RTT Positioning Field Performance

The performance of cellular-positioning methods is characterized in terms of availability, response time, and accuracy. This paper discusses the measured field performance of Ericsson's round-trip time (RTT) positioning method in terms of the aforementioned parameters. The results are based on more than 1200 position fixes performed in a large commercial wideband code-division multiple-access (WCDMA) network. More than 100 surveyed test points were used, these being located in indoor, urban, suburban, and rural radio environments. Overviews of the RTT positioning algorithm, the test points, the test equipment, and the measurement procedures are given first. Then, this paper presents measurement geometries (for example, in soft handover), as well as the achieved performance in each radio environment. The radial distance accuracy was found to be excellent, despite the fact that propagation conditions were difficult with many open water surfaces. A bias of less than 5 m at the 50% point of the cumulative distribution function and a 95% error just above 150 m were obtained, averaged over all radio environments.