Reliability analysis of mobile radio systems: application to the railway system

The mainstream literature has widely dealt with the reliability and availability of systems since 1950s, however the reliability analysis for communication network has not been thoroughly investigated. To the best of our knowledge my work bridges this gap by investigating reliability analyses for an LTE network applied to a railway system. Notably, the support for GSM-R, which is the communication network for railways, is deemed to come to an end in 2030 and a possible technology that can replace the GSM-R is the LTE. The goal of this research is to perform a reliability analysis and select the most suitable LTE model according to Italian Infrastructure Manager’s (hereinafter RFI) needs. The LTE network (currently the GSM-R network, and in the future the FRMCS) interfaces with the railway signalling system, which is the ETCS, and both are parts of the ERTMS. If a fault in the LTE network occurs, it may bring to a disruption of rail traffic ETCS. In order to determine the LTE network that best satisfies the needs of the Italian Infrastructure Manager (RFI), it is acceptable to have a total down-time of 8 minutes per year for blocking faults, meaning faults that impede rail traffic. Through the Isograph tool, this research has designed 6 LTE network models. The data for each component have been provided by an international supplier, selecting the characteristic values for each railway element. The six models have hence been compared based on the most sensitive parameter to small changes, which is the total down-time and the most suitable model has been then selected. Therefore, among the 6 models designed, my research shows that Model 5 meets this requirement. Model 5 allows the LTE network to have a redundant architecture in the core parts, to be deployed to different (geographical) nodes and to work in the pool area. In conclusion, my research shows that Model 5 is an adequate balance that combines, besides the value of total down-time, the high availability and the possibility to have a redundant network architecture. Those advantages enable RFI to satisfy the safety requirements of ERTMS, since safety is a priority regardless the price. Another technology that can possibly substitute the GSM-R in the future may be the 5G. However, this research shows that starting the reliability analysis from the LTE technology is a correct choice because the philosophy behind the functioning of the LTE and the 5G network is the same. Both technologies are compatible, since the 5G is a natural development of LTE and they share many features. In addition to that, today the 5G has not been tested on field. Even though the future railway mobile communication technology chosen may be the 5G this research is significant because it lays the groundwork also for reliability analysis of the 5G.