Proactive Modulation Format Allocation Method with Selective Downgrading to Enhance Inter-core Crosstalk Tolerance in SDM-EONs

In elastic optical networks using multi-core fibers, modulation formats should be allocated for lightpaths considering the tolerance to inter-core crosstalk (IC-XT) as well as spectrum resource utilization efficiency. Using higher-level modulation formats, which can transmit more bit strings in one wavelength, consumes fewer frequency slots (FSs) to establish lightpaths, but because of lower tolerance to IC-XT, fewer lightpaths can be established with same FSs of cores that are adjacent to each other, which decreases core utilization efficiency. We propose a proactive modulation format selection method that maximizes the core and spectrum utilization efficiency by intentionally using lower-level modulation formats to the extent that core utilization efficiency improved by higher tolerance to IC-XT outweighs spectrum utilization efficiency decreased by consuming more FSs. We have demonstrated that our proposed method can tolerate approximately 70% and 20% higher average arrival rates of lightpath setup requests for the Kanto 11 and JPN 12 topologies respectively, compared to the conventional method that selects the highest-level modulation formats among available ones.