Exploiting Multi-User Diversity for Ultra-Reliable and Low-Latency Communications

In this paper, we study how to exploit multi-user diversity for ultra-reliable and low-latency communications. The basic idea is that the users with good channel conditions share resources with the users with bad channel conditions. We propose a method to optimize resource allocation among multiple users under the quality-of-service (QoS) constraints, including transmission delay, transmission error probability, queueing delay bound and queueing delay violation probability. If the minimal transmit power required to satisfy these constraints is less than the total transmit power of the base station, then the global optimal resource allocation policy can be obtained. Otherwise, some packets are dropped proactively. Simulation results show that compared with an existing policy that does not exploit multi-user diversity, the proposed policies can double the number of users with QoS guarantee or reduce proactive packet dropping probability remarkably with given total bandwidth and transmit power. This indicates that with multi-user diversity, a better tradeoff between reliability and throughput (or spectral efficiency) can be achieved.