Performance Analysis of Hybrid Scheme of Slotted ALOHA and PD‐NOMA for Massive Machine‐Type Communications

ABSTRACT This paper investigates the characteristics of slotted ALOHA and power‐domain nonorthogonal multiple access (PD‐NOMA) hybrid schemes, focusing on two key performance metrics, namely device transmission success probability and base station throughput, while also considering distance‐based unfairness among devices. We analyse three distinct hybrid schemes: a scheme where all devices transmit signals with equal power without utilising received signal strength (RSS) targets (Scheme 1), a scheme where devices randomly select one of multiple RSS targets at the nearest base station (Scheme 2), and a scheme where devices select one of multiple RSS targets based on their proximity to the nearest base station (Scheme 3). Our findings reveal that while Scheme 1 has the highest performance, it also has the most pronounced distance‐based unfairness. Conversely, Scheme 2 has the lowest performance but effectively mitigates distance‐based unfairness. The performance of Scheme 3 improves as the number of RSS targets increases; however, this coincides with an increase in distance‐based unfairness. These results suggest that achieving a balance between fairness and performance improvement may be inherently challenging in grant‐free access schemes.