Analysis of High-Accuracy Satellite Messages for Road Applications

Future road applications will require positioning accuracy on the order of one or a few decimeters and a convergence time measured in seconds. A high-accuracy service (HAS) provided by the Global Navigation Satellite System becomes a key enabler to meet these requirements. In particular, the Galileo program has committed to provide a free HAS. This entails several design challenges; namely, to achieve the necessary performance for all users, high-accuracy messages must be optimally formatted, encoded, and broadcast. This article presents an overview of satellite-based HASs and evaluates different transmission schemes based on field and laboratory results, proposing some recommendations for the implementation of an HAS. The article concludes that satellite-based, high-accuracy messages, such as Galileo's, can provide fast convergence and sufficient accuracy worldwide, even in low-visibility environments.