A Multicarrier Underwater Acoustic Modem with Precise-Ranging Capability

智力优势：本项目研究水声通信的范式转变，从单载波传输到正交频分复用（OFDM）形式的多载波调制。OFDM在处理长频散信道上的高速率传输方面有其独特的优势，在最近的宽带无线无线电应用中占有主导地位。然而，由于水声信道具有较大的带宽与载波频率比、较大的传播延迟、较大的多径扩展和快速的信道变化，因此水声信道比无线电信道更具挑战性。结合水声信道的独特特性，我们的首要任务是使OFDM在具有快速移动平台的水下环境中工作。初步的实验结果已经证明了我们提出的方法的有效性，即使在发射器和接收器之间的相对速度高达10节的情况下，这是目前最先进的。在我们的第二个任务中，我们为多载波调制解调器配备了精确测距能力。关键是开发精确的同步算法，在密集的多路径条件下定位“第一到达点”，并在快速变化的水下信道中工作良好。在我们的第三个任务中，我们开发了一个基于数字信号处理器的独立调制解调器原型，该处理器集成了本项目中开发的收发器算法。更广泛的影响：提供具有测距能力的多载波声学调制解调器，该项目有可能直接有利于水下无线传感器网络的各种应用的发展。由于水声信道的带宽与载波频率比大，所提出的方法和算法也可能对宽带和超宽带无线电应用产生影响。该项目整合了研究和教育，以提高本科和研究生课程的内容，特别是提供创新的高级设计项目。

Intellectual Merit: This project investigates a paradigm shift in acoustic underwater communication from single-carrier transmission to multi-carrier modulation in the form of orthogonal frequency division multiplexing (OFDM). OFDM has its unique strength in handling high-rate transmissions over long dispersive channels and has prevailed in recent broadband wireless radio applications. However, underwater acoustic channels are far more challenging than their radio counterparts due to their large bandwidth-to-carrier-frequency ratio, large propagation delay, large multipath spread, and fast channel variations. Incorporating the unique characteristics of underwater acoustic channels, our first task is to make OFDM work in underwater environments with fast-moving platforms. Preliminary experimental results have demonstrated the effectiveness of our proposed approach even when the relative speed between the transmitter and the receiver is up to 10 knots, which is the current state of the art. In our second task, we equip the multi-carrier modem with precise-ranging capability. The key is to develop precise synchronization algorithms that can locate the "first arrival" in the presence of dense multi-path conditions and that can work well in fast-varying underwater channels. In our third task, we develop a standalone modem prototype based on a digital signal processor that integrates the transceiver algorithms developed in this project.Broader Impact: Providing a multi-carrier acoustic modem with ranging capability, this project has the potential to directly benefit the development of underwater wireless sensor networks for a variety of applications. Due to the large bandwidth-to-carrier-frequency ratio of underwater acoustic channels, the proposed methodology and algorithms may, also, have an impact on wideband and ultra-wideband radio applications. This project integrates research and education to enhance the content of undergraduate and graduate classes and, in particular, provides innovative senior design projects.