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Precision agriculture machine control requires the use of Real Time Kinematic Global Positioning Systems (RTK GPS) that achieve centimeter-level positional accuracy, specifically on rough or rolling terrain. To receive RTK GPS corrections that achieve this level of precision, a farmer must have access to GPS base stations which provide real-time corrections to account for the inaccuracies of GPS. Precision agriculture machine control exists without the use of RTK GPS, but RTK GPS gives machines the ability to “minimize skips and overlaps in areas with rolling terrain and rough ground” (Trimble, 20010a).
There are two ways to transmit RTK GPS corrections from a base station. The simplest is through a radio modem that receives data from a local base station that omni-directionally broadcasts corrections and is set up on the farm. However, these systems have limited radio communications spans (limitation range is a function of the radio output power and terrain, including line of sight to base station radio). Outside the communication radius, tractors cannot get data that is accurate enough for machine control to have high quality results in reducing skips and overlap areas. These systems cost ~$24-32,000 US (Base Station and Rover) which limits the number of farmers who can financially afford machine control using local base station technology.
The second method to receive RTK GPS corrections is through wireless Internet. Public agencies and private companies have setup numerous base station networks around the country that broadcast corrections through the Internet. This type of network is known as a Real Time Network GPS (RTN GPS) system. In order to use this type of system, farmers must have Internet access at the tractor. Precision equipment designed with cellular Internet capabilities can access these RTN GPS systems, but to achieve centimeter level accuracy the data must be transmitted through high speed 3G/4G cellular connections. Unfortunately 3G/4G coverage outside metro areas in the rural community is limited. Clusters of service are found along main transportation arteries, but sparsely populated areas with small amounts of revenue for cellular suppliers have limited expansion of updated towers. The USDA reported that 55% of rural homes have broadband internet from dial-up, wired, satellite or cellular solutions in 2009 (Stenburg et al., 2009).
Rover RTK GPS systems have the ability to take advantage RTN correction with radio modem and cellular communication systems. Where limited broadband via cellular and wired communication exists, an alternative option is to communicate with a RTN GPS systems through a satellite Internet connection directly to a tractor. The methodology to transmit RTK GPS corrections to agricultural machinery with different radio communication has been developed using a variety of different configurations. Use of satellite Internet in the field has not been fully implemented (McKinion et al., 2004).
RTK GPS corrections along with geospatial data have been successfully downloaded to agriculture machines in the field via radio modem bridges from repeater stations. The radio modem bridges showed a limitation of 1500m range, but with multiple radios distances could be extended to 10,000 meter (McKinion et al., 2004). This was tested to try and provide broadband to the equipment in the field when the limitation is based on terrain, line-of-sight to antenna, and radio frequency/power output.
This experiment investigates how a system could be built in a combination of McKinion et al. and Lyle and Mulcare’s findings to: (1) connect to a mobile satellite Internet solution, and (2) connect to a RTK GPS RTN solution. This type of solution could hopefully eliminate the need for repeaters, personal GPS receiver base stations and a cellular data plan for each tractor system.