Multi-Antenna Air–Ground Cooperative Cognitive Radio Networks Enhanced by Rate-Splitting Multiple Access

Cooperative cognitive radio networks (CCRANs) not only improve spectrum utilization efficiency by sharing spectrum resources between primary and secondary systems but also expand wireless coverage by relay cooperative communications, while UAV communication is a crucial supporting technology for the low-altitude economy. Conventional single-antenna rate-splitting multiple access (RSMA)-enabled CCRAN can only benefit from the power resource allocation and the associated system performance is limited. Against this background, a multi-antenna RSMA and UAV-enabled CCRAN is examined to improve the network transmission capability, and a two-phase communication protocol with scalable transmission duration is established to coordinate the information transmission between the primary and secondary systems. Consequently, two additional degrees of freedom (DoFs) of space and time resources are utilized in the proposed system as compared with conventional single-antenna CCRANs. To accomplish the system design, we formulate a non-convex optimization problem and derive the associated iterative algorithm based on successive convex approximation. Simulation results show that the proposed scheme can significantly enhance the system’s transmission capability.