Performance improvements of communication-based train control (CBTC) systems with unreliable wireless networks

Communication-based train control (CBTC) uses wireless networks, such as wireless local area networks (WLANs), to transmit trains status and control commands. CBTC systems have stringent requirements for train-ground communications, as the train control system depends on the accurate, timely and reliable data over the communication links. However, since WLANs are not originally designed for high mobility environment, random packet delay and losses are inevitable in WLAN-based CBTC systems, which could result in unnecessary traction, brake or even emergency brake of trains, losses of line capacity and passenger satisfaction. In this paper, we study the impacts of random packet delay on the performance of CBTC systems, and propose a novel scheme to improve the CBTC performance by mitigating the impacts of random packet delay. Unlike the existing works that only consider a single train, we consider a group of trains in CBTC systems to improve the CBTC performance. Extensive field test and simulation results are presented. We show that the current adopted control scheme in CBTC systems needs to keep stability and performance under transmission delays through increasing the distance between trains in steady state which means cost of line capacity. By contrast, our proposed scheme can significantly improve the CBTC performance.