173 research outputs found
La pandemia. Año 2: experiencias diferenciadas, dilemas compartidos y reflexiones mĂşltiples desde la antropologĂa mĂ©dica en torno a la COVID 19
Hemos invitado a tres especialistas que desde la antropologĂa mĂ©dica pudieran reflexionar a partir de sus respectivas experiencias y conocimientos situados, aportando sus reflexiones de MĂ©xico, Gran Bretaña, Estados Unidos y la India, todos ellos paĂses profundamente afectados por la pandemia aun si de manera muy diferentes entre sĂ, y cuyo manejo de Ă©sta se ha orientado en direcciones distintas. Esto nos permite contrastar la diversidad de respuestas oficiales a la crisis sanitaria y econĂłmica
On the feasibility of a channel-dependent scheduling for the SC-FDMA in 3GPP-LTE (mobile environment) based on a prioritized-bifacet Hungarian method
We propose a methodology based on the prioritization and opportunistic reuse of the optimization algorithm known as Hungarian method for the feasible implementation of a channel-dependent scheduler in the long-term evolution uplink (single carrier frequency division multiple access system). This proposal aims to offer a solution to the third generation system’s constraint of allocating only adjacent subcarriers, by providing an optimal resource
allotment under a fairness scheme. A multiuser mobile environment following the third generation partnership project TS 45.005v9.3.0/25.943v9.0.0 was also implemented for evaluating the scheduler’s performance. From the results, it was possible to examine the channel frequency response for all users (four user equipments) along the whole bandwidth, to visualize the dynamic resource allocation for each of the 10,000 channel realizations
considered, to generate the statistical distribution and cumulative distribution functions of the obtained global costs, as well as to evaluate the system’s performance once the proposed algorithm was embedded. Comparing and emphasizing the benefits of utilizing the proposed dynamic allotment instead of the classic static-scheduling
and other existent methods.Peer ReviewedPostprint (published version
Gibbsian Method for the Self-Optimization of Cellular Networks
In this work, we propose and analyze a class of distributed algorithms
performing the joint optimization of radio resources in heterogeneous cellular
networks made of a juxtaposition of macro and small cells. Within this context,
it is essential to use algorithms able to simultaneously solve the problems of
channel selection, user association and power control. In such networks, the
unpredictability of the cell and user patterns also requires distributed
optimization schemes. The proposed method is inspired from statistical physics
and based on the Gibbs sampler. It does not require the concavity/convexity,
monotonicity or duality properties common to classical optimization problems.
Besides, it supports discrete optimization which is especially useful to
practical systems. We show that it can be implemented in a fully distributed
way and nevertheless achieves system-wide optimality. We use simulation to
compare this solution to today's default operational methods in terms of both
throughput and energy consumption. Finally, we address concrete issues for the
implementation of this solution and analyze the overhead traffic required
within the framework of 3GPP and femtocell standards.Comment: 25 pages, 9 figures, to appear in EURASIP Journal on Wireless
Communications and Networking 201
The ac stark shift and space-borne rubidium atomic clocks
open7sìDue to its small size, low weight, and low power consumption, the Rb atomic frequency standard (RAFS) is routinely the first choice for atomic timekeeping in space. Consequently, though the device has very good frequency stability (rivaling passive hydrogen masers), there is interest in uncovering the fundamental processes limiting its long-term performance, with the goal of improving the device for future space systems and missions. The ac Stark shift (i. e., light shift) is one of the more likely processes limiting the RAFS' long-term timekeeping ability, yet its manifestation in the RAFS remains poorly understood. In part, this comes from the fact that light-shift induced frequency fluctuations must be quantified in terms of the RAFS' light-shift coefficient and the output variations in the RAFS' rf-discharge lamp, which is a nonlinear inductively-couple plasma (ICP). Here, we analyze the light-shift effect for a family of 10 on-orbit Block-IIR GPS RAFS, examining decade-long records of their on-orbit frequency and rf-discharge lamp fluctuations. We find that the ICP's light intensity variations can take several forms: deterministic aging, jumps, ramps, and non-stationary noise, each of which affects the RAFS' frequency via the light shift. Correlating these light intensity changes with RAFS frequency changes, we estimate the light-shift coefficient, K-LS, for the family of RAFS: K-LS = -(1.9 +/- 0.3) x 10(-12) /%. The 16% family-wide variation in K-LS indicates that while each RAFS may have its own individual K-LS, the variance of K-LS among similarly designed RAFS can be relatively small. Combining K-LS with our estimate of the ICP light intensity's non-stationary noise, we find evidence that random-walk frequency noise in high-quality space-borne RAFS is strongly influenced by the RAFS' rf-discharge lamp via the light shift effect. Published by AIP Publishing.openFormichella, V.; Camparo, J.; Sesia, I.; Signorile, G.; Galleani, L.; Huang, M.; Tavella, P.Formichella, V.; Camparo, J.; Sesia, Ilaria; Signorile, Giovanna; Galleani, L.; Huang, M.; Tavella, Patrizi
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