Indoor Experiment on Near Ground Path Loss in Near Fieldįrom Figure 2, it is evident that path loss values are increasing with decrease in antennas height. The results have been employed in a context aware environment based on WSN deployment and integration, applied in a Smart Agriculture use case. A comparison between path loss and RSSI results for different antennas heights has been completed. These nodes are working at 2.4 GHz under ZigBee protocol. In another scenario, we analyzed the communication quality between sensor nodes dedicated to smart agriculture, when placing them at the same two different antenna heights, but only for the case of a short grass field, by measuring the RSSI values. The path loss was then estimated as dependent of the radio link range. We measured the received power at the receiver antenna at two different heights, 20 cm and 40 cm above ground. Radio communication, using transmitter and receiver antennas working at 868 MHz, 2.4 GHz and 5.8 GHz, has been implemented in soil, short and tall grass fields. This paper presents a developed channel model, which considers the path loss caused by agriculture fields found in the propagation link when a near ground radio communication occurs. These losses are reason of bad communication between nodes, thus unsuccessful application since the success of the wireless sensor network applications highly depends on the reliable communication among the sensor nodes. Path loss caused by near-ground is explained in terms of Fresnel zones. However, when placing nodes near to the ground in agriculture fields, the transmitted signal experiences a high-level of attenuation due to the components of the field like grass and soil. Some agriculture related parameters, such as soil temperature, soil moisture, CO 2, PH value and soil nutrients, could be monitored and then controlled by wireless sensor networks. It provides a feasible way for low-cost, high-efficiency, and high-productivity agriculture farming. In the past few years, the WSN has emerged into the research field of agriculture. It has attracting applications in variety of fields as health care, machine surveillance and military uses. Wireless Sensor Network technology is based on collecting data from sensor nodes, which communicate between each other and between them and the gateway, which transmit the data through internet for storage, analysis and processing.
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