Energy-Efficient Content Placement With Coded Transmission in Cache-Enabled Hierarchical Industrial Internet of Things Networks

Industrial Internet of things (IIoT) is expected to improve efficiency and productivity by connecting massive devices, but it will cause potential congestions in backhual link and high energy consumptions. Caching with coded transmission is an effective method to reduce backhual load for content delivery. However, due to the hierarchy and heterogeneity in IIoT, it is very challenging to perform content placement with lower energy consumption. In this article, we propose an energy-efficient content placement strategy in cache-enabled hierarchical IIoT network with coded transmission. We derive a closed-form expression including the energy consumption for content placement and transmission by the macro base station and the small base stations. In addition, we establish an optimization problem to minimize the total energy consumption, whereby we find the optimal content placement matrix and optimal cache size allocation, respectively. Simulation results show that, the proposed content placement strategy can greatly improve energy efficiency in IIoT.