The novel concept of near-field non-orthogonal multiple access (NF-NOMA) communications is proposed. The near-filed beamfocusing enables NOMA to be carried out in both angular and distance domains. Two novel frameworks are proposed, namely, single-location-beamfocusing NF-NOMA (SLB-NF-NOMA) and multiple-location-beamfocusing NF-NOMA (MLB-NF-NOMA). 1) For SLB-NF-NOMA, two NOMA users in the same angular direction with distinct quality of service (QoS) requirements can be grouped into one cluster. The hybrid beamformer design and power allocation problem is formulated to maximize the sum rate of the users with higher QoS (H-QoS) requirements. To solve this problem, the analog beamformer is first designed to focus the energy on the H-QoS users and the zero-forcing (ZF) digital beamformer is employed. Then, the optimal power allocation is obtained. 2) For MLB-NF-NOMA, the two NOMA users in the same cluster can have different angular directions. The analog beamformer is first designed to focus the energy on both two NOMA users. Then, a singular value decomposition (SVD) based ZF (SVD-ZF) digital beamformer is designed. Furthermore, a novel antenna allocation algorithm is proposed. Finally, a suboptimal power allocation algorithm is proposed. Numerical results demonstrate that the NF-NOMA can achieve a higher spectral efficiency and provide a higher flexibility than conventional far-field NOMA.

翻译：本文提出了近场非正交多址接入（NF-NOMA）通信的新概念。近场波束聚焦使得NOMA能够在角度域和距离域中同时实现。提出了两种新型框架，即单位置波束聚焦NF-NOMA（SLB-NF-NOMA）与多位置波束聚焦NF-NOMA（MLB-NF-NOMA）。1）对于SLB-NF-NOMA，将位于同一角度方向但具有不同服务质量（QoS）需求的两个NOMA用户归类为一个簇。通过混合波束成形器设计与功率分配问题的建模，以最大化高QoS（H-QoS）用户的总速率。为解决该问题，首先设计模拟波束成形器以将能量聚焦于H-QoS用户，并采用迫零（ZF）数字波束成形器，随后获得最优功率分配。2）对于MLB-NF-NOMA，同一簇中的两个NOMA用户可具有不同角度方向。首先设计模拟波束成形器以将能量同时聚焦于两个NOMA用户，随后设计基于奇异值分解（SVD）的ZF（SVD-ZF）数字波束成形器。此外，提出了一种新型天线分配算法，并进一步提出了一种次优功率分配算法。数值结果表明，与传统远场NOMA相比，NF-NOMA能够实现更高的频谱效率并提供更强的灵活性。