The marine environment is complex and variable, with the absorption and scattering effects of seawater and turbulence causing significant attenuation of received optical signals and introducing random jitter, which limits the communication range and stability of underwater wireless optical communication systems. This paper presents the Superposition UEP-Spinal Code structure, which utilizes unequal error protection (UEP) to adjust the transmission performance of different types of information in underwater composite data communication by adjusting the superposition weighting factors in the encoding algorithm. This encoding method enhances the noise immunity of important data, and with the same bandwidth utilization, the overall decoding complexity is reduced by 13.3% compared to the previously improved Spinal code encoding algorithm. The results show that the Superposition UEP-Spinal Code provides a more stable, reliable, and efficient communication solution for underwater wireless optical communication systems with randomly varying channel conditions.

Fiber optic communication while drilling can transmit downhole geological and engineering parameter data at high speed, serving as a crucial component of intelligent drilling. However, the complex and highly dynamic downhole environment, characterized by strong vibrations and high temperatures, can lead to random attenuation of light intensity, phase mismatch, and signal distortion, thereby reducing the signal-to-noise ratio of the optical signal. This paper proposes a superposition UEP-Spinal code structure to enhance the noise resistance of signals under low SNR conditions. This structure utilizes Unequal Error Protection and adjusts the duty cycle of the superposition weighting factor P to separately encode the head and tail codes of the signal, simplifying the structural complexity of the tail code and reducing complexity by 2.01dB for the same code length. Meanwhile, it enhances the noise resistance of the head code, reducing the bit error rate by 1.21dB for the same channel capacity, and the overall decoding complexity is reduced by 13.3%. The results demonstrate that the superposition UEP-Spinal code can achieve stable and reliable communication in low SNR environments.

The complex environments of Measurement-While-Drilling (MWD), characterized by intense vibrations and high temperatures, can lead to random attenuation of optical intensity, phase mismatch, and signal distortion, thereby reducing the signal-to-noise ratio (SNR) of optical signals. Under severe channel fluctuations, forward stack decoding (FSD) tends to search more invalid nodes, increasing decoding complexity. This paper proposes an unquantized forward stack decoding algorithm that dynamically adjusts the number of retained candidate nodes based on channel conditions. With the ability to evaluate channel status dynamically, the proposed method achieves low-complexity decoding and enhances transmission performance. In simulations under channel conditions with SNR ranging from -14 to 5 dB, the average decoding complexity was reduced by 58% compared to conventional FSD. In communication experiments using a dynamically variable optical attenuator to generate random attenuation between 0 and -30 dB, the average decoding complexity was reduced by 23.6% compared to FSD. Furthermore, this work integrates the non-quantized forward stack decoding with the superposition UEP-Spinal code to construct a novel MWD communication system. In simulated MWD environment, the proposed system achieved an average bit error rate (BER) of 5.58×10^-5, with BER consistently below 0.1% across all intervals. Compared to the traditional Spinal code system, the decoding complexity was reduced by 31.5%. The results demonstrate that the newly developed communication system exhibits high reliability, low decoding latency, and high effective transmission rates in simulated drilling platform scenarios, making it well-suited for MWD communication applications.