CBTC over WI-FI: gathering clouds

This paper explores the challenges that modern Communications-Based Train Control (CBTC) systems pose to IEEE 802.11 Wi-Fi radio networks. We will describe how Wi-Fi, in spite having been designed as a lbest-effortr system, became the radio bearer of choice for a safety-critical and mission-critical application such as CBTC. We will explore the limitations inherent in the IEEE 802.11 protocols with regards to range, mobility, radio resource access, Quality of Service and interference. We will then briefly describe some potential mitigations, and we will mention the latest development in the industry that are moving towards a replacement of the Wi-Fi-based CBTC radio for an LTE system.