Joint Optimization of UAV Trajectory and Number of Reflecting Elements for UAV-Mounted Intelligent Reflecting Surface-Assisted Data Collection in Wireless Sensor Networks Under Transmission Prioritized Scheme

To address the non-line-of-sight (NLOS) transmission challenge between wireless sensor nodes (SNs) and a fusion center in smart agriculture, the unmanned aerial vehicle (UAV)-mounted intelligent reflecting surfaces (IRS) is applied to assist data collection in wireless sensor networks in this paper. The fly-hover-communicate protocol (FHCP) is considered, where the UAV visits a set of hovering positions and communicates with one corresponding SN while hovering at each position. The optimization problem of making a trade-off between spectrum and energy efficiency (EE) under the transmission prioritized scheme (TPS) in FHCP is analyzed. For the single-SN case, the problem is decomposed into two sub-problems: UAV trajectory and number of reflecting elements (NoRE) optimization. For the multi-SN case, it is decomposed into three sub-optimization problems: user association, NoRE, and UAV trajectory planning. An efficient alternating optimization algorithm incorporating the genetic algorithm, conditional judgment-binary search algorithm, and successive convex approximation algorithm are applied to tackle this problem. Simulation results indicate that the TPS effectively increases EE compared with that when the UAV hovers directly above each SN.