ABER performance investigation of LDPC-coded multi-hop parallel underwater wireless optical communication system

The average bit error rate (ABER) performance of a low-density parity-check (LDPC)-coded multi-hop parallel underwater wireless optical communication (UWOC) system is investigated with the combined effects of absorption, scattering, the misalignment characterized by the beam spread function, and the ocean turbulence-induced fading modeled by log-normal distribution. With the max-min criterion as the best path selection scheme, the cumulative distribution function for identically and independently distributed and non-identically and independently distributed links are derived, respectively. Then, the analytical ABER expressions of binary phase shift keying and multiple phase shift keying subcarrier intensity modulation schemes are deduced with the help of the Gauss-Laguerre quadrature rule, and they are also confirmed by Monte Carlo simulation. In addition, LDPC codes are applied in the simulation to improve the system performance. The results show that the combined degrading effects are mainly limited by the link length, especially under the coastal ocean condition. And the multi-hop parallel transmission demonstrates good ABER performance and can expand the communication range in ocean. Furthermore, LDPC codes can significantly improve the ABER performance of the UWOC system, and the coding gain is strongly affected by channel conditions and the corresponding parameters of LDPC codes. This work is beneficial for the UWOC system design.