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In this paper,the concept of grantfree non-orthogonal multiple access (NOMA) for uplink data transmission is elaborated.NOMA in combination with grant-free can be applied to ultra reliability low latency communication (URLLC),massive machine type communication (mMTC),enhanced mobile broadband (eMBB) small packet and two-step random-access channel (RACH) scenarios.The advantages of grant-free NOMA are low latency and signaling overhead,high access capability and efficient resource utilization.Candidate uplink NOMA schemes are sum marized and preliminary comparison among a subset of schemes are presented.Furthermore,design aspects for grant-free NOMA are discussed,with special notes on particular issues such as blind UE identification and transmitter/receiver (Tx/Rx) impairments in realistic deployment.