Hybrid beamforming designs for 5G new radio with fronthaul compression and functional splits

Abstract

In this study, the authors investigate the intra-physical functional splits of 5G new radio protocol stack proposed by different groups. Based on the location of the digital beamforming block, the radio units (RUs) are divided into two categories: Category A and Category B. Two implementation modes of hybrid beamforming at the physical layer are considered, in which digital beamforming is performed either at the distributed unit (DU), as in the Category A RU based hybrid beamforming (HBF-A) scheme, or at the RUs, as in the Category B RU based hybrid beamforming (HBF-B) scheme. To maximise the weighted sum rate, the authors formulate the problems of jointly designing hybrid beamforming, analogue combining and fronthaul compression strategies for both HBF-A and HBF-B. The formulated problems are simplified by adopting the codebook-based design, and further tackled by leveraging the majorisation–minimisation algorithm. Finally, numerical results confirm that the HBF-A scheme outperforms the HBF-B scheme in the large power regime. Compared with the HBF-A method, the HBF-B method is more sensitive to changes in system parameters, such as the compression noise and the number of receive antennas, in the large power regime, while it is less sensitive in the small power regime.