Research On The Characteristics Of Wireless Channel In Granary Based On Ray Tracing

Food security has become a national strategy in 2016.Grain detection can timely found abnormal grain information in grain heap,such as internal temperature,mildew,foreign bodies,and prepare in early warning of food security and policy regulation.The existing wired sensor detection has many problems,include difficult layout,single monitoring parameters,small coverage,difficult to upgrade and so on.Therefore,it is necessary to develop a fast and effective non-invasive non-destructive testing method to improve the detection efficiency and saving the cost of testing.Grain heap is a kind of multi-layer structure which is closely related to the type of granary and grain,the height of large grain storage is high,and the distribution of density,humidity and temperature of each layer is non-uniform.This lead to the application of the technology of wireless detection in inhomogeneous grain medium need to accurately estimate the characteristics of RF signal transmission link,this is also the problem of the physical layer of wireless data transmission.In order to solve this problem,the electromagnetic characteristics of the granary channel,the simulation platform and the deterministic modeling of the granary channel are studied in this dissertation.The main achievements and innovations include the following aspects:1.The particularity of the radio wave propagation in the granary is studied based on the theory of wireless channel.According to the relationship between the temperature,humidity and density and the dielectric properties of grain medium,the influence of the electric wave frequency and dielectric properties on the electromagnetic wave attenuation of the grain heap is analyzed.The measured data and theoretical analysis show that the humidity and frequency are the main factors that affect the path loss.2.Comparative analysis of statistical,deterministic and semi deterministic channel modeling theory,the efficient and accurate ray tracing algorithm based on deterministic method is used as the research method of wireless channel.The direct algorithm and inverse algorithm of ray tracing channel modeling methods are proposed,the received power,path loss,time delay and angle of arrival of each transmission path in the medium are calculated quantitatively.The results show that the two algorithms can reflect the attenuation characteristics of the electromagnetic wave in the grain heap,and the error range is basically the same.Compared with the direct algorithm with low complexity and high efficiency,the inverse algorithm can not only obtain the path loss characteristics,but also obtain the information of the phase,delay and polarization of the different transmission paths.3.The simulation platform of two kinds of granary channel is established,which can achieve flexible settings of the granary model and simulation parameters.The influence of the frequency,humidity and distance on the ray amplitude distribution is studied based on inverse algorithm channel modeling platform using MATLAB,the important conclusion is obtained that only the direct path and paths with one-reflection are considered in the warehouse.The path loss model consistent with the inverse algorithm is obtained based on direct algorithm using electromagnetic simulation software Wireless InSite.