This article describes the design, implementation, and evaluation of an indoor localization system based on Received Signal Strength Indicator (RSSI) measurements in wireless sensor networks. While the majority of the literature uses the IEEE 802.15 standard for this type of system, all of the measurements in this study were performed using a test bench operating under the IEEE 802.11ax standard in the 2.4 GHz band. RSSI is widely used due to its simplicity and availability; however, its accuracy is limited by signal attenuation, electromagnetic interference, and environmental variability. To mitigate these limitations, the present work proposes the implementation of advanced techniques, including weighted averages and positioning algorithms such as Min–Max, Maximum Likelihood, and trilateration, aiming to achieve an accuracy of 2 m in controlled conditions. The design also included a specialized test bench to calculate the coordinates and estimate the location of unknown nodes using anchor node positioning. This approach combines the simplicity of RSSI with optimized algorithms, providing a robust and practical solution for indoor localization. The results validate the system’s effectiveness and highlight its potential for future applications in real-world environments, opening new possibilities for optimizing wireless sensor networks and addressing the current challenges in localization systems.

According to the dominance prescription of point-ions in the non-linear Poisson-Boltzmann theory, proposed by Valleau and Torrie almost 40 years ago, the microscopic and thermodynamic properties of an asymmetric binary electrolyte converge asymptotically to those of a completely symmetric electrolyte, in the limit of an infinite surface charge density of a planar electrode, if the properties of the counterions are the same in both instances. By using the Grahame equation and the non-linear Poisson-Boltzmann theory, we show here that this prescription is certainly exact for the mean electrostatic potential at the electrode's surface and for the capacitive compactness. Contrastingly, analytical and numerical solutions of the non-linear Poisson-Boltzmann equation show that, in the limit of an infinite surface charge density of the planar electrode, it is possible to observe finite differences between the local mean electrostatic potentials and electric fields associated to a 1:1 and a 1:z electrolyte at places near the electrode's surface. Thus, we prove here that even in the absence of ion correlations and ionic excluded volume effects, the counterions do not fully dominate the structural properties in the entire electrical double layer in the non-linear Poisson-Boltzmann picture, which is confirmed through comparisons with new Monte Carlo simulations. GRAPHICAL ABSTRACT

In a recent review, “Size and/or charge asymmetry effects in coulombic fluids in the presence of external fields: From simple electrolytes to molten salts”, Guerrero-García, Biophysical Chemistry 282, 106747 (2022), one of the present authors analyzed some consequences of breaking the symmetry in the valence and/or ionic size of charged fluids, such as aqueous electrolytes, macroion solutions, or molten salts, when ion correlations and ionic excluded volume effects were taken into account. In this review article, we would like to discuss some additional effects of breaking the symmetry in the valence and/or size of charged particles of coulombic fluids (i) next to a rigid cylindrical charged polymer, and (ii) in the electrostatic properties of an electrical double layer planar supercapacitor. These effects were studied in approaches beyond the classical non-linear Poisson-Boltzmann theory of point ions, by using classical integral equations theory, the Modified Poisson-Boltzmann theory, and Monte Carlo simulations in implicit solvent. As a result, the relevance of the asymmetry in the valence and/or size of charged particles, at microscopic level, is illustrated here either in simple electrolytes or in aqueous colloidal suspensions of macroions, when both are under the influence of an external electric field.