Cost-Efficient SDM/BDM Network Planning Based on Hierarchical Optical Cross-Connects

Following the trend of spatial-division multiplexing (SDM) and band-division multiplexing (BDM) for expanding the network capacity, we propose cost-efficient SDM and BDM (SDBDM) network planning based on hierarchical optical cross-connect (HOXC). The HOXC consists of wavelength cross-connect (WXC) and band cross-connect (BXC), and the switchings of corresponding wavelength-/band-paths are configured so that the total network cost is minimized. The novelty of this study compared to previous studies on HOXC is that it incorporates band-dependent component costs: this allows us to efficiently utilize the components and spectrum resource on each band. To find the optimal network planning considering band-dependent costs, we first formulate an integer linear programming (ILP) problem and then propose a heuristic to make it applicable to practical-scale problems. The heuristic introduces auxiliary graphs that accurately model the considered network architecture and component costs and configures each wavelength-/band-path with minimal additional cost. The proposed heuristic has an average optimality gap of less than 9%, and it well approximates the proportion of utilized components and bands in the optimal solution. The numerical simulations demonstrated that the proposed SDBDM network planning can reduce network cost by up to 20%, while reducing the number of wavelength-selective switches (WSSs) by up to 95%. The results also indicated that the preferred architecture and number of multiplexed bands differ depending on traffic volume and average link length.