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 (cMTC). 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 (mMIMO) 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 cMTC device and the gNB 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 cMTC, and has the potential applications in supporting massive cMTC devices in 6G.