  With the phenomenal growth of the Internet of Things (IoT), Ultra Reliable
Low Latency Communications (URLLC) has potentially been the enabler to
guarantee the stringent requirements on latency and reliability. However, how
to achieve low latency and ultra-reliability with the random arrival remains
open. In this paper, a queue-aware variable-length channel coding is presented
over the single URLLC user link, in which the finite blocklength of channel
coding is determined based on the random arrival. More particularly, a
cross-layer approach is proposed for the URLLC user to establish the optimal
tradeoff between the latency and power consumption. With a probabilistic coding
framework presented, the cross-layer variable-length coding can be
characterized based on a Markov chain. In this way, the optimal delay-power
tradeoff is given by formulating an equivalent Linear Programming (LP). By
solving this LP, the delay-optimal variable-length coding can be presented
based on a threshold-structure on the queue length.
