Spatial Group-Based NOMA-IRSA With Adaptive Degree Distribution in IoT-Enabled WSNs

A non-orthogonal multiple access (NOMA)-based irregular repetition slotted ALOHA (IRSA) based on spatial group (SG-NOMA-IRSA) with adaptive degree distribution scheme is proposed to improve the performance of the random access (RA) system. In the proposed scheme, the reverse power control is employed to increase the difference in received power by fully utilizing the difference in path loss when the range of transmit power at sensors is limited, and a spatial group NOMA scheme is proposed to improve the throughput of RA system. To utilize adaptive degree distribution for access control and low-power consumption transmission, an adaptive degree distribution function integrating with the access class barring (ACB) scheme is further proposed for IRSA. Moreover, a joint optimization problem is formulated and solved to maximize system throughput. The simulation result shows that the peak throughput of RA system with the SG-NOMA-IRSA scheme is about 70% larger than that of RA system with the conventional IRSA-based protocols. The packet loss rate (PLR) performance and the power consumption performance of the proposed scheme also outperform those of the conventional schemes. More importantly, as a novel NOMA technology, the SG-NOMA-IRSA scheme solves the problem of high transmit power requirements in existing NOMA schemes, making NOMA suitable for practical RA system.