农业工程学报
農業工程學報
농업공정학보
2015年
4期
224-231
,共8页
数据传输%模型%信号%绕射%人工林
數據傳輸%模型%信號%繞射%人工林
수거전수%모형%신호%요사%인공림
data transfer%models%signaling%diffraction%man-made forest
为解决无线传感器信号在人工林内传输时节点接收不到信号或通信质量差的问题，该文根据人工林的特点，采用4层独立介质简化方法，将人工林内场强模型简化成自由空间模型、衰减屏模型、吸收屏模型3个独立模型，基于波传播的局部性原理和过渡区一致性劈绕射理论，应用Kirchhoff- Huygens近似，推导了吸收屏绕射场强模型。并以白杨木人工林为采样区域采集数据，将90组实测样本平均分为9组，分别用3种模型计算各组的预测值并与实测值进行t检验，结果表明：绕射场强理论预测 t 值[0.242,2.193]小于 t0.05，无显著性差异，可以用理论预测值代替实测值进行信号的分析和计算，距离越近可信度越高，而经验模型和半经验模型存在显著性差异，不适合用于人工林内绕射场强预测。研究结果为无线传感器网络林内优化布置策略提供了一个新思路，成果也可为林区的其他射频信号通讯技术开发提供理论支撑。
為解決無線傳感器信號在人工林內傳輸時節點接收不到信號或通信質量差的問題，該文根據人工林的特點，採用4層獨立介質簡化方法，將人工林內場彊模型簡化成自由空間模型、衰減屏模型、吸收屏模型3箇獨立模型，基于波傳播的跼部性原理和過渡區一緻性劈繞射理論，應用Kirchhoff- Huygens近似，推導瞭吸收屏繞射場彊模型。併以白楊木人工林為採樣區域採集數據，將90組實測樣本平均分為9組，分彆用3種模型計算各組的預測值併與實測值進行t檢驗，結果錶明：繞射場彊理論預測 t 值[0.242,2.193]小于 t0.05，無顯著性差異，可以用理論預測值代替實測值進行信號的分析和計算，距離越近可信度越高，而經驗模型和半經驗模型存在顯著性差異，不適閤用于人工林內繞射場彊預測。研究結果為無線傳感器網絡林內優化佈置策略提供瞭一箇新思路，成果也可為林區的其他射頻信號通訊技術開髮提供理論支撐。
위해결무선전감기신호재인공림내전수시절점접수불도신호혹통신질량차적문제，해문근거인공림적특점，채용4층독립개질간화방법，장인공림내장강모형간화성자유공간모형、쇠감병모형、흡수병모형3개독립모형，기우파전파적국부성원리화과도구일치성벽요사이론，응용Kirchhoff- Huygens근사，추도료흡수병요사장강모형。병이백양목인공림위채양구역채집수거，장90조실측양본평균분위9조，분별용3충모형계산각조적예측치병여실측치진행t검험，결과표명：요사장강이론예측 t 치[0.242,2.193]소우 t0.05，무현저성차이，가이용이론예측치대체실측치진행신호적분석화계산，거리월근가신도월고，이경험모형화반경험모형존재현저성차이，불괄합용우인공림내요사장강예측。연구결과위무선전감기망락림내우화포치책략제공료일개신사로，성과야가위림구적기타사빈신호통신기술개발제공이론지탱。
The ability of 2.4 GHz signal diffraction which is adopted by WSN (wireless sensor networks) is worse in forests, because the range behind standing tree in forests has blind signal area. Diffraction law of transmission attenuation and clinging trunk of 2.4 GHz radio-frequency signal in forests has been studied. To describe the diffraction effects of the edges of surfaces using a relatively simple mathematical method, the Kirchhoff–Huygens approximation is employed. Based on the uniform geometrical theory of diffraction (UTD), the region of transition is uniform. To account for the disposal of the sensor, only the illuminated region and the shadow are considered. According to the Kirchhoff approximation, the substitution is used to perform integral transform and the model of wedge diffraction gets simplification. Accounting for the influence of the diffusion factor and according to UDT, the aforementioned approach can also be used to derive the field at the receiver point. The research object is wireless radio-frequency signal transmission in man-made forests. The main contents and conclusions are as follows: 1) The signal transmission characteristics in plantation were studied. Tree trunks are replaced by absorbing screens. The leaves and branches are replaced by partial attenuation screens. The phase and attenuation screen is located directly above the absorbing screen for simplicity. The wireless sensor placed at a breast height of 1.3 m can be further lowered to the basal area in the current paper, so only the effects of the basal area of breast height are considered. Circular area expressions are used for the measurements of the basal area of breast height and standing wood volume, with an average error of ±3%. The configuration characteristics of plantation are combined. Through the modeling methods of hierarchical independent analysis using four-storey independent dielectric layer, the overall propagation model of RF signal in plantation is simplified. The concepts of crown attenuation screen and truck absorbing screen are put forward. And the formula of loss was given equation, when electromagnetic wave was mathematically spreading in plantation medium. 2) The diffraction fields and the shadow of standing tree diffraction are solved using polygons as approximate substitutes for the circle. When shadow results from a single object, such as a standing tree, the attenuation attributable to diffraction can be estimated by considering the obstruction of a diffracting wedge-edge. According to the Kirchhoff approximation, the receiver point can be written as an integral for the complex amplitude over the plane. 3) Taking man-made birch as the example: the frequency of the source point in the base station is 2.4 GHz, the circumference of the standing tree is 800 mm, the radius of standing tree is l/2π, and source and receiver are equal in height, that is, their diameters are both at breast height of 1.3 m. It shows that the propagation loss of the receiver power, transmission height and distance increase with an increase in the distance of the source, i.e., if the propagation loss increases, the free space propagation loss also increases. Application of t-test to test, takes the significance level of 0.05, below which the results are not significantly different, got fired from the receiving point near models more reliable results. 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.
