A Priority-Based Semi-Grant-Free NOMA: Protocol Design and Performance Analysis

This paper introduces a novel semi-grant-free non-orthogonal multiple access protocol that ensures reliable massive connectivity of both scheduled and random access devices of diverse data rate (DR) requirements while tripling the network’s capacity. In more detail, the protocol classifies the devices into two categories, namely primary and secondary. Primary devices (PDs) require high-data-rate scheduled or random access with high-transmission probability, and are one-third of the total number of devices, while, the rest, are classified as secondary devices (SDs) and have low-DR requirements as well as access the network in a random fashion. The base-station generates a number of radio resource blocks (RRBs) that is equal to the number of PDs and allocates a primary and two SDs in each RRB. The allocation is based on the requested DRs of the primary and SDs as well as on the transmission probability of the SDs. To prove the feasibility and efficiency of the presented protocol, we conduct a performance analysis that results in the extraction of novel and insightful closed-form expressions for the outage probability and achieved throughput for all devices.