receiving, from a base station, high layer configuration information for a contention-based physical uplink shared channel (PUSCH) transmission;

monitoring a first downlink control information (DCI) scrambled with a first radio network temporary identity (RNTI) in a first physical downlink control channel search space based on the high layer configuration information;

determining a contention-based PUSCH resource based on the detected first DCI;

transmitting data and a first contention resolution UE identity (ID) on the contention-based PUSCH resource;

monitoring a second DCI scrambled with a second RNTI in a second physical downlink control channel search space based on the higher layer configuration information, wherein the second DCI indicates the second contention resolution UE ID or schedules a retransmission of the PUSCH;

transmitting, to the base station, the retransmission of the PUSCH in case that the second DCI schedules a retransmission of the PUSCH; and

transmitting, to the base station, an acknowledgement (ACK) to indicate successful contention resolution of the PUSCH in case that the second contention resolution UE ID is same as the first contention resolution UE ID;

receiving configuration information of multiple transmission block size (TBS) values of the contention-based PUSCH, wherein the PUSCH transmission corresponding to a largest TBS value among the multiple TBS values uses all symbols or time slots allocated in time domain of the contention-based PUSCH resource, and PUSCH transmissions corresponding to the other TBS values among the multiple TBS values use a part of symbols or time slots allocated in the time domain, and transmission starts from the first symbol or time slot allocated in the time domain; and

selecting a TBS value that causes the MAC layer to add a least amount of bits to transmit the contention-based PUSCH based on the amount of data arrived.