Distributed MIMO Systems for 5G and Beyond-5G Wireless Networks

Massive Multiple-Input-Multiple-Output (MIMO) is a recent technlogy that will be exploited for 5G and beyond-5G wireless network due to the constraints given by the future wireless networks, such as low latency and high spectral efficiency. In this thesis, MIMO systems have been taken into account in order to study two different network architectures. The former is called Cell-Free (CF), and it has been studied at millimeter Wave (mmWave) and microwave frequencies, and the latter is called Distributed Multiple Input Multiple Output (D-MIMO) for factory automation. The first chapter of this thesis gives an overview of massive MIMO, so why there is the need to exploit this technology and gives some mathematical concept. In the second chapter the CF at mmwave frequencies has been studied. The CF is a recent network architecture, in order to alleviate the cell-edge problem and thus increase the system performance of unlucky users that happen to be located very far from their serving Access Point (AP). In this architecture a large number of distributed APs, connected to a central processing unit (CPU), simultaneously and jointly serve a much smaller number of mobile Station (MS) or users. Both APs and users are equipped with multiple antennas. Then, it has been analyzed an architecture that generalizes the CF, the so called User-centric (UC), where each AP has to serve only a limited number of users. A power control algorithm has been introduced by resorting a method called successive lower bound maximization, aimed at maximizing the sum-rate and the energy efficiency. At mmwave, a lot of antennas can be employed, this means that there is the need of using hybrid architecture at each AP in order to reduce complexity and cost by using a small number of radio frequency (RF) chains. With CF or UC, channel estimation and beamforming are locally evaluated, reducing the traffic load on the backhaul network. So, a comparison between a fully digital (FD) and hybrid (HY) architecture will be shown. What it is possible to anticipate is that the FD architecture provides better performances than the hybrid one. In the numerical results, the performances in term of energy efficiency and sum-rate on Downlink and Uplink, with uniform and optimal power allocation and with a fully digital and hybrid architectures will be addressed. Then, this thesis also focuses on the comparison between D-MIMO and CF architectures for factory automation, at microwave frequencies. In this case, communications between actuators (ACs) and APs inside an industrial scenario is considered by adopting those different communication systems. Then, different transmission modes are taken into account, Joint transmission joint transmission (JT), Cell-Free transmission (CFT), single AP transmission (SAT), and User-centric transmission (UCT). In SAT mode each AC is served by only one AP. Even for this scenario a power control rule has been taken into account. In the end, in numerical section, it has been shown the performances in terms of SINR and achievable rate, evaluated with the finite block length capacity (FBLC) formula, when different transmission modes and beamformers are employed, and moreover the improvement given by the use of a power control.