Connection-Free Transmission for Critical MTC

In this paper, a contention-based connection-free transmission scheme is proposed to meet the stringent requirements of ultra-reliability and low-latency for critical machine-type communication（c MTC）. To improve reliability, we design multiple independent sparse orthogonal pilots（MISOP） to significantly reduce the probability of pilot collision to the order of 10-5. Besides, the advancements of massive MIMO（m MIMO） are exploited to further enhance the reliability. To achieve low latency, connection-free slot-based one-shot transmission without retransmissions is adopted. On the receiver side, single round of multi-user detection（MUD） without interference cancellation（IC） can reduce the processing delay. The imprecise synchronization between c MTC device and the g NB in connection-free transmission, e.g., time and frequency offsets, are also considered. The simulation results shows that the proposed scheme can well satisfy the ambitious requirements of c MTC, and has the potential applications in supporting massive c MTC devices in 6G.