Figure 1 shows the logical reference model for LCS whereby an LCS Client is enabled to request location information for one or more certain target UEs from the LCS Server supported by a PLMN. The LCS Server employs a positioning function to obtain the location information and furnish the information to the LCS Client. The particular requirements and characteristics of an LCS Client are made known to the LCS Server by its LCS Client Subscription Profile. The particular LCS-related restrictions associated with each Target UE are detailed in the Target UE Subscription Profile. The LCS feature shall allow a Target UE to be positioned within a specified Quality of Service. The LCS feature shall allow the location of a Target UE to be determined at any time whilst the UE is attached.
The LCS feature shall support conveyance of both the location Quality of Service (QoS) requirements of the LCS Client and the location information returned to the LCS Client in a universal standard format.
An LCS Client is a logical functional entity that makes a request to the PLMN LCS server for the location information of one or more than one target UEs within a specified set of parameters such as QoS. The LCS Client may reside in an entity (including an UE) within the PLMN or in an entity external to the PLMN. When the LCS client resides in an entity external to the PLMN, the LCS client may be connected to several Requestors who originate the location requests. The specification of the LCS Client's internal logic and its relationship to any external user (e.g. Requestor) is outside the scope of this document.
An LCS server consists of a number of location service components and bearers needed to serve the LCS clients. The LCS server shall provide a platform which will enable the support of location based services in parallel to other telecommunication services such as speech, data, messaging, other teleservices, user applications and supplementary services and therefore enable the market for services to be determined by users and service providers. The LCS server may respond to a location request from a properly authorized LCS client with location information for the target UEs specified by the LCS client if considerations of target UE privacy are satisfied. The LCS server may enable an LCS client to determine the services provided to it by the LCS server through a process of provisioning.
Positioning is the basic function that performs the actual positioning of a specific target UE. The input to this function is a positioning request from a LCS Client with a set of parameters such as QoS requirements. The end results of this function are the location information for the positioned target UE.
The Target UE is the object to be positioned by the LCS Server. For network-based positioning methods, no support for LCS is required by the target UE. For mobile assisted and mobile based positioning methods, the target UE actively supports LCS. For all positioning methods, the ability to control privacy may be required to be given to the UE user for each location request and/or to the UE subscriber through the Target UE subscription profile to satisfy local regulatory requirements (see the previous section on Privacy).
The LCS client/server use LCS messages to exchange information. Each LCS message contains a set of parameters.
In the case of UE Based positioning methods, if the LCS Client is located in the UE, then an internal LCS Client /LCS Server interface may be supported.
Using the Location Service Request, an LCS client communicates with the LCS server to request the location information for one or more target UEs within a specified set of quality of service parameters.
As shown in Table 1, a location service may be specified as immediate or deferred.
If a positioning attempt fails, the LCS server may make another positioning attempt. This attempt should be made when the target UE can be detected by the network. It may be possible for the LCS client to set this action as an option. This optional action should be applied for both request types.
When using the Deferred type (event driven), the LCS client shall be able to set the following items:
Time interval of positioning
Number of responses (if needed)
Valid period of the request (if needed)
Type of event
Currently following events are introduced:
Change of Area
It shall be possible for the LCS client to cancel the pre-arranged request.
It shall be possible for the LCS server to set the minimum time interval of positioning allowed.
It shall be possible to limit the area where the Change of Area event will be reported e.g use the OSA messages defined in 3GPP TS 29.198.
For Emergency Services, LCS shall support requests for the initial, the current (updated), or the last known position of an ME while a voice connection is established.
The Location Service Response provides the result of a Location Service Request from the LCS Server to the LCS Client.
A LCS response is either 'immediate' or 'deferred'. The LCS Request indicates the type of response the LCS Client wishes to receive. The two types of location response are described in Table 2.
A Location Response is referred to as 'immediate`, when a response to a request for location information is answered immediately (within a set time). The response shall be single and not dependent to any event.
A Location Response is referred to as 'deferred', when a response to a request for location information is returned after the occurrence of an event specified by the LCS client. The response can be single or periodic.
When the location positioning for the target UE has failed, the LCS server may be able to report the reason for failure and Last Known Location with the relevant timestamp.
The Location Service Request Report provides the result of a deferred Location Service Request from the LCS Server to the LCS Client. The report is provided using a dialog between the LCS Client and the LCS Server that is initiated by the LCS Server.
It shall be possible for the location determining process to make use of several sources of information in determining the location. Propagation and deployment conditions may limit the number or quality of measurements or additional measurements may be possible. Some ME may also have additional (independent) sources of position information. The LCS shall be capable of making use of the restricted or the extra information as appropriate for the service being requested.