Optimum Pilot Overhead in Wireless Communication: A Unified Treatment of Continuous and Block-Fading Channels

The optimization of the pilot overhead in single-user wireless fading channels is investigated, and the dependence of this overhead on various system parameters of interest (e.g., fading rate, signal-to-noise ratio) is quantified. The achievable pilot-based spectral efficiency is expanded with respect to the fading rate about the no-fading point, which leads to an accurate order expansion for the pilot overhead. This expansion identifies that the pilot overhead, as well as the spectral efficiency penalty with respect to a reference system with genie-aided CSI (channel state information) at the receiver, depend on the square root of the normalized Doppler frequency. Furthermore, it is shown that the widely-used block fading model is only a special case of more accurate continuous fading models in terms of the achievable pilot-based spectral efficiency, and that the overhead optimization for multiantenna systems is effectively the same as for single-antenna systems with the normalized Doppler frequency multiplied by the number of transmit antennas.Comment: Submitted to IEEE Trans. Wireless Communication

We must know. We will know

The after-dinner talk has by now become a tradition of this Conference series on Quark Confinement and the Hadron Spectrum. On this occasion, I have tried to combine a free-style and (hopefully) amusing presentation with deep questions of physics especially connected with the dynamics of strong interaction. To this end some masterpieces of classical music (by Beethoven, Mozart, Dvorak, Stravinsky ...) and pop music (by Bob Dylan, Eric Clapton) were employed to illustrate certain aspects of physics. By no means was this presentation (nor this paper) intended as a comprehensive review of the different topics examined during the Conference, but rather a call for further thinking on the sinergy of different branches of physics and the excitement of foreseen discoveries in a not too distant future.Comment: 6 pages, 8 figures, After-dinner talk given at the IX Conference on Quark Confinement and the Hadron Structure, Madrid, August 30th to September 3rd 201

Heavy metals effects on life traits of juveniles of Procambarus clarkii

An incubation experiment of juvenile crayfish (Procambarus clarkii) following a three- level treatment design approach was performed to assess the effect of different heavy metal concentrations on their life history traits (lifespan, growth, moult and feeding activity). The aims were to: (1) address the response of the life traits; (2) check for the correlation between heavy metal concentrations in crayfish whole bodies with the ones of the experimental solutions; (3) analyse the variation of crayfish carbon and nitrogen stable isotopes signatures grown under these treatments. Treatments were: control or absence of pollutants (C); low level contamination (L) similar to those found in the water of the Guadiamar River (SW, Spain) one year after the Aznalcóllar mine accident, and high level contamination (H) maximum concentrations of metals measured in the water of the river after the spill. The study concludes that the H treatment produced lethal effects on juveniles of crayfish, whereas those undergoing the L treatment showed less marked effects. Crayfish’s juveniles grown in L treatment seemed able to regulate and manage this range of pollution while maintaining their biological traits. Juvenile’s capacity to bioaccumulate toxic substances also changes with the nature of the particular metals. The reduction in lifespan was mainly influenced by Cu, Zn and As. 13C of C and juveniles from L treatment had similar values but different from those individuals of H treatment, reflecting the isotopic signature of the food source used (liver), and were also influenced by the concentration of Cu and AsThis work was part of the PICOVER program financed by the “Consejería de Medio Ambiente, Junta de Andalucía“ – Project title: Uso del cangrejo rojo americano (Procambarus clarkii) como especie centinela en el Corredor Verde del Guadiamar – Implicaciones de la especie en las redes tróficas – in 2002–200

Searching for hidden sectors in multiparticle production at the LHC

Most signatures of new physics in colliders have been studied so far on the transverse plane with respect to the beam direction. In this work however we study the impact of a hidden sector beyond the Standard Model (SM) on inclusive (pseudo)rapidity correlations and moments of the multiplicity distributions, with special emphasis in the LHC results.Comment: Presentation given at ICHEP 2014 Valenci

The ridge effect and three-particle correlations

Pseudorapidity and azimuthal three-particle correlations are studied based on a correlated-cluster model of multiparticle production. The model provides a common framework for correlations in proton-proton and heavy-ion collisions allowing easy comparison with the measurements. It is shown that azimuthal cluster correlations are definitely required in order to understand three-particle correlations in the near-side ridge effect. This is similar to the explanation of the ridge phenomenon found in our previous analysis of two-particle correlations and generalizes the model to higher-order correlations.Comment: 16 pages, 7 figures. arXiv admin note: text overlap with arXiv:1610.0640

Three-particle correlations in QCD jets and beyond

In this paper, we present a more detailed version of our previous work for three-particle correlations in quark and gluon jets [1]. We give theoretical results for this observable in the double logarithmic approximation and the modified leading logarithmic approximation. In both resummation schemes, we use the formalism of the generating functional and solve the evolution equations analytically from the steepest descent evaluation of the one-particle distribution. In addition, in this paper we include predictions beyond the limiting spectrum approximation and study this observable near the hump of the single inclusive distribution. We thus provide a further test of the local parton hadron duality (LPHD) and make predictions for the LHC. The computation of higher rank correlators is presented in the double logarithmic approximation and shown to be rather cumbersome.Comment: 34 pages and 14 figure

Fundamental Limits of Cooperation

Cooperation is viewed as a key ingredient for interference management in wireless systems. This paper shows that cooperation has fundamental limitations. The main result is that even full cooperation between transmitters cannot in general change an interference-limited network to a noise-limited network. The key idea is that there exists a spectral efficiency upper bound that is independent of the transmit power. First, a spectral efficiency upper bound is established for systems that rely on pilot-assisted channel estimation; in this framework, cooperation is shown to be possible only within clusters of limited size, which are subject to out-of-cluster interference whose power scales with that of the in-cluster signals. Second, an upper bound is also shown to exist when cooperation is through noncoherent communication; thus, the spectral efficiency limitation is not a by-product of the reliance on pilot-assisted channel estimation. Consequently, existing literature that routinely assumes the high-power spectral efficiency scales with the log of the transmit power provides only a partial characterization. The complete characterization proposed in this paper subdivides the high-power regime into a degrees-of-freedom regime, where the scaling with the log of the transmit power holds approximately, and a saturation regime, where the spectral efficiency hits a ceiling that is independent of the power. Using a cellular system as an example, it is demonstrated that the spectral efficiency saturates at power levels of operational relevance.Comment: 27 page

RCS of engine inlets by a spectral iterative technique

A novel algorithm designed to compute efficiently and accurately the HF electromagnetic scattering from open-ended waveguide cavities is presented. The cavity is converted into a stepped-waveguide model so that the field spectrums are propagated, forward and backward, along each waveguide section. As boundary conditions for perfect electric conductors are applied via image theory, they are of local nature and take into account only the first order interactions between each pair of waveguide sections. Accordingly, additional forward-backward iterations must be performed if multiple interactions are to be taken into account. Finally, the RCS due to the interior irradiation is calculated by a Kirchhoff-based aperture integral. Good agreement with Method of Moments and Hybrid Modal solutions is found, as well as with experimental data, for 2-D and 3-D cavities.Peer ReviewedPostprint (published version