For the existing near-field multiuser communications based on hybrid beamforming (HBF) architectures, high-quality effective channel estimation is required to obtain the channel state information (CSI) for the design of the digital beamformer. To simplify the system reconfiguration and eliminate the pilot overhead required by the effective channel estimation, we considered an analog-only beamforming (AoBF) architecture in this study. The AoBF is designed with the aim of maximizing the sum rate, which is then transformed into a problem, maximizing the power transmitted to the target user equipment (UE) and meanwhile minimizing the power leaked to the other UEs. To solve this problem, we used beam focusing and beam nulling and proposed two AoBF schemes based on the majorization-minimization (MM) algorithm. First, the AoBF scheme based on perfect CSI is proposed, with the focus on the beamforming performance and regardless of the CSI acquisition. Then, the AoBF scheme based on imperfect CSI is proposed, where the low-dimensional imperfect CSI is obtained by beam sweeping based on a near-field codebook. Simulation results demonstrate that the two AoBF schemes can approach the sum rate of the HBF schemes but outperform HBF schemes in terms of energy efficiency (EE).

翻译：对于现有基于混合波束赋形架构的近场多用户通信系统，需要高质量的有效信道估计来获取信道状态信息以设计数字波束赋形器。为简化系统重构并消除有效信道估计所需的导频开销，本研究考虑了一种仅模拟波束赋形架构。该架构以最大化总速率为设计目标，该目标可转化为在向目标用户设备传输最大功率的同时最小化泄漏至其他用户设备的功率的优化问题。为解决此问题，我们采用波束聚焦与波束置零技术，并基于最大化-最小化算法提出了两种仅模拟波束赋形方案。首先，提出了基于完美信道状态信息的方案，该方案聚焦于波束赋形性能而不考虑信道状态信息获取过程。随后，提出了基于非完美信道状态信息的方案，其中通过近场码本进行波束扫描获取低维非完美信道状态信息。仿真结果表明，两种仅模拟波束赋形方案在总速率上可逼近混合波束赋形方案，且在能量效率方面优于混合波束赋形方案。