Hybrid Digital and Analog Modulation for Multibeam Systems Based on 4-D Antenna Arrays

Multibeam generation is regarded as a crucial capability for future wireless systems. The utilization of digital arrays enables a superior degree of beamforming flexibility, facilitating the effortless generation of multiple beams. However, the conventional digital beamforming (DBF) approaches require a substantial number of digital and radio frequency (RF) chains, resulting in elevated hardware complexity and increased power consumption. Hybrid DBF and analog beamforming (ABF) approaches may lead to a reduction in hardware complexity and power consumption. However, these approaches also result in a reduction in the degree of freedom (DoF) for beamforming, which cannot meet the requirements of highly flexible multibeam scenarios. Regarding this issue, this article has developed a novel approach based on 4-D antenna arrays, which can be used to generate flexible multibeams with low hardware complexity. In contrast to the traditional method that solely focuses on time modulation parameter design, the proposed approach makes full use of both baseband and time modulation DoFs. As a result, it enables highly flexible multibeam generating using simple <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small>–<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> modulation techniques, thereby overcoming the contradiction between beamforming flexibility and hardware complexity. Simulation and experimental results are also presented to validate the effectiveness of the proposed approach.