Analysis Of Propagation And Diffraction Of Wireless Telemetry Signal In Man-made Forests

The ability of 2.4GHz signal diffraction which is adopted by WSN(Wireless Sensor Networks) is worse in forests, because of the range behind standing tree in forests exists blind signal area. Diffraction law of transmission attenuation and clinging trunk of 2.4GHz radio-frequency signal in forests has been studied. Establishment of field intensity model and computing method of blind signal area of alive standing tree can serve as the theoretical basis of optimum arrangement strategy, which is in standing tree DBH(Diameter at Breast Height) of forests of WSN.Based on the analysis and learning from signal transmission attenuation in forests, the theory of electromagnetic propagation and other related research achievements at home and abroad. The research object is wireless RF signal transmission in man-made forests. Diffraction field strength and blind area have been studied. The main contents and conclusions as follows:1. In this paper, signal propagation environment and transmission facilities was analyzed.2.The signal transmission characteristics in plantation was studied. The configuration characteristic of plantation was combined. Through the modeling methods of hierarchical independent analysis at using four-storey independent dielectric layer, to simplify the overall propagation model of RF signal in plantation. The concept of crown attenuation screen and truck absorbing screen were put forward. And the formula of loss(L= L(Z)+L(S)+L(X)) was given, when electromagnetic wave mathematical were spreading in plantation medium.3.The UTD was used and the alive standing tree model was simplified by polygonal approximation. Information storage of model was studied and through the reverse ray tracing method to solve the problem of path search and transmission tracing of signal in plantation. The general solution(Q(t)= p1+t(p2-P1)) of receiving point was found under the cases between known and unknown.4. On the basis of overall transmission model and results of ray tracing, the of absorption screen (trunk in trees) was research primarily:(1) The diffraction models of alive standing tree was proposed under vertical incidence and oblique incidence.(2) The diffraction field solution formula of standing tree was deduced through the Electromagnetic Wave Theory, the law of Fresnel-Kirchhoff and the theory of UTD, which is given by En(s)= En-1(Q)D(θ)A(s)exp(-jks sinγ)exp(-jkzcosy).(3) The transition zone of shadows boundary was not continuous by approximate calculation, the transition zone correction was used to solve and the expression of modified diffraction coefficient was obtained, which is given by D=-exp(-jπ/4) x cotγ(1) F (2κLn2 sin2γ(1)/2n√2πκ(4) The influence factors of diffraction blind area were analyzed. When the caustics distance was calculated, the formula of blind area was obtained, which is given by一(κΡc/2)1/3+π/2≤θ≤(κΡc/2)1/3+π/2.(5) To take the white poplar as the sampling area, the diffraction field of alive standing was carried analogue simulation. The correctness of the model was tested and verified.In this article, the research result provides a new thread for network optimization decoration strategy of WSN. Meanwhile it can provide theoretical support for communication technology development of other radio-frequency signal.