Digital Twin-Assisted Edge Computation Offloading in Industrial Internet of Things With NOMA

Integrating digital twins (DTs) and multi-access edge computing (MEC) is a promising technology that realizes edge intelligence in 6 G, which has been recognized as the key enabler for Industrial Internet of Things (IIoT). In this paper, we explore a DT-assisted MEC system for the IIoT scenario where a DT server is created as a virtual representation of the physical MEC server, via estimating the computation state of the MEC server within the DT modelling cycle. To achieve spectrally efficient offloading, we consider that IIoT devices communicate with industrial gateways (IGWs) through a non-orthogonal multiple access (NOMA) protocol. Each IIoT device has an industrial computation task that can be executed locally or fully offloaded to IGW. We aim to minimize the total task completion delay of all IIoT devices by jointly optimizing the IGW's subchannel assignment as well as the computation capacity allocation, edge association, and transmit power allocation of IIoT device. The resulting problem is shown to be a mixed integer non-convex optimization problem, which is NP-hard and challenging to solve. We decompose the original problem into four solvable sub-problems, and then propose an overall alternating optimization algorithm to solve the sub-problems iteratively until convergence. Validated via simulations, the proposed scheme shows superiority to the benchmarks in reducing the total task completion delay and increasing the percentage of offloading IIoT devices.

I. Introduction

The recent advancements in Industrial Internet of Things (IIoT) and wireless communications technologies have motivated a variety of delay-sensitive and computation-intensive industrial applications, such as asset tracking, predictive maintenance, and smart factories [1]. The success of these applications enables industries and enterprises to have better efficiency and reliability in their operations. However, due to the limited computation resources and processing capabilities of IIoT devices, it is a critical challenge for them to run these intensive computing applications locally. Multi-access edge computing (MEC) is a promising solution for this challenge, where the whole or a fraction of industrial computation tasks of IIoT devices can be offloaded to MEC servers deployed at the IIoT edge, e.g., computation access points (CAPs), via industrial gateways (IGWs) [2], [3], [4], [5]. By leveraging the superior computing capabilities of MEC servers, the tasks can be successfully processed in a timely manner.