Fully-Connected Beamforming Enabled by Hybrid Digital-Analog Modulation in 4-D Antenna Arrays

Conventional fully-connected array provides significant degrees of freedom (DoFs) in beamforming. However, the practical applicability of fully-connected array architecture is limited due to the high hardware complexity. To address this issue, this paper presents a novel approach for achieving efficient fully-connected beamforming by integrating the digital and analog modulation of four-dimensional (4-D) antenna arrays. The proposed approach can be easily implemented in practice due to the low hardware complexity of the 4-D antenna array. In addition, unlike conventional 4-D antenna array designs, this approach incorporates both analog time and digital modulation. The multi-channel signals can be pre-coded and weighted through the hybrid digital and analog modulation, facilitating their transmission to each antenna element to achieve fully-connected mapping. Finally, some selected numerical results are provided to validate the effectiveness of the proposed approach.