A Three-Dimensional Location Algorithm Based On AOA And TDOA For Wireless Sensor Networks

Wireless Sensor Networks(WSN) refers to the self-organizing multi-hop network, which is composed of many micro-sensor nodes deployed in the monitoring area and organized by wireless communication, collaboratively aiming to perceive,collect and dispose the information from the perceived object in the network overlay area and then send to the observer. With very wide application prospect WSN can be applied to military and national defense, urban management, medical and health, environmental monitoring, emergency rescue and disaster relief, the danger zone remote control and so on. Localization technology is a support technology of sensor network, a premise for WSN to carry out target identification,monitoring,tracking and many other applications, and also a hot issues in the study of sensor network.The paper first introduces the basic concepts and methods of WSN localization technology, illustrates the evaluation indexes and classification methods, then analyzes and summarizes several existing typical localization algorithms. The paper does researches deeply on the sensor nodes angle measurement algorithm based on wave interference. The algorithm needs to install two ultrasonic transmitter at beacon nodes and only one ultrasonic receiver at unknown nodes while the AOA algorithm request to install an ultrasonic transmitter at beacon node and two or more ultrasonic receiver at unknown nodes. Since there is a small number of beacon nodes and a large number of unknown nodes, this method reduces the hardware requirements and power consumption. But there is some dead angle the algorithm can not measure. The paper proposes an improved algorithm, in which two pairs of ultrasonic transmitters are installed on the beacon nodes. The parameters of ultrasonic transmitters are the same, and the perpendicular bisectors of the two pairs of ultrasonic transmitters are perpendicular, and the distance between a pair of ultrasonic transmitters is 2r. If the angle couldn't be measured by one pair, the other pair begins to work. Mathematical analysis and simulation results show that the improved algorithm completely solved the blind spot of the primal one.Most of the existing localization algorithms are aiming at two-dimensions, but in realistic application, the sensor nodes always distributes in three-dimensions, so study on the localization in three-dimensions will be much more in line with the actual application. This paper proposes a combined localization algorithm based on wave interference angle measurement (AOA) and time difference of arrival (TDOA). With higher accuracy this algorithm can effectively estimate the location of the sensor nodes in three-dimensions. The algorithm is divided into three steps. Firstly calculate the angle between beacon nodes and unknown nodes using the angle measurement algorithm based on wave interference. Second compute the distance between beacon nodes and unknown nodes with TDOA. And then using the measured angle and distance above, calculate the coordinates of unknown nodes accurately according to the formula derived in this paper.Simulation results show that the algorithm has low complexity and high precision, only needs three beacon nodes at least, and effectively estimates the location of the sensor nodes in three-dimensions.