Study on coexistence and anti-interference solution for subway CBTC system and MiFi devices

A new portable and mobile relay device called MiFi which can provide personal Wi-Fi access with the aid of the cellular networks as the backhaul becomes increasing popular. However, as MiFi can be deployed without operators´ planning, the devices can cause interference problems when they are brought in subway carriages. Hence, to investigate the interference on the Communication Based Train Control (CBTC) system imposed by MiFi devices, the coexistence scenario and system models are proposed. Based on the models, the performance loss of the CBTC downlink and the effectiveness of a proposed anti-interference algorithm with the Constant Contention Window (CCW) Distributed Coordination Function (DCF) protocol are studied. Research results show that the metro train indeed may be forced to stop by MiFi devices with the growth of the MiFi devices and the MiFi Data Frame Length (DFL). Additionally, our anti-interference algorithm can reduce the performance loss of the CBTC system without any change of the existing CBTC hardware equipments.