Research On Localization Algorithm In Wireless Sensor Networks

Wireless sensor networks(WSNs)have been widely used in various fields because of their powerful distributed data sensing and processing capabilities.Many wireless sensor network applications acquire knowing the location of nodes in the network.As a classic range-free localization algorithm,DV-Hop can be implemented easily but often generates large errors.Localization technology based on Received Signal Strength Indication(RSSI)has been used extensively because it can achieve high precision without any additional hardware.In this paper,we mainly study and improve the localization algorithms based on RSSI ranging,which are further combined with classical DV-Hop algorithm to improve the positioning accuracy in WSN.The main contributions are as follows:(1)Based on Bluetooth and Zigbee devices,the path loss model and the RSSI ranging error principle are analyzed and verified.First,the theoretical model between RSSI and transmission distance is deduced.Second,we analyzed the relationship between ranging error and transmission distance,loss parameter as well as sampling times.Third,we collected the RSSI values of BLE and Zigbee devices at different distances in the real environment.After calculating the standard deviation of sampled data and doing the model fitting,we verified that the RSSI ranging error is proportional to the transmission distance.(2)Based on the relationship between RSSI ranging eror and transmission distance,we proposed a weighted nonlinear least squares method for coordinate calculation.In the case of known anchor coordinates and distances,we first introduce two common methods for coordinate calculation,which is least squares(LLS)and nonlinear least squares(NLS).At the same time,L-M algorithm is used to optimize the nonlinear objective function.Then,based on the theory that the ranging error is proportional to the transmission distance,a weighted nonlinear least squares method(WNLS)is proposed.This method is built on the objective function of NLS,and we assign smaller weights on further nodes.The simulation results show that the accuracy of the weighted nonlinear least squares method is better than comparison algorithms under different parameter configurations.More precisely,the average localization error is reduced by 70%and 40%compared with the least squares and the non-weighted algorithm,respectively.(3)Aiming at the problem of DV-Hop's low positioning accuracy,a hybrid localization algorithm(RDLA)is proposed,which combines the RSSI ranging and the DV-Hop flooding.There are two main improvements in this algorithm:1.Taking advantage of RSSI ranging to optimize the distance estimation between adjacent nodes,and by the coordinate broadcasting mechanism of unknown nodes,nodes can now update each other;2.The weighed nonlinear least squares method is used to calculate the coordinate of unknown nodes.The positioning error is reduced by appropriate weight assignment and nonlinear target optimization.The experimental results show that,compared with the original DV-Hop algorithm,the average positioning accuracy of RDLA is significantly improved by 50%?64%.At the cost of higher complexity,this algorithm performs well under different environmental parameters.