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Candidate: Joao Paulo Pinto Galdino Marques
Date: June 17, 2025
Time: 1:30pm
Location: EIT 3145
Supervisor: Catherine Rosenberg
All are welcome!

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MU-MIMO systems provide high performance through the transmission of multiple data streams to users (resp. from users) on the Downlink (DL) (resp. Uplink (UL)) at the same frequency and time. Multiple antennas at the users can further improve performance by using the multiple antennas to create one strong data stream or to create several independent data streams per user. To achieve the potential of MU-MIMO systems with Multi-Antenna (MA) users, the Radio Resource Management (RRM) processes must be carefully executed. The necessary RRM processes are stream selection, Beamforming (BF), power management and Modulation and Coding Scheme (MCS) selection. We consider Zero-Forcing (ZF) BF that nullifies inter-stream interference. There are three primary ZF BF strategies based on the number of data streams used per scheduled user: Coordinated-Transmit-Receive-1 (CTR1) that uses exactly one stream per user (the strongest), Block Diagonalization (BD) that uses all possible streams per user, and Coordinated-Transmit-Receive-Flexible (CTRF), which allows a flexible stream allocation per user. CTRF can offer enhanced performance, but at the cost of higher complexity compared to the other strategies.

In this work, we conduct novel studies to evaluate the performance of MU-MIMO systems under proportional fairness with BD, CTR1 and CTRF, on the DL and UL in realistic systems characterized by 3GPP-based scenarios where the Base-Station (BS) employs practical MCSs. These studies can guide the design of real-time RRM heuristics. To enable the study on the DL, we employ RRM heuristics from the literature adapted to consider practical systems with MCSs and fairness, whereas we propose the necessary RRM tools for the UL study. The DL and UL results indicate that CTRF outperforms the other strategies regardless of the system parameters and scenarios. However, in some cases, the performance gap is marginal. More specifically, on both the DL and UL, BD performs closely to CTRF for a large number of BS antennas and a few users, but the gap between them widens as the number of users increases. In contrast, the performance disparity between CTR1 and CTRF is small for a large number of users and increases for a large number of BS antennas and a few users. Therefore, despite the superior performance of CTRF, BD or CTR1 could replace it in some cases, given their comparable performance and lower complexity.