Mobile Originated Location Request

Description

Mobile Originated Location Request (MO-LR) is a procedure within the 3GPP Location Services (LCS) architecture that enables a User Equipment (UE) to act as a LCS Client, initiating a request to determine its own location or the location of another specified target UE. The process involves signaling between the UE, the serving core network, and the Location Management Function (LMF) in 5G or the Evolved Serving Mobile Location Centre (E-SMLC) in LTE. The UE sends a location request via a dedicated LCS protocol message over the control plane.

Upon receiving an MO-LR request, the network authenticates and authorizes the requesting UE based on subscriber profiles. For a self-location request, the network then invokes the appropriate positioning method. This could be network-based (e.g., Observed Time Difference of Arrival - OTDOA in LTE, Downlink Time Difference of Arrival - DL-TDOA in NR), UE-based (using assistance data like GPS/GNSS), or hybrid methods. The serving node (MME/AMF) coordinates with the positioning server (E-SMLC/LMF) which calculates the location estimate. The resulting position (latitude, longitude, accuracy) is then delivered back to the requesting UE in a location response message.

If the request is for another target UE (subject to privacy verification), the network performs a location request towards that target (akin to a Mobile Terminated Location Request - MT-LR), obtains the location, and returns it to the originating UE. Key architectural components include the LCS Client in the UE, the LCS protocol in the NAS layer, the core network control node (MSC, SGSN, MME, AMF), the positioning server (SMLC, E-SMLC, LMF), and the radio access network which provides measurement data (e.g., PRS measurements for OTDOA).

The role of MO-LR in the network is to support user-centric location-based services (LBS). It empowers the end-user to actively retrieve location information, differentiating it from network-initiated or emergency location services. It is a fundamental enabler for commercial applications, providing the standardized control-plane mechanism for devices to obtain their own coordinates for use in mapping, social networking, asset tracking, and augmented reality applications. The procedure includes privacy safeguards, requiring user consent and authorization checks.

Purpose & Motivation

MO-LR was developed to standardize a method for mobile devices to actively request location information from the network, enabling a wide range of user-driven location-based services. Prior to standardized LCS, location capabilities were proprietary or limited to network-initiated services (e.g., for lawful intercept). The creation of MO-LR addressed the growing market demand for applications like turn-by-turn navigation, location-aware search, and person-to-person location sharing.

It solved the problem of providing a reliable, secure, and operator-controlled mechanism for devices to obtain accurate positioning. Without MO-LR, applications would rely solely on onboard GPS, which has limitations indoors, in urban canyons, and for devices without GPS hardware. MO-LR leverages network-based positioning methods (e.g., cell-ID, OTDOA) and assisted-GNSS (A-GNSS) to provide faster, more accurate, and more battery-efficient location fixes than standalone GPS.

The technology was motivated by the commercial potential of LBS and the need for interoperability across devices and networks. It provided a standardized API of sorts within the network signaling, allowing application developers to build services knowing that a consistent method to retrieve location existed. It also introduced necessary privacy controls, ensuring that a user's location could not be retrieved by another party without authorization, balancing service innovation with subscriber protection.