CDMA-Based Broadband UAC Modem: A Modulation and Demodulation Design Approach

With recent advancements in artificial intelligence, the development of unmanned systems has accelerated, spurring growing interest in Autonomous Underwater Vehicles (AUVs). These platforms collect highresolution imagery and sensor data, which must be transmitted in real time from underwater to surface stations. This paper presents a CDMA(Code Division Multiple Access)-based modulation and demodulation scheme for a broadband underwater acoustic communication modem[1]. A wideband system was designed based on analysis of various ocean environments to ensure robust performance. The proposed scheme dynamically adapts to environmental parameters under different underwater conditions, providing strong resilience. The simulation environment, implemented in MATLAB, was configured to evaluate the SNR(Signal Noise Ratio) to BER(Bit Error Rate) performance of the proposed CDMA transmission technique under varying Doppler shift conditions. Spreading factors of 10 and 14 were tested, with maximum Doppler shifts ranging from 1 Hz to 10 Hz. In the corresponding figures, circular markers represent Doppler shifts from 1 Hz to 7 Hz, while star-shaped markers indicate shifts from 8 Hz to 10 Hz, each color-coded for clarity. The results show that the proposed scheme exhibits minimal performance degradation, demonstrating strong robustness against Doppler-induced distortion.