  In this paper, we propose a joint dynamic power control and user pairing
algorithm for power-efficient and low-latency hybrid multiple access systems.
In a hybrid multiple access system, user pairing determines whether the
transmitter should serve a certain user by orthogonal multiple access (OMA) or
non-orthogonal multiple access (NOMA). The proposed optimization framework
minimizes the long-term time-average transmit power expenditure while reducing
the queueing delay and satisfying time-average data rate requirements. The
proposed technique observes channel and queue state information and adjusts
queue backlogs to avoid an excessive queueing delay by appropriate user pairing
and power allocation. Further, user scheduling for determining the activation
of a given user link as well as flexible use of resources are captured in the
proposed algorithm. Data-intensive simulation results show that the proposed
scheme guarantees an end-to-end delay smaller than 1 ms with high
power-efficiency and high reliability, based on the short frame structure
designed for ultra-reliable low-latency communications (URLLC).
