State-Recovery Protocol for URLLC Applications in 5G Systems

In 5G systems, ultra-reliable low latency communication (URLLC) services are expected to support an end-to-end latency of up to 5ms, while guaranteeing a minimum of 99.999% packet delivery reliability. Providing such strict service requirements is potentially difficult. As a solution, the 5G standard suggests taking advantage of the packet duplication strategy whereby two data sessions are established between one or two base stations and the node running the URLLC service. However, the technical specifications of the duplication strategy are not addressed by the standard, and thus, its implementation is left up to the mobile network operators. In this paper, we propose a state-recovery protocol for URLLC applications that assists packet-duplication frameworks by recovering the state of transmitted packets in the case of acknowledgment loss. Based on such state information, packet-duplication frameworks can intelligently control the duplication rate to provide URLLC-level reliability while using as little resource as possible based on the current network conditions. We validate our protocol through multiple experiments on srsRAN nodes implemented on Colosseum, the world's largest radio frequency emulator.