Sensors_**2014**, _14_, 19767-19784; doi:10.3390/s141019767  
_Sensors_  
ISSN 1424-8220  
www.mdpi.com/journal/sensors  
_Article_  
Wi-Fi and Satellite-Based Location Techniques for Intelligent Agricultural Machinery Controlled by a Human Operator  
**[PERSON] 1, [PERSON] 1, [PERSON] 2 and [PERSON] 3,*  
1 The Telecommunications Research Center Vienna (FTW), Vienna 1220, Austria; E-Mails: [EMAIL_ADDRESS] (D.D.); [EMAIL_ADDRESS] (S.T.)  
2 Universidad de Cordoba, Area de Mecanizacion y Tecnologia Rural, Dpto. de Ingenieria Rural. Cordoba 14005, Spain; E-Mail: [EMAIL_ADDRESS]  
3 Aerospace Engineering and Fluid Mechanics Department, University of Seville, Ctra. Sevilla-Utrera km 1, Seville 41013, Spain  
* Author to whom correspondence should be addressed; E-Mail: [EMAIL_ADDRESS]; Tel./Fax: +34-954-481-389.  
External Editor: [PERSON]  
_Received: 14 July 2014; in revised form: 29 August 2014 / Accepted: 16 October 2014 / Published: 22 October 2014_  
**Abstract:** In the new agricultural scenarios, the interaction between autonomous tractors and a human operator is important when they jointly perform a task. Obtaining and exchanging accurate localization information between autonomous tractors and the human operator, working as a team, is a critical to maintaining safety, synchronization, and efficiency during the execution of a mission. An advanced localization system for both entities involved in the joint work, _i.e._, the autonomous tractors and the human operator, provides a basis for meeting the task requirements. In this paper, different localization techniques for a human operator and an autonomous tractor in a field environment were tested. First, we compared the localization performances of two global navigation satellite systems' (GNSS) receivers carried by the human operator: (1) an internal GNSS receiver built into a handheld device; and (2) an external DGNSS receiver with centimeter-level accuracy. To investigate autonomous tractor localization, a real-time kinematic (RTK)-based localization system installed on autonomous tractor developed for agricultural applications was evaluated. Finally, a hybrid localization approach, which combines distance estimates obtained using a wireless scheme with the position of an autonomous tractor obtained using an RTK-GNSS system, is proposed. The hybrid solution is intended for user localization in unstructured environments in which the GNSS signal is obstructed. The hybrid localization approach has two components: (1) a localization algorithm based on the received signal strength indication (RSSI) from the wireless environment; and (2) the acquisition of the tractor RTK coordinates when the human operator is near the tractor. In five RSSI tests, the best result achieved was an average localization error of 4 m. In tests of real-time position correction between rows, RMS error of 2.4 cm demonstrated that the passes were straight, as was desired for the autonomous tractor. From these preliminary results, future work will address the use of autonomous tractor localization in the hybrid localization approach.  
Keywords:DGNSS; autonomous vehicle; RTK-GNSS; trilateration +
Footnote †: journal: Journal of Scientific Computing