Joint Beamforming and Waveform Optimization in 4-D Antenna Arrays for Integrated Sensing and Communication Systems

Integrated sensing and communications (ISAC) has emerged as an essential technique for next-generation wireless networks. Despite sharing fundamental similarities in their underlying hardware architectures, sensing and communication systems exhibit substantial conflicts in specific beamforming requirements. Specifically, sensing systems typically require narrow beams to improve angular resolution, whereas wireless communication demands array antennas with adequate beamwidth to accommodate a substantial number of users. The conflicts in beamforming would significantly constrain the performance of the ISAC systems. The four-dimensional (4-D) antenna array, which offers greater design flexibility and lower hardware complexity compared to traditional arrays, undoubtedly serves as an excellent platform for addressing the beamforming conflicts. However, the separate design paradigm of beam and waveform in the conventional approach significantly constrains the beamforming capability of 4-D antenna array. In this paper, through joint optimization of beamforming and baseband waveform, the 4-D antenna array can be utilized to form arbitrarily-shaped multiple beams. In this way, the beamforming conflicts between sensing and communication can be effectively mitigated, thereby enhancing the performance of the ISAC systems while maintaining low hardware complexity. Some selected numerical and experimental results are provided to validate the effectiveness of the proposed approach.