Flipped-Underlay in Power-Efficient Industrial IoT Sidelink-Assisted Communication

Future factories will rely on highly reliable wireless communication among the plenty of devices and the network. The 5G networks enable ultra-reliable low-latency communication (URLLC) service to address the reliability and latency requirements in factories, where device-to-device (D2D) connections can provide additional means for improving communication reliability. To this aim, we have proposed a sidelink (SL)-assisted cooperative retransmissions (CoRe) scheme in our previous work, where retransmissions via SL for unsuccessful downlink (DL) transmissions are used to improve communication reliability under strict latency constraints. In this paper, we evaluate the CoRe scheme for a realistic factory scenario using system-level simulations, where we consider interference coordination and an optimal power control (PC) scheme. Inspired by the outcome of small transmit powers needed for the SL-assisted retransmissions, we propose a novel resource management scheme named “flipped-underlay”, which is realized by underlay communication. While in conventional underlay, a D2D communication with small transmit power is assigned to resources already allocated for uplink (UL) communication and thus underlaid, the D2D resources are allocated firstly in our scheme, and hence called flipped-underlay. Results demonstrate that the gains from CoRe scheme, are three-fold: showing a significant reduction in the total number of SL-assisted retransmissions compared to conventional retransmissions via DL while maintaining the desired reliability and latency performance, reduced transmit power consumption by virtue of the optimal power allocation for retransmissions, and finally yet importantly, reuse of resources in our new flipped-underlay resource allocation (FURA) algorithm substantially reduces the total amount of resources occupied by the system.