Feature: Satellites


Getting the most out of correction


services with an agnostic receiver By Septentrio technical team


T


he demand for high- accuracy positioning is growing: we are increasingly seeing the need for this service not only in everyday


consumer items like smartphones, but in automation and robotics, too, and even lawn mowers. T is demand is driving developments in the Global Navigation Satellite System (GNSS) space, with new correction services and models appearing every day, off ering various degrees of accuracy and coverage, and diff erent delivery methods and business models. At present, the GNSS corrections


ecosystem is more like the “Wild West”, with many possibilities yet little standardisation, making it challenging for users, who need to select and use the most suitable service for their application. T e Agnostic Corrections Partner


Program has been created to serve as a bridge between the customer, the receiver and the correction services, allowing integrators to take advantage of reliable high-accuracy receivers in combination with the best suitable correction service. But, what is meant by “correction services” and how do they fi t into system design?


Correction services Satellite-governed positioning is inherently limited in accuracy due to errors caused by GNSS satellites. As GNSS signals travel toward the Earth, the atmosphere creates delays that result in errors, degrading accuracy to several meters. To compensate for these errors and achieve decimetre- or even centimetre-level accuracy, the receiver needs additional information, provided by a base station or a corrections service. T is is called “positioning augmentation”, or “augmented accuracy”. In addition to the widely-accepted real- time kinematic (RTK) centimetre-level positioning, there has been an expansion in the market of aff ordable precise point positioning (PPP)-RTK – aka state space representation (SSR) corrections – which provide continental coverage, sub-decimetre accuracy and a fast convergence rate, delivered over the Internet or a satellite. Traditionally, to get GNSS corrections,


users have connected to either a private network of RTK base stations, government networks or a correction service tied to their receiver manufacturer; see Figure 1. Today, new services are appearing, which are open to various receivers and off er new, innovative and more-aff ordable business models.


48 July/August 2024 www.electronicsworld.co.uk Unlike broadcasting (L band), correction


delivery over the Internet allows connection checks so that providers can keep track of service usage. T is is giving rise to pay-per- use service subscription models, similar to those in the mobile phone world. In some regions PPP-SSR services are off ered free of charge, such as CLAS, which is now operational in Japan, and the European High Accuracy Service. Inspired by the blockchain mining


economy, some companies have found a new approach to providing corrections by allowing users to set up correction base- stations at their home or offi ce. T is creates a community-powered, shared network, which has the potential of becoming highly dense.


Locking receiver to service? As the footprint of correction providers grows, there is an increase in the number of services that are not bound to the receiver, and the classical model of locking a receiver to a particular correction service is receding. T is results in a large service range, with the following variable parameters: • Accuracy: from the centimetre-accurate RTK to the sub-decimetre PPP-RTK;


• Coverage: local, continental or global access to corrections;


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