# Queue-Aware Variable-Length Coding for Ultra Reliable Low Latency Communications with Random Arrival

## TL;DR

This paper proposes a queue-aware variable-length coding scheme for URLLC that dynamically adapts to random arrivals, optimizing the delay-power tradeoff using a cross-layer approach and Markov chain modeling.

## Contribution

It introduces a novel cross-layer variable-length coding framework for URLLC with random arrivals, optimizing delay and power consumption through LP formulation.

## Key findings

- Optimal delay-power tradeoff derived from LP
- Threshold-based queue length policy for coding
- Probabilistic coding framework modeled by Markov chain

## Abstract

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.