located further away from the RF site behind the backhaul connection. The example timing in Figure 6.29 works with FDD operation when there is always the possibility of uplink transmission. This allows, with the 1 ms allocation period, the retransmission to reach the UE 4 slots later; thus, there is an extra delay of 4 ms from a single retransmission. In the case of TDD operation, the slots are shorter, but uplink is not necessarily available in all cases, and thus there is more variance in the exact delay. With the 2 ms TDD structure, as shown in Figure 6.7, there is anyway an uplink resource available every 2 ms, and thus at most the extra delay experienced would be on the order of 2 ms, but typically less. Thus, the average delay experienced would be comparable to the FDD case due to the shorter slot duration period with 30 kHz SCS. 6.11.2 Uplink Power Control With 5G, there are initially two types of power control operation, open loop and closed loop. Open loop refers to setting the power based on the received downlink signal, while closed loop refers to the explicit signaling from the gNB to increase or decrease the power. The power control is important to reduce the interference created for the net- work as well as to minimize the UE power consumption. The first step with power control occurs on the PDCCH with the scheduling message for the Random Access Response (RAR) in the -6 to 8 dB range. During the operation, the PDCCH can be used to further control the uplink TX power of the UE. With dual connectivity with LTE and 5G, there are two possible approaches to power control and sharing: Retransmission Downlink Slot n Slot n + 4 Uplink feedback UE decoding Figure 6.29 Timeline for HARQ operation with FDD case and 15 kHz subcarrier spacing. 6.12 5G MIMO and Beamforming Operation LTE eNB 5G gNB LTE power control 5G power control Determine LTE TX Use Max_TX_Power- power for next TTI LTE_power for 5G UE with LTE/5G Figure 6.30 Power control with LTE-5G dual connectivity. Dynamic power sharing between LTE and 5G