Future wireless networks will utilize extremely large-scale antenna arrays (ELAAs) over high-frequency bands, which, however, produce near-field spherical wavefronts and spatial wideband effects. To exploit and mitigate these, this paper proposes a rate-splitting multiple access (RSMA)-enabled transmit scheme for wideband near-field communications (NFC). Our solution leverages true-time-delay (TTD)-based hybrid beamfocusing architectures to mitigate spatial wideband effect and reduce radio frequency chain requirements. The objective is to maximize the minimum rate by jointly optimizing frequency-dependent analog beamfocusing, frequency-independent analog beamfocusing, digital beamfocusing, and common rate allocation. To solve this complicated non-convex problem, we develop a penalty-based iterative algorithm that partitions the variables into three blocks and then employs block coordinate descent (BCD) to optimize each block alternately. This algorithm is further extended to support the sub-connected TTD-based analog beamfocusing architectures. Comprehensive simulation results indicate that our transmit scheme: 1) effectively compensates for spatial wideband effect, addressing a critical challenge in wideband operation; 2) achieves performance comparable to full digital beamfocusing while maintaining lower hardware complexity; 3) achieves substantial performance gains over the other two benchmarks.

翻译：未来的无线网络将在高频段使用超大规模天线阵列（ELAAs），然而，这会产生近场球面波前和空间宽带效应。为利用并缓解这些效应，本文提出了一种用于宽带近场通信（NFC）的速率分割多址接入（RSMA）使能发射方案。我们的解决方案利用基于真实时延（TTD）的混合波束聚焦架构来缓解空间宽带效应并降低射频链需求。目标是通过联合优化频率相关的模拟波束聚焦、频率无关的模拟波束聚焦、数字波束聚焦以及公共速率分配，来最大化最小速率。为解决这一复杂的非凸问题，我们开发了一种基于惩罚的迭代算法，该算法将变量划分为三个块，然后采用块坐标下降法（BCD）交替优化每个块。该算法进一步扩展以支持子连接式基于TTD的模拟波束聚焦架构。全面的仿真结果表明，我们的发射方案：1）有效补偿了空间宽带效应，解决了宽带运行中的一个关键挑战；2）在保持较低硬件复杂度的同时，实现了与全数字波束聚焦相当的性能；3）相较于其他两个基准方案，实现了显著的性能增益。