131 research outputs found
Non-Orthogonal Multiple Access For Near-Field Communications
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
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