Radio Map Enabled Path Planning for Multiple Cellular-Connected Unmanned Aerial Vehicles
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摘要: 针对多网联无人机协同作业场景中,因冲突规避引发的个体服务质量不均衡问题,该文提出了一种基于无线电地图辅助的协同路径规划方案。该方案以最小化所有无人机中最大任务完成时间与通信断联时间加权和为目标,构建了多无人机路径规划模型,并设计了一种改进的冲突搜索(ICBS)算法进行求解。该算法采用分层搜索架构:高层结构通过引入邻近冲突检测以确保满足安全距离约束,并基于重构的代价函数引导以公平性为导向的冲突消解与路径选择;低层结构则采用基于双向A*的最优路径算法,通过双向并行搜索机制提升寻优效率。仿真结果表明,相较于基准方案,所提方案能够有效降低所有无人机中最大加权时间,显著提升多无人机协同的公平性与整体性能。Abstract:
Objective In collaborative operation scenarios of cellular-connected Unmanned Aerial Vehicles (UAVs), conflict avoidance strategies often cause unbalanced service quality. Traditional schemes focus on reducing total task completion time but do not ensure service fairness. To address this issue, a radio map-assisted cooperative path planning scheme is proposed. The objective is to minimize the maximum weighted sum of task completion time and communication disconnection time across all UAVs to improve service fairness in multi-UAV scenarios. Methods A Signal-to-Interference-plus-Noise Ratio (SINR) map is constructed to assess communication quality. The two-dimensional airspace is discretized into grids, and link gain maps are generated through ray tracing and Axis-Aligned Bounding Box detection to determine Line-of-Sight (LoS) or Non-Line-of-Sight (NLoS) conditions. The SINR map is produced by selecting, for each grid, the base station with the highest expected SINR. To solve the optimization problem, an Improved Conflict-Based Search (ICBS) algorithm with a hierarchical structure is developed. At the high-level stage, proximity conflicts are managed to maintain safety distances, and the cost function is reformulated to emphasize fairness by minimizing the maximum weighted time. The low-level stage applies a bidirectional A* algorithm for single-UAV path planning, using parallel search to improve efficiency while meeting the constraints set by the high-level stage. Results and Discussions The proposed scheme is evaluated through simulations across different scenarios. Building heights and positions are shown, where base station locations are marked by red stars and building heights are represented with color gradients from light to dark to indicate increasing height ( Fig. 2 ). The wireless propagation characteristics between UAVs and ground base stations are demonstrated by the SINR map at an altitude of 60 m (Fig. 3 ), which shows significant SINR degradation in areas affected by building blockage and co-channel interference, resulting in communication blind zones. Trajectory planning results for four UAVs at an altitude of 60 m with a SINR threshold of 2 dB show that all UAVs avoid signal blind zones and complete tasks without collision risks under the proposed scheme (Fig. 4 ). The trade-off between task completion time and disconnection time is controlled by the weight coefficient (Fig. 5 ). The maximum weighted time increases monotonically as the weight coefficient increases, whereas the maximum disconnection time decreases. The bidirectional A* algorithm achieves higher computational efficiency than Dijkstra’s and traditional A* algorithms while maintaining optimal solution quality (Table 1 ). All three algorithms yield identical weighted times, confirming the optimality of the bidirectional A* approach, and its runtime is reduced significantly due to parallel search. Compared with three benchmark schemes, the proposed scheme achieves the lowest maximum weighted time for different SINR thresholds (Fig. 6 ). Performance analysis at different UAV altitudes shows that the proposed scheme maintains stable maximum weighted time below 75 m, while sharp increases appear above 75 m due to intensified interference from non-serving base stations (Fig. 7 ). The scalability analysis further shows clear improvements over benchmark schemes, especially when conflicts occur more frequently (Fig. 8 ).Conclusions To address fairness in cellular-connected multi-UAV systems, a radio map-assisted path planning scheme is proposed to minimize the maximum weighted time. Based on a discretized SINR map, an ICBS algorithm is developed. At the high-level stage, proximity conflicts and a reformulated cost function ensure safety and fairness, and at the low-level stage, a bidirectional A* algorithm increases search efficiency. Simulation results show that the proposed scheme lowers the maximum weighted time compared with benchmark schemes and improves fairness and overall multi-UAV collaboration performance. -
Key words:
- Cellular-connected UAV /
- Radio map /
- Path planning /
- Conflict-based search algorithm
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1 ICBS算法
输入: $ K $架无人机的起点集合$ \left\{{\boldsymbol{u}}_{k,\text{I}}\right\} $,终点集合$ \left\{{\boldsymbol{u}}_{k,\text{F}}\right\} $,SINR地图$ {[\boldsymbol{R}]}_{i,j} $,SINR阈值$ {\gamma }_{\text{th}} $,安全距离$ {d}_{\text{s}} $ 输出: 无冲突的最优路径集合$ \left\{{\boldsymbol{U}}_{k}\right\} $ (1) 初始化:优先队列$ \text{OPEN}\leftarrow \varnothing $,创建根节点$ {\text{CT}}_{\text{root}} $,设置其约束集$ {\text{CT}}_{\text{root}}.{C}\leftarrow \varnothing $,并调用双向A*算法规划初始路径作为$ {\text{CT}}_{\text{root}} $的路
径集合及根据式(21)计算代价$ {\text{CT}}_{\text{root}}.\text{cost} $,将$ {\text{CT}}_{\text{root}} $插入OPEN(2) while $ \text{OPEN}\neq \varnothing $ do (3) 当前节点$ {\text{CT}}_{\text{curr}}\leftarrow \arg {\min }_{\text{CT}\in \text{OPEN}}\text{CT.cost} $,检测$ {\text{CT}}_{\text{curr}} $路径集合中的邻近冲突 (4) if 路径无冲突 then (5) return $ {\text{CT}}_{\text{curr}} $的路径集合$ \left\{{\boldsymbol{U}}_{k}\right\} $ (6) end if (7) for参与冲突的两架无人机 do (8) 创建子节点$ {\text{CT}}_{\text{child}} $,$ {\text{CT}}_{\text{child}}.{C} $继承$ {\text{CT}}_{\text{curr}} $的约束集并添加新冲突约束 (9) 调用双向A*规划算法重新规划路径作为$ {\text{CT}}_{\text{child}} $的路径集合并计算$ {\text{CT}}_{\text{child}}.\text{cost} $,然后将$ {\text{CT}}_{\text{child}} $插入OPEN (10) end for (11) end while 表 1 低层路径规划算法的性能对比(s)
任务编号 加权时间成本 算法运行耗时 Dijkstra A* 双向A* 任务1 51.3 0.35 0.13 0.10 任务2 106.0 0.84 0.60 0.35 任务3 136.7 1.31 0.74 0.59 -
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