Location Information Relay Function

Description

The Location Information Relay Function (LIRF) is a functional entity defined within the 3GPP architecture, specifically detailed in TS 25.305 for UTRAN (UMTS Terrestrial Radio Access Network). Its primary role is to act as a relay point for location-related signaling and data between the mobile device and the core network's location services infrastructure. It does not compute the location itself but is crucial for the transport of the necessary information, such as measurement reports or assistance data, required by positioning methods like Observed Time Difference Of Arrival (OTDOA) or Assisted GNSS (A-GNSS).

Architecturally, the LIRF is typically implemented within the Radio Network Controller (RNC) in a UMTS network. It interfaces with the UE over the Uu radio interface and with the core network's location server, often a Serving Mobile Location Centre (SMLC) or a Gateway Mobile Location Centre (GMLC), via the Iupc interface. The function handles protocol adaptation and message routing, ensuring that location requests from the network are conveyed to the UE and that the UE's positioning measurements or capabilities are reported back reliably.

In operation, when a location service is triggered (e.g., for an emergency call), the LIRF receives a location request from the core network. It then initiates the appropriate positioning procedures with the UE, which may involve sending assistance data to the UE to improve positioning speed and accuracy. The UE performs the required measurements (e.g., of satellite signals or neighboring cell timing) and sends a measurement report back through the LIRF. The LIRF forwards this raw data to the location server, where the actual position calculation is performed. This separation of relay and calculation functions allows for optimized network architecture and supports various positioning technologies.

The LIRF's role is integral to meeting regulatory requirements for emergency caller location and enabling commercial location-based services. By standardizing this relay function, 3GPP ensured interoperability between network equipment from different vendors and provided a consistent mechanism for supporting evolving positioning techniques across multiple 3GPP releases, from the initial UMTS specifications through to later enhancements.

Purpose & Motivation

The LIRF was created to address the need for a standardized, reliable mechanism to support location services (LCS) in 3GPP networks, particularly for UMTS. Prior to its specification, location services were less standardized, potentially leading to interoperability issues between network elements from different manufacturers. The LIRF provides a clear architectural point for relaying location-specific signaling, separating the transport of positioning data from its computation.

The primary problem it solves is enabling efficient communication between the UE, which contains the radio measurements, and the network-based location server, which has the computational resources and database information (like cell coordinates) to calculate a position. Without a dedicated relay function, this communication would need to be handled ad-hoc by other network entities, complicating protocol design and network management. The LIRF standardizes interfaces and procedures, ensuring that location requests can be served accurately and within the latency constraints required for services like E-911.

Its creation was motivated by the growing regulatory and commercial demand for mobile location services in the early 2000s. Regulators began mandating the ability to locate emergency callers, while operators sought to deploy services like navigation, friend-finder, and location-based advertising. The LIRF, as part of the broader 3GPP LCS architecture, provided the foundational framework to meet these demands in a scalable and future-proof manner, supporting both network-based and terminal-based positioning methods.

Key Features

• Relays location-specific signaling between UE and network location server
• Supports multiple positioning methods (e.g., OTDOA, A-GNSS) by transporting relevant measurement and assistance data
• Implemented typically within the Radio Network Controller (RNC) in UTRAN
• Utilizes standardized Iupc interface for communication with the core network location server
• Enables compliance with emergency services location requirements (e.g., E-112)
• Facilitates interoperability between vendor equipment by providing a standardized functional entity

Evolution Across Releases

Defining Specifications