IEEE Photonics Journal | Year: 2016
The sub-Nyquist time-frequency packing (TFP) technique was demonstrated in a superchannel field trial transmission over long-haul distances. The technique allows high spectral efficiency even with low-order modulation formats. The transmission was successfully performed on an installed link between Milan and Finkenstein (Austria) in a loop back configuration, which included 2 × 660 km of ITU-T G.655 fiber. The superchannel is composed by eight subchannels with low-level modulation format, i.e., polarization multiplexed (PM)-quadrature phase shift keying (QPSK). The use of low-order modulation format guarantees better robustness in terms of optical-signal-to-noise ratio (OSNR) and reduced complexity with respect to higher order formats. At the receiver side, coherent detection was used, together with iterative maximum a posteriori probability (MAP) detection and decoding. A 992-Gb/s PM-QPSK superchannel was successfully transmitted between Milan-Finkenstein-Milan with spectral efficiency (SE) of 6.2 bit/s/Hz. Long-term measurements confirm the system reliability. © 2016 IEEE.
Bolla R.,University of Genoa |
IEEE Communications Surveys and Tutorials | Year: 2014
The convergence towards the IP protocol has made Internet access available almost everywhere; this has leveraged new expectations about continuous and seamless communication, especially when portable devices are involved. Mobility management is a key issue in this context. The original IP specification does not account for mobility. Nevertheless, since the beginning of the Internet there has been a continuous interest in managing nomadic hosts; this has brought to a large number of approaches and protocols that have faced the problem from different perspectives. This paper reviews different approaches to mobility management that have arisen during the years. It is intended to serve as a tutorial for this topic, which draws out the lesson learned until now and depicts a comprehensive picture to foster new ideas and solutions while avoiding duplication of past work. © 2014 IEEE.
Pintus P.,SantAnna School of Advanced Studies |
Optics Express | Year: 2014
In this work, a dielectric waveguide mode solver is presented considering a general nonreciprocal permittivity tensor. The proposed method allows us to investigate important cases of practical interest in the field of integrated optics, such as magneto-optical isolators and anisotropic waveguides. Unlike the earlier developed mode solver, our approach allows for the precise computation of both forward and backward propagating modes in the nonreciprocal case, ensuring high accuracy and computational efficiency. As a result, the nonreciprocal loss/phase shift can be directly computed, avoiding the use of the perturbation method. To compute the electromagnetic modes, the Rayleigh-Ritz functional is derived for the non-self adjoint case, it is discretized using the node-based finite element method and the penalty function is added to remove the spurious solutions. The resulting quadratic eigenvalue problem is linearized and solved in terms of the propagation constant for a given frequency (i.e., γ-formulation). The main benefits of this formulation are that it avoids the time-consuming iterations and preserves the matrix sparsity. Finally, the method is used to study two examples of integrated optical isolators based on nonreciprocal phase shift and nonreciprocal loss effect, respectively. The developed method is then compared with the perturbation approach and its simplified formulation based on semivectorial approximation. © 2014 Optical Society of America.
Sambo N.,SantAnna School of Advanced Studies |
Castoldi P.,SantAnna School of Advanced Studies |
Cugini F.,CNIT |
Bottari G.,Ericsson AB |
Iovanna P.,Ericsson AB
IEEE Communications Magazine | Year: 2012
The evolution of optical technologies is driving the introduction of multirate optical networks exploiting advanced transmission techniques and efficient switching devices. In the short term, optical connections operating at 10 and 100 Gb/s will coexist in the same multi-rate network infrastructure. This, however, might introduce significant issues due to detrimental inter-channels effects, which need to be considered during network planning or connection provisioning. In the long term, connections at higher bit-rates (e.g., 400 Gb/s) and based on complex modulation formats (e.g., quadrature amplitude modulation - QAM) are expected, together with the adoption of innovative and flexible bandwidth-variable optical cross-connects (BV-OXCs). BV-OXCs have the potential to significantly improve the overall network spectrum efficiency. However, critical issues might arise in the dynamic control of network operations. This article discusses the enhancements required during operation and control of future optical networks with quality of transmission guaranteed. A first network evolution scenario is considered, where 100 Gb/s lightpaths are introduced in a native 10 Gb/s network. In such a scenario, inter-channel effects between 10 and 100 Gb/s lightpaths are highlighted. Relevant methods to account for these effects are discussed and evaluated. Then, a second network evolution scenario is assumed, in which traditional OXCs are replaced with BV-OXCs, and even higher bit-rates (e.g., 400 Gb/s 16-QAM) are introduced in the network. In particular, the problem of scalability when advertising and storing spectrum resource (i.e., frequency slices) availability is presented for flex-grid optical networks (i.e., optical networks exploiting BVOXCs). Consequently, a method to efficiently handle availability information is proposed and evaluated, showing the capability to overcome scalability issues without impacting the overall network resource utilization. © 1979-2012 IEEE.
Costa F.,University of Pisa |
IEEE Transactions on Antennas and Propagation | Year: 2012
Microstrip reflectarray antennas consist of a grounded quasi-periodic array of printed elements able to compensate the phase displacement of a non-coherent electromagnetic excitation generated by a feeder. The design of reflectarray antennas is usually accomplished by tracing the reflection phase diagram of the periodic version of the printed surface, which is analogous to a high-impedance surface (HIS). Reflection losses of this periodic structure are here analyzed through a simple equivalent transmission line model. The analytical expressions of the surface impedance offered by a HIS (real and imaginary part) as a function of the imaginary part of the dielectric permittivity of the substrate are derived through well justified approximations. Some useful practical examples are then presented both for verifying the accuracy of the derived closed-form expressions and for studying the effect of the geometrical and electrical parameters of the periodic surface on the reflection losses. The dependence of the input impedance on the capacitance associated with the printed pattern is highlighted, demonstrating that highly capacitive elements (tightly coupled subwavelength elements) are preferable for minimizing reflection losses. © 1963-2012 IEEE.