  In this work, we propose a cross-layer framework for optimizing user
association, packet offloading rates, and bandwidth allocation for
Mission-Critical Internet-of-Things (MC-IoT) services with short packets in
Mobile Edge Computing (MEC) systems, where enhanced Mobile BroadBand (eMBB)
services with long packets are considered as background services. To reduce
communication delay, the 5th generation new radio is adopted in radio access
networks. To avoid long queueing delay for short packets from MC-IoT,
Processor-Sharing (PS) servers are deployed at MEC systems, where the service
rate of the server is equally allocated to all the packets in the buffer. We
derive the distribution of latency experienced by short packets in closed-form,
and minimize the overall packet loss probability subject to the end-to-end
delay requirement. To solve the non-convex optimization problem, we propose an
algorithm that converges to a near optimal solution when the throughput of eMBB
services is much higher than MC-IoT services, and extend it into more general
scenarios. Furthermore, we derive the optimal solutions in two asymptotic
cases: communication or computing is the bottleneck of reliability. Simulation
and numerical results validate our analysis and show that the PS server
outperforms first-come-first-serve servers.
