# A New Approach to Estimating the Path Loss in Underground Wireless Sensor Networks
## 5 Conclusions  
A large proportion of the infrastructure that our everyday life is dependent on is buried under the ground. Similar to any other infrastructure, buried infrastructure ages and degrades over its lifetime. This makes continuous monitoring of these assets a very important aspect of buried infrastructure management. WSNs have commonly been used for monitoring of above-ground assets due to their scalability and ease of development. However, due to significantly higher attenuation of wireless signals in soil as compared to air, the wireless communication aspect of WSUNs is extremely challenging. In addition, soil is a very complex and dynamic medium which makes accurate estimation of signal attenuation difficult. Therefore, a robust, reliable and easy-to-use method for approximation of the attenuation in soil can hugely benefit the development and deployment of WSUNs. In addition, such a method will provide valuable information for other asset monitoring techniques that rely on propagation of electromagnetic signals in soil (e.g., GPR surveys). In this paper, the RF attenuation was measured at three field locations with different soil conditions, and these results were then compared to the RF attenuation calculated for these soils using the two main attenuation prediction models (i.e., the Modified-Friis and CRIM-Fresnel models). It has been demonstrated that, for each of the three soils at the locations tested, the Modified-Friis model for estimating signal attenuation more closely fitted the field data compared to the CRIM-Fresnel model. Although only three soil types were used, they represented a wide range of soil conditions. However, confidence in the findings could be increased by adding more test data. In addition, an alternative method for determining the soil permittivity for use in the Modified-Friis model was also investigated in this paper. This technique estimates the effective frequency of the Time Domain Reflectometry (TDR) signal in the soil by using the rise time of the signal at the end of the TDR probe, and uses this effective frequency to calculate the complex permittivity. The use of the steady state reflection coefficient was proposed as a more robust way to determine the upper intercept of the rise time over the conventional method for rise time extraction. Using this steady state reflection coefficient significantly improves the reliability and robustness of this process by eliminating the inaccuracies caused by the common end reflections in the TDR waveform. The use of the TDR measured permittivity is suggested to improve the accuracy of the Modified-Friis model as it is based on measurements of the dielectric parameters of the soil at the WUSN location. In addition, it removes the need for laboratory-based tests for calculating the dielectric parameters, which makes it more suitable for field use (e.g., prior to conducting GPR surveys). The performance of this alternative Modified-Friis method for estimating the RF attenuation was analysed by comparing the predicted attenuation with the measured field data, and also with the CRIM-Fresnel and conventional Modified-Friis models. These comparisons showed that in all three field trial locations the Modified-Friis model with the complex permittivity extracted from TDR data of the soils provided a better estimation of the RF attenuation over the distances measured. These results are extremely promising, and provide evidence for the proposed alternative TDR-based method for estimating the RF attenuation in soil and even show that this method results in estimations that are more accurate. The authors gratefully acknowledge the support by the University of Birmingham, UK and Water Industry Research (UKWIR) who funded different parts of this project. [PERSON] conducted the research and trials. [PERSON], [PERSON] and [PERSON] supervised the research and added their intellectual property and experience into the system, particularly the field trials. All the authors helped write the paper. The authors declare no conflict of interest.