Aspects of the present disclosure provide a code block group (CBG) based HARQ retransmission process in which HARQ retransmission is performed based on CBG units. The CBG based HARQ process uses a CBG failure mask that can reduce the signaling overhead of CBG-based HARQ retransmissions. A base station can determine the error CBGs from different UEs that share a slot, and generate a CBG failure mask that capture all the CBGs NACKs from the UEs.