Improved Routing and Spectrum Assignment formulations for optical OFDM networks

Efficient resource allocation in OFDM-based optical networks is directly affected by definition and formulations of Routing and Spectrum Assignment (RSA) problem. In this paper, we propose new Binary Linear Programming (BLP) formulations for the RSA problem that provide more efficient resource allocation in comparison with previous formulations. Unlike the conventional formulations that mainly aim at minimizing used spectrum slots, our formulations simultaneously aim at defragmentation and minimization of the assigned spectrum slots. We show contiguity constraint of the conventional formulations may incorrectly make a feasible solution unattainable. To solve this problem, we remove the contiguity constraint and embed its effect as a penalty term in the goal function. Two performance metrics for evaluating the amount of contiguity and defragmentation in a typical network are also defined. Simulation results show that the new formulations provide a considerable improvement in the performance of the RSA process in terms of the amount of contiguity and defragmentation with respect to the previous formulations.