Resumo em Inglês:

Abstract High-Definition Digital Terrestrial Television (HDDTT) replaces analogue, requiring further research on propagation links due to atmospheric variables potentially disrupting signals during uplink and downlink reception. This study examines the impact of surface meteorological parameters on the downlink Receive Signal Strength (RSS) of an HDDTT station in a tropical location-Abuja, Nigeria. The impact of k-factor, Radio Refractivity (RaR), refractivity gradient, and Radio Horizon distance (dRH) on HDDTT RSS are also investigated. The assessments were based on an experimental setup over 12-months (Jan.-Dec., 2020). The RSS link values showed strong negative correlations with temperature, pressure, and water vapor during the day, while weak negative correlations were observed with relative humidity. A very weak correlation was also observed between RSS link and RaR, which implies a significant influence of RaR on the RSS under clear weather. With average peak and lowest values of about 364.73 and 271.91 (N-units), respectively, RaR values are slightly higher during the rainy periods, with the dry component accounts for more than 69.70% of the total values. The mean monthly k-factor and dRH are 1.39 and 133.17 km, respectively. This information will assist radio engineers in enhancing HDDTT broadcast signals, ensuring high-quality service, and fostering customer service agreements.

Resumo em Inglês:

Abstract LoRaWAN (Long Range Wide Area Network) is an innovative and mature solution for IoT (Internet of Things) applications. It allows network devices to transmit their data whenever necessary, without the need for any coordination or scheduling mechanism, by employing the multichannel P-ALOHA (PureALOHA) random access protocol. However, in massive LoRaWAN scenarios, transmissions on the same channel often result in collisions, significantly reducing throughput and quality of service. In this context, this work aims to analyze the performance of the uplink of a massive LoRaWAN through computational simulations for different operation conditions and propagation scenarios. To obtain more realistic and representative results, signal propagation losses are estimated by combining the COST231-Walfisch-Ikegami (COST231-WI) model with the TMM (Terrain Modeling Module), the DEM (Digital Elevation Model) and the DTED (Digital Terrain Elevation Data) of the OPNET Modeler simulation platform. The results obtained in the analyses carried out highlight the challenges imposed on the LoRaWAN in terms of scalability and energy efficiency, especially in environments with high device density.

Resumo em Inglês:

Abstract Modeling is the safest and most cost-effective way to test new and complex technologies. A model represents a system created by combining concepts that help to understand, simulate, or predict the behavior of the object or process being represented. Signal propagation modeling tools have become increasingly relevant as analytical resources for detailing the scenario of interest and predicting outcomes. This study uses a supervised machine learning technique to propose a simulation and analysis method for transmission systems in atypical and remote environments. Its main goal is to suggest choices that maximize efficiency regarding the propagation models used in the scenarios under analysis. For validation purposes, a case study was conducted in the Amazon region, specifically on Combú Island, in the state of Pará, Brazil, where aspects related to the system's reference parameters were analyzed using the proposed algorithm named SINMCEL V.2.

Resumo em Inglês:

Abstract In this paper, the design of a 4 element MIMO antenna system for Terahertz (THz) communication applications is reported. The proposed antenna system is engineered with a focus on enhancing isolation between closely spaced antenna elements. Our approach leverages a photonic bandgap (PBG) substrate to suppress mutual coupling and improve isolation performance. 2x2 MIMO with patch dimension of 510×570×40 µm3, is designed to operate in the frequency of 2.4 THz. The return loss, isolation, radiation pattern, Envelope Correlation Coefficient (ECC) and Total Active Reflection Coefficient (TARC) are further analyzed by incorporating PBG. The proposed antenna produces the return loss as -32.97 dB and a gain of 3.69 dB. Moreover, the mutual coupling is less than -32.54 dB. The proposed antenna system offers promising prospects for advancing THz communication networks, enabling high-speed data transmission and reliable connectivity in future wireless communication systems.

Resumo em Inglês:

Abstract This article presents the design and analysis of a sextuple-patch antenna fabricated on Flame Retardant 4 (FR-4) substrate having a copper cladding of 0.5mm for the radiating patches and the ground plane. The antenna can operate at six distinct frequencies, 0.9 GHz, 1.2 GHz, 1.5 GHz, 2.5 GHz, 2.7 GHz, and 3.6 GHz, all of which fall within the communication bands of GSM, GPS, DCS, UMTS, and IEEE 802.11b/g. This versatility renders the antenna highly suitable for various communication devices. To achieve high gain and hexa-band characteristics at the resonant frequencies, the stepped-impedance resonator technique is implemented. The designed antenna's front surface is covered with rectangular-shaped radiating elements while the rear surface is the ground layer. Simulation results confirm that the antenna exhibits very good performance in terms of high gain across the specified frequencies and maintains a favourable impedance matching of 50Ω to observe minimal transmission losses. To ensure compactness and ease of integration with other circuits, the antenna is fed using a coaxial feeding technique. CST Studio is employed to design and validate the antenna's performance. The advanced features and capabilities of the designed antenna make it a compelling choice for integration into smart communication devices.