Joint Beamforming and Temporal Resource Allocation for RIS-Aided Integrated Terrestrial and Aerial Networks Based on Reverse TDD

By utilizing the flexible operation of unmanned aerial vehicles (UAVs), the integrated terrestrial and aerial network (ITAN) can expand both coverage and network capacity, which are the main key performance indices (KPIs) in 6G wireless networks. For the ITAN, since an additional wireless backhaul link for UAV should be considered, an appropriate access and backhaul strategy that accounts for interference is required. To this end, this paper investigates the in-band reverse time division duplexing (RTDD)-based ITAN. It consists of multiple gNodeBs (gNBs) and a single UAV, where cooperative transmission by the gNBs is employed to support both access and backhaul links. In addition, reconfigurable intelligent surfaces (RISs) are taken into account to enhance interference management and desired signal transmission. Specifically, a sum-rate maximization problem for the ITAN is formulated, and a joint optimization algorithm of transmit beamforming (BF) of gNBs and UAV, the RIS phase shift matrix, and a temporal resource allocation (RA) is developed. Numerical results show that our proposed scheme outperforms other baseline schemes, demonstrating the efficiency of RIS, cooperative transmit BF, and temporal RA in the ITAN.