In this article we present a survey on the technical challenges of future radio access networks beyond LTE-Advanced, which could offer very high average area throughput to support a huge demand for data traffic and high user density with energy-efficient operation. We highlight various potential enabling technologies and architectures to support the aggressive goal of average area throughput 25 Gb/s/km² in beyond IMT-Advanced systems. Specifically, we discuss the challenges and solutions from the controlling/ processing perspective, the radio resource management perspective, and the physical layer perspective for dense urban cell deployment. Using various advanced technologies such as interference mitigation techniques, MIMO, and cooperative communications as well as cross-layer self-organizing networks, we show that future urban wireless networks could potentially offer high-quality mobile services and offer an experience similar to the wired Internet.