Spectrum Defragmentation Window in SDM-EON Networks

Space division multiplexing (SDM) technology expands the capacity of elastic optical networks (EONs) by adding spatial dimensions, positioning SDM-EONs as a strong candidate for future high-throughput infrastructures. However, SDM introduces new challenges, especially vertical fragmentation, where frequency slots become misaligned across multiple cores. This fragmentation decreases spectral efficiency, reduces resource availability, and increases connection blocking. This work proposes WDefrag, a novel RMSCA algorithm that tackles these issues through Slot Window Defragmentation, an original strategy developed in this study. WDefrag segments the spectrum into cost-evaluated windows and identifies regions where fragmentation most severely limits allocation. The algorithm reallocates resources locally, avoids unnecessary disruptions, and improves spectrum organization while managing crosstalk and fragmentation in both spatial and spectral dimensions. WDefrag operates in both proactive and reactive modes and adjusts window sizes to match traffic dynamics. Simulations compare it against non-defragmenting and state-of-the-art approaches. WDefrag outperforms these baselines by up to 30% in bandwidth blocking reduction, particularly in proactive scenarios. By applying cost-aware decisions and prioritizing fragmented regions that limit connectivity, WDefrag enhances spectrum utilization and delivers consistent performance improvements under real network demands.