owever, working toward enabling the use of dynamic TDD in conditions where cross-link interference (CLI) could be sufficiently mitigated. The difference to earlier TDD generations is the use of higher frequency bands (where the signal is more attenuated) as well as the use of beamforming (as discussed in Chapter 6), which allows more spatial separation. The work under the work item on CLI handling and Remote Interference Management (RIM) [9] is looking at scenarios in which one could relax the uplink/downlink alignment requirements. From the results obtained SO far, the following could be expected: Macrocell deployment, especially if operators have some co-located gNBs, must stay with synchronized operation and uplink/downlink alignment. Also, deployments with a small coupling loss between different operator base stations (line-of-sight situations especially) likely need to follow the Release 15 approach. Deployments with non-located gNBs, and not using macro power levels, could allow for less stringent uplink/downlink synchronization requirements. This requires some operator coordination, for example, when deploying an indoor network, to avoid, for example, line-of-sight deployments (when trying to use different uplink/downlink allocations) as gNB-to-gNB interference is static. 3GPP will need to also define RF requirements for UEs and gNBs which are intended to be operated without the uplink/downlink alignment across the network. Figure 15.5 shows an example deployment with the macro level being fully synchronized and time aligned while with a smaller cell size and power level, a lower level of synchronization 15.2 3GPP Release 16 Timing and Key Themes Public Indoor cells Indoor cells without with coordination Co-located/co- coordination (one (no line of sight etc) sited macro cells operator per building) Indoor cell with independet UL/DL alignment Unsynchronized low power installations Synchronized & UL/DL aligned marco layer Figure 15.5 Heterogeneous TDD network deployment with varying synchronization and upli