Target Mobile Station

Description

In 3GPP location services (LCS), the Target MS is the mobile station (user equipment) that is the subject of a positioning request. The term is used primarily in specifications related to location services, such as 23.271 (Functional stage 2 description of Location Services) and 43.059 (Functional stage 2 description of Location Services in GERAN). The Target MS is the entity whose geographical position is to be determined, and it can be a mobile device used by a subscriber, an emergency caller, or any device that needs to be located.

The positioning of a Target MS involves a series of interactions between the network and the device. The network may initiate positioning either from a request by an external LCS client (e.g., an emergency service, a location-based application) or from an internal request within the network (e.g., for mobility management). The Target MS may be in idle mode or connected mode. Depending on the requested quality of service (accuracy, response time), different positioning methods may be used, such as cell ID, OTDOA, E-CID, A-GNSS, or hybrid methods. The Target MS may need to perform measurements and report them to the network, or it may be positioned entirely by network-based measurements.

The Target MS is identified by a target identity, which could be an IMSI, MSISDN, or other identifier. The location service architecture includes entities such as the Gateway Mobile Location Centre (GMLC), the Serving Mobile Location Centre (SMLC), and the Location Retrieval Function (LRF). The GMLC is the first point of contact for external LCS clients, and it requests the location of the Target MS from the core network. The core network then coordinates with the radio access network to perform the necessary measurements and calculations.

In emergency situations, the Target MS is typically the caller, and its location is used to dispatch emergency services. In commercial applications, the Target MS could be a vehicle, a person, or any asset being tracked. The privacy of the Target MS is a key concern, and location services are subject to strict privacy regulations. The Target MS may need to grant consent for positioning, except in emergency cases.

The term 'Target MS' is used across different radio access technologies, including GERAN, UTRAN, and E-UTRAN. In 5G, the equivalent term is often 'Target UE' (User Equipment), but the concept remains the same. The evolution of the term reflects the shift from circuit-switched to packet-switched and the increasing importance of location-based services.

Purpose & Motivation

The Target MS concept exists to provide a clear and unambiguous reference to the device being positioned in location services. Before its standardization, location systems might have used various terms, leading to confusion in specifications and implementations. The Target MS defines the entity whose location is sought, enabling consistent procedures across different network elements and technologies. It solves the problem of identifying which device is the subject of a location request, especially in multi-device or multi-subscriber scenarios.

Historically, location services were initially developed for emergency call positioning (E-911 in the US, E-112 in Europe). The Target MS was the emergency caller, and accurate location was critical for dispatching help. As commercial location-based services emerged, the need for a standardized way to refer to the positioned device became more pressing. The Target MS concept allowed network operators to offer location services to third-party applications while maintaining privacy and security.

The term has evolved with technology. In early releases (R99), the definition was simply 'the MS being positioned'. Later releases refined the wording to 'Mobile Station being positioned', but the core meaning remained. In 5G, the term is often replaced by 'Target UE', reflecting the broader capabilities of user equipment beyond mobile stations. The Target MS remains a foundational concept in 3GPP location services.