Improved Block-Based Wavelength Assignment Strategies for DWDM Networks with All-Optical Wideband Converters

Block-based wavelength assignment heuristics are widely used in DWDM optical networks to mitigate spectrum fragmentation. The Longest Block First (LBF) algorithm selects the longest contiguous available spectral block to minimize blocking probability, but its first-fit expansion strategy for covering remaining path segments generates excessive wavelength conversions. This paper proposes and evaluates two improved strategies: All Longer Blocks First (aLBF) and Longest Block Last Edge Blocks (LBLeB). Both algorithms maintain the same sorting and longest-block selection as LBF, but employ alternative left/right subrange covering policies. aLBF uses an optimal greedy expansion that actively minimizes the start node (leftward) and maximizes the end node (rightward) of each covering block, while LBLeB uses a passive last-valid-block strategy. Simulation results on the CORONET continental topology with incremental traffic and fiber augmentation demonstrate that aLBF-B and LBLeB-B both approach the efficiency of the OEOWC reference in terms of blocking probability, while achieving significantly better converter utilization than OEOWC. aLBF-B in particular achieves the best trade-off, reducing conversions by 23.6% and converters by 21.8% relative to LBF-B while approaching the OEOWC reference in blocking performance. In contrast, LBLeB shows more modest improvements over standard LBF.