A solution to the MCSP problem considering physical layer degradations in transparent optical networks
In all-optical networks, the physical layer impairments cause a degradation in the transmitted signal. Sometimes, the degradation causes an inadmissible Optical Signal to Noise Ratio (OSNR), which is translated into blocking due to low quality of transmission. The Impairment Aware -- Routing and Wavelength Assignment (IA-RWA) should choose the route and wavelength considering the physical layer impairments. The Choice of the Best Combination among M Combinations of Shortest Paths (MCSP) problem consists of choosing the best of the shortest paths for a network topology aiming to reduce the blocking probability. This paper presents a pioneer study of the MCSPs problem assuming Amplified Spontaneous Emission (ASE), co-wavelength crosstalk, self-wavelength crosstalk, neighbor wavelength crosstalk, Polarization Mode Dispersion (PMD) and attenuations caused by fiber and devices. In this context, we propose a new routing algorithm that aims to resolve the MCSP problem considering the physical impairments.
Impact of physical layer impairments in all-optical networks
We investigate the impact of different physical impairments in the performance of all-optical networks. The physical impairments considered are the gain saturation and amplified spontaneous emission noise depletion in amplifiers, homodyne crosstalk in optical switches, four wave mixing and polarization mode dispersion in the transmission fibers. Our simulation results are presented in terms of blocking probability of requested calls as a function of network device parameters.
In search of optimum chest radiography techniques.
A nation-wide study of chest radiography in Sweden had previously revealed a large variation in the physical and technical factors involved, in particular the radiation dose. In this study the image quality could not be assessed unambiguously. The aim of the present study was to try to establish a correlation between visual grading of radiographs and physical and technical factors in order to find the optimum chest X-ray system. The physical and technical performance of 24 chest units was evaluated. Radiographs were taken of an anthropomorphic chest phantom supplied with test structures simulating various pathologies. Image quality was assessed by visual grading analysis of the radiographs. The physical and technical parameters of the units rated best were used to exemplify good radiographic practice. The results were in agreement with the recommendations issued by the Commission of the European Communities (CEC). It was also shown that low radiation dose is compatible with high-quality radiographic imaging of the chest.