Non-uniform Beam Design for Multi-user MmWave Systems

For multi-user millimeter wave (mmWave) communications, different users can be served using various time-frequency resources through their corresponding preferred beams which can provide the highest beamforming gain among all candidate beams. However, when the non-uniform distribution of users is considered, beams selected by fewer users can provide more time-frequency resources to each user than the beams serving more users, which indicates that the conventional uniform beam pattern may lead to unfair resource allocation and hence the loss of system spectral efficiency. In this paper, a novel non-uniform beam design is proposed, wherein a two-level codebook which supports both wide and sharp beams is adopted for data transmission. Specifically, two neighboring sharp beams selected by fewer users can be merged into one wide beam which can cover the same angular space. Thus, the saved resources can be assigned to other sharp beams selected by relatively more users. Theoretical analysis and numerical simulations demonstrate the superiority of our proposal on fairness of resource allocation as well as the spectral efficiency compared with its conventional counterpart.