Facilitating URLLC in UAV-Assisted Relay Systems With Multiple-Mobile Robots for 6G Networks: A Prospective of Agriculture 4.0

In the upcoming sixth-generation (6G) networks, ultra-reliable and low-latency communication (URLLC) is considered as an essential service that will empower real-time wireless systems, smart grids, and industrial applications. In this context, URLLC traffic relies on short blocklength packets to reduce the latency, which poses a daunting challenge for network operators and system designers since classical communication systems are designed based on the classical Shannon's capacity formula. Therefore, to tackle this challenge, this article considers an unmanned aerial vehicle (UAV) acting as a decode-and-forward relay to communicate short URLLC control packets between a controller and multiple-mobile robots in a cell to enable a use-case of Agriculture 4.0. Moreover, this article employs perturbation theory and studies the quasi-optimization of the UAV's location, height, beamwidth, and resource allocation, including time-varying power and blocklength for the two phases of transmission from the controller to UAV and from UAV to robots. In this regard, we propose an iterative optimization method to find the optimal UAV's height and location, the antenna beamwidth, and the variable power and blocklength allocated to each robot inside the circular cell to minimize the average overall decoding error. It is demonstrated that the proposed algorithm outperforms other benchmark algorithms based on fixed parameters and performs nearly as well as the smart exhaustive search. Lastly, our results emphasize the need to jointly optimize all of the abovementioned UAV's system parameters and resource allocation for the two phases of transmission to achieve URLLC for multiple-mobile robots.