 recovered using CSI-RS. In this case, the UE must repeat the initial access procedure or try to recover the link using the SS block bursts while the user experiences a service unavailability. Beam switching and recovery: Beam recovery involves a procedure when the link between the gNB and the UE can no longer be maintained and needs to be reestablished. These procedures are periodically repeated to update the optimal transmitter and receiver beam pair over time. There are two network deployment scenarios for NR, that is, non- standalone and standalone, which can affect the way these procedures are performed. In non-standalone scenario, an NR gNB uses an LTE cell as an anchor for the control-plane management and mobile terminals exploit multi-connectivity to maintain multiple connec- tions to different cells SO that any link failure can be overcome by switching data paths. However, such an option may not be available in standalone deployments. The beam man- agement procedure is further illustrated in Fig. 4.44. The beam management operation in general is based on the control messages which are periodically exchanged between transmit and receive nodes. The reference signals used for beam management depend on the state of the UE. In idle mode, the PSS, SSS, and PBCH DM-RS are used, whereas in the connected mode, the CSI-RS and SRS are used in the downlink and uplink, respectively. A radio connection between a gNB with NgNB-beam ana- log beams and a UE with NUE-beam analog beams has a total of NUE-beam RX beam pairs. Given that the number of TX/RX beams is typically large in mmWave bands to achieve sufficient coverage, efficient beam measurement and reporting procedures are important to ensure minimal overhead and UE complexity. A gNB capable of transmit- NgNB-beam analog beams can configure up to NRS reference signals for beam measure- ment. Each RS is beamformed with its associated analog beam pointing in a particular direction. The analog beam associated with each reference signal may also be kept fixed over cert