Near-Field Beam Training for Holographic MIMO Communications: Typical Methods, Challenges and Future Directions

Holographic multiple-input multiple-output(HMIMO)has become an emerging technology for achieving ultra-high frequency spectral efficiency and spatial resolution in future wireless systems.The increasing antenna aperture leads to a more significant characterization of the spherical wavefront in near-field communications in HMIMO scenarios.Beam training as a key technique for wireless communication is worth exploring in this near-field scenario.Compared with the widely researched far-field beam training,the increased dimensionality of the search space for near-field beam training poses a challenge to the complexity and accuracy of the proposed algorithm.In this paper,we introduce several typical near-field beam training methods:exhaustive beam training,hierarchical beam training,and multi-beam training that includes equal interval multi-beam training and hash multi-beam training.The performances of these methods are compared through simulation analysis,and their effectiveness is verified on the hardware testbed as well.Additionally,we provide application scenarios,research challenges,and potential future research directions for near-field beam training.

机能增进补剂HMB的补充效用及机制研究

亮氨酸代谢产物β-羟基-β-甲基丁酸(beta-hydroxy-beta-methylbutyrate,HMB)作为一种机能增进补剂被广泛运用,通过补充HMB来提高骨骼肌肌肉量,增强肌肉有氧能力,提高运动成绩,防治肌肉减少症(sarcopenia),降低血液低密度胆固醇和总胆固醇含量,增强免疫系统功能等。HMB作为一种机能增进补剂被广泛运用,特别是对于健美运动员和力量型运动员来说,他们通过补充HMB来使骨骼肌增大,提高运动成绩。虽然大量的研究已经证实HMB在运动训练和临床康复条件下的有效性,但是也存在许多相互矛盾的结论。因此,本文首先进一步对HMB的研究进行分析,检验补充HMB的有效性,以及解释已有文献中存在的矛盾,并对训练年限、肌肉的代谢状态以及最理想的HMB剂量等多种调节变量进行分析。其次,对HMB起作用的可能机制进行了广泛的讨论,并展望未来的研究方向。

β-羟基-β-甲基丁酸盐(HMB)运动功效的研究进展

β-羟基-β-甲基丁酸盐(HMB)是亮氨酸的代谢中间产物,国内外大量的动物和临床试验证明:HMB具有促进肌肉蛋白质合成、抑制肌肉蛋白质分解、维持瘦体重、提高运动能力、维护细胞膜完整性、提高免疫功能和降低炎症反应等作用。本文对HMB的作用机制,特别是HMB与运动和肌肉减少症之间的关系进行了回顾,为其应用于运动营养食品和功能性食品奠定一定的理论基础。