control com- mand. The situation is even more critical in the mixed TTI scenarios (e.g. with LTE in FR1 and NR in FR2). Figure 13.7 shows two approaches to solving the problem. On the left is an architec- ture in which the LTE baseband module signals its power control parameters to the NR baseband modules, which then calculates the adjustment NR transmission needs to take to accommodate the LTE module's power usage. Alternatively, the architecture on the right adds a mediator circuit in the front-end and RF system module. The circuit takes in power control parameters from both baseband modules and can thus dynamically balance between the two to achieve the optimal usage of the power. 13.4.2 Impact of LTE/NR Coexistence on Modem Design For FR1 deployment, NR could operate in the new NR band (e.g. C-band4) or a lower legacy LTE band. The design challenges for uplink transmission in these two scenarios are described in the following. 13.4.2.1 Operating in the New NR Band The C-band is one of the most important NR sub-6-GHz bands; sitting between the low bands for wide area coverage and the high bands for high capacity, the C-band provides a sound compromise between coverage and capacity which can help build NR coverage at reasonable costs while meeting the expected demand in data capacity. The C-band is likely to operate in Time Division Duplex (TDD) mode, for which a link budget issue was observed [2]: the uplink coverage is much smaller than the downlink coverage. To bridge this coverage gap, the first option is a stronger gNB antenna capability under the assumption that the gNB has better reception capability than the UE. A second option is to transmit uplink signals in the lower band for reducing the propagation loss. For this latter option, two mechanisms are standardized: Supplementary Uplink (SUL) and CA. 13.4.2.2 Supplementary Uplink The UE is configured with an additional uplink (i.e. SUL) set in a different frequency band than the one used for the downlink and the normal uplink (NUL). One example 4 C-band: