Indoor positioning in LTE
Regulatory requirements on emergency call positioning have historically been based on horizontal accuracy for outdoor terminals. However, most emergency calls are made from wireless phones and from indoor locations. Therefore, the American FCC (Federal Communications Commission) launched new requirements in February of this year, to address indoor accuracy requirements in particular. 3GPP, the standardization organization behind LTE, is finalizing a study on how well LTE can meet the requirements in some considered scenarios, and what possible enhancements can be made in future LTE and WCDMA releases.
The study found that the existing positioning, based on Observed Time Difference of Arrival (OTDOA) in LTE does meet the FCC indoor user requirements for horizontal accuracy.
Location-based services and emergency call positioning drive the development of positioning in wireless networks. Global navigation satellite system (GNSS, for example GPS) -enabled terminals can determine outdoor positions within a few meters. A plethora of applications and services take advantage of such accurate positioning.
Positioning support in LTE was introduced in the second release, Rel. 9, in 2009, and improvements have been made in later releases. With today’s technology, the User Equipment (UE) position is determined based on a combination of cell identity, OTDOA and A-GNSS information from the UE. In in adequately deployed and synchronized networks, operators can retrieve position information for use by location-based services and good enough to meet regulatory emergency call positioning requirements.
Regulatory requirements for emergency call positioning have to date mainly been driven by the American FCC. Until recently, these were only formulated as horizontal positioning requirements. In February 2015, FCC tightened the requirements on operators:
- A 50 meter horizontal accuracy must be provided for 40, 50, 70, 80 % of emergency calls within 2, 3, 5, 6 years respectively.
- For vertical performance, operators should propose an accuracy metric within 3 years – to be approved by the commission – and comply with the metric within 6 years.
The now soon-to-finish 3GPP release 13 study item on indoor positioning enhancements has accomplished two things: established aligned baseline performance results and examined various enhancements. Scenarios with macro base stations only, and scenarios with 4 and 10 additional micro base stations per macro cell respectively have been studied.
In all cases, the baseline performance for horizontal accuracy is very promising:
- Indoor calls can be positioned with an accuracy of 50 m for 86 %, 93 % and 97 % of the calls in the macro, macro + 4 small cells and macro + 10 small cells per macro cell.
- Floor level vertical accuracy can also be achieved for close to all calls in buildings with dense indoor deployment of pico cells.
All results are summarized in the technical report 3GPP TR 37.857 "Study on Indoor Positioning Enhancements for UTRA and LTE", available from the 3GPP web site. We in Ericsson recently presented some of the results at the International Conference on Localization and GNSS (ICL-GNSS) conference, in the paper "Baseline Performance of LTE Positioning in 3GPP 3D MIMO Indoor User Scenarios".
Selected enhancements will be further investigated and considered for LTE and WCDMA standardization updates in a subsequent 3GPP work item.