mit/receive beam(s). In beam determination, the gNB and the UE find a beam direction to ensure good radio link quality for the unicast control and data channel transmission. Once a link is established, the UE measures the link quality of multiple transmit and receive beam pairs and reports the measurement results to the gNB. Furthermore, the UE mobil- ity, orientation, and channel blockage can change the radio link quality of the transmit- ted and received beam pairs. When the quality of the current beam pair degrades, the gNB and the UE can switch to another beam pair with better radio link quality. The gNB and the UE can monitor the quality of the current beam pair along with some other beam pairs and perform beam switching when necessary. When the gNB assigns a transmit beam to the UE via downlink control signaling, the beam indication procedure is used. Beam reporting: The procedure used by the UE to send beam quality and beam decision information to the gNB where the UE reports its observation of beamformed signal(s) based on beam measurement to the gNB. For the initial access, after beam 512 Chapter 4 determination, the UE must wait for the gNB to schedule the random-access channel (RACH) opportunity corresponding to the best direction that the UE has determined, for performing the random access and implicitly informing the selected serving infrastruc- ture of the optimal direction (or set of directions) through which it must steer its beam, in order to be properly aligned with the UE. As we mentioned earlier, with each SS block, the gNB will specify one or more RACH opportunities with a certain time and frequency offset and direction, SO that the UE knows when to transmit the RACH pre- amble. This may require an additional complete directional scan of the gNB, thus fur- ther increasing the time it takes to access the network. For beam tracking in the connected mode, the UE can provide feedback using the control channel that it has already established, unless there is a link failure and no directions can be