The E-UTRAN is layered into a Radio Network Layer (RNL) and a Transport Network Layer (TNL). The E-UTRAN architecture, i.e. the E-UTRAN logical nodes and interfaces between them, are defined as part of the Radio Network Layer.
The overall architecture for UE positioning is described in TS 36.305
. The E-UTRAN network based positioning architecture consists of a set of LMUs (either standalone or eNB-integrated LMUs as described in TS 36.305
) contained in the E-UTRAN connected to the E-SMLC in the EPC through the SLm.
This subclause specifies only the architecture of the SLm interface, and shall not constrain the network architecture of either core or radio access networks.
The SLm interface is specified at the boundary between the LMUs and the E-SMLC. Figure 1 depicts the logical division of the SLm interface. From the SLm perspective, the E-UTRAN access point is an LMU, and the EPC access point is the E-SMLC.
The E-UTRAN may thus have several SLm access points towards the EPC. As a minimum, each SLm access point (in E-UTRAN or EPC) shall independently fulfil the requirements of the relevant SLm specifications (36.x1x series - see clause 7
SLm is a logical interface.
There is only one SLm logical interface between an LMU and a given E-SMLC. However, an LMU can be connected to multiple E-SMLCs using different logical SLm interfaces.
The general principles for the specification of the SLm interface are as follows:
the SLm interface should be open;
the SLm interface shall support the exchange of signalling information between the LMU and E-SMLC;
from a logical standpoint, the SLm is a point-to-point interface between an LMU within the E-UTRAN and an E-SMLC in the EPC. A point-to-point logical interface should be feasible even in the absence of a physical direct connection between the LMU and E-SMLC.
The SLm interface specification shall facilitate the following:
inter-connection of E-SMLCs with LMUs supplied by different manufacturers;
separation of SLm interface Radio Network functionality and Transport Network functionality to facilitate introduction of future technology.
The SLm interface supports:
procedures to establish, maintain and release connections between the E-SMLC and LMUs;
the separation of each LMU on the protocol level for specific signalling management;
location services by transferring location requests from the E-SMLC to LMUs, and UL RTOA measurements from LMUs to E-SMLC;