Joint Trajectory and Communication Design for UAV-Assisted Symbiotic Radio Networks

Owing to their controlled mobility, extensive coverage and low cost, unmanned aerial vehicles (UAVs) have significant promise in the field of military, civilian and commercial applications, which has sparked a lot of research interest. This paper explores the application of the UAV in the symbiotic radio (SR) system. Specifically, we study the multi-user SR system assisted by the UAV and intelligent reflecting surface (IRS), and the modulation scheme with high flexibility is adopted to embed the IRS symbols into the UAV signals. First, we focus on minimizing the maximum bit error rate (BER) among all ground devices (GDs) while meeting the minimum communication rate requirements by jointly designing the active transmit beamforming and flight trajectory of the UAV as well as IRS reflective phase shifts. Then, we develop an iterative algorithm based on block coordinate descent (BCD) technology to address this optimization problem. Specifically, the optimization problem is decoupled into three sub-problems to be alternately solved, which are solved by invoking the semidefinite relaxation (SDR) and successive convex approximation (SCA) techniques. Moreover, the convergence performance and computational complexity of the proposed algorithm are analyzed. Finally, simulation results show the proposed algorithm can significantly improve the quality of IRS transmission.