Experimental analysis in Massive MIMO antennas for O-RAN systems

This work investigates the integration of Massive Multiple-Input Multiple-Output (Massive MIMO) technology within an Open Radio Access Network (O-RAN) architecture, with a particular focus on the O-RAN split 7.2 functional deployment. As 5G networks are being deployed globally to meet increasing demands for high data rates, low latency, and flexible service provisioning, traditional Radio Access Network (RAN) architectures face challenges related to cost, scalability, and vendor lock-in. O-RAN addresses these challenges by enabling disaggregation, virtualization, and interoperability through open interfaces, allowing network functions to be implemented as software on standard computing platforms.

The study provides an overview of O-RAN architecture and its key components, including the Radio Unit (RU), Distributed Unit (DU), and Central Unit (CU), interconnected through standardized interfaces such as the 7.2 fronthaul and the F1 midhaul.

A central contribution of this thesis is the experimental evaluation of a Massive MIMO O-RAN system. Initial tests focus on verifying basic system functionality, including synchronization, control signaling, and data transmission between O-RAN components. These tests confirm the feasibility of operating a Massive MIMO system within a split 7.2 O-RAN architecture. The core of the work concentrates on beamforming performance, which is essential for exploiting the spatial multiplexing capabilities of Massive MIMO. The study evaluates beam steering accuracy, beam shape, and multi-user MIMO (MU-MIMO) operation. A particular emphasis is placed on the analysis of out-of-band (OOB) emissions caused by hardware nonlinearities in the RU. The spatial characteristics of these emissions are examined to understand their impact on beamforming performance, spectral efficiency, and interference toward adjacent frequency bands. Understanding OOB emissions is increasingly important for ensuring regulatory compliance and enabling efficient spectrum coexistence, especially as future wireless systems move toward higher frequencies and denser deployments. The findings provide valuable insights for improving hardware design, system optimization, and future standardization efforts, including those relevant to emerging 6G networks. Most of the experimental validation in this work is conducted using the OpenAirInterface (OAI) platform, demonstrating the suitability of open-source tools for realistic testing and research on advanced O-RAN and Massive MIMO systems.