We study the problem of persistent monitoring of a finite number of
inter-connected geographical nodes by a group of heterogeneous mobile agents.
We assign to each geographical node a concave and increasing reward function
that resets to zero after an agent's visit. Then, we design the optimal
dispatch policy of which nodes to visit at what time and by what agent by
finding a policy set that maximizes a utility that is defined as the total
reward collected at visit times. We show that this optimization problem is
NP-hard and its computational complexity increases exponentially with the
number of the agents and the length of the mission horizon. By showing that the
utility function is a monotone increasing and submodular set function of
agents' policy, we proceed to propose a suboptimal dispatch policy design with
a known optimality gap. To reduce the time complexity of constructing the
feasible search set and also to induce robustness to changes in the operational
factors, we perform our suboptimal policy design in a receding horizon fashion.
Then, to compensate for the shortsightedness of the receding horizon approach
for reward distribution beyond the feasible policies of the agents over the
receding horizon, we add a new term to our utility, which provides a measure of
nodal importance beyond the receding horizon's sight. This term gives the
policy design an intuition to steer the agents towards the nodes with higher
rewards on the patrolling graph. Finally, we discuss how our proposed algorithm
can be implemented in a decentralized manner. A simulation study demonstrates
our results.