Underwater Acoustic Localization with Applications to Multiuser Communications

Multiuser underwater acoustic communications (UACs) have gained attention because of a number of applications. To assess the performance of multiuser UACs and reduce the cost of experiments, simulations of the signal transmission are used. However, the existing underwater signal transmission simulators suffer from complexity and signal length limitation
when investigating multiuser UACs. Therefore, it is useful to develop a signal transmission simulator for UACs. To improve the performance and bandwidth efficiency of multi-user systems, arrays can be used at the transmitter with transmit beamforming, which require the channel state information (CSI) available at the receiver to be sent as a feedback message to the transmitter. A long feedback message in UAC is a waste of the throughput and sometimes impractical. Therefore, it is important to develop an advanced transmit beamforming method for the multiple transmit sensor array systems.
In this thesis, an underwater channel simulator based on acoustic field computation is proposed. We pre-compute and store the acoustic field in the investigation area, thus speeding up the computation whilst maintaining the performance. Based on this, an underwater receiver localization method is then proposed. In the localization, the CSIs at specific points in the investigation area are pre-computed and compared with the CSI measured at the receiver, thus the position of the receiver is estimated as the point with the best match. It offers a more practical solution to the underwater localization problem. A receiver trajectory estimation technique combining the proposed localization and smoothing approach is also proposed to reduce the cost of infrastructure, and it can be applied in a two-dimensional plane and a three-dimensional space. An advanced beamforming technique is introduced in the transmitter design based on the proposed localization technique. It offers accurate detection performance and the length of the feedback message is reduced significantly.