Serenity Station is an Immense-class starbase in the Fahleena System, on the edge of the nebula known as the "Badlands", in the Cardassia Sector of the Alpha Quadrant.  It is about a day's travel from DS9 for a fast Starfleet starship.  Its primary task is search and rescue, although like any starbase they also take on many other jobs as needed.

The starbase has something of a reputation for being a place Starfleet officers are sent when they have been misbehaving.

See: http://serenitystation.forumotion.com/