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Even if Passive Optical Networks (PONs) have proven to be more energy-efficient that other access solutions, energy consumption minimization is becoming an important research target also in PON. In particular, to sustain the increased bandwidth demand of emerging applications in the access section of the network, new hybrid PON solutions employing WDM/TDM are being investigated. Compared with classics PON, the architecture of WDM/TDM-PONs requires more transceivers/receivers, hence they are expected to be more energy hungry than classical PONs. In this paper, we focus on the power consumption minimization in WDM/TDM-PONs and we propose an energy-efficient mechanism based on Dynamic Bandwidth and Wavelength Allocation whose objective is to switch off, whenever possible, the unnecessary receivers for upstream traffic at the Optical Line Terminal (OLT). Our proposed energy saving mechanism is able to decrease energy consumption at the OLT of about 30%, while maintaining the penalty introduced in terms of channel utilization and packet delay within an acceptable range. Detailed implementation of the proposed algorithm is presented, and simulation results are reported to quantify energy savings and effects on network performance on different network scenarios.

Long-Reach Passive Optical Network (LR-PON) using hybrid TDM/WDM techniques is one of the candidates for the future optical access that can solve the expected increase in terms of traffic demand and area coverage. One of its advantages is the possibility to share the capacity of any wavelength among more than one user, through TDM/WDM hybrid multiplexing. However, it is still an open issue which transmission technology (DWDM transmitters, colorless transmitters, coherent detection, direct detection) can more effectively satisfy the requirements and characteristics of the future long-reach access network. In this article we propose a new optimization model based on Mixed Integer Linear Programming (MILP) that formalizes the problem of selecting the most cost-effective transmission technology in LR TDM/WDM PONs while also assigning the wavelength-channels line rate and the splitting ratio of the remote nodes at different levels, under bandwidth and power budget constraints. Using this proposed MILP formulation we can identify the optimal transmission technology for a wide set of possible LR-PON scenarios of interest. In this work we provide an evaluation of the optimal transmission technologies under several PON scenarios with varying traffic loads and area coverage. We also analyze the cost sensitivity of the optimization process for coherent-detection technology since it is still under research and development

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