Next-generation mobile communication will not be available until after 2020. The global research efforts already underway are exemplified by , as well as by projects such as the METIS project in Europe. Research is likely to continue for a few more years from now before the standardization and eventual commercialization of the system begin. However, we already have a relatively clear view of the main challenges and opportunities, as well as the key technology components of the future 5G systems .