Techniques for determining an uplink (UL) acknowledgment (ACK) resource based on a physical downlink control channel (PDCCH) carrying a resource allocation for a user equipment (UE) are disclosed. The mapping between the UL ACK resource and the PDCCH may be implicit, which may reduce overhead. The UL ACK resource may be associated with a time-varying cyclic shift of a base sequence used by the UE to send ACK information. The UE may send the ACK information based on the time-varying cyclic shift of the base sequence, which may randomize interference.