Computation Offloading at Field Level: Motivation and Break-Even Point Calculation

TL;DR

This paper investigates the impact of complex control algorithms on resource-constrained PLCs in smart manufacturing, proposing a method to determine when computation offloading becomes beneficial based on simulated scenarios and communication benchmarks.

Contribution

It introduces a realistic factory scenario with benchmarks and calculates break-even points for computation offloading on Siemens S7 PLCs, considering both wireline and wireless communication delays.

Findings

Break-even points for offloading are identified for specific PLCs.

Communication latency significantly influences offloading benefits.

Simulation results guide when to offload computations in industrial settings.

Abstract

Smart manufacturing has the objective of creating highly flexible and resource optimized industrial plants. Furthermore, the improvement of product quality is another important target. These requirements implicate more complex control algo-rithms. Processing these algorithms may exceed the capabilities of resource constrained devices, such as programmable logic controllers (PLCs). In this case, the necessity for computation offloading is given. Due to the fact that industrial plants are currently designed for a life-cycle-time of more than ten years, in a realistic smart manufacturing scenario, these devices have to be considered. Therefore, we investigate the impact of complex algorithms on conventional PLCs by simulating them with a load generator. In addition, we propose a realistic factory scenario including benchmarks for both wireline and wireless communication systems. Thus, their round-trip time (RTT) is measured with and without additional load on the network. With the help of these investigations, break-even points for the application of computation offloading of two typical PLCs of Siemens S7 series can be calculated.