Grant-free UL transmissions based on non-orthogonal multiple access (NOMA) may be considered as applicable various use cases including massive connectivity for machine type communication (MTC) and low overhead UL transmission schemes that minimize device power consumption for transmission of small data packets. Described herein are methods, apparatus, and mechanisms are described for MA resource configuration and MA resource selection in the context of grant-free UL transmission. Also described herein are methods and apparatus that incorporate retransmission and HARQ schemes for grant-free UL NOMA transmissions.