Ensuring high-precision positioning for GNSS auto-steering systems with H-PPP
GNSS auto-steering systems for agricultural vehicles have become increasingly popular in major agricultural regions worldwide. These systems not only relieve the driver from manual steering but also achieve centimetre-level precision, making them indispensable for many farmers. However, these systems rely heavily on GNSS positioning technologies, and it is inevitable that there will be situations where GNSS RTK correction signals are unavailable. How can this problem be addressed? This article explores the transmission and reception of GNSS high-precision positioning correction data to help you find a solution quickly.
3 Main Methods for Receiving High-Precision Correction Data Signals
GNSS RTK Networks
One of the most widely used technical methods for GNSS RTK service is the establishment of a network of fixed reference stations, also known as Continuously Operating Reference Stations (CORS). CORS networks, consisting of numerous base stations, synchronize and process GNSS data from multiple satellites in real time to provide precise and continuous 3D corrections. China, for example, has built more than 6,000 CORS stations, while the United States has built more than 2,000. Germany’s satellite positioning service, SAPOS, consists of about 300 permanent GNSS reference stations with an average spacing of about 40 km. Japan, which is prone to geological disasters, has about 1,400 permanent GNSS tracking reference stations with an average density of about 20 km.
Agricultural GNSS auto-steering systems can typically connect directly to the CORS network via 4G networks, Wi-Fi, or mobile hotspots to obtain RTK corrections. In areas with a lower density of CORS base stations, users may choose to build their own reference stations. A single GNSS reference station can provide RTK corrections within a range of 30-50 km.
Single GNSS Station
In mountainous or less developed areas where cellular networks are unreliable, receiving network RTK corrections can be a challenge. In such cases, users can set up a mobile GNSS RTK reference station. These stations transmit RTK correction data over UHF and typically support protocols such as Transparent TT450S and SATEL 3AS. The coverage of a mobile base station is typically 5-8 km, which is sufficient for most agricultural scenarios.
Major manufacturers of agricultural GNSS auto-steering systems often include radio modules in their receivers, providing users with additional RTK correction source options beyond GNSS RTK networks. This flexibility reduces downtime and ensures continuous operation. However, radio signals can be attenuated by obstructions such as tall buildings or dense forests. For larger farms beyond the range of a mobile GNSS base station, combining the GNSS receiver with a radio modem can extend the range to 25-30 km and provide more stable signals.
Satellite-based PPP
Is there an alternative for GNSS auto-steering users? Yes. Satellite-based Precise Point Positioning (PPP) technology provides global coverage without the need for ground-based reference stations. By broadcasting corrections directly from satellites, PPP enables auto-steering systems to achieve centimetre-level positioning accuracy, with the potential to support an unlimited number of terminals, provided there is sufficient satellite visibility.
Benefits of PPP Corrections for Precision Agriculture
Free access
The Galileo navigation satellite system now offers a globally accessible High Accuracy Service (HAS) based on PPP technology. CHCNAV has developed a free H-PPP service for its precision agriculture solutions using Galileo HAS. With just one click, users can activate H-PPP when other RTK corrections are unavailable, a feature highly valued by farmers.
Ease of use
There is no need to set up a mobile GNSS base station, configure complex parameters, or pay for expensive RTK correction services. The GNSS auto-steering system can achieve high-precision with H-PPP, saving users the cost of purchasing mobile RTK base stations or subscribing to RTK services.
Fast, high precision
A drawback of traditional PPP is the longer convergence time required to achieve the required accuracy. However, the optimised H-PPP requires only 5-10 minutes to reach a positioning accuracy of 5-10 centimetres. While this is slightly less accurate than traditional RTK’s ±2.5 centimetres, advanced control algorithms ensure that the operational accuracy of agricultural vehicles in H-PPP mode meets most practical needs. This feature is especially valuable in remote areas with poor network coverage, significantly improving operational efficiency.
Satellite-based H-PPP offers a reliable solution for precise farm machinery auto-steering without the need for ground-based GNSS RTK corrections. By optimising workflows and minimising downtime, it enables farmers to make data-driven decisions that enhance their farming operations. Ultimately, H-PPP empowers farmers to adapt confidently to diverse agricultural environments, increasing efficiency in today’s competitive landscape.
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