NEMO: A flexible and highly scalable network EMulatOr

Evaluating novel applications and protocols in realistic scenarios has always been a very important task for all stakeholders working in the networking field. Network emulation, being a trade-off between actual deployment and simulations, represents a very powerful solution to this issue, providing a working network platform without requiring the actual deployment of all network components. We present NEMO, a flexible and scalable Java-based network emulator, which can be used to emulate either only a single link, a portion of a network, or an entire network. NEMO is able to work in both real and virtual time, depending on the tested scenarios and goals, and it can be run as either a stand-alone instance on a single machine, or distributed among different network-connected machines, leading to distributed and highly scalable emulation infrastructures. Among different features, NEMO is also capable of virtualizing the execution of third-party Java applications by running them on top of virtual nodes, possibly attached to an emulated or external network. Keywords: Network emulation, Protocol stack, Jav

From Fibers to Satellites: Lessons to Learn and Pitfalls to Avoid when Optical Communications Move to Long Distance Free Space

The paper summarizes the recent investigation on feasibility of adapting state-of-the-art coherent fiber-optics (FO) systems for Free Space Optical (FSO) scenarios. This investigation is critically dependent on the intertwined aspects of architecture, as well as device and propagation impairments (including the channel) appearing in the aforementioned systems. Towards this, the work identified the key system differences between the two systems. Particularly, the FSO channel model was investigated, impact of atmospheric turbulence on FSO was discussed and a channel series was generated. Subsequently, relevant FO techniques including coherent detection, wavelength division multiplexing and Time-Frequency packing (TFP) were reviewed. Another departure from FSO works was the emphasis on coherent reception; receiver architectures and diversity schemes were first investigated. The former strived to make fair comparison amongst the receivers considering the diverse nature of perturbation added, while the latter indicated gain in performance through increase of diversity order (2-4 dB gain). An immediate conclusion is a suggestion on adaptation of wavelength diversity when coherent receivers . The investigation also evaluated the capacity and outage of fast and slow fading channels with parameters motivated by the channel modelling work. The shaping gain was evaluated and an LDPC code design example was provided for FSO downlinks. Finally, TFP enabled a remarkable performance gain when applied to coherent detection schemes, but only marginal with direct detection. The paper concludes by pointing to the next steps that build on this investigation and the need to corroborate with measurements

A Novel Device to Enhance the OSNR Based on Lossless Polarization Attraction

We introduce a novel all-optical “noise cleaning” device, based on lossless polarization attraction, that provides an OSNR gain close to the theoretical 3dB limit. In addition, we demonstrate the robustness of polarization attraction against additive noise

Performance characterization and guidelines for the design of a counter-propagating nonlinear lossless polarizer

We characterize the performance of a nonlinear lossless polarizer, an all-optical fiber-based device that allows for the control of the state of polarization of an optical signal. The device relies on the lossless polarization attraction generated by the nonlinear interaction between the controlled signal and a controlling pump. Choosing a counterpropagating pump, we quantify its performance by introducing the degree of attraction (DOA), which highlights the trade-off between the average attraction of the signal polarization and the unavoidable degradation of its degree of polarization (DOP). We investigate, by numerical simulations, the dependence of the DOA on the injected power and on the fiber length, thus providing the design guidelines to reach the desired performance. We find that an effective attraction can occur even for strongly unbalanced signal and pump power levels, and that fibers longer than a few kilometers yield only a marginal improvement of the DOA

All-optical noise cleaning based on co-propagating lossless polarization attraction

We exploit a recently proposed nonlinear lossless polarizer to suppress the noise component that is (bitwise) orthogonal to an optical signal. It is shown how the proposed technique yields an optical signal-to-noise ratio (OSNR) gain close to 3dB and how this gain can be theoretically predicted, for different input OSNR values, from the degree of polarization (DOP) of the repolarized output signal

Lossless polarization attraction of telecom signals: application to all-optical OSNR enhancement

We propose an all-optical fiber-based device that is able to accomplish polarization control and OSNR enhancement of an amplitude modulated optical signal at the same time. The proposed device is made of a nonlinear lossless polarizer (NLP), which performs polarization control, followed by an ideal polarizing filter, which removes the orthogonally polarized half of additive noise. The task of the NLP is to impose signal polarization aligned with the transparent eigenstate of the polarizing filter. In order to effectively control the polarization of an amplitude modulated signal in the presence of additive noise, we show how one of the two different NLP configurations (with counter- or co-propagating pump laser) is needed, as a function of the signal polarization coherence time. We demonstrate that an OSNR gain close to 3 dB can be achieved by using the proper NLP configuration. Finally, we show how the achievable OSNR gain can be estimated theoretically

Performance characterization and guidelines for the design of a counter-propagating nonlinear lossless polarizer

We characterize the performance of a nonlinear lossless polarizer, an all-optical fiber-based device that allows for the control of the state of polarization of an optical signal. The device relies on the lossless polarization attraction generated by the nonlinear interaction between the controlled signal and a controlling pump. Choosing a counterpropagating pump, we quantify its performance by introducing the degree of attraction (DOA), which highlights the trade-off between the average attraction of the signal polarization and the unavoidable degradation of its degree of polarization (DOP). We investigate, by numerical simulations, the dependence of the DOA on the injected power and on the fiber length, thus providing the design guidelines to reach the desired performance. We find that an effective attraction can occur even for strongly unbalanced signal and pump power levels, and that fibers longer than a few kilometers yield only a marginal improvement of the DOA