# 3 PRB # 4 30 kHz (p=1) PRB # o PRB # 1 PRB # 3 PRB # 4 PRB # 5 PRB # 6 PRB # 7 15 kHz (u = O) Figure 4.25 - Overlapping due to subcarrier spacing All resource grids for each numerology are available at the same time and they overlap, as shown in the preceding figure. Duplexing scheme The duplexing scheme is harmonized in NR. We have Frequency Division Duplex (FDD), static Time Division Duplex (TDD), and dynamic TDD in NR. These are used for downlink and uplink transmissions. FDD-Only Half-duplex FDD TDD-Only Dynamic TDD fDL/UL Figure 4.26 - A harmonized FDD and TDD concept As a result of harmonizing FDD and TDD, the maximum commonality between FDD and TDD modes is achieved, which is crucial to LTE/NR coexistence. We expect to have mainly FDD employment below 3 GHz deployments. For frequencies above 6 GHz, TDD will mainly be used. However, between 3 GHz and 6 GHz, we expect to see a mixture of FDD and TDD deployments. Waveform, numerology, and frame structure Mainly FDD FDD/TDD? Mainly TDD 1 GHz 3 GHz 10 GHz 30 GHz 100 GHz Figure 4.27 - FDD/TDD deployments among the frequency band The slots can be either all downlinks or uplinks, or a mixed combination of the downlink and uplink resource sets. We typically include a downlink symbol at the beginning of the slot and an uplink symbol at the end of the slot. An NR slot can be statically configured using a similar scheme as the uplink/downlink configurations in LTE TDD. They can be also semi-statically and dynamically configured, meaning that a network can dynamically and individually change the downlink and uplink direction of the regions in the slot from one to another. The transmission direction of data (uplink or downlink) is determined per slot as part of the scheduling process. The main advantage of dynamic TDD is better spectrum efficiency, since uplink and downlink resources can be dynamically scheduled based on traffic requirements. But how are these dynamically changing downlink and uplink slots happening? The Slot Format Indication (SFI) is defined for tha