Research On RF Signal Estimation Of Nodes Location In The Urban Environment

As a novel application technology that acquires more and more attention in the world, wireless sensor networks can perform the process of cooperative detection, data processing and signal transmission. Meantime, it can transport he message to the user automatically. Wireless sensor networks make the objective word and the electronic information world have a connection. As a result, people can perceive the objective material directly. Wireless sensor networks expands the functions of existing networks, enhances the cognitive abilities of human beings. In the future, wireless sensor networks will change our daily lives greatly.The location information plays a key role in the wireless networks application. The sensory information and the location information collected by the sensor nodes must be bundled together to make sense. Experiments show that the number of beacon nodes is larger or the distribution is more uniform, the target location accuracy is higher, so is the construction cost. Usually the number of beacon nodes is small in the deployment of the wireless sensor networks due to the ordinary nodes will upgrade to the beacon nodes when they are located. The nodes upgrade can fulfill the precision need and decrease the construction cost.The algorithm based on ranging can be divided into signal Time of Arrival algorithm, signal Time Difference of Arrival algorithm, signal Angle of Arrival algorithm and Received Signal Strength Indicator algorithm according to the measurement of quantities. The procedure of location algorithm based on ranging is: distance measuring, coordinate calculation and location correction. It is clear that the accuracy of the distance measurement directly determines the node localization accuracy. The former algorithms have high requirement for the signal visual and have drawbacks in the obstruction and multipath effects. But the algorithm based on Received Signal Strength Indicator is not so. And it could perform the detecting process automatically without any extra hardware and it is used in nodes location and object tracking. The present problem is how to increase the received signals estimation precision in the environment where obstructions blocking and multipath exist.In the urban environment, loud noisy exist in the signal transmission channels. The channels will be influenced by signal reflection, diffraction and multipath. It is difficult to estimate the strength value of RF signal. The algorithm we proposed is based on the Shadowing mode. In this algorithm, the frequently mutation of RF signal is considered. We build the wireless transmission mode in the urban environment and the mutation detect function is used to check the signal mutation. We proposed a Threshold-Based Kalman Algorithm due to the valuation strength of Kalman Algorithm. In the proposed algorithm firstly judges the threshold used for comparison and adjusts the parameters when detecting the happening of saltation. The proposed algorithm has high convergence rate and can estimate RF signal precisely. It can be used in the nodes location algorithm based on ranging in the urban environment and it has strong robustness.