DMRS-Applied Repetition Transmission (DART): Grant-Free Scheme for mMTC

In this paper, we develop a repetition-based grant-free scheme, called DMRS-Applied Repetition Transmission (DART), to support mMTC user equipments (UEs). In DART, the demodulation reference signals (DMRSs) are exploited to estimate the channels as well as to implicitly inform the repetition patterns to the gNB. Based on the detected DMRSs, the gNB performs successive interference cancellation (SIC) to further decode the data of mMTC UEs that transmit their data on the same resource block. DART achieves high success rate, low latency, and low SIC overhead by adopting DMRS-based SIC ordering. Simulation results show that DART is able to support mMTC UEs effectively.