e more practical representa- tion of user activity. Small-cell enhancements target high network energy efficiency and a reasonable system complexity. The small cells can save energy by switching to a dormant mode due to increased likelihood of periods of low or no user activity during operation. The trade-off 50 Chapter 1 between user throughput/capacity per unit area and network energy efficiency is an impor- tant consideration for small cell deployments. The small cells can further achieve UE energy efficiency considering the small cell's short-range transmission path, resulting in reduced energy/bit for the uplink transmission, mobility measurements, cell identification, and small cell discovery. Given that some of the heterogeneous network deployments include user-installed access nodes in indoor environments, a self-organizing mechanism for deployment and operation of the small cell without direct operator intervention is required. 3GPP self-organizing net- works (SON) solutions aim to configure and optimize the network automatically, SO that the intervention of human can be reduced and the capacity of the network can be increased. These solutions can be divided into three categories [85]: Self-configuration: This is the dynamic plug-and-play configuration of newly deployed access node. As shown in Fig. 1.20, the access node configures its physical cell identity (PCI), transmission frequency, and power, leading to faster cell planning and rollout. eNB power on IP address configuration Gateway association Basic setup Authentication Software and configuration data download Neighbor list configuration Initial radio configuration Configuration of coverage parameters Neighbor list optimization Optimization Optimization of coverage and capacity Failure detection and localization Self-healing Healing scheme Figure 1.20 SON framework [85]. 5G Network Architecture 51 The network interfaces (e.g., S1 and X2 in the case of LTE) are dynamically config- ured, and the IP address as well as connection to IP backhaul is est