hase of 5G specifications that define basic features of 5G systems. 3GPP Rel-16 will specify the second phase of 5G specifications defining additional features of 5G that combined with those of the first phase will satisfy the IMT-2020 requirements. The two phases of 5G specifications development in 3GPP are scheduled to end in September 2018 (already completed in March 2019) and March 2020, respectively [34]. While the prospect of the next-generation networks has inspired extensive and non-back- ward compatible changes in the air interface design (e.g., channel coding schemes, use of 3GPP, http://www.3gpp.org/. Introduction and Background Ixxix non-orthogonal multiple access) and the transport layer [e.g., information centric networking (ICN)26], it has further stimulated the development of numerous incremental improvements in the current networks. Many of these technologies are already in the pipeline for develop- ment, standardization, and deployment. In fact, what 3GPP calls LTE-Advanced Pro, that is, revisions of LTE technology that build upon 3GPP Rel-8 through 14, along with the first drop of the NR air interface features with Rel-15 in late 2018, will form the basis of 5G in its initial deployments around 2020. Full satisfaction of IMT-2020 requirements is not antic- ipated until the completion of 3GPP Rel-16 in late 2019. The momentum is clearly and strongly behind what is being provided with many enhancements to LTE in a sequence of new releases. LTE has already been significantly improved since its inception with 3GPP Rel-8 and with further improvements in LTE-Advanced, as initially standardized in 3GPP Rel-10. In the LTE track of 5G in 3GPP, enhancements will continue to enable the standard to support as many 5G requirements and use cases as possible. In order to increase the performance of the existing systems by an order of magnitude, it would require a combination of new spectrum, improved spectrum efficiency and increased network density. In particular, carrier aggregation which was introduced in 