Positioning procedures in the E-UTRAN are modelled as transactions of the LPP protocol using the procedures defined in this specification. A procedure consists of a single operation of one of the following types:
Exchange of positioning capabilities;
Transfer of assistance data;
Transfer of location information (positioning measurements and/or position estimate);
Parallel transactions are permitted (i.e. a new LPP transaction may be initiated, while another one is outstanding).
As described in clause 6.2.1
, the protocol operates between a "target" and a "server". In the control-plane context, these entities are the UE and E-SMLC respectively; in the SUPL context they are the SET and the SLP. The terms "target" and "server" are used in the flows in this clause to avoid redundancy between the two versions of the positioning operations. A procedure may be initiated by either the target or the server. Both target initiated and server initiated procedures are supported.
A UE request for capability from E-SMLC or delivery of the E-SMLC capability to the UE is not supported in this version of the specification.
Capabilities in an LPP context refer to the ability of a target or server to support different position methods defined for LPP, different aspects of a particular position method (e.g. different types of assistance data for A-GNSS) and common features not specific to only one position method (e.g. ability to handle multiple LPP transactions). These capabilities are defined within the LPP protocol and transferred between the target and the server using LPP transport.
The exchange of capabilities between a target and a server may be initiated by a request or sent as "unsolicited" information. If a request is used, the server sends an LPP Request Capabilities message to the target device with a request for capability information. The target sends an LPP Provide Capabilities message.
Figure 184.108.40.206 1: LPP Capability Transfer procedure
The server may send a request for the LPP related capabilities of the target.
The target transfers its LPP-related capabilities to the server. The capabilities may refer to particular position methods or may be common to multiple position methods.
LPP Capability Indication procedure is used for unsolicited capability transfer.
Figure 220.127.116.11-2: LPP Capability Indication procedure
Assistance data may be transferred either by request or unsolicited. In this version of the specification, assistance data delivery is supported only via unicast transport from server to target.
Figure 18.104.22.168 1: LPP Assistance Data Transfer procedure
The target may send a request to the server for assistance data and may indicate the particular assistance data needed.
The server transfers assistance data to the target. The transferred assistance data should match any assistance data requested in step 1.
Optionally, the server may transfer additional assistance data to the target in one or more additional LPP messages.
LPP Assistance Data Delivery procedure is used for unilateral assistance data transfer.
Figure 22.214.171.124-2: LPP Assistance Data Delivery procedure
This procedure is unidirectional; assistance data are always delivered from the server to the target.
The term "location information" applies both to an actual position estimate and to values used in computing position (e.g., radio measurements or positioning measurements). It is delivered either in response to a request or unsolicited.
Figure 126.96.36.199 1: LPP Location Information Transfer procedure
The server may send a request for location information to the target, and may indicate the type of location information needed and associated QoS.
In response to step 1, the target transfers location information to the server. The location information transferred should match the location information requested in step 1.
Optionally (e.g., if requested in step 1), the target in step 2 may transfer additional location information to the server in one or more additional LPP messages.
LPP Location Information Delivery procedure is used for unilateral location information transfer.
Figure 188.8.131.52 2: LPP Location Information Delivery procedure
Multiple LPP transactions may be in progress simultaneously between the same target and server nodes, to improve flexibility and efficiency. However, no more than one LPP procedure between a particular pair of target and server nodes to obtain location information shall be in progress at any time for the same position method.
In this example, the objective is to request location measurements from the target, and the server does not provide assistance data in advance, leaving the target to request any needed assistance data. A message flow is shown in Figure 184.108.40.206-1.
Figure 220.127.116.11-1: Example of multiple LPP procedures
The server sends a request to the target for positioning measurements.
The target sends a request for particular assistance data.
The server returns the assistance data requested in step 2.
The target obtains and returns the location information (e.g., positioning method measurements) requested in step 1.
LPP procedures are not required to occur in any fixed order, in order to provide greater flexibility in positioning. Thus, a UE may request assistance data at any time in order to comply with a previous request for location measurements from the E-SMLC; an E-SMLC may instigate more than one request for location information (e.g., measurements or a location estimate) in case location results from a previous request were not adequate for the requested QoS; and the target device may transfer capability information to the server at any time if not already performed.
Despite the flexibility allowed by LPP, it is expected that procedures will normally occur in the following order:
Assistance Data Transfer;
Location Information Transfer (measurements and/or location estimate).
Specific examples for each positioning method are shown in clause 8
The procedure is used to notify the sending endpoint by the receiving endpoint that the receiving LPP message is erroneous or unexpected. This procedure is bidirectional at the LPP level; either the target or the server may take the role of either endpoint in Figure 18.104.22.168-1.
Figure 22.214.171.124-1: Error handling
The target or server (indicated as "Target/Server" in Figure 126.96.36.199-1) sends a LPP message to the other endpoint (indicated as "Server/Target").
If the server or target ("Server/Target") detects that the receiving LPP message is erroneous or unexpected, the server or target transfers error indication information to the other endpoint ("Target/Server").
The procedure is used to notify the other endpoint by one endpoint to abort an ongoing procedure between the two endpoints. This procedure is bidirectional at the LPP level; either the target or the server may take the role of either endpoint in Figure 188.8.131.52-1.
Figure 184.108.40.206-1: Abort
A LPP procedure is ongoing between target and server.
If the server or target ("Server/Target") determines that the procedure must be aborted, and then the server or target sends an LPP Abort message to the other endpoint ("Target/Server") carrying the transaction ID for the procedure.
NB-IoT UEs may perform measurements for some positioning methods only when in idle state.
Figure 7.1.3-1 shows the general positioning procedure where the UE performs positioning measurements in idle state.
The E-SMLC is aware of the UE access type and/or coverage level if applicable from the Location Service Request message received from the MME. The E-SMLC may send a LPP Request Capabilities message to the UE to obtain the UE positioning method capabilities from the UE, as described in clause 220.127.116.11
The UE sends its positioning method capabilities to the E-SMLC in a LPP Provide Capabilities message, including an indication of position methods for which the UE needs to make measurements in idle state.
The E-SMLC may determine the assistance data required for the selected position method or methods, and sends them in one or more LPP Provide Assistance data messages to the UE, as described in clause 18.104.22.168
. If an LPP acknowledgement was requested, the UE sends an LPP acknowledgment for each received LPP Provide Assistance data message to the E-SMLC.
If the UE capabilities from step 2 indicate that idle state is required for positioning measurements, the E-SMLC may allow additional response time to the UE to obtain the location measurements, and sends one or more LPP Request Location Information messages to the UE requesting positioning measurements or a location estimate, and including the required response time, as described in clause 22.214.171.124
. For E-CID positioning method, when NRSRP/NRSRQ measurements are requested the UE is requested to provide NRSRP/NRSRQ measurements for intra-frequency neighbour cells and for inter-frequency neighbour cells. The UE may use inter-frequency information in system information of the serving cell specified in TS 36.331
to decide on which inter-frequency cells to measure.
The UE sends an LPP acknowledgement for each received LPP Request Location Information message to the E SMLC, if an LPP acknowledgement was requested at step 4 but does not perform the requested measurements.
The UE may finish any other activities in progress (e.g., SMS or data transfer), and waits until the network releases or suspends the connection (after a certain period of inactivity). The UE will then receive an RRC connection release or suspend from the eNodeB due to the expiration of the inactivity timer.
When the UE has entered idle state, the UE performs the measurements requested in step 4.
Before the location measurements are to be sent to the E-SMLC, the UE instigates a UE triggered service request or, when User Plane CIoT EPS optimization applies, the Connection Resume procedure as defined in TS 23.401
, if the UE is not using Control Plane CIoT EPS Optimisation, in order to establish a signalling connection with the MME. If the UE is using Control Plane CIoT EPS Optimisation, procedures for Mobile Originated Data Transport in Control Plane CIoT EPS optimisation as defined in TS 23.401
are performed by the UE to establish a signalling connection with the MME.
When the LPP response time received in step 4 expires (or when location measurements are available before expiry), the UE sends one or more LPP Provide Location Information messages containing the requested location measurements or location estimate obtained in step 7 to the E-SMLC.