OFDM underwater acoustic communication system implementation on FPGA

Abstract

This thesis focuses on the design and implementation of a highly flexible underwater acoustic (UWA) communications prototype that can be used for rapid testing and research purposes. The prototype contains software and hardware targeted to the Programmable Logic (PL) and Processing System (PS) sections of the Xilinx Zynq System on a Chip (SoC) device, respectively. The system model is developed by exploiting the Simulink software tool, which offers both model simulation and hardware description language (HDL) code generation. The HDL code is deployed onto the embedded Field Programmable Gate Array (FPGA) of the Zynq SoC. We propose a system model based on orthogonal frequency division multiplexing (OFDM) with cyclic prefix and differentially coherent detection. OFDM is a robust multi-carrier modulation technique used to combat the frequency-selectivity and multipath effects of the UWA channels. The innate OFDM virtue of having narrowband signal on each carrier, motivates the straightforward implementation of differentially coherent detection. This technique avoids estimating the channel coefficients by taking advantage of the existing coherence between consecutive OFDM carriers, and thus, the overall system complexity is reduced significantly. Finally, the prototype is evaluated for short range point-to-point communication links established in tank and pool setups. We report on the system performance in terms of data detection mean squared error and bit error rate from a system that uses the 120 - 130 kHz band.