  Ultra reliable low latency communications (URLLC) is one of the most
promising and demanding services in 5G systems. This service requires very low
latency of less than $1-10$ ms and very high transmission reliability: the
acceptable packet loss ratio is about $10^{-5}$. To satisfy such strict
requirements, many issues shall be solved. This paper focuses on the link
adaptation problem, i.e., the selection of a modulation and coding scheme (MCS)
for transmission based on the received channel quality indicator (CQI) reports.
On the one hand, link adaptation should select a robust MCS to provide high
reliability. On the other hand, it should select the highest possible MCS to
reduce channel resource consumption. The paper shows that even for one URLLC
user, link adaptation is still a challenging problem, especially in
highly-variant channels. To solve this problem, a conservative link adaptation
algorithm is designed. The algorithm estimates the strongest channel
degradation at the time moment of the actual packet transmission and selects an
MCS taking into account the worst degradation. The obtained results show that
the proposed algorithm is efficient in terms of both the packet loss ratio and
the channel resource consumption.
