Control structures and techniques for transmission time interval (TTI) shortening in wireless communication systems are provided. Exemplary techniques can comprise establishing a UE device connection to a base station having a first TTI, wherein the UE device is configured to employ TTI shortening and has a second TTI different from the first TTI and monitoring a first short physical downlink control channel (PDCCH) region for a scheduled downlink (DL) transmission via the second TTI, wherein a time distribution associated with multiple second TTIs within the first TTI is determined based on a control format indicator (CFI) value indicated via the first TTI. Exemplary techniques can further comprise receiving a DL transmission via the second TTI and transmitting a hybrid automatic repeat request (HARQ) acknowledgement (ACK) (HARQ-ACK) feedback on an associated UL channel for HARQ-ACK feedback, wherein for a number of DL transmissions via the second TTI within one of the first TTI on the associated DL, a number of associated UL channels for HARQ-ACK feedback occur within the same one of the first TTI on the associated UL. Further control structures and techniques for TTI shortening for wireless communication systems are described.