Robust Transmit Beamforming in MIMO Dual-Functional Radar-Communication Systems for Unidirectional Multi-User Communication

The integration of multiple-input multiple-output (MIMO) technology with the dual-functional radar and communication (DFRC) system is pivotal for enhancing the capabilities of the Internet of Vehicles (IoV). However, conventional MIMO-DFRC designs lack support for simultaneous multi-user communication in the same direction, limiting their utility in IoV applications. To overcome this limitation, we propose a novel robust transmit beamforming approach for the MIMO-DFRC system, facilitating multi-user communication through beampattern modulation. Initially, the orthogonal Oppermann sequences are allocated to each user. Subsequently, these sequences are embedded into sub-beampatterns, which encode communication symbols for multi-user information transmission. Furthermore, the encoded information is strategically placed within the sidelobes of the transmit beampattern, aiming to minimize the integrated sidelobe levels. This goal serves as the objective function while maintaining mainlobe detection performance, which imposes a constraint, forming an optimization model for transmit beamforming. Due to the non-convex nature of the optimization model, it is decomposed using a coordinate rotation strategy and addressed iteratively via a convex optimization algorithm. Simulations validate that our method facilitates reliable unidirectional communication among multiple users and preserves the integrity of radar detection performance, contributing to the IoV application of the DFRC technology.