Hybrid particle swarm-based algorithms and their application to linear array synthesis

A heuristic particle swarm optimization (PSO) based algorithm is presented in this work and the novel hybrid approach is applied to linear array synthesis considering complex weights and directive element patterns so as to analyze its usefulness and limitations. Basically, classical PSO schemes are modified by introducing a tournament selection strategy and the downhill simplex local search method, so that the hybrid algorithms proposed combine the strengths of the PSO to initially explore the search space, the pressure exerted by the genetic selection operator to manage and speed up the search, and finally, the ability of the local optimization technique to quickly descend to the optimum solution. Four classical real-valued PSO schemes are taken as reference and synthesis results for a 60-element linear array comparing those classical schemes and the hybridized ones are reported and discussed in order to show the improvements achieved by the hybrid approaches.This work was supported by the Spanish Ministry of Science and Innovation (project number TEC2008-02730/TEC)

On the impact of the radiation pattern of the antenna element on MU-MIMO indoor channels

This paper presents an analysis of the effect that the radiation pattern of the antenna element that makes up the base station array has on the structure of multi-user multiple-input multiple-output (MU-MIMO) channels. In this paper, the analysis focuses on the uplink. It is well known that the antennas are an inseparable part of the radio channel. The use of more or less directional antennas as elements of the base station array of a MIMO system influences the channel in two fundamental parameters that affect the performance of MU-MIMO systems: on the one hand, the coherence bandwidth, which determines the necessary overhead in the channel estimation; and, on the other hand, the orthogonality of the subchannels between the multiple users and the base station, which influences the degree with which the condition of "favorable propagation" is fulfilled. Based on an experimental analysis using both omnidirectional and directional antennas, conclusions are drawn about how these two parameters are affected and their influence on the spectral efficiency obtainable. The measurement campaign was carried out in an indoor environment in the 3 to 4 GHz band.This work was supported by the Spanish Ministerio de Economía, Industria y Competitividad, under the project TEC2017-86779-C2-1-R

A lower bound for the coherence block length in mobile radio channels

A lower bound for the coherence block (ChB) length in mobile radio channels is derived in this paper. The ChB length, associated with a certain mobile radio channel, is of great practical importance in future wireless systems, mainly those based on massive multiple input and multiple output (M-MIMO) technology. In fact, it is one of the factors that determines the achievable spectral efficiency. Firstly, theoretical aspects regarding the mobile radio channels are summarized, focusing on the rigorous definition of coherence bandwidth (BC) and coherence time (TC) parameters. Secondly, the uncertainty relations developed by B. H. Fleury, involving both BC and TC, are presented. Afterwards, a lower bound for the product BCTC is derived, i.e., the ChB length. The obtained bound is an explicit function of easily measurable parameters, such as the delay spread, mobile speed and carrier frequency. Furthermore, and especially important, this bound is also a function of the degree of coherence with which we define both BC and TC. Finally, an application example that illustrates the practical possibilities of the bound obtained is presented. As a further conclusion, the need to determine what degree of correlation is required to consider mobile channels as effectively flat-fading and stationary is highlighted.This work has been supported by the Spanish Ministry of Economy, Industry and Competitiveness (TEC2017-86779-C2-1-R)

Characterisation of indoor massive MIMO channels using ray-tracing: A case study in the 3.2-4.0 GHz 5G band

In this paper, research results on the applicability of ray-tracing (RT) techniques to model massive MIMO (MaMi) channels are presented and discussed. The main goal is to show the possibilities that site-specific models based on rigorous RT techniques, along with measurement campaigns considered for verification or calibration purposes where appropriate, can contribute to the development and deployment of 5G systems and beyond using the MaMi technique. For this purpose, starting from the measurements and verification of the simulator in a symmetric, rectangular and accessible scenario used as the testbed, the analysis of a specific case involving channel characterisation in a large, difficult access and measurement scenario was carried out using the simulation tool. Both the measurement system and the simulations emulated the up-link in an indoor cell in the framework of a MaMi-TDD-OFDM system, considering that the base station was equipped with an array consisting of 10 × 10 antennas. The comparison of the simulations with the measurements in the testbed environment allowed us to affirm that the accuracy of the simulator was high, both for determining the parameters of temporal dispersion and frequency selectivity, and for assessing the expected capacity in a specific environment. The subsequent analysis of the target environment showed the high capacities that a MaMi system can achieve in indoor picocells with a relatively high number of simultaneously active users.This work has been supported by the Spanish Ministry of the Economy, Industry and Competitiveness (TEC2017-86779-C2-1-R

Synthesis of planar arrays using a modified particle swarm optimization algorithm by introducing a selection operator and elitism

A modified particle swarm optimization (PSO) algorithm applied to planar array synthesis considering complex weights and directive element patterns is presented in this paper. The modern heuristic classical PSO scheme with asynchronous updates of the swarm and a global topology has been modified by introducing tournament selection, one of the most effective selection strategies performing in genetic algorithms the equivalent role to natural selection, and elitism. The modified PSO proposed combines the abilities of the classical PSO to explore the search space and the pressure exerted by the selection operator to speed up convergence. Regarding the optimization problem, the synthesis of the feeds for rectangular planar arrays consisting of microstrip patches or subarrays of microstrip patches is considered. Results comparing the performance and limitations of classical and modified PSO-based schemes are included considering both test functions and planar array complex synthesis to best meet certain far-field radiation pattern restrictions given in terms of 3D-masks. Finally, representative synthesis results for sector antennas for worldwide interoperability for microwave access (WiMAX) applications are also included and discussed

Aplicación de algoritmos genéticos y recocido simulado a la reconstrucción del diagrama de radiación de antenas

The performance of different local and global optimisers applied to antenna far-field pattern prediction from planar near-field information is presented. The method proposed replaces the antenna under test by equivalent magnetic surface currents whose components are computed from reference near-field data using an appropriate optimisation technique. From the optimised equivalent model, antenna far-fields can be reconstructed. The Nelder Mead downhill simplex algorithm, along with global optimisers such as genetic algorithms (GA) and simulated annealing (SA) were all investigated and compared. Numerical results demonstrate that hybrid GA outperform local optimisers, classical real and binary encoding GA and SA. Results of near-field to far-field transformation are also included and discussed

Optimización con enjambre de partículas aplicada a la reconstrucción del diagrama de radiación de antenas

A particle swarm optimization (PSO) based algorithm applied to antenna far-field radiation pattern prediction from planar near-field data is presented. The radiation of the antenna is modelled using equivalent magnetic surface currents (EMC) whose components are optimized using a global PSO with asynchronous updates of the swarm. A general overview of the PSO algorithm is included and the most widely used schemes of the optimizer are presented and discussed. A parametric study of the main parameters to be tuned in PSO, along with results of near-field to far-field transformation are also included to demonstrate the usefulness of the optimization method

Transformación de campo cercano a campo lejano utilizando corrientes equivalentes y algoritmos genéticos

A method for computing far-field antenna patterns from planar near-field samples is presented. The method, based on the equivalence principle, replaces the antenna under test by a set of equivalent magnetic currents (EMC), and a binary micro genetic algorithm is used to optimise the amplitudes of the EMC from the near-field data. A second approach, using an equivalent model for the source made up of electric short dipoles, is also analysed. From the optimised equivalent model, the antenna far-field pattern can be easily computed. Numerical results using synthetic near-field data are reported and discussed

Influence of the N-N Coligand: C-C coupling instead of formation of imidazol-2-yl complexes at {Mo(η(3)-allyl)(CO)2} fragments. Theoretical and experimental studies

New N-methylimidazole (N-MeIm) complexes of the {Mo(η3-allyl)(CO)2(N–N)} fragment have been prepared, in which the N,N-bidentate chelate ligand is a 2-pyridylimine. The addition of a strong base to the new compounds deprotonates the central CH group of the imidazole ligand and subsequently forms the C–C coupling product that results from the nucleophilic attack to the imine C atom. This reactivity contrasts with that previously found for the analogous 2,2′-bipyridine compounds [Mo(η3-allyl)(CO)2(bipy)(N-RIm)]OTf [N-RIm = N-MeIm, N-mesitylimidazole (N-MesIm, Mes= 2,4,6-trimethylphenyl); OTf = trifluoromethanesulfonate) which afforded imidazol-2-yl complexes upon deprotonation. Density Functional Theory (DFT) computations uncover that the reactivity of the imine C atom along with its ability to delocalize electron density are responsible for the new reactivity pattern found for the kind of molybdenum complexes reported herein.Financial support from the Ministerio de Economia y Competitividad (Projects CTQ2010-18231, CTQ2012-37370-C02-01, and CTQ2012-37370-C02-02) is gratefully acknowledged.Peer Reviewe

Diseño de reflectarrays mediante PSO y CG–FFT

A method for the design of reflectarray antennas that uses the PSO optimizer to carry out the synthesis of the phases at each reflectarray element and the CG-FFT method to obtain the design curves for the elements, is presented in this work. The analysis method has been validated against results available in the literature for rectangular patches. Furthermore, the method is able to analyze any geometry that can be properly modeled by a uniform mesh on both directions in the unit cell. At this moment, only one metallic layer, apart from the ground plane, can be analyzed. Radiation patterns for both medium and large size reflectarrays are included