The paper focuses on the downlink RRM in a millimeter-wave system with codebook-based hybrid beamforming, where the base station has fewer radio frequency chains than the number of user equipment (UEs) in the cell. This creates a coupling between subchannels within a time slot, as the analog beam selection cannot vary across subchannels.
The key highlights and insights are:
The paper formulates an offline joint RRM optimization problem that includes beam set selection, UE set selection, power distribution, modulation and coding scheme selection, and digital beamforming as part of the hybrid beamforming.
The offline study provides valuable insights on the importance of considering the constraint of fixed analog beam selection across subchannels within a time slot, which is often overlooked in the literature. Neglecting this constraint can overestimate the performance by up to 20%.
The offline study investigates the impact of various system parameters, power distribution, and digital beamforming on the performance. It shows that zero-forcing digital beamforming can improve the performance by 32% compared to the case without digital beamforming, and optimized power distribution can provide a 22% performance increase compared to equal power distribution.
The paper proposes low-complexity online heuristic RRM schemes that can provide good performance, with the best online heuristic achieving at least 92.3% of the best offline benchmark performance.
The paper also extends the formulations and solutions to the case where multiple beam pairs are selected for each UE during the beam alignment process.
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arxiv.org
Key Insights Distilled From
by Yuan Quan,Sh... at arxiv.org 04-22-2024
https://arxiv.org/pdf/2404.12492.pdfDeeper Inquiries