Future steps of LTE-A: evolution toward integration of local area and wide area systems

In the future steps of 3GPP LTE-Advanced, we will need to ensure the sustainability of 3GPP radio access technologies in order to respond to the anticipated challenging requirements of the future. To this end, this article presents our views on the evolution concept and candidate technologies for future steps of LTE-A taking into account the ever increasing importance of local area (small cells) and the need for further spectrum extension to higher frequency bands. In our evolution concept, we emphasize the integration of the local area with the wide area as a new form of cooperation between conventional macrocells in lower frequency bands and small cells deployed in higher frequency bands. Furthermore, we identify the potential key technologies for further spectrum efficiency enhancements for both the local area and the wide area, and for the efficient integration of the local and wide areas while assuming frequency separation between macrocells and small cells. In particular, multicell cooperation based on macrocell assistance of small cells (referred to as Phantom cell) is introduced, and the related benefits are discussed. Finally, in order to demonstrate the potential capacity gains of our evolution concept, system-level simulation results are provided for using outdoor small cells in higher/wider frequency bands.