) in Fig. 2-23. BWPs (defined per component carrier in the case of carrier aggregation) are communicated to the UE through RRC layer configuration of the BWP definition and ID through a "bandwidthPartId" (<4 per UE) and configuration of location [frequency/physical resource block (PRB) offset], bandwidth, SCS, and cyclic prefix (CP) configuration. See outline of the associated information elements (IEs) per RRC specification (3GPP 38.331 and copied in Fig. 2-24). When BA is configured, the UE monitors the control channel (PDCCH) on the active BWP(s). It does not have to monitor PDCCH on the entire DL frequency of the cell. A BWP inactivity timer (independent from the DRX inactivity timer described earlier) is used to switch the active BWP to the default one: the timer is restarted by the MAC entity upon suc- cessful PDCCH decoding and the switch to the default BWP takes place when it expires. On deactivated BWPs, the UE does not monitor the control channel and does not transmit on any channel. Fig. 2-25 shows the concept. Carrier bandwidth part is a contiguous subset of the PRBs defined for a given numerology on a given component carrier. Supplementary Uplink operation Supplementary Uplink (SUL) operation is proposed in 3GPP 38.300 as a method to improve cell edge coverage, in a situation where the UE transmit power is (likely) lower than the base station power, giving reduced performance in the uplink as opposed to the downlink. DL Logical Channel DL-SCH Transport Channel PDCCH PDSCH DL Physical Channel FIGURE 2-26 Downlink 5G channels. 70 Open Radio Access Network (O-RAN) Systems Architecture and Design The idea involves using a different RF band (at a lower RF frequency and thus with better propagation characteristics) for uplink transmission. Several bands are defined for potential SUL use (n80,., n84 and N86), all of them below 2 GHz. SUL operation is designed to require only a single uplink MAC/Physical Layer instance to be operational at each point in time, even when the client is configured to sup- port m