  In this work, we propose an adaptive system design for an Internet of Things
(IoT) monitoring network with latency and reliability requirements, where IoT
devices generate time-critical and event-triggered bursty traffic, and an
unmanned aerial vehicle (UAV) aggregates and relays sensed data to the base
station. Existing transmission schemes based on the overall average traffic
rates over-utilize network resources when traffic is smooth, and suffer from
packet collisions when traffic is bursty which occurs in an event of interest.
We address such problems by designing an adaptive transmission scheme employing
multiuser shared access (MUSA) based grant-free non-orthogonal multiple access
and use short packet communication for low latency of the IoT-to-UAV
communication. Specifically, to accommodate bursty traffic, we design an
analytical framework and formulate an optimization problem to maximize the
performance by determining the optimal number of transmission time slots,
subject to the stringent reliability and latency constraints. We compare the
performance of the proposed scheme with a non-adaptive power-diversity based
scheme with a fixed number of time slots. Our results show that the proposed
scheme has superior reliability and stability in comparison to the
state-of-the-art scheme at moderate to high average traffic rates, while
satisfying the stringent latency requirements.
