Channel Impulse Response Correlation Analysis and Channel Estimation for WDM Underwater Wireless Optical Communication Systems

The wavelength division multiplexing (WDM) underwater wireless optical communication (UWOC) systems need a lot of pilots to obtain the accurate channel impulse response (CIR) of multi-wavelengths, resulting in decreased spectral efficiency. To address this problem, we propose a method based on two-dimensional principal component analysis (2D-PCA) to analyze the CIR correlation for WDM UWOC systems with various wavelengths. Numerical results suggest that the multi-wavelength CIR has a strong correlation and the eight largest main eigenvalues account for more than 99% of all eigenvalues. Based on the correlation analysis, we further propose a channel estimation method using 2D-PCA, which can estimate WDM UWOC systems CIR by some reference wavelengths. The proposed channel estimation algorithm significantly outperforms prior approaches in terms of mean square error (MSE) performance under the same pilot overhead. Meanwhile, the proposed algorithm is capable to alleviate or solve the over fitting issue caused by too many reference wavelengths, which greatly reduces the pilot overhead.