Design and performance enhancement of multi-cluster multi-user massive MIMO-NOMA networks

Abstract

Non-orthogonal multiple access (NOMA) and massive multiple-input multiple-output (MIMO) have arisen as essential enabling technologies for meeting the demanding requisites of the fifth-generation (5G) of wireless communication networks. Specifically, massive MIMO explores the space domain through a massive number of antennas to serve multiple users in parallel, while NOMA can also serve multiple users simultaneously, but differently from MIMO, the parallel transmission is performed by multiplexing the users in the power domain, in which successive interference cancellation (SIC) is employed for reception. The combination of massive MIMO and NOMA can provide even further performance improvements. However, due to various impairments, such as closely spaced antennas, high spatial correlation, or deep fading in wireless channels, the system performance can still be degraded and the communication reliability impacted, which is not desired in the demanding 5G networks. Fortunately, it has been demonstrated that the installation of co-located orthogonal polarized antennas can alleviate the inter-antenna space limitations and correlation issues. The use of diversity strategies is also an effective way of mitigating the harmful effects of fading channels. In this context, this dissertation aims to enhance the performance of multi-cluster multi-user massive MIMO-NOMA networks through the application of both multi-polarization and diversity techniques. First, we design and evaluate the performance of dual-polarized massive MIMO-NOMA systems, in which a single base station communicates in downlink mode with multiple users, with all terminals being equipped with multiple co-located dual-polarized antennas. In particular, two precoder designs are proposed: (i) the first one aims to maximize the number of user groups that are simultaneously served within a cluster; and (ii) the second approach aims to provide further improvements compared to the first one by exploring polarization diversity. In the second part of this dissertation, we propose a novel successive sub-array activation (SSAA) diversity scheme for a single-polarized massive MIMO-NOMA system, in which we also consider the downlink mode. In this scenario, the base station sends redundant symbols through multiple transmit sub-arrays to multi-antenna receivers, based on which a low-complexity two-stage precoder, that is constructed based only on the long-term channel statistical information, is proposed. For both dual-polarized and SSAA systems, we carry out in-depth analytical studies, in which closed-form expressions for the outage probabilities are derived. High signal-to-noise ratio (SNR) outage approximations are obtained, and the systems diversity orders are determined. The ergodic sum-rates are also derived. Numerical and simulation results are provided to validate the analytical analysis and to demonstrate the performance superiority of the proposed designs.