Relativistic Positioning Systems: current status

TL;DR

This paper reviews the current state of relativistic positioning systems, which use four clocks broadcasting proper time signals to determine positions without external references or synchronization.

Contribution

It provides an overview of the theoretical development and current understanding of relativistic positioning systems and auto-located configurations.

Findings

Current theory of relativistic positioning systems is well-developed.

Auto-located systems enable position determination without external references.

No synchronization needed in auto-located systems.

Abstract

A {\em relativistic positioning system} consists in a set of four clocks broadcasting their respective proper time by means of light signals. Among them, the more important ones are the {\em auto-located positioning systems,} in which every clock broadcasts not only its proper time but also the proper times that it receives from the other three. At this level, no reference to any exterior system (the Earth surface, for example) and no synchronization are needed. The current status of the theory of relativistic positioning systems is sketched.