Joint Uplink and Downlink Nonorthogonal Resource Allocation for URLLC in Distributed Antenna Systems

Ultrareliable and low-latency communications (URLLC) is expected to support mission-critical services in industrial Internet of things with its stringent quality-of-service (QoS) metrics. This demands a large consumption of spectrum resource, which is scarce and requires to be configured appropriately. To enhance spectral efficiency and mitigate latency caused by control signaling, we propose a grant-free nonorthogonal multiple access (NOMA) scheme. Packet duplication with frequency diversity (PDFD) is utilized to ensure reliability. The distributed antenna system (DAS) is deployed to further mitigate interdevice interference for URLLC in industrial automation scenarios. With the proposed scheme and antenna configuration, we jointly optimize the uplink and downlink bandwidth assignment and delay components to minimize the total spectrum consumption under the QoS requirements of end-to-end URLLC. A two-step method is then proposed to find the globally optimal solution. In addition, we expand our framework to block segmentation with independent coding mechanism for comparison with PDFD and validate the spectral efficiency superiority of PDFD. Simulation results show the spectral efficiency gain of the two-step method under our proposed schemes, indicating that NOMA integrated with DAS is superior for URLLC with massive devices.