The Highway Localization Algorithms Based On RSSI In WSN

As a new area, Low power Wireless Sensor Networks (WSN) has a widely prospect of application for security, environment, health, family, military and so on. Localization of WSN is not only very important for the unknown spot in the WSN range but also have some reference for the WSN topology. The localization system of the highway is the component of the ITS. The combination with the WSN is very important for both of the two systems.A node localization mechanism is introduced and the existing localization systems and protocols in WSN are induced and summarized in this paper. One potential assumption used in most localization algorithms is that the network topology is isotropic. However, the characteristics of anisotropic which result from various factors such as the anisotropic terrain conditions, the different node densities and the irregular radio paths make the performances of localization algorithms get worse. RSSI localization algorithm proposed in the paper based on the highway environment is the localization algorithm applied for the low network connectivity. Most of the pre-algorithm on the RSSI worked in the room. There is no RSSI location algorithms have been applied for highway t before.The node in the WSN which need be localized is called an unknown node。The node which is settled and coordinated by people has been known in the localization system is called an anchor, it is also called a beacon. The neighbor node is the node that can be communicated in the node covering area. The wireless range of the node express by the letter"R",In cording to the coordinate system the WSN localization algorithm can be divided into the absolute localization algorithm and relative localization algorithm. The absolute localization algorithm must use the same reference frame. The result of the absolute localization is an entire standard coordinate position. The relative localization algorithm can use different references frame for every localization spot. WSN localization can also be divided into the Range-based localization and Range-free localization. The range based on localization includes the trilateration localization, triangulation method localization, ML method and so on. The range free can be achieved through only the information of the network connectivity. It includes the centroid algorithm, DV-Hop algorithm, MDS-MAP algorithm and so on. The localization precision is improved with the increase of the network connectivity degree in the Range-free algorithm. But the error is very large when it is in the low network connectivity.The outside surrounding affects the signal attenuation seriously. So the receive power varies with surrounding even at the same distance and the same equipment. The attenuation of signal is estimated by surrounding parameter in the paper. The RSS distance measuring precision is improved by calculating the surrounding parameter in a fixed time.The algorithm of ML makes the distance measuring results transformed into unknown localization nodal coordinate. Location coordinate is dispersed after multiple bearing when the coordinate is estimated only by ML parameters estimation due to the measure error brought in the power measurement. The location results could be more satisfied when used the ML parameters estimation again. The centroid weighted algorithm is used for the great dicergence of some localization nodal during localization process. The effect of anchor point, especially nearby the localization nodal is improved by the centroid weighted algorithm. The converging action is better and the location precision is enhanced.The anchor points of WSN distribute symmetrically at both sides of the highway. Every localization cell covers all the three traffic lanes. The situation that more than one vehicle in the same localization cell appears quite often. Under this kind of situation, the unknown vehicles usually become the obstacle factor of each other and difficult to evaluate. The related algorithm presented in this paper is to solve the question of localization in this case.When a vehicle enter from one localized cell into another, the localization result will often change in the scope of two different localized cells due to the error in the edge localization while the cell switches. This article will present the protective edge algorithm to judge the moving directions of unknown device and while they will enter into the adjacent localized cells through the calculation and comparison of the receive power of two reference device symmetrically positioned in the edge of localized cell.The paper demonstrates the algorithm which is used in localization in the highway by the connection of the theoretic analysis and the emulation lab. It may be found that the spots of unknown devices coordinates are close to each other, so the system can accomplish the localization function. It is used to avoid shaking in the edge of adjacent cell and filter the inefficacy coordinate by adding parameter protection algorithm. It solves the localization problem both of single unknown spot and several unknown spots together in one localization cell. There are 92 percent of the localization spots in the area which has a distance of 5m from the true data. And 98 percent of the localization spots have the distinction less than 4m comparing with the true data in the y-axis.It is believed that with the maturity of the WSN technology, the development of the topology frame and the improvement of the network carrying capacity, its application scope will be wider. It has more precise localization and more mature networks resulting in expanding highway vehicle positioning function to improve the management and control of the vehicle on the highway efficiency. All these can create abundance of higher economical and social returns for the benefit of mankind.