Critical machine-type communication(Critical MTC)has extremely high requirements for latency and reliability.Supporting massive critical MTC terminals simultaneously is a huge challenge.A connection-free transmission scheme for critical MTC is proposed.To reduce latency,a contention-based connection-free one-shot transmission scheme is proposed.To achieve ultra-reliability,multiple sparse or-thogonal pilots with extremely low probability of pilot collision are designed.Furthermore,the gain of massive multiple-input multiple-output(MIMO)is used to improve reliability and multiplex a large number of users in the spatial domain.The simulation results show that the proposed scheme can support a large number of critical MTC terminals while meeting the stringent requirements of low latency and ultra-reliability.
connection-free transmissionCritical MTCultra reliable low latencypilot collisionsparse orthogonal pilot
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