The fluid antenna system (FAS) has emerged as a disruptive technology that promises outstanding diversity and multiplexing gains comparable to or better than multiple-input multiple-output (MIMO), but without the issues of channel state information (CSI) acquisition and the advantage of requiring smaller physical spaces of upcoming user devices. This work investigates the potentialities of this technology to provide secure transmissions by analysing the secrecy outage probability (SOP) of two different implementations of FAS undergoing spatial correlated Nakagami- $m$ fading by assuming $i)$ non-diversity FAS and maximum-gain combining-FAS (MGC-FAS) diversity scheme at the legitimate node and $ii)$ multiple-antennas performing maximal ratio combining (MRC) at the eavesdropper. Specifically, using a novel asymptotic matching method, a simple and accurate closed-form approximations to the end-to-end signal-to-noise-ratio (SNR) distributions are derived in terms of well-known functions without incurring tricky functions or multi-fold integrals. Our findings reveal that the secrecy performance of the MGC-FAS beats the non-diversity FAS counterpart only when $i)$ the antenna size of the FAS tube is large enough, and $ii)$ the average SNR of the legitimate path is much greater than that of the eavesdropper link. Finally, numerical results validate our approximations of the SOP for the MGC-FAS scheme and demonstrate its accuracy under different FAS conditions.

Sparse code multiple access (SCMA) is an interesting proposal for supporting massive machine-type communications (mMTC) in future mobile networks. In this use case, mobile networks connect to Internet of Things (IoT) devices, which may have low computational processing capacities, and thus, they are exposed to different security threats. In this regard, physical-layer security (PLS) arises as an alternative technique to protect information. This work proposes a new scheme based on the design of unknown codebooks to an external eavesdropper aiming at guaranteeing PLS in the uplink of SCMA systems over generalized $\kappa$ - $\mu$ fading channels. Considering that the SCMA codebook design can be realized from the rotation of base quadrature-amplitude modulation (QAM) constellations using the signal-space-diversity (SSD) technique, a novel upper-bound expression to calculate the average bit error probability (ABEP) of multidimensional SSD systems is derived. Then, a metric to select the best rotation matrices is determined. With this, a set of optimal and suboptimal rotation matrices can be acquired. A strategy to obtain secret keys in the SCMA system is presented by considering imperfect channel estimation. The secret keys are used to select matrices for rotating the base QAM constellations used in the codebooks generation. Finally, an uncoded and turbo-encoded SCMA system is evaluated using Monte Carlo simulations. The results show that our proposal ensures a near-optimal SCMA performance while the eavesdropper cannot decode the information.

The growing complexity and uncertainty in modern power systems—driven by increased integration of renewable energy sources and variable loads—underscore the need for robust tools to assess dynamic stability. This paper presents an enhanced methodology for modal analysis that combines Adaptive Variational Mode Decomposition (A-VMD) with Prony’s method. A novel energy-based selection mechanism is introduced to determine the optimal number of intrinsic mode functions (IMFs), improving the decomposition’s adaptability and precision. The resulting modes are analyzed to estimate modal frequencies and damping ratios. Validation is conducted using both synthetic datasets and real synchrophasor measurements from Ecuador’s national power grid under ambient and disturbed operating conditions. The proposed approach is benchmarked against established techniques, including a matrix pencil, conventional VMD-Prony, and commercial tools such as WAProtector and DIgSILENT PowerFactory. The results demonstrate that A-VMD consistently delivers more accurate and robust performance, especially for low signal-to-noise ratios and low-energy ambient conditions. These findings highlight the method’s potential for real-time oscillation mode identification and small-signal stability monitoring in wide-area power systems.

Ensuring a balance between supply and demand is critical within electricity grids, requiring a supply composition that guarantees consistent service provision in the short and medium term. Between 2008 and 2017, Ecuador’s electricity generation capacity expanded significantly, with an investment of approximately USD 8150 million into harnessing the potential energy of water. This led to the construction of five high-capacity hydroelectric projects by 2017, contributing 33.4% of the sector’s energy output by 2023. However, it is important to note that if installed hydroelectric projects operate as run-of-river plants, with limited reservoir capacity, they can only regulate water use for electricity generation on an hourly basis. As of 2023, these run-of-river plants represent 68.8% of Ecuador’s total hydroelectric capacity within the National Interconnected System (SNI). Consequently, during periods of low inflows, supplementary energy from other power generation plants is necessary to prevent energy crises. This paper addresses the impact on energy storing for electricity generation resulting from the evolution of hydroelectric power plant entry from 2006 to 2023. This aspect has not been thoroughly examined in hydrothermal systems, which primarily focus on potential energy obtained from dams. Our approach involves a statistical analysis of hydroelectric dam reservoir operational levels. We further explore the influence on demand service within Ecuador’s electricity system, particularly during observed energy crises towards the end of 2023.

We analyze the outage probability (OP), ergodic capacity (EC), and average bit error probability (ABEP) of L -branch diversity systems using maximal-ratio-combining (MRC) over Multi-cluster-Fluctuating-Two-Ray (MFTR) fading channels, a model well-suited for sub-terahertz bands. We derive exact OP, EC, and ABEP expressions. For this latter metric, we assume M -ary quadrature amplitude modulation ( M -QAM), and we also perform its asymptotic analysis to obtain the coding gain and diversity order. Unlike previous works for simpler fading models, our expressions retain consistent complexity regardless of the number of MRC branches and depend on functions available in standard mathematical software. The results show that coding gain relies on fading distribution parameters, L , and M . Meanwhile, diversity order is determined by multiplying L with the number of multipath clusters in the MFTR model.

In this paper, we evaluate the performance of equal-gain-combining (EGC) receivers operating in Rayleigh fading channels in terms of the outage probability (OP) and the average symbol error rate (ASER). For this, we first derive novel, improved, fast, and exact series representations for the probability density function (PDF) and the cumulative distribution function (CDF) of the sum of independent and identically distributed Rayleigh random variables by employing complex analysis as well as the properties of the moment-generating function (MGF). With these results, exact and closed-form-asymptotic expressions to evaluate the OP and the ASER are derived. The efficiency of our expressions, defined in terms of tractability, computational burden, and computation time, overcome the state-of-the-art solutions. Monte-Carlo simulations and a time comparison analysis with the state-of-the-art study support our results.