Multi-RF Beamforming-Based Cellular Communication Over Wideband mmWaves

• Published in: IEEE transactions on communications Vol. 70; no. 4; pp. 2772 - 2787
• Main Authors: Varshney, Nancy, De, Swades
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.04.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Array signal processing; Baseband; Beamforming; Broadband; Cellular communication; Complexity; Frame structures; Interference; millimeter wave (mmWave) communications; Millimeter waves; multi-RF; OFDM; optimal beamwidth; Optimization; Precoding; Radio frequency; Scheduling; sector sojourn time; user distribution; Wideband
• ISSN: 0090-6778; 1558-0857
• DOI: 10.1109/TCOMM.2022.3147510

The existing literature on cellular multi-user mmWave communication focus on joint baseband and RF precoding designs to enable spatial multiple access with minimum interference. These studies either assume the number of users <inline-formula> <tex-math notation="LaTeX">M </tex-math></inline-formula> is less than the number of RF units <inline-formula> <tex-math notation="LaTeX">N_{RF} </tex-math></inline-formula> or schedule the users in time domain by dedicating one RF unit to each user if <inline-formula> <tex-math notation="LaTeX">M >N_{RF} </tex-math></inline-formula>. It is expected that serving multiple users over OFDMA in each analog beam will offer better utilization of the wideband channel. To this end, for the scenario with <inline-formula> <tex-math notation="LaTeX">M \gg N_{RF} </tex-math></inline-formula> we propose a sectored-cell model that is supported by multi-RF chains over the wideband mmWave channel, with each beam serving multiple users within a sector and the sectors being scheduled in round-robin fashion. We also propose a variable time frame structure that conducts sector-wise initial access, with simultaneous access to all users within a sector. It provides improved spectrum efficiency and decreased initial access delay as compared to the initial access using exhaustive beam search method. We then jointly estimate the optimum beamwidth and optimum <inline-formula> <tex-math notation="LaTeX">N_{RF} </tex-math></inline-formula> that offer maximum average long-run user rate. Further, we introduce a reduced-complexity sector sojourn time optimization for non-homogeneously distributed users, that improves fairness of long-run user rates leveraging the variable time frame structure. The numerical results show that, while a high value of <inline-formula> <tex-math notation="LaTeX">N_{RF} </tex-math></inline-formula> causes more interference to peak data rate, the average long-run user rate improves. Additionally, using a very narrow beam is also not optimal for providing maximum rate support. The proposed beamforming method offers a higher average long-run user rate over the competitive beamforming schemes while the complexity of user scheduling is independent of <inline-formula> <tex-math notation="LaTeX">M </tex-math></inline-formula>.