t blocks into an acknowledgment bitmap, when multiple TBs need to be acknowledged at the same time or alternatively multiple acknowledgments need to be transmitted in the uplink at the same time in carrier aggregation and CBG-based retransmission scenarios. This bitmap can be signaled either via a semi-static codebook or a dynamic codebook both configured through RRC signaling. The semi-static codebook can be viewed as a matrix consisting of a time-domain dimension and a component-carrier, CBG, or MIMO layer dimension, both of which are semi-statically configured. The size in the time domain is given by the maximum and minimum HARQ acknowledgment timings and the size in the carrier domain is given by the number of simultaneous transport blocks or CBGs across all component carriers. An example is shown in Fig. 4.59, where the acknowledgment timings are one, two, three, and four slots, respectively, and three carriers, one with two TBs, one with one TB, and one with four CBGs, are configured. Since the codebook size is fixed, the number of bits to transmit in a HARQ-ACK is known and an appropriate format for the uplink control signal- ing can be selected. Each entry in the matrix represents successful/unsuccessful outcome of the decoding of the corresponding downlink transmission. A NACK is sent in position of unused transmission opportunities in the codebook, resulting in improved robustness in the case of missed downlink assignment where the gNB can retransmit the missing TB or the CBG [14]. Time span of the HARQ-ACK codebook Time span of the HARQ-ACK codebook CC1 with one TB per slot (0,4) (5,8) (11,16) CC2 with up to two TBs per (6,8) (12,16) CC3 with one TBs and CBG- (1,4) (9,10) (13,16) based retransmission (7,8) (10,10) ACK/NACK ACK/NACK NACK ACK/NACK Fixed-sized HARQ-ACK report ACK/NACK ACK/NACK (2,4) (14,16) ACK/NACK ACK/NACK ACK/NACK ACK/NACK ACK/NACK (3,4) (8,8) ACK/NACK ACK/NACK ACK/NACK ACK/NACK Unscheduled transmission is (4,4) (16,16) set to NACK (cDAl,tDAI) Comparing cDAI and tDAI The UE knows 17 AC