Flexible physical layer based resource allocation for machine type communications towards 6G
The exponential growth of Internet of Things applications necessitates the design of next generation cellular systems to provide native support for machine type communications (MTC). While 5G aims at providing this native support under domain of massive MTC (mMTC) as one of the three major domains it focuses; i.e., enhanced mobile broadband, ultra reliable low latency communication, and mMTC, the enabling technologies and communication architectures are still limited and incomplete considering the nearly standardized efforts under 3GPP Releases 15 and 16. Studies towards 6G should elaborate on enabling truly massive MTC flexibly to support fast growing machine-to-machine (M2M) services with massive number of devices and very diverse quality of service (QoS) requirements. In this paper, we study radio resource allocation for mMTC based on the envisioned flexible physical layer architecture for 5G and beyond, possibly including 6G. We first present an overview of the 5G New Radio physical layer aspects particularly focusing on multiple numerologies and discuss the 3GPP features in Releases 15-17 as possible enablers of a flexible radio resource allocation scheme. Then, we propose a polynomial-time persistent resource allocation scheme for M2M communications aiming at meeting diverse QoS requirements of the M2M applications while achieving spectral efficiency. Finally, we present some numerical results and discuss future research directions for access schemes to enable truly massive MTC.