6 UMTS LCS Architecture

23.1713GPPFunctional descriptionLocation Services (LCS)Release 1999Stage 2 (UMTS)TS

Figure 6.1 shows the general arrangement of the Location Service feature in UMTS. This illustrates, generally, the relation of LCS Clients and servers in the core network with the UMTS Access Network. The LCS entities within the Access Network communicate with the Core Network (CN) across the Iu interface. Communication among the Access Network LCS entities makes use of the messaging and signalling capabilities of the Access Network.

As part of their service or operation, the LCS Clients may request the location information of user equipment UE (UE without a valid SIM/USIM) or mobile stations. There may be more than one LCS client. These may be associated with the UMTS network or the Access Network operated as part of a UE application or accessed by the UE through its access to an application (e.g. through the Internet).

The clients make their requests to a LCS Server. There may be more than one LCS Server. The client must be authenticated and the resources of the network must be co-ordinated including the UE and the calculation functions, to estimate the location of the UE and result returned to the client. As part of this process, information from other systems (other Access Networks) can be used. As part of the location information returned to the client, an estimate of the accuracy of the estimate and the time-of-day the measurement was made shall be provided.

Note 1): The usage of CBC for LCS assistance data in UMTS is for further study. The assistance data is generated in SRNC.

Figure 6.1: General arrangement of LCS in UMTS, UTRAN example

6.1 Schematic functional description of LCS operations in UMTS

The allocation of LCS functional blocks to the Client, LCS server, Core Network, Access Network and UE is based on the schematic functional description below. The detailed functions and interactions are specified later in the present document and in TS 25.305 and corresponding Stage 3 specifications.

The operation begins with a LCS Client requesting location information for a UE from the LCS server. The LCS server will pass the request to the LCS functional entities in the UMTS core network. The LCS functional entities in the core network shall then:

– verify that the LCS Client is authorized to request the location of the UE or subscriber;

– verify that LCS is supported by the UE;

– establish whether it is allowed to locate the UE or subscriber, for privacy or other reasons;

– establish which Serving RNC should receive the Location request if necessary by establishing a connection with the UE;

– request the Access Network (via the Iu interface) to provide location information for an identified UE, with indicated QoS;

– receive information about the location of the UE from the Access Network and forward it to the Client;

– send appropriate accounting information to an accounting function.

The Access Network LCS functional entities shall typically:

– request measurements, typically from the UE and radio network apparatus;

– send the measurement results to the appropriate calculating function within the Access Network;

– receive the result from the calculating function within Access Network;

– indicate the geographical co-ordinates of the Target UE corresponding to the cell(s) the Target UE is associated with;

– perform any needed co-ordinate transformations;

– send the results to the LCS entities in the core network.

In the event that the client is internal to the Access Network the request may be made directly to the Access Network LCS entities as the internal clients are considered to be "pre-authorised".

As part of its operation, the calculating function may require additional information. This may be obtained by the function directly by communication with a database, or it may be through a request to LCS entities that will mediate the request and return of information from the appropriate database (or databases if more than one is needed to fulfil the requests). The LCS application may make use of the position information itself, or further process and then forward the information to other authorised applications within or external to the Access Network.

There may possibly also be available independent information that is able to supply the location information directly, or may be able to supply auxiliary information to the calculation function. The LCS co-ordination function, as part of its activity to supervise the positioning process, may query the UE or other elements of the network to determine their capabilities and use this information to select the mode of operation.

6.2 Allocation of LCS functions to UMTS network elements

Table 6.1 shows a summary of the Functional Groups and Functional Blocks for Location services in UMTS. Table 6.2 and Figure 6.2 show the generic configuration for LCS in UMTS and the distribution of LCS functional blocks to UMTS network elements. Different positioning methods, including network-based, mobile-based, mobile-assisted and network-assisted positioning methods may be used. With this configuration both the network and the mobiles are able to measure the timing of signals and compute the mobile’s location estimate. Depending on the applied positioning method it is possible to utilise the corresponding configuration containing all needed entities. For instance, if network-based positioning is applied, the entities that are involved in measuring the mobile’s signal and calculating its location estimate are allocated to the network elements of the access stratum. On the other hand, in case mobile-based or network-assisted methods are used these entities should be allocated to the mobile station.

LCS is logically implemented on the UMTS structure through the addition of one network node, the Mobile Location Center (MLC). It is necessary to name a number of new interfaces. The LCS generic architecture can be combined to produce LCS architecture variants.

Table 6.1: Summary of Functional Groups and Functional Blocks for Location services in UMTS

Funct.
Group

Functional component

Full name of Functional Block

Abbrev.

Loc. Client

Location Client

component

(External) Location Client Function

LCF

Internal Location Client Function

U-LCF

-internal

LCS Server in PLMN

Client handling component

Location Client Control Function

LCCF

Location Client Authorization Function

LCAF

Location Client Zone Transformation Function

LCZTF

System handling component

Stand-alone LMU Mobility Management Function

LMMF

Location System Control Function

LSCF

Location System Control Function in RNC

U-LSCF

Location System Billing Function

LSBF

Location System Operations Function

LSOF

Subscr. handling component

Location Subscriber Authorization Function

LSAF

Location Subscriber Privacy function

LSPF

Positioning component

UMTS- Positioning Radio Control Function

U-PRCF

UMTS- Positioning Calculation Function

U-PCF

UMTS- Positioning Signal Measurement Function

U-PSMF

UMTS- Positioning Radio Resource Management

U-PRRM

Table 6.2 and Figure 6.2 illustrate the allocation of functional entities in the reference configuration of LCS in UMTS. It is assumed that the CS and PS have either their own independent mobility management or use the joint mobility management through the optional Gs interface.

It is also seen that LCS in UMTS shall take benefit of the standardized Iur interface between RNSs, when uplink radio information and measurement results are collected.

The functional model presented in the figure includes functional entities for CS related LCS. In addition, it consists of all the entities needed for different positioning methods, i.e. network based, mobile based, mobile assisted, and network assisted positioning, exploiting either uplink or downlink measurements.

Table 6.2: Allocation of LCS functional entities to network elements

UE

RAN

GMLC

3G-MSC

Client

Location client functions

LCF

X

X

X

U-LCF

Internal

ffs

X

Client handling functions

LCCTF

X

LCCF

X

LCAF

X

LCZTF

X

System handling functions

LMMF

?

LSCF

X

U-LSCF

X

LSBF

X

X

LSOF

X

X

X

X

Subscriber handling functions

LSAF

X

LSPF

X

Positioning functions

PRCF

X

PCF

X

X

PSMF

X

X

PRRM

X

UE

RAN

GMLC

3G-MSC

Client

Figure 6.2: Generic LCS Logical Architecture

6.3 Functional description of LCS per network element

6.3.1 Access Network

The Access Network is involved in the handling of various positioning procedures.

Specific UTRAN functionality is specified in each of the positioning procedures sections in the UTRAN Stage 2, TS 25.305.

6.3.2 LCS Clients and LCS applications

There are two classes of LCS Application – Internal applications and External applications. Internal applications represent entities internal to the UMTS that make use of location information for the (improved) operation of the network. External applications represent entities (such as Commercial or Emergency services) that make use of location information for operations external to the mobile communications network. The LCS Applications interface to the LCS entities through their Location Client functions (LCF).

The LCS Client and LCS applications are outside the scope of the present document.

6.3.3 Gateway Mobile Location Center, GMLC

The Gateway Mobile Location Center (GMLC) contains functionality required to support LCS. In one PLMN, there may be more than one GMLC.

The GMLC is the first node an external LCS client accesses in a GSM PLMN (i.e. the Le reference point is supported by the GMLC). The GMLC may request routing information from the HLR via the Lh interface. After performing registration authorization, it sends positioning requests to and receives final location estimates from the 3G-VMSC via the Lg interface.

6.3.4 Serving RNC, UTRAN case

The Serving RNC (SRNC) is a network element of UTRAN and contains functionality required to support LCS in PLMN. The LCS functionality of SRNC is given in [1].

6.3.5 (void)

6.3.6 LMU

The Location Measurement Unit LMU entity makes measurements (e.g. of radio signals) and communicates these measurements within the Access Network. The LMU is described in [1].

6.3.7 3G-MSC/VLR

The 3G-MSC/VLR contains functionality responsible for UE subscription authorization and managing call-related and non-call related positioning requests of LCS. The 3G-MSC is accessible to the GMLC via the Lg interface. The LCS functions of 3G-MSC are related to charging and billing, LCS co-ordination, location request, authorization and operation of the LCS services.

6.3.8 (void)

6.3.9 Home Location Register, HLR

The HLR contains LCS subscription data and routing information. The HLR is accessible from the GMLC via the Lh interface. For roaming UEs, HLR may be in a different PLMN than the current SRNC.

6.3.10 gsmSCF

The Lc interface supports CAMEL access to LCS and is applicable only in CAMEL [phase 3?]. The procedures and signaling associated with it are defined in TS 23.078 and TS 29.002, respectively.

6.4 Addressing the target UE for LCS purposes

It shall be possible to address and indicate the target UE using MSISDN addresses. This is FFS in later releases.