  This work introduces, for the first time, non-orthogonal multiple access
(NOMA) into short-packet communications to achieve low latency in wireless
networks. Specifically, we address the optimization of transmission rates and
power allocation to maximize the effective throughput of the user with a higher
channel gain while guaranteeing the other user achieving a certain level of
effective throughput. To demonstrate the benefits of NOMA, we analyze the
performance of orthogonal multiple access (OMA) as a benchmark. Our examination
shows that NOMA can significantly outperform OMA by achieving a higher
effective throughput with the same latency or incurring a lower latency to
achieve the same effective throughput targets. Surprisingly, we find that the
performance gap between NOMA and OMA becomes more prominent when the effective
throughput targets at the two users become closer to each other. This
demonstrates that NOMA can significantly reduce the latency in the context of
short-packet communications with practical constraints.
