UTRAN Location System Control Function in SAS

Description

The UTRAN Location System Control Function in SAS (U-LSCFS) is a variant of the standard U-LSCF, where the 'SAS' denotes a Standalone SMLC (Serving Mobile Location Centre) architecture. While the standard U-LSCF is typically integrated as a software function within the Radio Network Controller (RNC), the U-LSCFS is implemented as a physically or logically separate network node. This standalone entity performs all the core control functions of location service management but does so from a dedicated platform. It maintains the same logical interfaces and procedures as defined for the U-LSCF, primarily the Iupc interface to the Core Network and the necessary signaling links to the UTRAN radio nodes (Node Bs and LMUs).

Operationally, the U-LSCFS works by receiving location service requests from the Core Network's GMLC via the Iupc interface. Upon receiving a request, it initiates a positioning session. It sends control commands to the relevant RNC or directly to Node Bs (depending on the exact implementation and interface support) to orchestrate the required radio measurements. For methods like U-TDOA or enhanced OTDOA, it also communicates with standalone Location Measurement Units (LMUs) deployed in the network. The U-LSCFS collects the measurement reports, performs the position calculation using the appropriate algorithm, and then returns the calculated location estimate to the requesting GMLC. Its standalone nature means it can serve multiple RNCs or even a pool of RNCs, centralizing the positioning intelligence for a larger area of the network.

The architectural separation offered by the U-LSCFS provides significant deployment flexibility. It allows network operators to decouple the evolution of location services from the lifecycle of their RNC hardware. New positioning features or performance enhancements can be introduced by upgrading the standalone SAS node without requiring costly and complex upgrades to every RNC in the network. This model also facilitates more straightforward capacity scaling, as additional SAS nodes can be deployed independently of the RAN infrastructure. Furthermore, it can simplify network management and operation by creating a centralized point for monitoring and troubleshooting all location service activities across the UTRAN footprint.

Purpose & Motivation

The U-LSCFS was developed to address deployment and scalability limitations associated with the integrated U-LSCF model. While integrating the control function within the RNC is efficient for a tightly coupled system, it can constrain an operator's ability to rapidly deploy advanced location services or scale them independently of the RAN capacity. The standalone SAS architecture, and thus the U-LSCFS, was motivated by the need for operational flexibility and the desire to offer location-based services as a more modular, potentially outsourced, network capability.

This approach solves problems related to vendor lock-in and heterogeneous networks. An operator with RNCs from multiple vendors could deploy a single, vendor-neutral U-LSCFS node to provide a uniform location service platform across the entire network. It also future-proofs the network for the introduction of more computationally intensive positioning techniques, which can be hosted on dedicated server hardware in the SAS rather than relying on RNC processing resources. The creation of the U-LSCFS reflects a strategic shift towards service-layer abstraction, allowing location services to evolve as an application separate from the underlying radio access technology, a concept that gains further importance with the transition to 4G and 5G networks.

Key Features

• Implements U-LSCF functionality in a standalone network node (Standalone SMLC)
• Provides centralized location service control for a pool of multiple RNCs
• Decouples positioning feature evolution from RNC hardware lifecycle
• Supports all standard UTRAN positioning methods (Cell-ID, OTDOA, U-TDOA)
• Utilizes the standard Iupc interface for communication with the Core Network GMLC
• Enables flexible, scalable deployment and easier network management

Evolution Across Releases

Defining Specifications