Global Positioning System

Description

Within 3GPP specifications, GPS is referenced as an external positioning system that can be used by User Equipment (UE) and the network to determine the geographical location of a mobile device. The 3GPP architecture integrates GPS as one of several positioning methods, often categorized under UE-based or UE-assisted modes. In UE-based positioning, the UE contains a GPS receiver, calculates its own position using signals from GPS satellites, and may report it to the network. In UE-assisted positioning, the UE measures GPS signal parameters (like pseudoranges) and sends these raw measurements to the network's positioning node (e.g., E-SMLC in LTE, LMF in 5GC), which then computes the location. 3GPP defines control plane and user plane protocols (e.g., LPP, SUPL) to facilitate the exchange of GPS assistance data (like ephemeris, almanac) from the network to the UE, which significantly improves time-to-first-fix (TTFF) and accuracy. The network can request a location estimate using GPS either standalone or in combination with other methods (A-GNSS). Specifications detail performance requirements (e.g., in TS 25.171, 36.171), testing procedures, and how GPS measurements are incorporated into broader positioning architectures like Control Plane LCS or OMA SUPL.

Purpose & Motivation

GPS is incorporated into 3GPP standards to provide a highly accurate, widely available method for mobile device positioning, which is a fundamental requirement for regulatory services (like emergency call location), commercial location-based services (LBS), and network optimization functions. Prior to the integration of GPS, cellular positioning relied primarily on network-based methods like Cell-ID, timing advance, or OTDOA, which offered limited accuracy, especially in rural or suburban areas. The inclusion of GPS (and later other GNSS constellations) addressed the need for meter-level accuracy demanded by applications such as turn-by-turn navigation, asset tracking, and enhanced 911 (E911) mandates. 3GPP's work standardized how the cellular network can assist the GPS receiver in the UE (creating A-GPS) to overcome limitations like slow standalone GPS startup times and poor indoor sensitivity, thereby making reliable, fast, and accurate positioning a viable service for mass-market devices. This integration was driven by both regulatory pressures for emergency services and the commercial potential of LBS.