Abstract
Wireless Underground Sensor Networks (WUSNs), an important part of Internet of things (IoT), have many promising applications in various scenarios. Signal transmission in natural soil undergoes path loss due to absorption, radiation, reflection and scattering. The variability and dynamic of soil conditions and complexity of signal attenuation behavior make the accurate estimation of signal path loss challenging. Two existing propagation models for predicting path loss are reviewed and compared. Friis model does not consider the reflection loss and is only applicable in the far field region. The Fresnel model, only applicable in the near field region, has not considered the radiating loss and wavelength change loss. A new two stage model is proposed based on the field characteristics of antenna and considers four sources of path loss. The two stage model has a different coefficient m in the near field and far field regions. The far field distance of small size antenna is determined by three criteria: 2 D2/λ, 5 D, 1.6 λ in the proposed model. The proposed two stage model has a better agreement with the field experiment data compared to Friis and Fresnel models. The coefficient m is dependent on the soil types for the proposed model in near field region. It is observed from experiment data that the m value is in the range of 0~0.20 for sandy soils and 0.433~0.837 for clayey silt.
Highlights
Wireless Underground Sensor Networks (WUSNs) have received much research interest in recent years since its promising potential applications in various scenarios, such as border intrusion control, underground structure monitoring, smart farming, environment pollution monitoring [1,2,3,4,5]
This paper develops a new two stage model which aims to tackle the disadvantages of the existing models
The Fresnel model proposed by Bogena et al is a semi-empirical model based on many years of practices of electromagnetic measurement techniques such as time domain reflectometry (TDR) and ground penetration radar (GPR) [18]
Summary
Wireless Underground Sensor Networks (WUSNs) have received much research interest in recent years since its promising potential applications in various scenarios, such as border intrusion control, underground structure monitoring, smart farming, environment pollution monitoring [1,2,3,4,5]. The Fresnel-CRIM model was proposed and validated by laboratory results to evaluate the signal attenuation of underground communication [17]. It is a linear model and has considered the signal reflection loss at the soil–air interface. Field trials and laboratory tests of signal attenuation in different types of soils were conducted to compare the Friis model and Fresnel model. (3) develop a new two stage model considering four sources of path loss and incorporate the advantages of existing models into the new model; (4) clarify the far field distance with three criteria for node antenna; (5) verify the proposed model using field experiments covering different frequencies, different soil types, different water contents and different antenna field regions
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