Location Identifier

Description

The Location Identifier is a concept in 3GPP location services that provides information about the current location of a UE in network-specific terms. Unlike the Location Estimate, which gives geographic coordinates, the Location Identifier describes the location using network identifiers such as the global cell ID in cellular networks, line-id in fixed broadband networks, or the MAC address of a WLAN access point. It may also be represented as a Location Object as defined by IETF RFC 4119. This term is used in specifications like 23.167 and 23.271.

The Location Identifier is particularly useful when the exact geographic coordinates are not required or not available, but the network needs to know the serving cell or access point for routing, policy, or charging purposes. For example, in emergency calls, the Location Identifier can help route the call to the correct Public Safety Answering Point (PSAP) based on the cell ID. In commercial services, it can be used to provide location-based content or advertisements without revealing precise geographic location.

The Location Identifier is generated by the network elements that are aware of the UE's connection point. In cellular networks, the Radio Access Network (RAN) provides the global cell ID (e.g., E-UTRAN Cell Global Identifier, ECGI). In WLAN interworking scenarios, the WLAN Access Point's MAC address can be used. The Location Identifier is then conveyed to the Location Services (LCS) client or other network functions via standardized interfaces.

One of the key advantages of the Location Identifier is its simplicity and availability. It does not require complex positioning calculations and can be obtained quickly from existing network signaling. However, it provides only coarse location information, which may not be sufficient for applications requiring high accuracy. Therefore, it is often used in conjunction with or as a fallback to the Location Estimate.

The term was introduced in Rel-7 to support location services in heterogeneous networks, including fixed broadband and WLAN access. It has been maintained in subsequent releases without significant changes, reflecting its stable role in the location services architecture. In 5G, similar concepts exist, such as the Cell Global Identifier (CGI) and the NR Cell Global Identifier (NCGI), which serve as Location Identifiers.

Purpose & Motivation

The Location Identifier exists to provide a network-centric way to identify a UE's location without relying on geographic coordinates. It solves the problem of locating a device when only network attachment information is available, such as in fixed broadband or WLAN networks where geographic positioning may not be supported. It enables location-based services to function in a wide range of access technologies.

Before the introduction of the Location Identifier, location services were primarily focused on cellular networks and geographic coordinates. However, with the convergence of fixed and mobile networks, there was a need to identify the location of a UE in network terms, such as the line-id in DSL or the MAC address of a WLAN AP. This allows service providers to offer location-based services across different access types.

The Location Identifier also supports regulatory requirements, such as emergency call routing, by providing the necessary information to route calls to the appropriate PSAP. Its simplicity and wide applicability make it a valuable complement to the Location Estimate.