(28 OFDM symbols) (28 OFDM symbols) rmtc-SubframeOffset-r13 rmtc-SubframeOffset-r13 rmtc-Period-r13 (40 ms) < rmtc-Period-r13 (40 ms) rmtc-Period-r13 (80 ms) rmtc-Period-r13 (80 ms) Measurement Measurement period report to the eNB (CO, average RSSI) Channel Occupancy (CO)=% RSSI samples > RSSI_Threshold 70 OFDM symbols 70 OFDM symbols 70 OFDM symbols measurement measurement measurement duration duration duration RSSI measurement RSSI measurement Periodicit Periodicit (40 ms) (40 ms) Figure 8.38 RMTC configuration for channel occupancy measurements based on R attempt. In NR-U, power ramping is not applied when preamble is not transmitted due to LBT failure. This will require an indication from the physical layer to the MAC sublayer. In addition, ra-Response Window is not started when the preamble is not transmitted due to LBT failure. It is assumed that ra-ContentionResolutionTimer may need to be extended with larger values to overcome the LBT impact. For 2-step RACH, the msgA is a signal to detect the UE and a payload while the second message is for contention resolution for CBRA with a possi- ble payload. The msgA will include the equivalent information, which is transmitted in msg3 for 4-step RACH [12]. 8.5 Implementation and Deployment Considerations The main challenge in the implementation and use of LTE/NR in the unlicensed bands, partic- ularly in 5 GHz band, is the coexistence with already deployed Wi-Fi networks, where LTE/ Operation in Unlicensed and Shared Spectrum 907 NR operation would adversely impact the performance of Wi-Fi systems, while the perfor- mance of LTE/NR would remain unchanged due to reliance of Wi-Fi systems on CSMA/CA mechanism. The issue is caused because of different channel usage and access procedures of these technologies. LTE/NR is designed to operate in the licensed bands based on the assump- tion that one operator has exclusive control of a given spectrum. They will continuously trans- mit with minimum time gap even in the absence of user traffic. LTE/NR also has an almost cont