Expressões analíticas aproximadas em forma fechada para a probabilidade média de erro de símbolo da modulação QAM cruzada nos canais de desvanecimento η–μ e κ–μ

Abstract

Introduction: Modern communication systems, such as 5G and 6G, require high reliability and low latency, but are heavily affected by channel fading, which compromises signal quality in multipath environments. Although traditional models, such as Rayleigh, Rician, and Nakagami-m, are widely used, they present limitations by assuming specific propagation conditions and failing to accurately represent the diversity of real-world scenarios, especially at millimeter-wave frequencies. To overcome these limitations, generalized models such as the η–μ and κ–μ have been proposed, offering greater flexibility by accounting for multiple dominant components and unbalanced scattering. However, the estimation of error probabilities associated with these models is essential for their practical implementation. Objectives: This work presents the derivation of approximate closed-form analytical expressions for the Average Symbol Error Probability (SEP) and investigates their performance for M-QAM modulation under generalized fading models. Materials and Methods: The adequacy of the derived expressions was analyzed considering standardized millimeter-wave frequency bands of 26, 28, 39, 55, 60, and 65 GHz. These analyses were based on channel modeling results obtained from an extensive measurement campaign in indoor environments under both Line-of-Sight (LoS) and non-Line-of-Sight (nLoS) conditions, as well as varying distances between transmitting and receiving antennas (Tx and Rx) with vertical and horizontal polarizations (VV and HV). Results: The expressions were validated through simulations performed using the MATLAB software, demonstrating strong agreement between the theoretical curves and the simulated results. The analyses revealed that line-of-sight scenarios exhibit significantly superior performance compared to nLoS cases. Furthermore, it was observed that increasing the frequency does not necessarily lead to worse performance, and that higher modulation orders require higher Eb/N0 values to achieve low error rates, highlighting the importance of employing robust coding techniques. The results contribute to a better understanding of the potential and challenges of M-QAM modulation in realistic 5G millimeter-wave communication scenarios.