This book looks at the recent progress of research and development for 5G mobile wireless networks, covering related topics on fundamental 5G requirements and enabling technologies. According to 5G Public-Private Partnership (5GPPP), 5G systems need to be capable of providing 1000 times higher capacity and a 90% reduction in energy consumption compared to the systems today, in order to cope with the tremendous increase of mobile data traffic and to reduce the ever increasing carbon emission footprint of mobile communications. This book surveys 5G service architecture and summarizes the enabling technologies towards the true 5G systems, including highly dense small cell and heterogeneous networks, device-to-device communications underlaying cellular networks, millimeter wave communications, etc., and video applications with QoE aware spectrum efficiency and energy efficiency in 5G systems.