 included in 3GPP Rel-13 onward. There has been significant interest expressed by some mobile operators and broadcasters for enhanced multimedia broadcast multicast service (eMBMS) in the past few years; neverthe- less, the use of eMBMS in general has been only nascent and the standardization work is ongoing with further improvements in 3GPP Rel-14. Reduction in end-to-end latency is required for various applications, including those envis- aged for 5G. However, somewhat lower latency than current levels is desirable for more conventional mobile broadband use cases. LTE control-plane latency figures vary quite widely among different networks with figures up to 75 ms quite common. This relatively high latency can result from the routing of data packets through many network elements before they reach a network gateway to the Internet. From that point onward, there will be additional packet-routing delays which are beyond operator's control. 3GPP has been study- ing the possibility of reducing the LTE TTI of 1 ms and to further identify additional latency reductions at layers 2 and 3 of the LTE protocol stack. While LTE evolution is mainly focused on eMBB aspects, 3GPP is also trying to fulfill some of the 5G use cases with the specific performance requirements in the LTE path. For example, a downscaled UE Category 0 was introduced in LTE Rel-12 for IoT applications. This and the subsequent LTE-based NB-IoT standardization could satisfy some of the 5G requirements for mMTC use cases. Introduction and Background lxxxi The scope of NR phase 1 standardized in 3GPP Rel-15 included both NSA and SA opera- tions. In NSA mode, 5G NR uses LTE as an anchor in the control plane. The SA mode allows 5G NR to work independently with full control plane capability. While focusing on eMBB use case, it also provides support for some URLLC services. The LTE and NR share much more than the common 3GPP release schedule shown in Fig. 18. It is inevitable that much of what is being developed for LTE will also significantly contribute to 5