A rateless frequency-phase modulation scheme for robust underwater acoustic communication

Underwater acoustic (UWA) communication faces significant challenges due to severe channel variability across time, space, and frequency. Traditional modulation and demodulation methods often lack adaptability to such complex and dynamic conditions, leading to performance degradation. To address this issue, we propose a novel rate less frequency-phase communication system that enhances robustness in complex environments. The system is built on an improved Spinal coding framework, where the encoded bitstream is divided into two segments: the first is mapped to frequency-shift keying (FSK) symbols for improved noise resilience, and the second to phase-shift keying (PSK) symbols for higher spectral efficiency. A frequency-hopping spread spectrum (FHSS) mechanism is introduced to further resist narrowband interference. The final signal is transmitted using a nonuniform-rate frequency-phase keying (FPK) modulation scheme. Owing to the Spinal decoder’s capability to reconstruct from any bit position, the FSK and PSK branches can be demodulated independently, maintaining coding consistency while enhancing flexibility. Simulation results show that the proposed system achieves lower bit error rates and greater transmission stability compared to traditional Spinal-PSK/FSK schemes and convolutionally coded FPK systems, demonstrating its strong potential for robust UWA communication.