A pre-forbidden spectrum strategy to conveniently consider crosstalk in SDM-EON

Inter-core crosstalk (XT) is a main disadvantage in space division multiplexing elastic optical network (SDM-EON). Two methods are commonly used to consider crosstalk, namely worst-case XT strategy and precise XT strategy. When assigning spectrum resources to a connection request, the former calculates the maximum possible crosstalk, and the latter calculates the precise crosstalk. The worst-case XT strategy costs less time but leads to a higher bandwidth blocking probability, while the precise XT strategy gets a lower bandwidth blocking probability yet spends more time. In this paper, we study crosstalk-aware spectrum assignment problem in SDM-EON and propose a pre-forbidden spectrum (PFS) strategy to consider crosstalk. In the proposed strategy, three spectrum segments in the central core and two fringe cores are pre-forbidden respectively, which reduces number of neighbors of the remainder spectrum segments. By using the PFS strategy, the maximum possible crosstalk decreases and then the maximum optional modulation level increases, which can reduce bandwidth blocking probability of connection requests. The proposed PFS strategy is compared with the worst-case XT and precise XT strategies. Simulation results show that, bandwidth blocking probability of the PFS strategy is much lower than the worst-case XT strategy and slightly higher than the precise one, while average running time of the PFS strategy is far less than the precise XT strategy and similar to the worst-case XT one. Hence, the PFS strategy has the benefits of both comparison strategies.