signaling overhead. Indications of localized/distrib- uted resource allocations to different UEs are transmitted via PDCCH. The resource allocation field in PDCCH is interpreted by the UE depending on the PDCCH DCI format. In the context of dual connectivity, the Special Cell refers to the primary cell of the MCG or the primary SCell of the SCG depending on whether the MAC entity is associated with the MCG or the SCG. Otherwise, the Special Cell refers to the PCell. A Special Cell supports PUCCH transmission and contention-based ran- dom-access procedure and is always activated [20]. New Radio Access Physical Layer Aspects (Part 1) 397 BWP switching BWP switching BWP configuration by DCI by DCI by RRC configuration P cell for P cell BWP 1 BWP 1 Initial BWP BWP 2 configuration S cell for S cell BWP 2 BWP 1 BWP 1 BWP switching BWP switching S cell activation by DCI by DCI Initial access Connected state Multiple activated cells Single activated cell Figure 3.51 Illustration of BWP adaptation, activation, and switching [42]. The resource allocation in NR is defined both in time domain and frequency domain. Unlike LTE where the resource allocation in time domain was determined based on a fixed/ predefined rule, in NR the resource allocation in time domain is more flexible, whereas the resource allocation in frequency domain is relatively similar to that of LTE [30]. Resource allocation type specifies the way in which the scheduler allocates physical resource blocks in frequency domain to each user for transmission in the downlink or uplink. 3.7.3.1 Resource Allocation in Time Domain In the downlink, when the UE is scheduled to receive PDSCH via a DCI, that is, the time domain resource assignment field of DCI provides a row index to an allocation table, where the indexed row defines the slot offset K0, the start and length indicator SLIV and the Chapter 3 BWP switch RF tuning and PDCCH MAC CE parsing MAC CE AGC settling monitoring BWP 1 BWP 2 Transition time 1 Transition time 2 BWP switch L1 RF tuning and signaling AGC