Cellular network positioning technologies use and combine a variety of methods to obtain accurate location fixes. These technologies can be classified in two broad categories:
- RAT-Dependent positioning technologies
- RAT-Independent positioning technologies
RAT Dependent positioning technologies use the cellular network radio signal to obtain the positioning measurements. These measurements can be based on the timing of the signal (e.g. DL-TDOA or Multi-RTT), on the power of the signal (e.g. ECID) or based on the angle of arrival / departure of the signal (e.g. DL-AoD).
A-GNSS positioning uses satellite systems (e.g. GPS or Galileo) for the location calculation. It is a type of RAT-Independent positioning technology and probably the most famous positioning method.
Brief history of cellular network positioning technologies
Support for A-GPS based positioning was added during the 2nd generation cellular networks. A-GPS takes advantage of the US satellite system. A-GPS is used to reduce the satellite acquisition time, which for standalone GPS can take a few minutes. The cellular network sends satellite assistance data and the acquisition reduces from minutes to just a few seconds.
In later releases, the denomination changed from A-GPS to A-GNSS to include as well other global satellite systems, such as Glonass, Galileo and Beidou.
The 2nd generation cellular networks also introduced the first network-based positioning technologies. GSM, for instance, defined Observed Time Difference (OTD), a hyperbolic localization system. OTD is based in the same localization principle as LORAN-C, a maritime navigation system used from the World War II until the early 2000s.
Up until LTE, the type of cellular network positioning technologies remained more or less constant: a combination of A-GNSS and ToA (Time of Arrival) and TDoA (Time Difference of Arrival) network techniques. The positioning accuracy increased naturally with technology, but the fundamental principles remained the same.
In the late 2000s / early 2010s, the FCC of the US published the wireless E911 positioning requirements. These requirements include not only outdoor but indoor positioning requirements as well.
Indoor environments pose an additional challenge for positioning technologies. The GNSS signal does not easily penetrate indoors, due to the low reception powers. On the other hand, RAT dependent technologies also suffer indoors, due among other reasons to the multipath conditions.
This resulted in the introduction of other RAT independent technologies, like Wi-Fi, Bluetooth and sensor-based positioning.
5G came with multiple new positioning use cases and requirements. Autonomous driving, automatic drone control, patient tracking in or outside hospital, traffic management, industry 2.0, ride sharing apps, etc.
These new demanding applications raised the need for more advanced positioning technologies. High accuracy GNSS enhancements, such as RTK and PPP promise centimeter level positioning accuracy. 5G has also defined a set of brand new RAT-dependent technologies, including new angle-based positioning methods that take advantage of 5G’s massive MIMO and beamforming capabilities.
These new technologies are meant to be the future of cellular network positioning.