Benchmarking Alternative Technologies for providing Voice Services onboard Trains

Providing cellular voice onboard trains has proven to be a challenging task. The metallic chassis and the energy-saving coating on the windows act as a radio shield. In combination with sparsely spaced cellular base stations on rural routes, the coverage onboard inter-city trains is under dimensioned. Since the late 1990s, analog “amplify and forward” radio repeaters have been used extensively to provide coverage of cellular voice onboard trains. However, repeater systems have proven to be both expensive and technically problematic for both trains as well as mobile network operators. In this study, three alternative technologies for providing cellular voice onboard trains are investigated and benchmarked. The technologies under investigation are: circuit-switched voice on GSM and 3G; Voice over IP on LTE (VoLTE); Voice over the onboard Wi-Fi network (VoWiFi). To benchmark these systems against each other, measurements were conducted onboard Swedish X2000 trains, en-route between Stockholm and Gothenburg. In particular we measure: the Availability; the Retainability: Geographical Coverage and Voice quality. Our results show that VoWiFi over the onboard Wi-Fi network outperforms GSM, UMTS as well as VoLTE provided over the onboard repeaters, with equal voice quality as VoLTE but nearly 100% availability and nearly 100% retainability.