Multi-RAT Random Access Scheme Utilising Combined Licensed and Unlicensed Spectrum for Massive Machine-Type Communications

Abstract

Dense deployment of huge number of Internet of Things (IoT) devices in the factories of the future (FoF) requires efficient and scalable massive Machine-Type Communication (mMTC). The simultaneous network access attempts of the ever-growing number of mMTC devices will cause serious congestion on the Random Access CHannel (RACH), resulting in intolerable delay and service unavailability. Moreover, the scarce licensed bands might not be sufficient for emerging mMTC applications, and therefore exploring the unlicensed spectrum becomes attractive. Recently developed MulteFire version 1.1, also labelled as eMTC-U, seems to be a promising technology to support mMTC by utilising the royalty-free unlicensed spectrum. Due to the growing mMTC importance in FoF, in this study, we evaluate the performance of random access procedure in terms of the success probability and access delay via analytical Markov analysis of eMTC-U and LTE Cat-M systems. We then propose a Multi-Radio Access Technology (Multi-RAT) random access procedure utilising both LTE Cat-M in licensed and eMTC-U in the unlicensed spectrum for mMTC services, especially to improve the random access reliability of devices in a dense FoF environment. Our study demonstrates that with suitable traffic offloading towards the licensed and unlicensed RAT, the access success probability of the proposed scheme can be maintained around 100% with the cost of the slight increase in access delay.