Caracterização matemática de sistemas MIMO massivos Cell-Free

Abstract

To meet the growing demand from users, cell-free architecture (CF) appears as an alterna tive to cellular systems, since the arrangement of the base station antennas in a distributed manner allows systems to take advantage of spatial macro-diversity to improve performance. Furthermore, due to the non-delimitation of cellular regions and the decentralization of the base stations, CF systems have the potential to offer a good quality service throughout the considered region, eliminating problems that may arise on the periphery of the cells, such as high large-scale losses and intercellular interference. Although CF systems are the subject of several scientific publications, little attention has been paid to the effects introduced by small-scale fading, with low-accuracy expressions being developed for metrics such as bit error probability, outage probability and average capacity of the channel. Therefore, this work presents a mathematical model for the received signal considering scenarios with or without line of sight and hybrids. From this model, expressions are derived for bit error probability, channel capacity and user outage probability, including the effects introduced by the presence of small-scale fading. Subsequently, through the use of derived expressions, an optimization technique for CF systems is developed with the purpose of optimizing the choice of access points serving users and applied together with an adaptive modulation technique with the purpose of maximizing the use of the channel. All theoretical results presented are compared with simulation data and, when possible, compared to data present in the literature. The contributions of this work include results that represent a gain in spectral efficiency of up to 40% when compared to results presented in the literature