Queue-Sync: A Queue-Aware Delay-Compensated Time Synchronization Framework for High-Dynamic V2X Networks

Vehicle-to-Everything (V2X) systems that support cooperative perception and control require precise network-wide time synchronization. In dense traffic, however, existing schemes often decouple synchronization from communication delay. As a result, rapidly varying uplink queueing delays remain uncompensated and introduce persistent asymmetric bias that degrades synchronization accuracy. To address this issue, we have proposed Queue-Sync, a delay-compensated time synchronization framework for a Cloud-RSU-EV (CRE) architecture. Queue-Sync consists of a roadside Dynamic Delay Prediction Module (DPM) and an on-vehicle Delay-Compensated Synchronization Module (DCM). The DPM combines an M/M/1 queueing model with an adaptive extended Kalman filter (AEKF) to estimate the uplink arrival rate and queueing delay online. The DCM performs asymmetric timestamp-based synchronization. It injects the predicted delay into the offset calculation for feedforward compensation, and feeds back the measured round-trip time (RTT) to calibrate the DPM. Based on an extended fine-grained clock model, simulation results show that Queue-Sync consistently yields a lower average synchronization error compared to baseline schemes. This improvement holds under different synchronization intervals and traffic densities. It achieves a smoother convergence and more stable clock synchronization performance at the cost of a modest increase in synchronization message overhead.