A user equipment (UE) is described. The UE is configured to determine a duplex method of a serving cell. The UE is also configured to determine that shortened transmission time interval (sTTI) is configured on at least one of one or more downlink subframes or one or more uplink subframes. The UE is further configured to determine a sTTI downlink size and a sTTi uplink size. The UE is additionally configured to determine an association timing reference sTTI size based on the sTTI downlink size and the sTTI uplink size. The UE is also configured to determine a sTTI PDSCH HARQ-ACK transmission timing for the serving cell. The UE is further configured to determine a sTTI PUSCH scheduling timing for the serving cell. The UE is additionally configured to determine a sTTI PUSCH HARQ-ACK transmission timing for the serving cell.