If there is only one station, its operation is simple.
When the drone's battery is fully charged, the drone flies up and performs its mission.
After completing the mission, it returns to the station and gets ready to be charged again.

Pros: Simple Structure, Easy to Operate
Cons: Not continuous operation.

Assume there are more than one station with the same number of drones.
With this topology, one drone can do a mission while other drones being charged and ready for flight.
This scheme will reduce the time for preparing another flight.

Pros: the continuity of service improves. The rest time between flights is shortened.
Cons: when the charging time increases in one of drones, the overall efficiency becomes bad.

Assume there are more than one station with only one drone.
A drone can land at any station when its battery is almost done.
When each station is properly located around the target area,
only one drone can cover wide area.

Pros: the coverage becomes wider.
Cons: cost for additional stations.

Assume there are more than one station with the same number of drones.
When all drones are charged, they can be rotated among stations.
For example, there are three stations (A, B, C) and three drones (1, 2, 3).
Initially, Drone 1 is at Station A, Drone 2 is at Station B, and Drone 3 is at Station C.
When the mission starts, Drone 1 moves to Station B, Drone 2 moves to Station C,
and Drone 3 moves to Station A simultaneously.
This routine can be kept going in a continuous loop.

Pros: the coverage is wider, and the system can monitor wider area simultaneously.
Cons: cost for additional stations and drones.