Current Location

Description

The term 'Current Location' is defined within the 3GPP Location Services (LCS) architecture. It refers specifically to the outcome of a location procedure: after a location attempt has been successfully completed, the resulting location estimate and the time at which it was obtained are collectively called the 'current location' at that point in time. This definition distinguishes the current location from other location concepts, such as the 'last known location' or a 'deferred location' report. The current location is the most up-to-date position available, and it is typically delivered to a requesting LCS client in response to a location request.

The LCS architecture in 3GPP involves several key components. The Gateway Mobile Location Centre (GMLC) is the first node that an external LCS client contacts to request location information. The GMLC authenticates the client, checks privacy constraints, and then forwards the request to the core network. Within the core network, the location request is handled by a Mobile Location Centre (MLC) function, which may be integrated with the Mobility Management Entity (MME) in LTE, the Serving GPRS Support Node (SGSN) in UMTS/GPRS, or the Access and Mobility Management Function (AMF) in 5G. The MLC coordinates with the Radio Access Network (RAN) to perform positioning measurements and compute a location estimate. The positioning methods used can include cell ID, E-CID, OTDOA, UTDOA, GNSS, and in 5G, NR positioning methods such as DL-TDOA and UL-TDOA. Once the location estimate is calculated, it is combined with a timestamp to form the current location.

The current location is a critical input for a wide range of location-based services. Emergency services (e.g., E911 in the United States, E112 in Europe) rely on accurate current location to dispatch responders to the correct place. Commercial services such as navigation, fleet management, asset tracking, and location-based advertising also depend on timely and accurate current location data. In addition, lawful interception and network optimisation can use current location information. The 3GPP specifications define stringent requirements for accuracy, latency, and reliability, particularly for emergency calls, which are detailed in TS 23.271 (functional stage 2 description of LCS) and TS 23.273 (5G LCS).

Privacy and security are paramount in the handling of current location. The LCS architecture includes privacy mechanisms such as subscription-based privacy classes, UE-based privacy checks, and notification to the target UE when its location is requested. The current location is only provided to authorised LCS clients, and the target UE can restrict or deny location requests depending on its privacy settings. These privacy features are specified in TS 23.171 (LCS for the CS domain) and its successors, ensuring that the current location is used responsibly.

In terms of procedures, obtaining the current location typically involves a Location Request from the LCS client to the GMLC, followed by a Location Report back to the client. The MLC manages the positioning procedure, which may involve signalling with the UE or the RAN to collect measurements. The resulting location estimate is then packaged with a timestamp and other parameters (such as accuracy and velocity) and returned as the current location. The entire procedure is designed to be efficient, scalable, and capable of supporting high volumes of location requests. In 5G, the LCS architecture has been enhanced to support new positioning methods with higher accuracy and lower latency, enabling new use cases such as industrial IoT and autonomous vehicles.

The current location concept has evolved over releases, from the early circuit-switched location services in R99 to the advanced 5G location services in Rel-17 and beyond. Its definition has remained essentially unchanged, which underscores its fundamental nature. However, the methods by which the current location is obtained and the accuracy achieved have improved dramatically. For instance, in R99, location was primarily based on cell ID, whereas today, 5G networks can provide sub-meter accuracy using NR positioning. This evolution reflects the growing importance of location in mobile networks.

In summary, the current location is the most recent successfully determined position of a UE, comprising a location estimate and a timestamp. It is the output of the LCS architecture and serves as the basis for emergency, commercial, and regulatory location-based services. The term is defined in multiple 3GPP specifications, including TS 23.171, TS 23.271, TS 23.273, and TS 23.700, and it remains a cornerstone of location services in all generations of 3GPP networks.

Purpose & Motivation

The concept of current location exists to provide a standardised, unambiguous way to refer to the most recent location information of a mobile device. In the early days of mobile networks, location was only known at the cell level and was primarily used for routing calls and managing mobility. With the advent of location-based services, there was a need for a precise definition of what constitutes a 'location' and how recently it was obtained. The term 'current location' was introduced to distinguish it from historical or predicted location data. It ensures that when an LCS client requests a location, the response clearly indicates the time at which the location was valid, allowing the client to assess the freshness of the data.

The current location definition solves several problems. First, it provides temporal context: by including a timestamp, it allows applications to determine whether the location is sufficiently recent for their needs. Second, it establishes a clear success criterion: only after a successful location attempt can a location estimate be called the current location. This prevents confusion with cached or failed location attempts. Third, it supports regulatory requirements for emergency calls, where the most accurate and current location is essential for public safety. The 3GPP LCS specifications have evolved to meet increasingly stringent accuracy and latency requirements, but the fundamental definition of current location has remained stable, proving its robustness and utility.

Historically, the need for current location became acute with the rise of E911 mandates in the late 1990s, which required mobile operators to provide accurate location for emergency calls. This drove the development of the LCS architecture and the definition of current location in R99. Since then, the scope has expanded to include commercial location services, and the definition has been carried forward into every subsequent release, including 5G. The current location concept is thus a foundational element of 3GPP location services, enabling a wide ecosystem of applications while ensuring privacy and security.