Beyond Throughput-Optimal: Second-Order Smooth Backpressure Algorithm for Reducing Jitter and Delay

In the imminent era of 6G, Quality of Service (QoS) emerges as a pivotal concern in wireless communications. The prescribed transmission rates and vast access demands mandated by 6G standards impose heightened requirements on network throughput and delay. However, the highly dynamic and often bursty nature of application demands presents challenges for routing and congestion control. The backpressure-based joint rate and routing control algorithm adaptively adjusts network traffic to achieve optimal throughput. However, varying traffic conditions hinder the algorithm's convergence to ideal states. Additionally, relying solely on first-order backlog differences for forwarding can lead to poor convergence and high delays. In this study, we propose a Second-Order Smooth Backpressure (SoSBP) algorithm, leveraging second-order backlog metrics and dual-level queue mapping, to address throughput, delay, and jitter issues in dynamic network environments. We validate the efficacy of this novel backlog metric using Lyapunov optimization techniques. Simulation results demonstrate that our approach significantly reduces end-to-end delay and data jitter while preserving throughput and eliminating routing loops.