Compensation of Communication Delays in a Cooperative ACC System

Xing, Haitao; Ploeg, Jeroen; Nijmeijer, Henk · 2019 · OpenAlex-citations

DOI: 10.1109/tvt.2019.2960114

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Summary

This paper addresses the challenge of maintaining string stability in Cooperative Adaptive Cruise Control (CACC) systems despite inherent wireless communication delays. While CACC allows for shorter inter-vehicle distances and increased road throughput compared to standard Adaptive Cruise Control (ACC), communication delays significantly compromise string stability, which requires the attenuation of disturbances along a vehicle platoon. Existing methods often require large time gaps or complex centralized controllers. The authors propose a novel control strategy that combines a master-slave architecture with a Smith predictor to actively compensate for these delays, thereby reducing the minimum string-stable time gap. The methodology involves restructuring the standard one-vehicle look-ahead CACC topology. In the proposed master-slave architecture, the controller for a following vehicle (slave) is relocated to the preceding vehicle (master). This arrangement places the communication delay in series with the plant dynamics, a necessary condition for applying a Smith predictor. The system employs bidirectional communication: the slave sends distance error data to the master (feedback), and the master sends calculated acceleration commands to the slave (feedforward). The Smith predictor is then applied to the feedforward channel to estimate the delay-free plant output, effectively removing the delay from the stability analysis loop. The study utilizes a simplified vehicle model with identified parameters ($\tau = 0.1$ s, actuator delay $\theta_a = 0.2$ s) and analyzes the system using Laplace transforms and frequency-domain string stability criteria. The results demonstrate that the proposed scheme significantly reduces the minimum string-stable time gap compared to both standard CACC and master-slave CACC without the predictor. While the master-slave architecture alone increases the required time gap due to added feedback delays, the integration of the Smith predictor compensates for this, allowing for extremely small time gaps even with communication delays. Theoretical analysis confirms that individual vehicle stability is guaranteed within specific controller gain ranges. Simulations validate that the system maintains string stability with minimal time gaps, and the approach remains robust against uncertainties in communication delay values, requiring only a slight increase in the theoretical minimum time gap to maintain stability. The significance of this work lies in providing a computationally efficient, distributed control solution that overcomes the limitations of communication delays in CACC systems. By enabling shorter inter-vehicle distances while guaranteeing string stability, the proposed method can substantially improve highway capacity and fuel efficiency. The study highlights that active compensation via the Smith predictor, enabled by the master-slave topology, is a viable alternative to restrictive delay bounds or complex multi-vehicle look-ahead strategies, offering a practical path toward high-density vehicle platooning.

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