Network Coding as Enabler for Achieving URLLC Under TCP and UDP Environments: A Survey

Abstract

In an era of rapidly evolving technology, the pursuit of higher data rates, extremely low latency, and robust reliability is becoming increasingly crucial. Applications such as Industrial Internet of Things (IIoT) demand that transmitted messages meet stringent time constraints. Traditional ARQ-based schemes struggle to achieve the required performance in the presence of feedback delays or feedback losses. Unlike conventional ARQ approaches, which acknowledge only original packets, network coding can acknowledge multiple degrees of freedom (DOF), making the feedback mechanism a pivotal factor for reliability-delay tradeoffs. On the other hand, UDP protocol operates blindly without feedback acknowledgments (ACKs). Thus, the selection of code to provide ultra-reliable and low-latency communications (URLLCs) over lossy channels without feedback ACKs is tedious. However, network coding inherent robustness against packet erasure positions it as a promising candidate for reliable communication without feedback ACKs. In this survey, we delve into cutting-edge opportunistic network coding schemes that can deliver high data rates and low latency, even in the face of feedback limitations such as feedback delays, feedback losses, or complete feedback absence. We focus on how network coding-based approaches maintain effective communication over lossy networks, regardless of these feedback limitations. In the context of UDP environments (i.e., blind coding), we present the interplay of some essential elements that must be integrated into network coding to enable reliable transmission without feedback ACKs. Our expectation is that this paper will set the stage and raise the interest of readers willing to explore Network codings (NCs) in the direction of URLLC for mission-critical (IIoT) applications.