User-centric ultra-dense networks for 5g Shanzhi Chen, Fei Qin, Bo Hu, Xi Li, Zhonglin Chen, Jiamin Liu

In recent years, with the growing popularity of smart devices and wide spreading of mobile Internet, the mobile data traffic is increasing dramatically. By 2020, the global mobile traffic volume will have about 1000 times growth compared to that of 2010 [1, 2]. According to the mobile cellular history from the first Generation Mobile Communication System (1G) to fourth Generation Mobile Communication System (4G), each generation has about ten times data rate enhancement related to the previous generation. The next generation of International Mobile Telecommunication towards 2020 (IMT-2020), i.e. the fifth Generation Mobile Communication System (5G), would thus reach 10 Gbps, which is ten times peak data rate to 4G. In 2015, International Telecommunications Union-Radio Communications Sector (ITU-R) published the recommendation on the framework and key capabilities on IMT-2020 [3]. Base on the recommendation, the area traffic capacity is one of the most important Key Performance Indicators (KPIs) for 5G and requirement value reaches 20 Tbps/km2 in dense urban or hotspot area. In addition, other requirements such as lower latency, higher spectral efficiency and energy efficiency are also included.