Trading Regeneration and Spectrum Utilization in Code-Rate Adaptive Flexi-Grid Networks

Introduced to improve the spectral efficiency, time-frequency packing technique allows the exploitation of different code rates, leading to different levels of spectral utilization and all-optical reach. To ensure quality of transmission of the optical signal, opto-electronic regeneration must be used to propagate the transmission beyond the maximum optical reach and can inherently offer conversion of spectrum and code rate. In this way, multiple code rates can be enabled in optical networks, leading to a flexible design in which spectrum utilization and regeneration can be properly optimized and traded. This paper addresses for the first time the joint problem of selecting the code rate, the regeneration nodes, the spectrum allocation and the route for the requested lightpaths in an optical network with a flexi-grid. A genetic algorithm is proposed that balances the contrasting objectives of minimizing the regeneration nodes and the spectrum utilization. Results show that when regeneration nodes are minimized, code-rate adaptation is able to reduce the regeneration nodes as well as the spectrum utilization with respect to rate-fixed optical networks. In general, a balance of the two contrasting objectives is preferred to achieve a low resource utilization.