# In-Band Pilot Overhead in Ultra-Reliable Low Latency Decode and Forward Relaying

## TL;DR

This paper analyzes the impact of pilot overhead on the reliability and latency of URLLC in cooperative and non-cooperative relay systems under imperfect channel estimation and power constraints.

## Contribution

It derives the optimal training length considering peak power constraints and evaluates how pilot overhead affects URLLC performance in various transmission schemes.

## Key findings

- Optimal training length depends on blocklength and power constraints.
- Pilot overhead significantly impacts reliability and latency in URLLC.
- Cooperative relaying can improve goodput under certain pilot overhead conditions.

## Abstract

In URLLC the performance of short message communications highly depends on the training sequence length due to the stringent latency and reliability requirements. In this paper, we study the performance of cooperative and non-cooperative transmissions under imperfect channel estimation and Rayleigh fading for URLLC. We assume a peak power constraint on pilot symbols in addition to the average power constraint which is used for comparison purposes. We obtain the optimal training length as a function of blocklength and power constraint factor to meet the URLLC requirements. Moreover, the simulation results show the impact of pilot overhead on reliability, latency, and goodput of cooperative communications compared to pointto-point transmission