LTE Along with 5G NR 5G is defined in at least two phases, with phase 1 specified in Release 15 and phase 2 starting from Release 16. With Release 15, approved in mid-2018, 5G NR defines a set of specifications that de- livers features like superior throughput, low latency, extreme reliability, device density, spectrum flexibility, heterogeneity, and energy efficiency to support existing and new sets of use cases. Two deployment options are defined for 5G in Release 15: The non-standalone (NSA) architecture, where the 5G RAN and its New Radio interface is used in conjunction with the existing LTE Core Network, thus making the NR technology avail- able without network replacement. The standalone (SA) architecture, where the NR is connected to the 5G Core network, which will allow the full set of 5G phase 1 (Release 15) services to be supported. As part of phase 2, Release 16 and Release 17, new feature extensions will be covered to address forward-looking use cases and deployment scenarios across eMBB, mMTC, and uRLLC. More de- tails on this topic are in the upcoming section "5G System Architecture." At the time of writing, many operators are deploying 5G and NR networks in NSA mode to coexist with their existing LTE/LTE-A networks as a temporary step toward a full 5G deployment. In this configuration, only 4G services are supported, but this allows the features offered by the 5G New Radio (such as lower latency) to be available without a massive migration. 5G is an evolved architecture, and to understand the synchronization requirements for 5G, it is ne- cessary to understand the basis of its architecture and requirements defined around the system design. The following sections discuss some of these aspects, after which the details of the 5G syn- chronization requirements are presented. 10.4.1 5G Spectrum Access to the correct type of spectrum is one of the most important factors needed to ensure success for 5G. Lower frequency bands (for example, under 1 GHz) have good coverage but lower capacity to carry data. 