Effective Capacity of NOMA with Finite Blocklength for Low-Latency Communications

In this paper, we investigate the link-layer rate of a two-users non-orthogonal multiple access (NOMA) network in finite blocklength (short packet communications) regime, where the two users are paired from a set of V users. The overall reliability consists of the transmission error probability and the queuing delay violation probability. The performance of the two-users NOMA network in finite blocklength is verified for achieving latency and reliability, using the effective capacity (EC) framework. Specifically, we derive closed-form expressions for the EC of the two-users NOMA network in finite blocklength regime, considering transmissions over Rayleigh fading channels. We also study a multiuser NOMA network and derive the total EC of two-users NOMA subsets, and show that the NOMA set with users having distinct channel conditions achieve maximum total EC. Focusing on a two-users NOMA network, we study the impact of the transmit signal-to-noise ratio, delay exponent, and transmission error probability, on the achievable EC of each user. The analysis shows that when the delay exponent is high, the delay violation probability does not improve below a certain value due to the dominant factor of the transmission error probability. The accuracy of the proposed closed-form expressions for the individual EC of a two-users NOMA is verified using the Monte-Carlo simulations.