Link-Layer Rate of NOMA with Finite Blocklength for Low-Latency Communications

Finite blocklength (short packet) communications with non-orthogonal multiple access (NOMA) is regarded as an enabler for ultra-reliable and low-latency communications (URLLC). In this paper, we investigate the link-layer rate, i.e., the effective capacity, of a two-user NOMA in finite blocklength regime. The delay performance of the NOMA users is analyzed by taking into consideration the queueing delay violation probability and the transmission error probability. We further provide closed-form expressions for the individual effective capacity of the NOMA users in Rayleigh fading environment. Through simulations, we investigate the impact of the transmit signal-to-noise ratio and the delay exponent on the achievable effective capacity and the queueing delay violation probability of the NOMA weak and strong users. In particular, results show that when using short-packet communications, the queueing delay violation probability cannot be improved below a threshold.