Impact of physical layer parameters on the design of core optical networks

The advent of Coherent-detection systems supported by Digital-Signal-Processing (DSP) makes it possible to carry out electronic fiber chromatic dispersion and allows us to use multi-level modulation formats. These formats are affected by fiber non-linearity due to small spacing between constellations, especially in the high cardinality number modulation formats. Main disadvantage of Non-Linear Interference (NLI), which is considered as a limiting factor for performance, is to limit the OSNR, which in turn limits the maximum reach of the link. In the novel Uncompensated Transmission (UT) propagation regimes, it is possible to carry out system performance prediction based on relatively simple analytical non-linear propagation models. In this thesis, we use what is called the Gaussian-Noise (GN) model which shows high prediction ability in a single span and multi-span links. The main target of the exploitation of the physical link is optical network optimization. OSNR was previously considered to depend upon the noise produced by the amplifier, the only source of noise; NLI now is considered as additive Gaussian noise as stated in the GN- model and it depends on all the physical link parameters, but independent of the transceiver. This dependency on physical parameters and in-dependency on the transceiver leads us to think of the optimization of the link which will be the target of our work and see how this optimization could be reflected at the network level. The thesis work regards the implementation of the GN-model in optical network, both the standard wavelength division multiplexing (WDM) and the Elastic Optical Networks (EONs). We investigate connection provisioning algorithms on optical infrastructures for three different architectures: fixed grid WDM with fixed-rate multilevel modulation, fixed-grid WDM with time-domain hybrid modulation formats and flexible grid. We perform a sensitivity analysis of network and physical layer parameters, such as the link length, the traffic load, different fiber types and the Q margin, to understand how each parameter influences the network design. Besides comparing the two paradigms of flexible and fixed grid networks, including both pure and hybrid modulation formats, in terms of their spectral efficiency and power consumption, we show the importance of integrating a detailed physical layer modelling in the network design phase. Flexible-grid optical networks turned out to be the most convincing candidate for the evolution of backbone optical networks in order to face the envisioned growth of IP traffic. They combine the maximization of spectral efficiency with the flexibility of traffic load per lightpath allowing a full exploitation of transmission level potentialities joined to the flexibility in satisfying traffic demand. In this network scenario, we propose an original approach to the logical topology design (LTD) problem in the offline planning phase. We deal with the LTD problem using heuristic algorithms incorporating a detailed transmission layer model. Several heuristic algorithms, dealing with traffic demands in different ordering, are considered for lightpath provisioning. Traffic ordering schemes are set based on two parameters: traffic demands capacity and lightpath physical route length. Through simulative analyses, we provide a performance comparison of different heuristics, using parameters like spectral efficiency, amount of blocked traffic and total number of transceivers. Furthermore, a constant need to improve network capacity and reduce power consumption in current fixed- grid WDM networks motivates researchers to find alternative solutions other than replacing the deployed equipment. One of the possible solutions is the use of hybrid EDFA/Raman amplifier, which improves signal- to-noise- ratio in a point to point link. This work aims at quantifying, by means of a detailed power model, the effect of these novel ideas on the power consumption of the network, which is key to build a future green Internet. Results show that hybrid amplification in moderate pumping regime minimizes total network power consumption for networks made up of all three fiber types in particular for non- zero dispersion- shifted fiber. Moreover, we analyze transparent wavelength routed optical networks using three different typical fiber types: NZDSF, SMF and PSCF and verify the effectiveness of Hybrid Raman/EDFA Fiber Amplification (HFA) with incremental pumping levels, up to the moderate pumping regime. Traffic is conveyed and retrieved in nodes by the use of flexible-grid elastic Nyquist Wavelength Division Multiplexing (WDM) transponders able to adapt the modulation format and the occupied bandwidth – and the corresponding delivered rate – to the quality-of-transmission of the available lightpath, using up to five ITU-T prescribed 12.5 GHz spectral slots. Impact of a detailed physical layer is considered considering both the impact of accumulation of ASE noise introduced by amplifiers and of non-linear interference generated by non-linear fiber propagation. We show that HFAs in moderate pumping regime reduces the spectral occupancy for all three fiber types with evidence in NZDSF. In essence to that, introduction of HFA is also beneficial to avoid blocking for higher traffic loads. Network Simulations considered several networking scenarios, where different heuristics are used to solve Resource and Spectrum Allocation (RSA) problems.Simulations are performed on different randomly generated and real networks to support the argument titling Next-Generation optical networks.