CEDAR RAPIDS — Long known to audiences as the U.S. Cellular Center, the city’s downtown arena and convention center will now be called the Alliant Energy Power House instead.Cedar Rapids and Alliant announced Friday a partnership to rename the approximately 470,000 square-foot arena and convention complex under a new deal.Jay Anderkin, general manager of the DoubleTree by Hilton hotel at the complex, said the 12-year naming rights agreement with Alliant Energy starts at $300,000 per year with an option for another five years, totaling $3.6 million.