Revisiting the modulation format selection problem in crosstalk-aware SDM-EONs

The problem of finding a lightpath to provision a connection request in space-division multiplexing elastic optical networks (SDM-EONs) involves routing, modulation, spectrum and core assignment (RMSCA). Aiming at maximizing spectrum efficiency, the lightpath is always established with the modulation format that gives the highest data rate within the transmission reach and crosstalk (XT) threshold. For SDM-EONs based on multi-core fibers (MCFs), highest rate modulation format leads to lowest XT tolerance/threshold, or more spectrum fragments in adjacent cores. We call this problem XT-fragmentation. XT-fragmentation has been ignored by all existing RMSCA algorithms. In this paper, we first propose a way to measure the potential spectrum loss due to more fragments. Then a new modulation format selection (MFS) algorithm is designed with XF-fragmentation in mind. Simulation results show that RMSCA algorithms with MFS achieves lower request blocking probability than that without MFS.