近场移动通信的吞吐量分析：波束聚焦还是焦散波束成形？
Throughput Analysis for Near-Field Mobile Communications: Beamfocusing or Caustic Beamforming?
AI总结：
本文针对太赫兹近场通信，通过分析波束聚焦和焦散波束成形的吞吐量，建立了切换开销阈值，证明在高移动性场景下焦散波束成形更优。
摘要：
向太赫兹频段的迁移和超大规模天线阵列的部署正在将无线通信过渡到辐射近场区域，从根本上将传统的角度波束转向演变为波束聚焦。然而，极窄波束宽度与用户移动性的结合需要频繁的波束聚焦重构，导致显著的切换开销，降低了系统可达吞吐量。在这方面，焦散波束成形是一种有前景的替代方案，它基于连续弯曲波束的合成，以分布式波束成形增益为代价消除了波束跟踪的需求。通过利用艾里波束作为典型模型，本文开发了一个分析框架来比较焦散波束成形和波束聚焦实现的吞吐量。我们的主要结果包括两种波束成形策略的闭式吞吐量表达式以及范式选择的性能边界。首先，我们通过建模由连续用户运动引起的散焦惩罚来推导波束聚焦的吞吐量。解析确定了最大化吞吐量的最优波束驻留时间，并量化了用户速度和切换开销对吞吐量的影响。对于焦散波束成形方案，我们证明其吞吐量由信噪比和用户轨迹的几何形状决定，但与用户速度无关。最后，我们解析建立了切换开销的阈值，以定义两种波束成形器可达吞吐量的交叉点。关键的是，该阈值在极高频率下渐近消失，使得连续焦散波束成形方案成为高移动性太赫兹通信的首选波束设计范式。
英文摘要：
The migration to the Terahertz (THz) band and the deployment of extremely large antenna arrays (ELAAs) are transitioning wireless communications into the radiative near-field regime, fundamentally evolving conventional angular beam steering to beamfocusing (BF). However, the combination of the extremely narrow beamwidth and the mobility of the users necessitates frequent beamfocusing reconfigurations, incurring a significant switching overhead that degrades the system achievable throughput. In this regard, caustic beamforming (CB) is a promising alternative based on the synthesis of a continuous curved beam, which eliminates the need for beam tracking at the expense of a distributed beamforming gain. By leveraging the Airy beam as a canonical model, this paper develops an analytical framework to compare the throughputs achieved by CB and BF. Our main results include closed-form throughput expressions for both beamforming strategies and a performance boundary for paradigm selection. First, we derive the BF throughput by modeling a defocusing penalty induced by continuous user movement. The optimal beam dwell time that maximizes the throughput is analytically determined, and the impact of user speed and switching overhead on the throughput is quantified. For the CB scheme, we demonstrate that its throughput is determined by the signal-to-noise ratio (SNR) and the geometry of the trajectory of the user, yet invariant to the user speed. Finally, we analytically establish a threshold for the switching overhead to define the crossover point of the achievable throughput of both beamformers. Crucially, this threshold asymptotically vanishes at extremely high frequencies, positioning the continuous CB scheme as the preferred beam design paradigm for high-mobility THz communications.
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