# 3D Global Path Planning Optimization for Cellular-Connected UAVs under Link Reliability Constraint
## 5 Conclusions  
In this work, we have proposed a 3D global path planning optimization method for cellular-connected UAVs to enhance the flight safety of low-altitude UAVs. In this regard, the preexisting knowledge of a mission and environment, such as locations of starting point, destination point, BSs, obstacles, and no-fly zones, can be given as the inputs to the algorithm. The output of the algorithms is a global optimized path in the form of 3D waypoints, which can be fed to the flight controller before its mission.  
The results of the conducted aerial drive test have been statistically analyzed to consider realistic constraints of cellular networks in the path planning problem. It has been revealed that within a radius of 500 m and a height of up to 85 m AGL, the existing 4G network can provide reliable aerial coverage for CC communications. The other real-world constraints, such as maximum flight distance and permitted flight height, have also been considered in the algorithm, which can be set based on the type of the UAV and the regulations of each country/region.  
The PSO, GA, and PSO-GA algorithms have been used to solve the defined problem. To assess the effectiveness of the algorithms, the performance of the algorithms has been investigated under different scenarios. The simulation results revealed some shortcomings of the GA and PSO algorithms, such as getting trapped in local minima, slow convergence speed, and instability. Thus, a combination of both algorithms has been used to address the issues. The PSO-GA algorithm is empowered by the powerful aspects of two algorithms, the information flow of PSO, and the crossover and mutation operations of GA. The simulation results showed that among all the three algorithms, PSO-GA provides the best solution for the 3D UAV path planning problem, surpassing the other two algorithms in terms of stability, reliable path length, reliable path ratio, convergence speed, and execution time. Finally, the comparison between the simulation results and the measurement results proved the effectiveness and feasibility of the proposed method in solving 3D UAV global path planning in suburban environments.  
The future work is to improve the accuracy of the RSRP and RSRQ models by taking into account the effect of the azimuth angle on the link reliability. Furthermore, the aerial  
Figure 20: Comparison of path planning optimization simulation results against aerial drive test measurements.  
coverage of 5G networks needs to be investigated in different scenarios, and the proposed method can be updated accordingly. Besides, the performance of the proposed model can be investigated with more state-of-the-art intelligent algorithms.  
Conceptualization, M.B. and R.N.; methodology, M.B.; software, M.B.; validation, M.B. and R.N.; formal analysis, M.B.; investigation, M.B.; resources, M.B., R.N. and N.F.A.; data curation, M.B. and M.A.Z.; writing--original draft preparation, M.B.; writing--review and editing, M.B., R.N. and N.F.A.; visualization, M.B. and M.A.Z.; supervision, R.N. and N.F.A.; project administration, R.N.; funding acquisition, R.N. All authors have read and agreed to the published version of the manuscript.  
We acknowledge the financial support from Universiti Kebangsaan Malaysia (DIP-2019-014 and DPK-2020-014) and Collaborative Research in Engineering, Science, and Technology (CREST) under grant T23C2-19.  
Not applicable.  
The utilized dataset in this study is publicly available on: [PERSON], 2022, UAVCellularDataset_suburban, GitHub, [[https://github.com/[PERSON]/UAVCellularDataset_Suburban](https://github.com/Mehranbjt/UAVCellularDataset_Suburban)]([https://github.com/Mehranbjt/UAVCellularDataset_Suburban](https://github.com/[PERSON]/UAVCellularDataset_Suburban)) (accessed on 16 September 2022).  
The authors would like to thank the Aerodyne Group for their support and guidance during this research.  
The authors declare no conflict of interest.