Joint Uplink and Downlink Resource Allocation in NOMA for End-to-End URLLC Services

Non-orthogonal multiple access (NOMA) has great potential to increase spectral efficiency and reduce latency. However, reliability problems of NOMA limit its applications in ultra-reliable and low-latency communications (URLLC). For the first time in this letter, the optimal resource allocation scheme is investigated for uplink (UL) and downlink (DL) NOMA in URLLC communications. Specifically, we consider an UL and DL NOMA system with two-pair of users, and try to minimize the overall error probability under stringent URLLC requirements. Then, an optimal scheme for both UL and DL resources allocation is proposed, and a global optimal solution for both power control and channel blocklength allocation is obtained. Finally, simulation results show that NOMA significantly outperforms the orthogonal multiple access (OMA) subjected to the same power and channel blocklength levels and demonstrate the availability of NOMA for end-to-end (E2E) URLLC services.