Polarization-Dependent Loss Mitigation via Orthogonal Design Precoding and Interference Cancellation
Mohannad Shehadeh, Frank R. Kschischang
TL;DR
The paper tackles polarization-dependent loss (PDL) in polarization-division multiplexed optical channels by applying orthogonal-design precoding and interference cancellation to approach capacity under a memoryless model with worst-case PDL characterized by $\alpha$. It extends the capacity-achieving scheme of Shehadeh and Kschischang to a practical 16-QAM setup with Chase decoding and introduces a single-code variant, $pD$, that obviates the need for two inner codes while preserving performance. Through simulations, the authors show that the original scheme remains effective up to a worst-case PDL of $6$ dB, but $pD$ provides a more practical alternative with comparable gains and simpler implementation; the complex-valued case behaves similarly to the real-valued case, validating the generality of the approach. The work also points to potential future directions, such as using spatially-coupled codes to realize universal performance and potentially removing precoding altogether.
Abstract
Recent work by Shehadeh and Kschischang provides a simple capacity-achieving scheme for channels with polarization-dependent loss (PDL) under common modeling assumptions via a careful choice of orthogonal-design-based precoding and interference cancellation. This letter extends that work with a simulation-based demonstration showing that this scheme remains highly effective at mitigating PDL in the highly practical setting of 16-QAM with Chase-decoded extended Hamming inner codes rather than the near-capacity inner codes considered in the original work. An alternative near-optimal variation of this scheme is also provided requiring only one inner code rather than two and suffering no penalty in the absence of PDL, making it much more practical.