Femtocell base stations (FBSs) have been widely considered in the next generation cellular systems to enhance spectrum efficiency, but macro-femto and femto-femto interferences are still challenging issues to solve. In this paper, we consider the backhaul interface of FBSs to be home broadband connection (such as ADSL and optical fiber) with capacity lower than the air interface, and propose a novel resource optimization for FBSs to mitigate both the macro-femto and femto-femto interferences. First, the user rate requirements are normalized according to the backhaul capacity. Then, the total spectrum utilized by FBSs is minimized to alleviate the macro-femto interference. To reduce the femto-femto interference, we integrate the Gibbs sampler into the resource optimization to make each FBS select the frequency bands which have lower probability to introduce interference. Via sophisticated simulations based on the 3GPP femtocell evaluation scenario, the resource optimization is demonstrated to be effective and ready for LTE-A.