Apparatus and methods are provided to enhance HARQ mechanism. The UE repeatedly transmits a data block with a first repetition number and retransmits the data block with a second repetition number. In one embodiment, the first and the second repetition number value are explicitly included in an uplink grant message. In another embodiment, the UE obtains a repetition number value by looking up a repetition number table indexed by the repetition number indicator, which is included in an uplink grant message for the first repetition number and included in a HARQ message for the second repetition number. In yet another embodiment, the UE determines a coverage enhancement degree value, a data block size value and an available transport resource block size. The UE obtains a repetition number by table-look-up based on the coverage-enhancement degree value, the data block size, and the transport resource block size.