FPGA Implementation of Adaptive Modulation Scheme-Based Underwater Acoustic Modem

Underwater environments are known for their challenging and variable communication channels, where factors such as multipath propagation, Doppler shifts, and noise severely affect signal integrity. Traditional fixed-modulation schemes often fail to maintain optimal performance under these conditions, leading to reduced data rates and increased error rates. This paper presents the design and implementation of an adaptive modulator for underwater acoustic communication systems, capable of dynamically switching between amplitude shift keying (ASK) and frequency shift keying (FSK) modulation schemes based on real-time channel conditions. The proposed modulator leverages the strengths of ASK and FSK, selecting the appropriate scheme based on an analysis of channel quality metrics, such as signal-to-noise ratio (SNR) and channel fading characteristics. ASK is preferred in high-SNR scenarios due to its higher data rate efficiency, while FSK is employed in low-SNR conditions for its robustness against noise and multi path effects. The novelty of this work lies in its adaptive approach, which contrasts with earlier works that predominantly focused on optimizing individual modulation schemes without considering real-time adaptability. Additionally, the implementation of this adaptive modulator on a field programmable gate array (FPGA) platform emphasizes simplicity and efficiency, making it suitable for deployment in real-world underwater communication systems. The transmitter section of the proposed scheme is implemented on the Zynq FPGA board. The hardware description language (HDL) design is modeled using Xilinx Vivado design suite 19.2 software along with an XST synthesizer and System Generator Simulator.