Power Consumption Minimization for Packet Re-Management Based C-NOMA in URLLC: Cooperation in the Second Phase of Relaying

Among the realm of ultra-reliable and low-latency communication (URLLC), a challenging problem is how to realize an efficient transmission meeting both latency and reliability requirements. As a promising technique to tackle the above problem, cooperative non-orthogonal multiple access (C-NOMA) has gained much attention in recent years. When the relay (R) is close to the source, the superior of C-NOMA has been verified if the cooperation is implemented in the first phase. However, the case where R is close to the destination, which also frequently appears in the cooperative transmission, has not been well investigated for URLLC yet. To fill up this gap, we propose a packet re-management based C-NOMA transmission scheme in which the cooperation is implemented in the second phase. Further, considering the importance of power consumption, we aim for jointly optimizing blocklength, power, re-managed packet size, and block error rate to minimize the power consumption subject to URLLC requirements and the maximum power constraint. To tackle the above non-convex and implicit problem, we first propose an algorithm to obtain a sub-optimal solution. Then, an extended algorithm is proposed to further approach the optimal solution. Simulation results verify the effectiveness of the proposed scheme and algorithms.