 different frequency bands, resulting in three scenarios: intra-band carrier aggregation with frequency-contiguous compo- nent carriers, intra-band carrier aggregation with non-contiguous component carriers, and inter-band carrier aggregation with non-contiguous component carriers. While the system-level operation for the three scenarios is the same, the architecture and complexity of RF transceivers can be very different. The NR supports up to 16 downlink/uplink carriers of different bandwidths and different duplex schemes, with the minimum and maxi- mum contiguous bandwidth of 5 and 400 MHz per component carrier, respectively [5,21]. A UE capable of carrier aggregation may receive or transmit simultaneously on multiple com- ponent carriers, while a device not capable of carrier aggregation can access one of the com- ponent carriers at any given time. In the case of inter-band carrier aggregation of multiple half-duplex TDD carriers (supplemental uplink or downlink), the transmission direction of dif- ferent carriers does not necessarily have to be the same, which implies that a carrier- aggregation-capable TDD device may need a front-end duplexer, unlike a typical carrier- aggregation-incapable TDD device that does not include a duplexer. In the LTE and NR spe- cifications, the carrier aggregation is treated as a cell, that is, a carrier-aggregation-capable UE is said to able transmit/receive to/from multiple cells. One of these cells is referred to as the PCell that is the cell which the device initially selects and connects to. Once connected to the gNB, one or more SCells can be configured. The SCells can be activated or deceived to meet various application requirements. Different UEs may have different designated cells as their PCell, meaning that the configuration of the PCell is UE-specific. Furthermore, the num- ber of carriers (or cells) does not have to be the same in uplink and downlink. In a typical scenario, there are more downlink carriers than uplink carriers, since there is often more traf- fic i