n applies to all configured and activated serving cells (i.e., identical active time for PDCCH monitoring). In other words, a common DRX is applied to all the serving cells. The difference in the case of LAA is that due to LBT there is no guarantee that the channel is obtained for scheduling the UE at the exact moment desired by the eNB. In addi- tion, even if CCA succeeds, the eNB transmitter can only occupy the channel for a limited duration due to limited maximum transmission duration requirement. This means that the DRX timers (on-duration, inactivity timer) should be long enough or DRX cycles should be short enough to allow time for obtaining access to the channel. In LAA, there are scenarios where multiple operators may operate in the same frequency channel. If these operators do not coordinate the allocation of physical cell identifier (PCI) values across their cells, it may lead to PCI confusion or PCI collision cases. PCI confusion refers to the case where a UE discovers and configures the LAA cell of another operator 904 Chapter 8 with the same PCI value as its own operator. PCI collision concerns a UE that is in the COV- erage area of two (or more) cells which have the same PCI value where the cells belong to different operators. If the same PCI value is used for cells on the same carrier frequency in the same area, PCI confusion or collision may occur. In LTE and NR, the number of PCIs is limited to 504 and 1008, respectively. If operators do not coordinate PCI assignment in their cells, the probability of PCI confusion or collision depends on the number of LAA cells of other operators the UE can find in the PCell coverage area, increasing the risk of collision when there is a dense deployment of LAA cells in a large PCell coverage area. PCI collision will happen with a lower probability than PCI confusion because PCI collision happens when the coverage areas of two cells with the same PCI partially overlap. Considering the LTE requirement for carrier aggregation where the UE is only required to handl