Various communication systems may benefit from techniques for handling inter-band carrier aggregation (CA). For example, systems of the third generation partnership project (3GPP) long term evolution (LTE) advanced (LTE-A) may benefit from a uplink (UL) downlink (DL) configuration zero handling, particularly in cases where there is no physical hybrid automatic repeat request (HARQ) indicator channel (PHICH). For example, certain embodiments may be applicable to inter-band CA having different UL/DL configuration in use. A method can include triggering in a downlink subframe a first physical uplink shared channel transmission in a first hybrid automatic repeat request process. The method can also include triggering in the downlink subframe a second physical uplink shared channel transmission in a second hybrid automatic repeat request process. The secondary cell can be configured with time division duplex uplink/downlink configuration number zero. The triggerings can be performed by means of a single uplink grant but without a hybrid automatic repeat request indicator.