Transmission Characteristics Of Wireless Sensor Signal In Limited Space

The paper is aimed at suitable work frequency for wireless communication in limited space (such as sewer), which is the theoretical foundation for successful application of New Slab Sensor for Flow Measurement. On the basis of previous studies, transmission characteristics of wireless sensor signal between sensor in the sewer and the receiving equipment on the ground is studied further. There are a lot of environmental factors in the process of wireless signal transmission underground. The main research contents of this paper are as follows:The communication equipment was installed in wildness without guarding. During the long distance detection, the data from the monitoring terminal is needed to respond in time, data transmission and data admission with low power consumption. From the aspect of energy consumption (the key of wireless communication) to study path loss of wireless sensor signal. Due to the restriction of installation position, wireless signal spreads in the sewer and soil.All possible factors of wireless signal transmission are considered, such as the electrical characteristics of the soil(conductivity,permittivity and permeability),soil type(relatively dry soil, partially saturated cohesionless soil and saturated cohesionless soil), the materials of sewer(cement and HDPE), the roughness of the wall of sewer, the inclination of sewer, the size of cross sectional area and so on. Taking into account these above factors to obtain suitable frequency range by theoretical analysis. And the conclusions as followsFor sewer:In the near region of sewer:the higher the frequency, the greater the attenuation of the signal. While in the far region of sewer, the higher the frequency, the less the attenuation of the signal. The influence of materials, roughness of the wall and the inclination of sewer to wireless communication the greater the roughness of the wall of sewer, the greater influence on100MHz-200MHz and1500-1900MHz, and the less compared to450MHz-900MHz. And the suitable work frequency rang is300MHz-1000MHz.With the increase of the of sewer size, the influence of roughness decreases markedly.For soil:The higher the frequency, the greater the attenuation of the signal.The longer of the distance between sensor and the receiver, the greater the attenuation of the signal too. For three different soil, conclusions are as follows: path loss of relatively dry soil is close to the half of partially saturated cohesionless soil’s or saturated cohesionless soil’s.(1)The relationship of path loss and porosity in relatively dry soil:the higher the porosity, the greater path loss, and when the porosity is in the percent of20-30,the path loss increases sharply, but the porosity is in the percent of32-34,the path loss decreases sharply.(2) The relationship of path loss and volume water content of mud in partially saturated cohesionless soil:the higher volume water content,the greater path loss.(3) The relationship of path loss and porosity or saturation rate in saturated cohesionless soil:when the saturation rate remains unchanged, the higher the porosity, the less path loss and when saturation rate remains unchanged, the higher the porosity, the less path loss.Transmission characteristics of wireless sensor signal and channel models in limited space such as indoor, mine and subway for reference. Combining what mentioned above and environmental factors to build suitable channel for sewer.