by the location server to provide assistance data to enable UE‑based and UE-assisted WLAN positioning. It may also be used to provide WLAN positioning specific error reason.

— ASN1START

WLAN-ProvideAssistanceData-r14 ::= SEQUENCE {

wlan-DataSet-r14 SEQUENCE (SIZE (1..maxWLAN-DataSets-r14)) OF WLAN-DataSet-r14

OPTIONAL, — Need ON

wlan-Error-r14 WLAN-Error-r13 OPTIONAL, — Need ON

}

— ASN1STOP

WLAN-ProvideAssistanceData field descriptions

wlan-DataSet
This field provides data for sets of WLAN APs.

wlan-Error
This field provides error information and may be included when a Provide Assistance Data is sent in response to a Request Assistance Data. It is allowed to include both a wlan-DataSet field and a wlan-Error field (e.g. when only some requested WLAN assistance data is provided).

6.5.6.8 WLAN Assistance Data Elements

WLAN-DataSet

The IE WLAN-DataSet is used by the location server to provide WLAN AP information for one set of WLAN APs.

— ASN1START

WLAN-DataSet-r14 ::= SEQUENCE {

wlan-AP-List-r14 SEQUENCE (SIZE (1..maxWLAN-AP-r14)) OF WLAN-AP-Data-r14,

supportedChannels-11a-r14 SupportedChannels-11a-r14 OPTIONAL, — Need ON

supportedChannels-11bg-r14 SupportedChannels-11bg-r14 OPTIONAL, — Need ON

}

SupportedChannels-11a-r14 ::= SEQUENCE {

ch34-r14 BOOLEAN,

ch36-r14 BOOLEAN,

ch38-r14 BOOLEAN,

ch40-r14 BOOLEAN,

ch42-r14 BOOLEAN,

ch44-r14 BOOLEAN,

ch46-r14 BOOLEAN,

ch48-r14 BOOLEAN,

ch52-r14 BOOLEAN,

ch56-r14 BOOLEAN,

ch60-r14 BOOLEAN,

ch64-r14 BOOLEAN,

ch149-r14 BOOLEAN,

ch153-r14 BOOLEAN,

ch157-r14 BOOLEAN,

ch161-r14 BOOLEAN

}

SupportedChannels-11bg-r14 ::= SEQUENCE {

ch1-r14 BOOLEAN,

ch2-r14 BOOLEAN,

ch3-r14 BOOLEAN,

ch4-r14 BOOLEAN,

ch5-r14 BOOLEAN,

ch6-r14 BOOLEAN,

ch7-r14 BOOLEAN,

ch8-r14 BOOLEAN,

ch9-r14 BOOLEAN,

ch10-r14 BOOLEAN,

ch11-r14 BOOLEAN,

ch12-r14 BOOLEAN,

ch13-r14 BOOLEAN,

ch14-r14 BOOLEAN

}

— ASN1STOP

WLAN-DataSet field descriptions

wlan-AP-List
This field provides information for WLAN APs in the data set.

supportedChannels-11a
This field defines the superset of all channels supported by all WLAN APs in the data set of type 801.11a (5GHz band).

supportedChannels-11bg
This field defines the superset of all channels supported by all WLAN APs in the data set of type 801.11b or
802.11g (2.4 GHz band).

WLAN-AP-Data

The IE WLAN-AP-Data is used by the location server to provide information for one WLAN AP as part of WLAN AP assistance data.

— ASN1START

WLAN-AP-Data-r14 ::= SEQUENCE {

wlan-AP-Identifier-r14 WLAN-AP-Identifier-r13,

wlan-AP-Location-r14 WLAN-AP-Location-r14 OPTIONAL, — Need ON

}

WLAN-AP-Location-r14 ::= SEQUENCE {

locationDataLCI-r14 LocationDataLCI-r14,

}

LocationDataLCI-r14 ::= SEQUENCE {

latitudeUncertainty-r14 BIT STRING (SIZE (6)),

latitude-r14 BIT STRING (SIZE (34)),

longitudeUncertainty-r14 BIT STRING (SIZE (6)),

longitude-r14 BIT STRING (SIZE (34)),

altitudeUncertainty-r14 BIT STRING (SIZE (6)) OPTIONAL, — Need ON

altitude-r14 BIT STRING (SIZE (30)) OPTIONAL, — Need ON

datum-r14 BIT STRING (SIZE (8)),

}

— ASN1STOP

WLAN-AP-Data field descriptions

wlan-AP-Location

locationDataLCI

This field provides the location of the WLAN AP in the form of Location Configuration Information (LCI) defined in [27] and includes the following subfields:

latitudeUncertainty: 6-bits quantifying the amount of uncertainty in latitude. A value of 0 is reserved to indicate that the uncertainty is unknown; values greater than 34 are reserved. Its relation with the corresponding value in degrees is expressed with the following formula:
latitudeUncertainty = 8 – ceil(log2(uncertainty in degrees))

latitude: A 34-bits fixed point value consisting of 9-bits of integer and 25-bits of fraction indicating the Latitude (+/- 90 degrees) of the AP.

longitudeUncertainty: 6-bits quantifying the amount of uncertainty in longitude. A value of 0 is reserved to indicate that the uncertainty is unknown; values greater than 34 are reserved. Its relation with the corresponding value in degrees is expressed with the following formula:
longitudeUncertainty = 8 – ceil(log2(uncertainty in degrees))

longitude: A 34-bits fixed point value consisting of 9-bits of integer and 25-bits of fraction indicating the Longitude (+/- 180 degrees) of the AP.

altitudeUncertainty: 6-bits value quantifying the amount of uncertainty in the altitude value. A value of 0 is reserved to indicate that the uncertainty is unknown; values greater than 30 are reserved. Its relation with the corresponding value in metres is expressed with the following formula:
altitudeUncertainty = 21 – ceil(log2( uncertainty in metres))

altitude: A 30-bit fixed point value consisting of 22-bits of integer and 8-bits of fraction indicating the altitude of the AP in metres.

datum: 8-bits indicating the map datum used for the coordinates. Defined codes are:
Bit 1: World Geodetic System 1984 (WGS-84)
Bit 2: North American Datum 1983 (NAD-83) with North American Vertical Datum 1988 (NAVD-88)
Bit 3: North American Datum 1983 (NAD-83) with Mean Lower Low Water (MLLW) vertical datum.
Bits 4 – 8 are reserved.

6.5.6.9 WLAN Assistance Data Request

WLAN-RequestAssistanceData

The IE WLAN-RequestAssistanceData is used by the target device to request WLAN assistance data from a location server.

— ASN1START

WLAN-RequestAssistanceData-r14 ::= SEQUENCE {

requestedAD-r14 BIT STRING { ap-identifier (0),

ap-location (1)} (SIZE (1..8)),

visibleAPs-r14 SEQUENCE (SIZE (1..maxVisibleAPs-r14)) OF WLAN-AP-Identifier-r13 OPTIONAL,

wlan-AP-StoredData-r14 SEQUENCE (SIZE (1..maxKnownAPs-r14)) OF WLAN-AP-Identifier-r13 OPTIONAL,

}

— ASN1STOP

WLAN-RequestAssistanceData field descriptions

requestedAD
This field specifies the WLAN AP assistance data requested. This is represented by a bit string, with a one-value at the bit position means the particular assistance data is requested; a zero-value means not requested. The following assistance data types are included:

ap-identifier: WLAN AP identity information
ap-location: WLAN AP location information

visibleAPs
This field enables a target to indicate to a server the identities of currently visible WLAN APs. This may assist a server to provide assistance data for WLAN APs nearby to the target. A target shall provide visible APs in order of received signal strength with the AP with the highest signal strength provided first.

wlan-AP-StoredData
This field enables a target to indicate to a server the identities of WLAN APs for which the target has stored assistance data received previously from the server. This may enable the server to avoid resending data for the same APs.