Device-free indoor localization using a distributed network of autonomous UWB sensor nodes

In this paper we describe a method for localization of multiple persons using a distributed network of autonomous ultra-wideband sensor nodes. The persons do not carry any devices or tags to aid their detection, but are instead detected by using the time variations they impose on the measured channel impulse response between a transmitter and a receiver. The described method uses background subtraction and constant false alarm rate algorithms for person detection. Range tracking is incorporated for removal of clutter and false observations. The range information of the persons with respect to each sensor is fused using a maximum likelihood function. Here, we analyze the influences of range tracking on location estimation. In addition, two location estimation approaches are compared. The first approach fuses the available range information of the persons with respect to all sensors of the network. In the second approach locations are estimated by each sensor node and are later fused with the location estimates from the other sensors. The system implementation and selected methods for device-free person range estimation and sensor data fusion are verified in a realistic measurement scenario with two moving persons and through-wall operation of all sensors. The method can be used for near real-time localization and tracking of multiple moving persons.