Jiacheng Shi’s PhD Dissertation Defense

Title:

Towards a Programmable, High Speed, and Robust Internet of Underwater Things

Location:

ISEC 232

Committee Members:

Prof. Tommaso Melodia (Advisor)

Prof. Stefano Basagni

Prof. Kaushik Chowdhury

Abstract:

Increasing demand of underwater exploration requires a platform with higher data rate, more robust performance, and hardware/software flexibility. The biggest challenge to realize these networked platforms is due to the availability of narrow bandwidth and the long propagation delay of acoustic wave transmission, which suffers from much less attenuation than radio-frequency (RF) electromagnetic waves. Meanwhile, wirelessly networked systems of underwater devices are becoming the basis of many commercial and scientific activities at sea. However, existing commercial modems are built with fixed hardware and insufficient data rate. Therefore, there is a demand for a platform to fully support higher data rate, underwater acoustic network functionalities and applications, as well as the capability of adapting their communication parameters in real time based on the environmental conditions.

Towards addressing these challenges, we first propose the SEANet Project, which is supported by the NSF, intends to develop a new generation of programmable platforms and a networking testbed to enable the goal of a programmable Internet of Underwater Things (IoUT). SEANet is built on new software-defined platforms with an open architecture that will allow users to specify, add, upgrade, and swap new hardware and software components with ease. Over short and moderate range links, SEANet is designed to offer data speeds at least one order of magnitude higher than existing commercial systems. Moreover, a new MIMO-OFDM transceiver configuration is suggested. We show a prototype of a 2×2 MIMO-OFDM transceiver node for the Internet of Underwater Things (IoUT), which intends to build a new generation of programmable and portable platforms a networking testbed with real-time processing and reconfiguration. The suggested receiver operates on a block-by-block basis, using pilot subcarriers for channel estimation to prevent matrix inversion and accommodate the hardware’s limited resources. We also use space-frequency block coding (SFBC) for transmission diversity. In addition, null-carrier based Doppler compensation enables high-resolution uniform Doppler drifting. We show that the suggested MIMO-OFDM IUoT prototype can support data speeds of up to 600kbit/s with 16QAM modulation.

We also investigate physical layer signal processing approaches to further enhance the robustness of underwater acoustic communication. First, we propose a novel modulation scheme based on Quasi-Orthogonal Chirp Multiplexing (QOCM). We introduce two sets of mutually quasi-orthogonal chirp signals, which are employed as transmission subcarriers. We provide the QOCM transmitter and receiver design, as well as digital implementation. The results of simulations and tank experiments reveal that QOCM has a high data rate and robustness against Doppler effect.