  The cellular Internet-of-Things has resulted in the deployment of millions of
machine-type communication (MTC) devices. These massive number of devices must
communicate with a single gNodeB (gNB) via the random access channel (RACH)
mechanism. However, existing RACH mechanisms are inefficient when dealing with
such large number of devices. To address this issue, we propose the
rate-splitting random access (RSRA) mechanism, which uses rate splitting and
decoding in rate-splitting multiple access (RSMA) to improve RACH success
rates. The proposed mechanism divides the message into common and private
messages and enhances the decoding performance. We demonstrate, using extensive
simulations, that the proposed RSRA mechanism significantly improves the
success rate of MTC in cellular IoT networks. We also evaluate the performance
of the proposed mechanism with increasing number of devices and received power
difference.
