Research on Autonomous Driving Technology for a Robot Vehicle in Mountainous Farmland Using the Quasi-Zenith Satellite System

The centimeter-level augmentation service (CLAS), which is provided by Michibiki of the Quasi-Zenith Satellite System (QZSS), can be utilized as a navigation sensor for a robot vehicle in orchards, which are often located in mountainous areas with great slopes. The CLAS was less affected by buildings, windbreaks, or the inclination of the antenna compared with the virtual reference station real-time kinematic (VRS-RTK) method, which is one of the most common navigation sensors for autonomous driving in agriculture. The time to first fix (TTFF) of the CLAS was 60 seconds earlier near buildings, and 90 seconds earlier in case of the antenna tilted, compared to the TTFF of the VRS-RTK. Moreover, an internet environment setting such as mobile broadband is not necessary for the CLAS, which uses the augmentation information from the QZSS. A positioning test in a real vineyard, where the grapevines are trained over the vertical trellis, yields that the CLAS could acquire the FIX solution constantly, whereas the VRS-RTK could not because of a weak internet signal. The accuracy of the CLAS was less than 6.4 cm for a 95% confidence interval at static positioning, and less than 3 cm root mean square (RMS) at dynamic positioning. A robot vehicle navigated by the CLAS autonomously traveled two paths including a turning maneuver, with less than 9 cm RMS and less than 20 cm MAX. Results showed that the robot vehicle could work autonomously without any collisions in an actual vineyard by the CLAS.