Packet Duplication for URLLC in 5G: Architectural Enhancements and Performance Analysis

URLLC use cases demand a new paradigm in cellular networks to contend with the extreme requirements with complex trade-offs. In general, it is exceptionally challenging and, resource usage-wise, prohibitively expensive to satisfy the URLLC requirements using the existing approaches in LTE. To address these challenges 3GPP has recently agreed to adopt PD of both UP and CP packets as a fundamental technique in 5G NR. This article investigates the theoretic framework behind PD and provides a primer on the recent enhancements applied in the NR RAN architecture for supporting URLLC. It is shown that PD enables jointly satisfying the latency and reliability requirements without increasing the complexity in the RAN. With dynamic control capability, PD can be used not only for URLLC but also to increase the transmission robustness during mobility and against radio link failures. The article also provides numerical results comparing the performance of PD in various deployment scenarios. The numerical results reveal that in certain scenarios, performing PD over multiple links results in lower usage of radio resources than using a single highly reliable link. It is also found that to improve radio resource utilization while satisfying URLLC requirements, enabling PD in scenarios such as cell edge is crucial where the average SNR of the best (primary) link and the variation in SNR between all accessible links is typically low. In essence, the PD technique provides a cost-effective solution for satisfying the URLLC requirements without requiring major modifications to the RAN deployments.