Collaborative Planning with Concurrent Synchronization for Operationally Constrained UAV-UGV Teams
Authors: Zihao Deng, Qianhuang Li, Peng Gao, Maggie Wigness, John Rogers, Donghyun Kim, Hao Zhang
Organizations: Zihao Deng, Qianhuang Li, Donghyun Kim, and Hao Zhang are with the University of Massachusetts Amherst, Amherst, MA, 01002, USA. · Peng Gao is with North Carolina State University, Raleigh, NC, 27695, USA. · Maggie Wigness and John Rogers are with the U.S. Army DEVCOM Army Research Laboratory (ARL), Adelphi, MD, 20783, USA.
Collaborative planning under operational constraints is an essential capability for heterogeneous robot teams tackling complex large-scale real-world tasks. Unmanned Aerial Vehicles (UAVs) offer rapid environmental coverage, but flight time is often limited by energy constraints, whereas Unmanned Ground Vehicles (UGVs) have greater energy capacity to support long-duration missions, but movement is constrained by traversable terrain. Individually, neither can complete tasks such as environmental monitoring. Effective UAV-UGV collaboration therefore requires energy-constrained multi-UAV task planning, traversability-constrained multi-UGV path planning, and crucially, synchronized concurrent co-planning to ensure timely in-mission recharging. To enable these capabilities, we propose Collaborative Planning with Concurrent Synchronization (CoPCS), a learning-based approach that integrates a heterogeneous graph transformer for operationally constrained task encoding with a transformer decoder for joint, synchronized co-planning that enables UAVs and UGVs to act concurrently in a coordinated manner. CoPCS is trained end-to-end under a unified imitation learning paradigm. We conducted extensive experiments to evaluate CoPCS in both robotic simulations and physical robot teams. Experimental results demonstrate that our method provides the novel multi-robot capability of synchronized concurrent co-planning and substantially improves team performance. More details of this work are available on the project website: https://hcrlab.gitlab.io/project/CoPCS.
Figures & tables
Fig. 1: A motivating scenario of a UAV-UGV team performing collaborative planning under operational constraints to visit all task points for environmental monitoring. UAVs are flight-time limited due to energy constraints, while UGVs are constrained by terrain traversability, preventing either platform from completing the mission alone. To overcome this, UGVs act as mobile recharging stations, carrying energy supplies and synchronizing with UAVs to sustain their operations. Task points are shown as white circles and recharging points as green circles, while colored lines denote UAV trajectories and black lines denote UGV paths.
Fig. 2: Overview of CoPCS ( Collaborative Planning with Concurrent Synchronization ), a unified learning-based method that integrates a heterogeneous graph transformer for synchronized collaboration among operationally constrained UAV-UGV teams and a transformer decoder for joint action co-planning. The CoPCS approach is trained end-to-end, and its co-planning policy is executed concurrently to coordinate all the robots, which enables concurrent synchronization.
Fig. 3: Qualitative results of CoPCS in a map-based simulator. The first four figures illustrate a mission with 15 tasks and 5 paths, while the last four figures show a mission with 45 tasks and 10 paths. The experiments evaluate different team configurations, ranging from 1 UAV and 1 UGV to 4 UAVs and 2 UGVs. Task points are depicted as white circles, recharging points as green circles, UAV trajectories as colored lines, and UGV paths as black lines.
Fig. 4: Qualitative results of co-planning with concurrent synchronization for a team of two Warthog UGVs and two quadrotor UAVs in a high-fidelity Unity-based 3D simulator integrated with ROS1. The mission includes 45 tasks and 10 traversable paths. The first column of the two subfigures illustrates the team starting configuration and a synchronized recharging event during execution, while the remaining subfigures depict trajectories at different timestamps.
Fig. 5: Qualitative results illustrating the generalizability of CoPCS in unseen environments. The large-scale suburban and urban maps are not used during training and also contain variations in starting points and road network layouts. In the top environment, a 2-UAV and 2-UGV team is required to visit 15 tasks, while in the bottom environment, a 4-UAV and 2-UGV team is required to visit 15 tasks.
Fig. 6: Qualitative results of CoPCS in real-world mixed-reality experiments using two Crazyflie UAVs and two Limo UGVs controlled through ROS2.
Collaborative planning under operational constraints is essential for heterogeneous robot teams in large-scale missions. Unmanned Aerial Vehicles (UAVs) provide rapid area coverage but are limited by onboard energy, while Unmanned Ground Vehicles (UGVs) can serve as mobile recharging stations yet are constrained by road-network traversability. Effective collaboration must enforce operational constraints during execution while enabling parallel, coordinated actions. Masked Diffusion Models (MDMs) have shown promise through token unmasking but have two key limitations: entropy-guided scheduling assumes distributional alignment and reliance on differentiable constraints for diffusion-time optimization. We propose Masked Error-bounded Neuro-Symbolic Diffusion (MEND), which formulates collaborative planning as a conditional masked generative process to generate context-aware action sequences for UAV-UGV teams. MEND introduces a neuro-symbolic diffusion paradigm that constrains conditional masked diffusion policies at execution by reweighting the learned action distribution with a logic-induced admissibility indicator, thereby enforcing compliance with operational constraints. MEND introduces an error-bounded inference scheduling at execution that constructs the unmasking schedule by selecting positions with minimal predictive entropy over the constraint-aware action distribution, enhancing collaborative planning optimality under operational constraints. Extensive experimental results in simulation, on real-world maps, and with physical robot teams demonstrate that MEND advances UAV-UGV collaborative planning under operational constraints.
Zihao Deng, Qianhuang Li, Maggie Wigness +3
University of Massachusetts Amherst · U.S. Army DEVCOM Army Research Laboratory
We consider energy-aware planning for an unmanned aerial vehicle (UAV) and unmanned ground vehicle (UGV) team operating in a stochastic environment. The UAV must visit a set of air points in minimum time while respecting energy constraints, relying on the UGV as a mobile charging station. Unlike prior work that assumed deterministic travel times or used fixed robustness margins, we model travel times as random variables and bound the probability of failure (energy depletion) across the entire mission to a user-specified risk level. We formulate the problem as a Mixed-Integer Program and propose PRO-SPECT, a polynomial-time algorithm that generates risk-bounded plans. The algorithm supports both offline planning and online re-planning, enabling the team to adapt to disturbances while preserving the risk bound. We provide theoretical results on solution feasibility and time complexity. We also demonstrate the performance of our method via numerical comparisons and simulations.
Roger Fowler, Cahit Ikbal Er, Benjamin Johnsenberg +1
Khoury Department of Computer Sciences, Northeastern University, Boston, MA · The Charles Stark Draper Laboratory, Inc., Cambridge, MA · Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA +1
We consider planning for unmanned aerial vehicle (UAV) and unmanned ground vehicle (UGV) teams in aerial monitoring missions with ordering requirements on the monitoring points to be visited by the UAV. The system consists of multiple UAV-UGV teams, each comprising one UAV and one UGV. UAV energy limitations are modeled through endurance, defined as the maximum flight time on a full battery. The UGVs serve as mobile charging stations and transport the UAVs between consecutive aerial tours. Given a set of monitoring points subject to ordering constraints and the teams' initial and terminal positions, the objective is to minimize mission completion time while satisfying UAV energy limits and the required visit order under bounded travel-time disturbances that may arise during execution. Unlike prior work, the plan jointly determines vehicle routes and their timing, allowing teams to slow down as needed to satisfy the ordering constraints. We develop a polynomial-time algorithm that generates efficient solutions to the underlying NP-hard planning problem. We establish feasibility guarantees, characterize the algorithm's computational complexity, and evaluate its performance via numerical comparisons.
Cahit Ikbal Er, Yasin Yazicioglu
Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA, USA · Departments of Mechanical and Industrial Engineering and Electrical and Computer Engineering, Northeastern University, Boston, MA, USA