# Low-Cost Wireless Sensing System for Precision Agriculture Applications in Orchards
###### Abstract  
Wireless sensor networks (WSNs) can be reliable tools in agricultural management. In this work, a low cost, low power consumption, and simple wireless sensing system dedicated for agricultural environments is presented. The system is applicable to small to medium sized fields, located anywhere with cellular network coverage, even in isolated rural areas. The novelty of the developed system lies in the fact that it uses a dummy device as Coordinator which through simple but advanced programming can receive, process, and send data packets from all End-nodes to the cloud via a 4G cellular network. Furthermore, it is energy independent, using solar energy harvesting panels, making it feasible to operate in remote, isolated fields. A star topology was followed for the sake of simplification, low energy demands and increased network reliability. The developed system was tested and evaluated in laboratory and real field environment with satisfactory operation in terms of independence, and operational reliability concerning packet losses, communication range (>250 m covering fields up to 36 ha), energy autonomy, and uninterrupted operation. The network can support up to seven nodes in a 30 min data acquisition cycle. These results confirmed the potential of this system to serve as a viable option for monitoring environmental, soil, and crop parameters. wireless networks; precision agriculture; IoT; agricultural sensors +
Footnote †: journal:Another important aspect in agricultural WSNs is the wireless communication among the different nodes within the network. Therefore, the selection of the appropriate communication protocol for the specific properties of each application is particularly important. Throughout the course of development of wireless sensing systems, several communication protocols and communication standards were developed, each presenting certain strengths and weaknesses. The ZigBee, LoRa, and SogFox wireless protocols show low power consumption and acceptable or long communication range; therefore, they are identified as suitable options for agricultural applications. However, LoRa and SigFox are not fully open-sourced protocols [8]. In addition, sensor networks based on 2.4 GHz, such as ZigBee, are prone to interference and range issues. The 868 MHz are less popular networks despite their positive characteristics. According to recent studies, their range can be up to 300 m without any packet losses, significantly further than the 2.4 GHz protocols, showing an average Received Signal Strength Indicator (RSSI) of above 40 percent [9]. Furthermore, special care should be taken into considering the definition of the topology for the wireless sensor node allocation [10]. The environment in urban ecosystems is relatively stable, without significant fluctuations of the shapes and obstacles that could deteriorate the connectivity of the wireless systems' nodes over time. Conversely, in agricultural ecosystems the environment is dynamic and constantly changes, following the seasonal climate fluctuations that affect the plants' physiology, as well as the natural growth of perennial plants with time. This fact makes the study of field topography and environment for proper positioning of the components of wireless sensing systems in agricultural environments a particularly complex task. For example, in tree crops, canopy development during spring blocks a significant proportion of the wireless signal, obstructing the communications between nodes installed in the orchard. A fundamental aspect when deploying wireless sensor networks in the field is studying the spatial properties of the parameters of interest and allocating the sensor nodes accordingly [11]. This practice requires performing a comprehensive study of the topology in order to make sure that the communication between the sensor nodes is not obstructed by obstacles that are deteriorating the communication range.