In　this　paper,　we　address　the　problem　of　energy　efficient　resource　optimization　for　downlink　transmission　in　user-centric　ultra-dense　networks　enabled　by　wireless　access　via　non-orthogonal　multiple　access　and　wireless　backhaul　via　beamforming.　Our　objective　is　to　maximize　the　system　energy　efficiency　by　jointly　optimizing　user/access　point　scheduling,　subchannel　assignment,　and　power　allocation.　The　problem　is　formulated　as　a　non-convex　mixed-integer　nonlinear　programming　problem　which　is　NP-hard.　We　then　transform　it　into　a　convex　subproblem　using　the　sum-of-ratios　decoupling　and　the　iterative　successive　convex　approximation　method.　An　overall　algorithm　is　further　developed　to　solve　the　subproblem　iteratively.　Simulation　results　show　that　the　proposed　algorithm　has　improved　the　system-wide　energy　efficiency　significantly　when　compared　to　the　benchmark　scheme.　©　2020　IEEE.