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In this paper, we study the joint resource allocation in flexible-grid networks based on a nonlinear physical layer impairment model. An optimization problem is formulated to assign resources and guarantee the signal quality for every channel. Compared with the resource allocation in fixed-grid wavelength-division multiplexing scenario, our method achieves significant bandwidth reduction and transmission distance extension in flexible-grid networks. The maximum spectrum usage is shown to be insensitive to the ordering of channels. We also analyze the relation between modulation formats and transmission distance based on the results of the proposed method. Finally, we demonstrate the performance and scalability of the proposed algorithm in ring networks.

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This paper proposes a novel network planning strategy to jointly allocate physical layer resources together with the routing and spectrum assignment in transparent nonlinear flexible-grid optical networks with static traffic demands. The physical layer resources, such as power spectral density, modulation format, and carrier frequency, are optimized for each connection. By linearizing the Gaussian noise model, both an optimal formulation and a low complexity decomposition heuristic are proposed. Our methods minimize the spectrum usage of networks, while satisfying requirements on the throughput and quality of transmission. Compared with existing schemes that allocate a uniform power spectral density to all connections, our proposed methods relax this constraint and, thus, utilize network resources more efficiently. Numerical results show that by optimizing the power spectral density per connection, the spectrum usage can be reduced by around 20% over uniform power spectral density schemes.