hould be able to send DL/UL transmissions as soon as possible whenever LBT/CCA procedure is completed, resulting in different slot duration. As illustrated in Fig. 8.22, the gNB can choose the type of the first slot, that is, mini-slot based on LBT/CCA success location and slot boundary, and then select the type of the following slots with a larger size. The type of the last slot(s) is chosen according to the remaining time within the MCOT. In the example shown in Fig. 8.22, the remainder of the MCOT is not enough for a normal slot, thus two mini-slots are allocated [17,28]. In the downlink, because a CORESET can be configured to start at any symbol, gNB can start downlink transmission from the nearest symbol after a successful LBT such that the reservation signal overhead can be minimized. However, this will cause increased blind detection complexity for the UE. Therefore, NR-U would rely on an efficient mechanism for the UE to detect the beginning of a downlink transmission. In LTE-based LAA, the ini- tial signal was discussed to facilitate the detection of downlink burst. The NR supports non- slot-based PUSCH scheduling in the uplink and the start symbol can be dynamically indi- cated by DCI. Therefore, the UE can transmit PUSCH starting from the indicated symbol. However, this position may not align with the nearest symbol where LBT succeeds. Consequently, more reservation signals may be needed for the uplink. Because NR already supports multiple start positions and durations, it can provide sufficient transmission flexi- bility for NR-U [10,33]. Operation in Unlicensed and Shared Spectrum Minimization of initial signal Minislot minislots CCA success Slot with 60 kHz SCS Slot with 15 kHz SCS 0.25 ms 7 OFDM symbol minislot with 60 kHz SCS 0.125 ms Slot with 15 kHz SC Slot with 15 kHz SCS 2 OFDM symbol minislot with 15 kHz SCS Figure 8.22 Multiple slot durations in an MCOT with different SCS [17,23]. In NR licensed operation, there are three patterns for multiplexing the SS/PBCH block and the RMSI transmissions