Performance Analysis of Random Access NOMA for Critical mIoT With Timer-Power Back-Off Strategy

Massive machine type communication (mMTC) and Internet-of-Things (IoT) networks provide global connectivity for massive number of end devices anytime-anywhere. The most challenging part in implementing such networks is the development of spectrum access strategies to provide ultra-reliable low-latency (URLL) transmissions for a large number of nodes with sporadic traffic behavior. Such networks have to deploy spectrum-efficient transmission schemes, and thus, non-orthogonal multiple-access (NOMA) is considered as a viable solution, that can be used to provide high number of URLL transmissions. We propose a random access NOMA transmission protocol (RA-NOMA) for IoT networks with large number of clustered IoT devices is proposed. The nodes in the proposed scheme adopt timer and power back-off strategies to transmit their short packets in a collision-free NOMA-based manner to achieve the URLL requirements. Closed-form expressions for network metrics, namely, delay violation probability, average packet latency, reliability, and effective sum rate (ESR) are analytically derived. Furthermore, the effect of blocklength, back-off timer (countdown value) and the number of active nodes on network metrics is explored. Additionally, the effect of the estimation error on the number of active nodes is analyzed and the impact of preamble transmit power on reliability in the presence of estimation error is investigated. Moreover, mathematical expressions for network metrics are also derived for NOMA-ALOHA with transmission diversity (NOMA-ALOHA-TD) in the underlying scenario, and the obtained results from NOMA-ALOHA-TD and the proposed RA-NOMA are compared.