Methods, systems, and devices for wireless communications are described that asynchronous carrier aggregation, including between high frequency band and lower frequency band transmissions. A user equipment (UE) may be configured to monitor transmissions in a first frequency band and a second frequency band. The UE may measure a timing difference between transmissions in the first frequency band and one or more of the transmissions in the second frequency band, and transmit an indication of the timing difference to a base station. The base station may use the timing difference to determine whether the UE is to use asynchronous carrier aggregation. If the base station determines that the UE is to use asynchronous carrier aggregation, the base station may configure the UE to observe at least a minimum amount of delay when conducting uplink signaling via one of the frequency bands.