A GPS-free localization scheme for wireless sensor networks

Localization is an important and extensively studied problem in ad-hoc wireless sensor networks. Most schemes require some nodes functioned as anchors with positions configured manually which are error-prone. In this paper, a GPS-free localization scheme is proposed. High accurate TOA is acquired by means of measure the time difference between two simultaneously transmitted radio and ultrasonic signals at the receiver. With the assistant of coarse AOA information, the flip ambiguity is fixed. The performance of our scheme is demonstrated with an accuracy of a few centimeters using our prototype nodes.