Techniques for contention window size (CWS) adaptation (CWSA) are discussed. One example apparatus can comprise a processor that can receive HARQ messages UEs in response to PDSCH transmissions in one or more reference subframes. The HARQ messages can comprise HARQ-ACK values that denote a HARQ-ACK state for a transport block associated with License Assisted Access (LAA) operation, wherein each of the HARQ-ACK states is one of a DTX state, an ACK state, a NACK state, or an “any” state. The processor can also; determine a metric value for each of the HARQ-ACK states; calculate a CWS adjustment metric based on the determined metric values; increase a CWS to a next higher allowed value when the CWS adjustment metric is greater than or equal to a threshold; and reset the CWS to a minimum allowed value when the CWS adjustment metric is less than the threshold.