Effective Capacity of Non-Orthogonal Multiple Access with Finite Blocklength for Low-Latency Communications

In this paper, we focus on investigating the link-layer rate within a non-orthogonal multiple access (NOMA) system operating in the finite blocklength (FBL) regime, specifically designed for short-packet communications. By leveraging the effective capacity (EC) framework, latency and reliability in FBL, encompassing parameters such as the block error probability and the delay outage probability, are analyzed for two scenarios, namely, system operation with multiple NOMA pairs and the two-user NOMA operation. Closed-form expressions for the EC in the two cases are derived by assuming that transmissions are subject to Rayleigh fading and adopting a practical path-loss model. Numerical results are provided to validate the analytical findings, and to highlight the impact of the transmit signal-to-noise ratio, the blocklength, the delay exponent, and the block error probability, on the EC and the delay outage probability. Furthermore, various pairing configurations are investigated and demonstrate that the paired NOMA set attains the highest total EC for users experiencing substantial differences in their channel conditions.