Analysis on Latency-Bounded Reliability for Adaptive Grant-Free Access With Multipackets Reception (MPR) in URLLCs

The steady-state analysis methods fail in the reliability analysis of ultra-reliable low-latency communications (URLLCs), since the resulted reliability is independent of latency. In this letter, we present an adaptive grant-free access scheme with multi-packet reception (MPR), and study its latency-constrained reliability via transient-state analysis. First, we use a two-dimensional absorbing Markov chain to model the transient system behaviors within the latency bound. Then, we calculate the state transition probabilities that are affected by both the access scheme and the MPR capability. Finally, we derive the latency-bounded reliability via calculating the probabilities of hitting transient states and hitting absorbing states for the given latency constraint. In addition, we calculate the minimum value of MPR capability that is required to achieve URLLCs. The simulation results show that our theoretical analysis is valid, and the unreliability seems to be in negative exponential dependence relationship with the latency bound.