De 5G a 6G: transmissão de dados através de MIMO massivo e superfícies inteligentes

Author(s)

Michelle Soares Pereira Facina

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Elétrica e de Computação
• Defense date: 2020-12-01

Examining board members

Gustavo Fraidenraich; Alvaro Augusto Machado de Medeiros; Cláudio Ferreira Dias; Eduardo Rodrigues de Lima; Fabbryccio Akkazzha Chaves Machado Cardoso

• Advisor: Gustavo Fraidenraich

Abstract

The evolution of technology is fast. At the beginning of the doctoral project, the most discussed topic was the fifth generation of cellular networks. Now, in the end, we are already talking about the sixth generation and what comes next. With this in mind, my thesis addresses topics related to massive MIMO and Large Intelligent Surfaces (LIS). Despite the chronological distance between them (the first in 2016 and the second in 2020), both represent a significant leap in developing a low latency access network and a drastic change in the mobile communications infrastructure. With numerous antennas on the base station and user, one of the problems inherent to massive MIMO is interference. Thus, we present an accurate approximation to signal-to-interference ratio in two scenarios: when the number of antennas at base station is finite or when this number is large enough to be considered infinite. We consider path loss and lognormal shadowing and prove the perfect match between simulation and our approximation from practical case studies. Concerning LIS, we compare the system performance already published in the literature to that we obtained from an LoS propagation modeled of Rician channels and Matched Filter (MF) from preliminary analyses. We propose an accurate approximation for spectral efficiency and evaluate the path-loss when the base station does not have channel state information and transmits the symbols with equal powers to all users. In the sequel, we do an in-depth analysis of a practical LIS-assisted Single-Input Single-Output (SISO) system in order to characterize its performance. We assume realistic imperfections for the values of reflection coefficients. In a first step, symbol error probability expressions are obtained for SISO scenarios with and without phase errors. We validate all the results by numerical simulations and have shown an excellent agreement. Comparisons with existing models show that practical systems present a considerable loss in performance. In the next stage, the study is even more comprehensive. Since quantization errors are unavoidable, we evaluate the influence of number of bits dedicated to the phase quantization on important performance such as spectral efficiency, symbol error rate, and outage probability. Based on Monte Carlo simulations, we prove the excellent accuracy of our approach and investigate the behavior of the power scaling law and the power required to reach a specific capacity, depending on the number of reflecting elements. We show that a LIS with approximately fifty elements and four dedicated bits for phase quantization outperforms the performance of a conventional system, i.e., a system without the assistance of a LIS. As a conclusion, we can say that the massive MIMO and LIS technologies offer substantial improvements and came to stay and coexist (AU)

• FAPESP's process: 16/16181-2 - Multiple-Input Multiple-Output (MIMO) wireless communication systems with high number of antennas
• Grantee: Michelle Soares Pereira Facina
• Support Opportunities: Scholarships in Brazil - Doctorate