An Optimized Link Layer Design for Communication-Based Train Control Systems Using WLAN

With the advent of machine-to-machine and vehicular-to-everything communication systems, next-generation train control systems known as communication-based train control (CBTC) systems are also gathering increased interests both from academia and industry. Unlike the traditional train control systems based on track circuits, CBTC systems are expected to provide greater transportation capacity while ensuring safety by exploiting wireless communications between trains and wayside access points. However, due to the nature of wireless channels, packet transmission delays between APs and trains can greatly affect the train control performance. Most previous works have adopted an adaptive modulation and coding (AMC) method that minimizes the average delay to improve the control performance taking care of transmission errors due to channel fading. However, medium access control (MAC) layer contention due to multiple competing trains, which can entail significant degradations of the delay and control performance, has not been considered. Therefore, we propose an optimized link layer AMC method for CBTC systems using wireless local area network that encompasses the impacts of fading channels as well as of MAC layer contention. With much reduced required information, the proposed scheme enables to select the transmission mode that minimizes this average delay in each control period. The simulation results show that the proposed method greatly outperforms the conventional schemes over a wide range of parameters and settings.