Multi-stage AUV-aided Localization for Underwater Wireless Sensor Networks

Underwater Wireless Sensor Networks (UWSNs) are expected to support a variety of civilian and military applications. Sensed data can only be interpreted meaningfully when referenced to the location of the sensor, making localization an important problem. In terrestrial WSNs, this can be achieved through a series of message exchanges (via RF communications) between each sensor and Global Positioning System (GPS) receivers. However, this is infeasible in UWSNs as GPS signals do not propagate through water. Acoustic communications is currently the most viable mode of wireless communications underwater. However, underwater acoustic channels are characterized by harsh physical layer conditions with low bandwidth, high propagation delay and high bit error rate. Moreover, the variable speed of sound, due to variations in temperature, pressure and salinity, and the nonnegligible node mobility due to water currents pose a unique set of challenges for localization in UWSNs. In this paper, we present a multi-stage AUV-aided localization scheme for UWSNs. The proposed method combines the flexibility and localization accuracy of an AUV-aided localization, the energy efficiency of "silent localization" and improved localization coverage with k-stage localization based on sensor nodes. We evaluate the performance of the proposed scheme in terms of the localization coverage, accuracy and communication costs using simulations. We show that while improved performance with multiple stages is traded off with higher communication costs in general, the latter can be minimized while maintaining good performance with an appropriate choice of the acoustic communication range.