TDD configuration may be dynamically and/or semi-statically signaled to user equipment devices by a base station. Semi-static TDD configuration may include: an initial portion for downlink transmission; a flexible portion; and a terminal portion for uplink transmission. TDD structure of the flexible portion may be determined later by transmission of dynamic physical layer configuration information such as downlink control information (DCI) and/or slot format indicator (SFI). (The SFI may be included in a group common PDCCH of a slot.) The downlink portion and/or the uplink portion may include subsets whose nominal transmit direction is subject to override by transmission of dynamic physical layer configuration information.