Space-time coding performance analysis for CDL-impaired multi-core fiber transmission

The space division multiplexing (SDM) is among the most promising candidates in order to solve the single mode fiber capacity limitation. Recently, SDM testbed is deployed in order to host research activities and near to be Implemented. The SDM supports the propagation of orthogonal spatial channels where the paths could be several cores in multi-core fiber (MCF). Each core is affected by different losses due to the crosstalk and the misalignment losses which induce the core dependent loss (CDL). The existence of the CDL breaks the orthogonality and disparities between the cores. In previous works, we presented MCF transmission system with deterministic core scrambling strategy for the 7-core heterogeneous MCF structure aiming to reduce the CDL impact Still, the CDL impact is not completely mitigated. In this paper, we introduce digital solution based on the Space-Time (ST) coding to mitigate the CDL. We show that the ST code can completely absorb the CDL impact when we apply Maximum-Likelihood (ML) decoder. In addition, we prove analytically the ST performance considering the ML decoder by deriving an upper bound error probability of the coded transmission system. Finally, we address the ML high decoding complexity issue by combining the core scrambling and the ST codes. This solution keeps the CDL penalty low and performs close to the optima] solution while reducing the decoding complexity by applying the Zero Forcing (ZF) decoder.