A Flexible Scheme for Critical mMTC

In this paper, a grant-free access scheme for massive machine-type communications (mMTC), along with a multiuser detection (MUD) aided processing for packet recovery, are inves-tigated. The proposed grant-free access and receiver processing are flexible, in that they can be applied both in a slotted but unframed configuration and in a slotted and framed one, to achieve different tradeoff points between scalability, reliability, and latency. This looks particularly interesting for emerging 'critical' mMTC applications, where reliability and latency requirements are more tightening than current 5G ones. An in-depth analysis of the considered scheme, performed through both numerical simulations and analytical tools, highlights a potential to support mMTC with diverse requirements. For example, reliable grant-free transmissions can be supported (e.g., packet-loss rates in the order of 10-4/10-5) with an application-specific latency-scalability tradeoff.