Wireless underground sensor networks (WUSNs) are becoming ubiquitous in many areas. The design of robust systems requires an extensive understanding of the underground (UG) channel characteristics. In this article, the UG channel impulse response is modeled and validated via extensive experiments in indoor and field testbed settings. Three distinct types of soils are selected with sand contents ranging from 13% to 86%, and clay contents ranging from 3% to 32%. The impacts of changes in soil texture and soil moisture are investigated with more than 1, 200 measurements in a novel UG testbed at the University of Nebraska-Lincoln that allows flexibility in soil moisture control. Moreover, the time-domain characteristics of the channel, such as the RMS delay spread, coherence bandwidth, and multipath power gain, are analyzed. The power delay profile analysis validates the three main components of the UG channel: direct, reflected, and lateral waves. Furthermore, it is shown that the RMS delay spread follows a log-normal distribution. The coherence bandwidth ranges between 650 kHz and 1.15 MHz for soil paths of up to 1 m and decreases to 418 kHz for distances above 10 m. Soil moisture is shown to affect the RMS delay spread non-linearly, which provides opportunities for soil moisture-based dynamic adaptation techniques. A statistical channel model for the wireless underground channel has been developed based on the measurements and analysis. The statistical model shows good agreement with the measurement data. The model and analysis pave the way for tailored solutions for data harvesting, UG sub-carrier communication, and UG beamforming.

中文翻译：

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基于无线地下信道经验表征的统计脉冲响应模型

无线地下传感器网络 (WUSN) 在许多地区变得无处不在。稳健系统的设计需要对地下 (UG) 通道特性有广泛的了解。在本文中，UG 信道脉冲响应通过在室内和现场测试台设置中的大量实验进行建模和验证。选择了三种不同类型的土壤，沙子含量从 13% 到 86% 不等，粘土含量从 3% 到 32% 不等。在内布拉斯加大学林肯分校 (University of Nebraska-Lincoln) 的新型 UG 试验台上进行了 1, 200 多次测量，研究了土壤质地和土壤水分变化的影响，该试验台可灵活控制土壤水分。此外，还分析了信道的时域特性，例如 RMS 延迟扩展、相干带宽和多径功率增益。功率延迟分布分析验证了 UG 信道的三个主要组成部分：直接波、反射波和横向波。此外，还表明 RMS 延迟扩展遵循对数正态分布。对于长达 1 m 的土壤路径，相干带宽范围在 650 kHz 和 1.15 MHz 之间，对于超过 10 m 的距离，相干带宽降低到 418 kHz。土壤水分被证明会非线性地影响 RMS 延迟扩展，这为基于土壤水分的动态适应技术提供了机会。基于测量和分析开发了无线地下信道的统计信道模型。统计模型与测量数据显示出良好的一致性。该模型和分析为数据采集、UG 子载波通信和 UG 波束成形的定制解决方案铺平了道路。