Cellular-connected unmanned aerial vehicle (UAV) has attracted a surge of research interest in both academia and industry. To support aerial user equipment (UEs) in the existing cellular networks, one promising approach is to assign a portion of the system bandwidth exclusively to the UAV-UEs. This is especially favorable for use cases where a large number of UAV-UEs are exploited, e.g., for package delivery close to a warehouse. Although the nearly line-of-sight (LoS) channels can result in higher powers received, UAVs can in turn cause severe interference to each other in the same frequency band. In this contribution, we focus on the uplink communications of massive cellular-connected UAVs. Different power allocation algorithms are proposed to either maximize the minimal spectrum efficiency (SE) or maximize the overall SE to cope with severe interference based on the successive convex approximation (SCA) principle. One of the challenges is that a UAV can affect a large area meaning that many more UAV-UEs must be considered in the optimization problem, which is essentially different from that for terrestrial UEs. The necessity of single-carrier uplink transmission further complicates the problem. Nevertheless, we find that the special property of large coherent bandwidths and coherent times of the propagation channels can be leveraged. The performances of the proposed algorithms are evaluated via extensive simulations in the full-buffer transmission mode and bursty-traffic mode. Results show that the proposed algorithms can effectively enhance the uplink SEs. This work can be considered the first attempt to deal with the interference among massive cellular-connected UAV-UEs with optimized power allocations.

翻译：蜂窝连接无人机（UAV）在学术界和工业界引起了广泛的研究兴趣。为支持现有蜂窝网络中的空中用户设备（UE），一种有前景的方法是将部分系统带宽专门分配给无人机用户设备。这对于大量无人机用户设备的应用场景尤为有利，例如在仓库附近进行包裹配送。尽管近视线（LoS）信道可能导致接收功率较高，但无人机在同一频段内可能相互产生严重干扰。本文聚焦于大规模蜂窝连接无人机的上行通信问题。基于连续凸逼近（SCA）原理，提出了不同的功率分配算法，以最小化频谱效率（SE）的最大值或最大化整体频谱效率，从而应对严重干扰。其中一个挑战在于，无人机会影响大面积区域，这意味着优化问题中必须考虑更多无人机用户设备，这与地面用户设备的情况本质不同。单载波上行传输的必要性进一步增加了问题复杂性。尽管如此，我们发现可以利用传播信道具有大相干带宽和相干时间的特殊性质。通过在满缓冲传输模式和突发流量模式下进行大量仿真，评估了所提算法的性能。结果表明，所提算法能有效提升上行频谱效率。本研究可视为首次尝试通过优化功率分配来解决大规模蜂窝连接无人机用户设备间的干扰问题。