12.713GPPLocation Services (LCS)Location services managementTS
The following GSM network entities are the subjects to be managed in LCS.
5.1 Location Measurement Unit (LMU)
An LMU makes radio measurements to support one or more positioning methods. These measurements fall into one of two categories:
a) Location measurements specific to one MS used to compute the location of this MS.
b) Assistance measurements specific to all MSs in a certain geographic area.
All location and assistance measurements obtained by an LMU are supplied to a particular SMLC associated with the LMU. Instructions concerning the timing, the nature and any periodicity of these measurements are either provided by the SMLC or are pre-administered in the LMU.
Two types of LMU are defined:
Type A LMU: accessed over the GSM radio interface (Um interface).
Type B LMU: accessed over the Abis interface.
The LMU Type A is accessed exclusively over the GSM radio interface (Um interface). There is no wired connection to any other network element. The LMU Type A has a serving BTS and BSC that provide signalling access to a controlling SMLC. With an NSS based SMLC, a Type A LMU also has a serving MSC and VLR and a subscription profile in an HLR. The Type A LMU always has a unique IMSI and supports all radio resource and mobility management functions of the GSM air interface that are necessary to support signalling using an SDCCH to the SMLC. The Type A LMU supports those connection management functions necessary to support LCS signalling transactions with the SMLC and may support certain call control functions to support signalling to an SMLC using a circuit switched data connection .
5.2 Serving Mobile Location Centre (SMLC)
The Serving Mobile Location Centre (SMLC) contains functionality required to support LCS. In one PLMN, there may be more than one SMLC.
The SMLC manages the overall co-ordination and scheduling of resources required for performing positioning of an MS. It may calculate the final location estimate and accuracy.
Two types of SMLC are possible:
NSS based SMLC: supports the Ls interface.
BSS based SMLC: supports the Lb interface.
An NSS based SMLC supports positioning of a target MS via signalling on the Ls interface to the visited MSC. A BSS based SMLC supports positioning via signalling on the Lb interface to the BSC serving the target MS. Both types of SMLC may support the Lp interface to enable access to information and resources owned by another SMLC.
The SMLC controls a number of LMUs for the purpose of obtaining radio interface measurements to locate or help locate MS subscribers in the area that it serves. The SMLC is administered with the capabilities and types of measurement produced by each of its LMUs. Signalling between an NSS based SMLC and LMU is transferred via the MSC serving the LMU using the Ls interface and either the Um interface for a Type A LMU or the Abis interface for a Type B LMU. Signalling between a BSS based SMLC and LMU is transferred via the BSC that serves or controls the LMU using the Lb interface and either the Um interface for the Type A LMU or the Abis interface for the Type B LMU.
5.3 Gateway Mobile Location Centre (GMLC)
The Gateway Mobile Location Centre (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 authorisation, it sends positioning requests to and receives final location estimates from the VMSC via the Lg interface.
The SMLC and GMLC functionality may be combined in the same physical node, combined in existing physical nodes, or reside in different nodes.