TY - JOUR TI - A study of OFDM in underwater wireless optical and acoustic communications DO - https://doi.org/doi:10.7282/t3-mmqd-zh41 PY - 2019 AB - With the development of marine applications in military and commercial fields, underwater communication techniques with high transmission data rate over long-range distances are in urgent demand. Two mainstream underwater wireless communications solutions are Underwater Acoustic Wireless Communications~(UAWC) and Underwater Optical Wireless Communications~(UOWC), which are based on acoustic and optical signals, respectively. In this thesis, a new physical-layer architecture is proposed for high-data-rate UOWC based on integrated hybrid Orthogonal Frequency Division Multiplexing~(OFDM) and Pulse Position Modulation~(PPM) with Time-Frequency~(TF) spreading. Such architecture is engineered to increase the transmission range compared to basic OFDM systems thanks to the robustness of the nonlinear PPM modulation in wireless fading channels. Frame error rate performance and physical-layer throughput results are obtained using a custom-made physical-layer simulator built to emulate hardware performance. It is found that, with the proposed hybrid OFDM-PPM modulation scheme, the range is extended by over 10 m for a single transmitting light source, and by over 20 m for four transmitting light sources. Moreover, with the TF-spreading, the proposed architecture can improve the coverage by several folds compared to the case without spreading. Importantly, the Doppler effect is mitigated effectively by the combination of OFDM-PPM and TF-spreading, as shown via thorough simulations. Besides, the implementation of UWAC has been studied with a testbed using universal software radio peripheral hardware device. The OFDM-based Single-Input and Single-Output and Multi-input and Multi-output are tested in a water tank and the pool at Sonny Werblin Recreation Center, Rutgers University. Data of experimental results are collected, and the performances of the testbed are evaluated. Moreover, the performances of using spatial multiplexing and spatial diversity techniques in a MIMO structure are analyzed. KW - Electrical and Computer Engineering KW - OFDM KW - Time-frequency spreading KW - Pulse position modulation KW - Underwater optical wireless communication KW - Underwater acoustic wireless communication KW - Orthogonal frequency division multiplexing LA - English ER -