Low-complexity Scheduling Method for Interleaved Hybrid Beamforming in mmWave Communications

This paper considers millimeter-wave access network systems using an interleaved hybrid beamforming structure (IL-HBF). The IL-HBF is a combination structure of digital and analog beamformers and antenna elements in each subarray scatter uniformly over the whole antenna array. In the IL-HBF, a subarray beam has grating lobes due to large element spacing. But they can be eliminated and multiple orthogonal beams can be created by forming subarray beams in the same direction for each other and applying an inter-subarray coding technique to the digital beamformer. We have proposed multiplexing users in the beam domain with the orthogonal beams to realize high-speed communications even in high population areas. It is needed to select users, beams, and subarrays that create the respective beams properly to avoid interferences in the IL-HBF, because phase differences between subarrays affect grating lobe elimination drastically. To evaluate a scheduling metric for each subarray may provide the suboptimal scheduling results but requires large computational complexity. Therefore, we propose a low-complexity greedy scheduling method for the IL-HBF exploiting the feature of the inter-subarray coding. System level simulation results demonstrate that the proposed method can provide almost the same throughput with much lower complexity compared with a suboptimal method.