Original papersAutomatic delivery and recovery system of Wireless Sensor Networks (WSN) nodes based on UAV for agricultural applications☆
Introduction
Recently, technologies such as geography information systems (GIS), Global positioning systems (GPS), Remote sensing(RS), cloud computing, big data, internet of things (IoT), Wireless Sensor Networks (WSNs), unmanned aerial vehicle (UAV) are becoming increasingly popular in agriculture domain (Ojha et al., 2015). For collection of agricultural process information, the need of automation is essential since data gathering and recording by manual is difficult due to its high cost and low efficiency. WSN technology is one of the important Information and Communication Technologies (ICTs) to achieve automatic collection of useful agronomy data and support subsequent analysis and intelligent decision making. At present, WSNs are widely applied in various agricultural applications such as irrigation management system, farming systems monitoring and pest/disease prediction, etc (Rehman et al., 2014, Ojha et al., 2015).
At present, most of the agricultural WSNs for research purpose are simple with less number of nodes. However, as a WSN becomes large and complex while there might be some advanced requirements such as scalable, proactive or reconfigurable. It is difficult to set up and adjust the whole WSN or multiple WSNs by manual. The primary difficulties include:
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Large number of nodes.
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Some nodes may be far from the remote management center and are scattered in a large area.
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Replacement of failure nodes.
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Maintenance or update of an existing node. Sensors need to be periodically repowered by battery change is point out by Rehman et al. (2014) The cost of maintenance is also mentioned by Ojha et al. (2015).
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The extension or rearrangement of existing nodes within a WSN.
In this paper, we present an UAV-based scheme for automatic delivery and recovery of nodes in the field to ease the node deployment and maintenance for large and complex WSNs in agriculture domain. The scheme includes a combination of specially designed UAV and node platforms. A node platform is used for the installment of sensors and equipments while also provides a landing apron for the UAV. An essential automatic alignment mechanism is mounted on the UAV to eliminate the position and angle error between the UAV and the platform after landing. Besides, a supporting GNSS-RTK (Global Navigation Satellite System, Real – Time Kinematic) system is deployed to provide high precision positioning for both the UAV and the node platform. The whole scheme is illustrated in Section 3. The major contributions of our work are listed below.
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A scheme and related prototype system for automatic delivery and recovery of nodes in the field.
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The design of essential automatic alignment mechanism.
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The experimental verification for the prototype system.
Section snippets
Related works
Due to advancement in technologies and reduction in size, Wireless Sensors and Network (WSN) applications are becoming popular and successfully used in various fields. However, there are some issues for application of WSN in agriculture domain. For example, a proper energy management strategy should be applied to conserve energy and extend battery life. The fault tolerance or reliability of the network is required. The resistance to heat, rain and physical mishandling by human or animals need
Proposed system architecture
A prototype system was built to test the UAV-based scheme for automatic delivery and recovery of nodes in the field. The whole system mainly includes the specially designed UAV and the node platforms, the GNSS-RTK positioning system, the automatic alignment mechanism and connecting mechanism.
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The UAV and the node platform
The node platform is a node of a WSN, which can be used for carrying various monitoring sensors and equipments such as ambient parameter sensors, communication module, GPS unit,
Indoor and field tests
The thickness of the body frame was not considered in the dimension design of Section 3. Therefore, there should be some minor adjustment of dimension parameters in practice. To assume the side length of the cross-section of the square aluminum profile is e, the following dimension parameters can be obtained. Where, e = 20 mm, a = 960−e = 940 mm, b = 430 mm−e = 410 mm, h = 1520+e = 1540 mm, = 760 mm, r = 145 mm, c = 430 mm, = 180 mm, = 50 mm. According to Eqs. (8), (9) and Eqs. (17),
Field test of landing accuracy
The landing tests of two hexa-rotor UAVs based on Pixhawk 2 system with conventional GPS device ‘HERE’ have been done 15 and 22 times respectively. Meanwhile, the landing tests of commercial agricultural UAV ‘XAIRCRAFT P30 2018’ with RTK system were carried out 15 times.
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Position errors of landing
As shown in Fig. 15, the landing position accuracy of two hexa-rotor UAVs is around five to six meters. The tests had been done between June 27 to July 3 2018, the temperature was between 23 and 35,
Conclusions
In this paper, we present an UAV-based scheme for automatic delivery and recovery of WSN nodes in the field. which can facilitate the node deployment and maintenance for large and complex WSNs in agriculture domain. A prototype system was built to test the UAV-based scheme. The results of the field tests show that the combination of conventional GPS module and magnetic compasses is incompetent for the landing accuracy of the proposed UAV-based scheme. The commercial RTK system with dual RTK
Acknowledgments
The research was supported by the Science and Technology Planning Project of Guangdong Province (2017B010116003, 2017B010117010, 2018A050506073, 2016A030310453, 2016A020210081). National Key Research and Development Plan (2017YFD0701001). National Natural Science Foundation of China (61773171). The leading talents of Guangdong province program (2016LJ06G689). Science and Technology Planning Project of Guangzhou (201807010039). 111 Project (D18019)
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