Experimental Technology and Management

针对传统传输损耗模型对LoRa无线通信系统在近地面应用中适用性不足，难以为构建近地面无线传输网络提供有效支撑问题，设计了包含通信和分析两部分的LoRa无线通信质量测试系统。通信部分使用集成了无线微控制器和无线通信功能的一体化芯片，设计了LoRa无线传输数据采集装置；分析部分设计了含有残差和、决定系数等数据处理与分析功能的上位机软件。实验采集了雪地、农田、水泥地三种场景下近地面传输时的信号强度数据，并利用该上位机软件进行处理分析。通过对比分析软件得到的多种参数，验证了所提改进模型的合理性及有效性，能够为LoRa近地面无线传输网络的构建提供参考。

[Objective] Traditional transmission loss models for LoRa wireless communication systems operating in near-ground environments exhibit limited applicability. Another issue is the difficulty of effectively supporting the design of near-ground wireless transmission networks. Furthermore, most of the currently available test methods for LoRa communication systems are costly and exhibit limited flexibility. Based on the above, we propose a new wireless communication system for testing the transmission quality of LoRa wireless communication systems operating in near-ground environments. [Methods] The proposed test system consists of a communication and an analysis part. The communication part includes a chip integrating a wireless microcontroller and wireless communication functions, as well as a Micro SD storage unit. The communication functions and the storage unit are used for LoRa signal communication, as well as the storage of the communication signals and their parameters(i.e., signal-to-noise ratio and signal strength); the microcontroller is used to implement visualization data functions and a key menu function for adjusting the communication parameters at any time during testing. The analysis is performed using the upper computer software, which is designed to read the communication quality parameters of the LoRa signals stored in the memory card. The strength of the transmitted signal is determined according to the traditional, empirical, and improved empirical transmission loss models. Finally, the host computer outputs the results generated by the three models. These results are the values of the parameters to be fitted for different models, the sum of residuals, and the correlation coefficient. [Results] The parameter fitting values are the environmental impact constant and the attenuation coefficient; these are used to represent the signal transmission characteristics in certain environments. The sum of residuals and the correlation coefficient represent the degree the fitted model represents the actual signal. When the sum of residuals is small and the correlation coefficient is large, the degree the model fits the actual signal increases. During testing, the strength values of the LoRa modulated signals near the ground(i.e., 1 m above the ground) are collected assuming three ground scenarios: snow-covered, farmland, and cement-covered ground; then, the signals are processed and analyzed using the proposed computer software. The value of the environmental impact constant obtained from the software using the empirical model with a one-step fitting was negative. This erroneous result indicates overfitting of the empirical model. Therefore, we employed an improved empirical model. In this model, the data are gradually fitted, starting from three pieces and ending with all nine pieces of data. Then, all fitting results are summed, and their average values are calculated. These values replace the corresponding parameter values in the empirical model to obtain a rational model. The rationality, validity, and convergence of the improved empirical model were verified using the proposed computer software. [Conclusions] The experimental results showed that the improved empirical model constructed using multistep fitting can reasonably and accurately describe the transmission loss characteristics of LoRa modulated signals in near-ground environments, providing a useful reference for the construction of future LoRa near-ground wireless transmission networks.