Radio Map Based 3D Path Planning for Cellular-Connected UAV
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In this paper, we study the three-dimensional (3D) path planning for a cellular-connected unmanned aerial vehicle (UAV) to minimize its flying distance from given initial to final locations, while ensuring a target link quality in terms of the expected signal-to-interference-plus-noise ratio (SINR) at the UAV receiver with each of its associated ground base stations (GBSs) during the flight. To exploit the location-dependent and spatially varying channel and interference over the air, we propose a new radio map based path planning for the UAV. Specifically, we first utilize the channel gain map of each GBS that provides its large-scale channel gains with uniformly sampled locations on a 3D grid over the region of interest, which are due to fixed and large-size obstacles and thus assumed to be time-invariant during the UAV's flight. Based on the channel gain maps of the GBSs and their loading factors, we construct an SINR map that depicts the expected SINR levels over the sampled 3D locations. By leveraging the obtained SINR map, we then derive the optimal UAV path by solving an equivalent shortest path problem (SPP) in graph theory. To reduce the computational complexity, we further propose a grid quantization method whereby the grid points in the SINR map are more coarsely sampled by exploiting the spatial channel/interference correlation over neighboring grids. Then, we solve an approximate SPP over the reduced-size SINR map more efficiently. Numerical results show that the proposed solutions can effectively minimize the UAV flying distance subject to its communication quality constraint, and a flexible trade-off between performance and complexity can be achieved by adjusting the quantization ratio in the SINR map. Moreover, the proposed solution significantly outperforms various benchmark schemes without fully exploiting the channel/interference spatial distribution in the network.
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