Precision Agriculture: RTK Base-to-Tractor Range Limitations Using RF Communication

Precision agriculture is heavily dependent upon Real-Time Kinematic (RTK) technology for real-time field positioning. To reduce RTK equipment costs, producers can access a shared reference station rather than purchasing portable units. However, those tractor operators that utilize a shared station may experience positioning failures while operating in remote outlying fields. These failures may be due to sporadic radio frequency (RF) communication links with the station. To examine possible RF communication issues impacting precision agriculture, a test was conducted employing a tractor-based RTK system mounted on a road vehicle. The instrumented vehicle was used to traverse the highways around two commercial RTK reference towers. A GIS viewshed analysis (line-of-sight, LOS) based upon tower distance and terrain blockage from landforms and woodlands was performed. Percentage results were compared to a comprehensive radio frequency path design tool (Pathloss Ver. 4), which is a commercial simulation model for radio links that operate in the frequency range of 30 MHz to 100 GHz. Highway tests of RTK base station reception show the Pathloss (PL) model predicted by percent the data fit of both high and low probability areas. The PL model prediction percentages were found slightly more robust in its prediction of RF reception than the LOS model. Both models performed better at predicting areas of reception than of non-reception. The PL model had higher inaccurate prediction percentages of reception regions, whereas the LOS model had higher inaccurate prediction percentages of non-reception regions. Base-to-tractor separation distances, forestation, and terrain blockages were the primary factors for maintaining the tractor RF link with the base station. As a low-cost tool, the site-specific success in communicating with a reference base station can be determined by using the positioning NMEA output from the RTK receiver plotted within Google Earth.