Internet of Underwater Things: Enabling Technologies of Underwater Communications and Hybrid Networking

The Internet of Underwater Things (IoUT) is an ideal intelligent approach for ocean exploration in the new era of IoT, which mainly relies on underwater acoustic communications (UAC) for the interconnections among underwater devices. However, two inherent drawbacks of UAC make it insufficient for some communication requirements. First, it cannot support latency-sensitive applications such as accurate synchronization due to the long propagation delay. The second one is the limited bandwidth available for long-range communications. To find an alternative communication solution, two different underwater communication paradigms are investigated in this dissertation, namely underwater magnetic induction (MI) wireless communications and stress wave communications. For the MI alternative that does not have latency issues, we focus on the integration of MI with autonomous underwater vehicles (AUVs). A ferrite-assisted geometry-conformal MI antenna was proposed to fit for AUVs with a metallic body that maintains their fluid-dynamic efficiency. A concise physical layer was designed for the robust MI channel. For long-range underwater communications, we turn to stress waves using offshore pipelines for a possible solution. The established stress wave channel model reveals that the frequency-dependent attenuation can be ignored, which tells us the available bandwidth will not be affected by the communication range. Zero-forcing equalization and OFDM modulation were utilized to tackle the dispersion and reverberation interference under different circumstances. An underwater wireless communication testbed was established based on software-defined radio (SDR) and universal software radio peripheral (USRP) to verify the communication feasibility of both the MI and the stress wave. Finally, a power-efficient underwater AUV data collection strategy was designed, which can significantly prolong the network lifetime by using hybrid networking with both underwater acoustic and MI wireless communications.