Mobile Based positioning

Description

Mobile Based positioning is a category of location determination techniques in 3GPP where the user equipment (UE) performs both the signal measurements and the computation of its own location estimate. The network provides assistance data that is useful or essential for these functions, but the final position calculation occurs within the UE. This approach is termed 'mobile based' because the mobile device is responsible for the core positioning computation, in contrast to Mobile Assisted positioning where the network computes the location. The assistance data may include information such as satellite ephemeris, reference time, reference signal configurations, or base station locations, which help the UE acquire signals and compute its position accurately.

The architecture for Mobile Based positioning involves the UE acting as the primary positioning engine. The network, typically via a location server (e.g., SMLC in GSM/UMTS, E-SMLC in LTE, LMF in 5G), provides assistance data to the UE through control plane or user plane protocols. The UE then uses this data along with its own measurements to calculate its location. For example, in Assisted GPS (A-GPS) with mobile-based mode, the UE receives GPS ephemeris and almanac data from the network, measures pseudoranges to GPS satellites, and then computes its own position using the assistance data. Similarly, in OTDOA-based mobile-based positioning, the UE measures reference signal time differences and uses assistance data about cell locations to compute its position. The key distinction is that the UE has the computational capability to perform the location calculation.

Mobile Based positioning relies on the UE having sufficient processing power and battery capacity to perform the calculations. It also requires that the UE receives the necessary assistance data from the network, which may be delivered via broadcast or point-to-point signaling. The assistance data can be essential (without which the UE cannot compute position) or useful (improving accuracy or speed). For instance, in GNSS positioning, satellite ephemeris data is essential for computing position from pseudoranges. In cellular positioning, assistance data about neighboring cells' timing and location is essential for OTDOA. The UE may also use its own sensors (e.g., accelerometer, gyroscope) to enhance positioning, but that is outside the scope of 3GPP definitions.

Mobile Based positioning offers several advantages. It reduces the signaling load on the network because the UE does not need to send raw measurements to the network for every location request; only assistance data is needed. It also allows for faster location updates and can operate in a more autonomous manner, which is beneficial for applications requiring frequent location updates. Additionally, it can enhance privacy because the UE can compute its location without revealing it to the network, unless it chooses to share. However, it requires more capable UEs and may consume more battery due to the computation. It also depends on the availability and accuracy of assistance data.

In 3GPP standards, Mobile Based positioning has evolved from GSM (R99) through UMTS, LTE, and 5G NR. The term itself has remained consistent in definition, though the specific positioning methods and assistance data types have expanded. For example, in 5G NR, new positioning methods like NR DL-TDOA and NR multi-cell RTT can be operated in mobile-based mode, with the UE computing its location using assistance data from the LMF. The core concept remains: the UE measures and computes, the network assists. This division of labor is fundamental to many commercial location-based services and enables a balance between network control and UE autonomy.

Purpose & Motivation

Mobile Based positioning was created to empower UEs to determine their own location, reducing dependency on the network for computation. In early cellular networks (R99), UEs had limited processing capabilities, so Mobile Assisted positioning was the norm. However, as UEs became more powerful, it became feasible to offload the computation to the device, which offers benefits such as reduced network signaling, faster location updates, and enhanced privacy. This approach solves the problem of network congestion and latency associated with sending measurements to the network for every location request.

Another motivation is to enable location services in scenarios where network connectivity is intermittent or where the network may not support location computation. For example, a UE with GNSS capability can compute its own position without network assistance once it has ephemeris data, which can be stored for hours. This is crucial for emergency services and navigation applications. Mobile Based positioning also allows for continuous location tracking without burdening the network, as the UE can compute positions locally.

Furthermore, Mobile Based positioning provides a fallback when network-based positioning is unavailable or unreliable. It gives UEs the ability to determine their location using assistance data that may be broadcast, reducing the need for dedicated signaling. This flexibility is important for supporting diverse applications and ensuring robust location services across different network conditions.