  Ultra-Reliable Low-Latency Communications (URLLC) is a novel feature of 5G
cellular systems. To satisfy strict URLLC requirements for uplink data
transmission, the specifications of 5G systems introduce the grant-free channel
access method. According to this method, a User Equipment (UE) performs packet
transmission without requesting channel resources from a base station (gNB).
With the grant-free channel access, the gNB configures the uplink transmission
parameters in a long-term time scale. Since the channel quality can
significantly change in time and frequency domains, the gNB should select
robust transmission parameters to satisfy the URLLC requirements. Many existing
studies consider fixed robust uplink transmission parameter selection that
allows satisfying the requirements even for UEs with poor channel conditions.
However, the more robust transmission parameters are selected, the lower is the
network capacity. In this paper, we propose an adaptive algorithm that selects
the transmission parameters depending on the channel quality based on the
signal-to-noise ratio statistics analysis at the gNB. Simulation results
obtained with NS-3 show that the algorithm allows meeting the URLLC latency and
reliability requirements while reducing the channel resource consumption more
than twice in comparison with the fixed transmission parameters selection.
