3 User location in a mobile network
3.4 Location Services (LCS) - Network Architecture
To enable the described location techniques, the network needs to be modified. The next sections will briefly discuss the functional description of the location procedure and the network architecture for the GSM and UMTS networks.
3.4.1 LCS services - Functional Description
The LCS model identifies two parties, an LCS client and an LCS server. The LCS client contains a client handling component, which can consist of a number of clients. The
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clients use the Location Client Functions (LCFs) to interface with the LCS server. The LCS server consists of four components, each component contains a number of functions. The figure shows how the components and functions interrelate. For each component, a brief description of the functions is given below.
•
•
•
•
Subscriber handling component
Location Subscriber Authorisation Function (LSAF):
authorise location request, verify subscription Location Subscriber Privacy Function (LSPF):
privacy related authorisation System handling component
LMU Mobility Management Function (LMMF):
maintain LMU status, register LMUs in SMLC, LMMF applies only to type A LMUs
Location System Control Function (LSCF):
coordinate location requests, allocate network resources, perform call set-up if necessary Location System Billing Function (LSBF): charging and billing for LCS, collect charging information Location Client Control Transformation Funstion (LCCTF): conversion of location estimates into a specified format
Location System Operations Function (LSOF):
provide data, positioning capabilities, client data, subscription data, validation, fault and performance management
Location System Broadcast Function (LSBcF):
broadcast capability for E-OTD or A-GPS Client handling component
Location Client Control Function (LCCF): manage interface towards LCF, request verification and
LCS Client
Client handling component
1 LCfl1 LCF,II LCF,I ... _.1 Lc~1
LocatJon Service Request Location Service Respons.
ResoLWces:
GSM protocols
- +
LCS Server
Figure 26: LCS capability authorisation through LCAF, mobility management for LCS, check QoS of result, flow control of requests, generate charging and billing data for LSBF
Location Client Authorisation Function (LCAF): provide access and subscription authorisation to a client
Positioning component
Positioning Radio Control Function (PRCF): co-ordination and scheduling of positioning resources (e.g. PSMF, PCF), determines the positioning method based on QoS requirement and MS capabilities
Position Radio Assistance Function (PRAF): support for PRCF for radio co-ordination, induce postioning signals from MS or network
Position Calculation Function (PCF): calculate MS' location
Positioning Signal Measurement Function (PSMF): gather up- and downlink radio signal measurements
3.4.2 LCS in GSM
The Generic GSM LCS logical architecture is displayed in Figure 27.
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CBC-SMLC
o ~
CBC t - - - + - - - - ;MS
Type
SMLC Lp
HLR Ls
Lg
Lc
Figure 27 Generic G8M LC8 logical architecture
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The Gateway MLC (GMLC) will be contacted by a LCS client through the Le interface.
The GMLC may request routing information from the HLR. The positioning request is sent to the MSC. The Serving MLC (SMLC) co-ordinates and schedules all resources needed to perform the positioning of a single mobile. The SMLC can be BSS-based (Base Station System), or NSS-based (Network Station System). The first approach means that the SMLC will signal the target MS via the BSC to which it is connected, using the Lb
interface. A NSS-based SMLC will support positioning of the MS via signalling over the Ls interface to the visited MSC. Both types of SMLC can access other SMLCs via the Lp interface. The SMLC contains all information about the capabilities of the LMUs in the serving area.
A LMU performs radio measurements for the positioning method, either to locate a specific MS or to help locate other MSs in a certain area. There are two types of LMUs. A Type A LMU can be accessed over the GSM air interface (Um) only. This is basically a MS with a fixed location. A Type B LMU has a wired connection to the network and can be accessed using the Abis interface. Type B LMUs can be combined with a BTS. For more information about the LCS architecture for GSM, see [14]. The appendix shows an allocation table for LCS functionality in the GSM network.
3.4.3 LCS in UMTS (R'99)
The UMTS LCS architecture is shown in the next figure.
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HLR
Lc
gsmSCF
Figure 28 General UMTS LCS Architecture
The UMTS LCS architecture is not much different from the GSM LCS architecture. The distinct differences are described below.
The Serving RNC (SRNC) co-ordinates and schedules the resources needed to localise an MS. It will also calculate the final location and determine its accuracy. The SRNC controls a number of LMUs to obtain the radio measurements. The SRNC knows the capabilities of the LMUs it controls. As can be seen in the architecture, the SRNC has SMLC functionality as described in the previous section. The associated LMUs (Type B) are located at the Node Bs. The stand-alone LMUs (Type A) work autonomously and have to be accessed over the UTRAN air interface (Uu). The SGSN together with 3G-MSCNLR handle user equipment (UE) subscription authorisation and manage all positioning requests.
For UMTS the LCS Client is divided in an internal and external LCF. The external LCF provides a logical interface between the LCS server and the LCS client. The internal LCF provides an interface between UTRAN location applications and system handling entities in the RNC. The LSCF has also been distributed. There is a LSCF in the core network (MSC) and in the access network (RNC). The control function in the access network co-ordinates all call- and non-call-related location requests. The access network function will therefore shield the core network function for all details involved with the positioning method. The access network control function can therefore be used with multiple positioning methods. For more information about the LCS for UMTS, see [15]. The appendix shows the allocation tables of LCS functions in the UMTS network and in the UTRAN
3.5 Summary
This chapter has looked into three location methods and the architecture that is needed to support the location measurement techniques. The methods differ in complexity, accuracy and the implications for the existing network. It can be concluded that Cell-ID based techniques can be implemented in the existing GSM network. The E-OTD and A-GPS systems require impressive changes to both the network as the mobile handset. It is therefore expected that the implementation of these systems will be combined with the installation of the UMTS network.
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