By recognizing the tremendous flexibility of the emerging fluid antenna system (FAS), which allows dynamic reconfigurability of the location of the antenna within a given space, this paper investigates the performance of a single-antenna FAS over spatially correlated Nakagami-m fading channels. Specifically, simple and highly accurate closed-form approximations for the cumulative density function of the FAS channel and the outage probability of the proposed system are obtained by employing a novel asymptotic matching method, which is an improved version of the well-known moment matching. With this method, the outage probability can be computed simply without incurring complex multi-fold integrals, thus requiring negligible computational effort. Finally, the accuracy of the proposed approximations is validated, and it is shown that the FAS can meet or even exceed the performance attained by the conventional maximal ratio combining (MRC) technique.

A realistic performance assessment of any wireless communication system requires the use of a fading channel model that reflects its main characteristics. The traditional Rayleigh and Nakagami-m models have been (and still are) the basis of most theoretical research on wireless technologies today, even for emerging technologies, such as millimeter-wave communications (mm-Wave). In this article, we show that the fluctuating multiple-ray (FMR) and $\kappa$-$\mu$ shadowed models had a better fit (i.e., lowest mean square error statistical test) to field measurements in outdoor environments at 28 GHz than the conventional channel models. Therefore, these generalized models are feasible alternatives that can be used as a benchmark when evaluating communication performance in mm-Wave scenarios.

The use of light-emitting diodes (LED) for ambient illumination leads to visible light communications (VLC) as a promising technology for providing both constant lighting and high-speed wireless services in indoor environments. Since multiple LED sources can transmit to several users, this scenario naturally forms a multiple user multiple-input single-output (MU-MISO) system. In this sense, transmit precoding (TPC) schemes based on channel state information at the transmitter (CSIT) originally devised for radio-frequency (RF) systems have been proposed for their implementation in VLC. However, beyond providing CSIT or the need for cooperation among transmitters, which also result challenging in RF systems, there are several constraints such as the non-negativity of the transmitted signal or providing constant illumination that hamper the performance of TPC schemes in VLC. Taking into consideration these constraints, this paper explores the use of Blind Interference Alignment (BIA) for achieving multiplexing gain without CSIT or cooperation among LED lights. To do that, we devise the concept of reconfigurable photodetector that allows to switch among distinct and linearly independent channel responses. Simulation results show that the use of vBIA schemes based on the proposed reconfigurable photodetector results suitable for VLC systems.

This paper investigates the impact of realistic propagation conditions on the achievable secrecy performance of multiple-input multiple-output systems in the presence of an eavesdropper (Eve). Specifically, we concentrate on the $\kappa$ - $\mu$ shadowed fading model because its physical underpinnings capture a wide range of propagation conditions, while, at the same time, it allows for a much better tractability than other state-of-the-art fading models. By considering transmit antenna selection and maximal ratio combining reception at the legitimate (Bob) and Eve's receiver sides, we study two relevant scenarios: 1) the transmitter knows Bob's channel state information (CSI) but not Eve's CSI, and 2) the transmitter is aware of the CSI of both Bob and Eve channels. For this purpose, we first obtain novel and tractable expressions for the statistics of the maximum of independent and identically distributed (i.i.d.) variates related to the legitimate channel. Based on these results, we derive novel closed-form expressions of the two aforementioned scenarios to assess the secrecy performance of the underlying system. Specifically, for cases: 1) the secrecy outage probability (SOP), the probability of strictly positive secrecy capacity (SPSC), and 2) the average secrecy capacity (ASC). Moreover, we develop analytical asymptotic expressions of the SOP and ASC in the high signal-to-noise ratio regime. In all instances, secrecy performance metrics are characterized in closed-form, without requiring the evaluation of Meijer-G or Fox-H functions. Some useful insights on how the different propagation conditions and the number of antennas impact the secrecy performance are also provided.

This paper presents an analysis of the Orthogonal Frequency Division Multiplexing (OFDM) signal with high Peak-to-Average Power Ratio (PAPR) that passes through different high power amplifiers (HPA) models. First, we present the main characteristics of the OFDM signal and the mathematical models of the HPAs. Then, we evaluate the performance of the OFDM signal with several HPA models in terms of the PSD (Power Spectral Density) and BER (Bit Error Rate) for different types of modulation and number of subcarriers. Finally, we show that for an OFDM-based system with N = 64 subcarriers and QSPK modulation, the Rapp Model outperforms the others whereas the Saleh model performs the worst with respect to the ideal HPA.