HARQ-ACK transmission on unlicensed spectrum

A remote unit comprising:

• a receiver that receives, from a base unit, one or multiple downlink transmissions within a channel occupancy time initiated by the base unit, a first message indicating a first candidate opportunity for transmission of a hybrid automatic repeat request-acknowledgement codebook corresponding to the one or multiple downlink transmissions and a second message indicating a number of allowed opportunities for transmission of the hybrid automatic repeat request-acknowledgement codebook;
• a processor that determines the hybrid automatic repeat request-acknowledgement codebook and a number of total candidate opportunities for transmission of the hybrid automatic repeat request-acknowledgement codebook;
• and
• a transmitter that, in response to a channel access for the first candidate opportunity being successful, transmits the hybrid automatic repeat request-acknowledgement codebook in the first candidate opportunity, and, in response to the channel access for the first candidate opportunity being failed and the number of the total candidate opportunities being larger than one, attempts to transmit the hybrid automatic repeat request-acknowledgement codebook in a second candidate opportunity.