# An Application of a LPWAN for Upgrading Proximal Soil Sensing Systems
## 5 System Test and Analysis
### Communication Test and Discussion  
In principle, a wireless communication gateway should be deployed at the highest possible position, such as a communication operator's iron tower or the roof of a high-rise building, to improve the communication distance and signal quality. In practical applications, the site environment, operating conditions, economic cost, and other factors need to be fully considered [39]. This test took the farms around the Red Azalea Agricultural Ecological Park (RAAEP) in the Baguazhou area as the test site, to evaluate the communication distance and signal coverage between the gateway and the nodes in a typical suburban natural farmland environment. No tower or high-rise building was available for the operators in the area, no advantageous terrain was available, and certain obstacles were contained in the communication space. The test took the RAAEP as the starting point, and considering the implementation difficulty and cost control, the LoRa gateway device was deployed on a billboard approximately 2.5 m above the ground (Figure 11(c)), while the mobile power supply was used to power the LoRa gateway (Figure 11(b)). A communication test route diagram is shown in Figure 13. The AHS was specially programmed for the data transmission test as a terminal node (Figure 11(a)). We drove along the lane with the terminal node for the communication test, and several test points were placed in the southwest direction. Tall and dense trees were located on both sides of the road, but there were relatively open road areas at 450-500 m and 750-800 m in front of the starting point. The system started to enter a village at 1000 m, passed through the village at 1100 m, and entered woods on the two sides of the road at the same time. A highway bridge was located at 2200 m, and the test route crossed under the highway bridge. At each test location, the terminal node sent a group of sequentially numbered data every 3 s, for a total of no less than 20 groups. The gateway received the data, printed the received signal strength indication (RSSI) and signal-to-noise ratio (SNR) information of the data, and uploaded this information to the cloud through a data transfer unit (DTU). We calculated the average RSSI and SNR of the test points at the same distance, which are shown in Figure 14.  
Figure 12: Communication test: the LoRa gateway was placed on a billboard 2.5 m above the ground. (**a**) LoRa terminal node; (**b**) LoRa gateway with the DTU; (**c**) Gateway placement location. Figure 15 shows the data packet loss rate. As seen from the figure, with the increase in the communication distance, the RSSI and SNR gradually decreased, and the packet loss rate gradually increased. At 500 m and 800 m from the test point, the area was relatively open, the influence of tree shielding was small, and the received signal improved. Although signals were still received at 1100 m, the packet loss rate was too high, and the communication accuracy was lost. Therefore, in practical applications, the communication quality evaluation should focus on more than the RSSI, and the packet loss rate was the prerequisite for the evaluation of communication quality. Figure 14: RSSI and SNR values. Figure 13: Communication test route for each designated test location, and the node used to send data in the simulations. The red star symbol indicates the starting point of the test. In a communication system, if the signal power value in the communication link is equal to, or greater than, the sensitivity of the receiver, the receiver can normally obtain the information contained in the transmitted signal; the communication is successful. On the contrary, if the signal power is lower than the sensitivity, the quality of information obtained will be far lower than the specified requirements [40]. Figure 16 shows the obtained signal strength distribution. We selected a set of test data under relatively poor test conditions (such as antennas without enhanced gain), where the analyzed system performance would have more redundancy space.