Examining cellular access systems on trains: Measurements and change detection

Access to reliable high-quality communication services on trains is important for today's mobile users. Train-mounted aggregation routers that provide WiFi access to train passengers and bundle external communication over multiple cellular modems/links is an efficient way of providing such services. Still, the characteristics of such systems have received limited attention in the literature. In this paper we examine the communication characteristics of such systems based on a large data set gathered over six months from an operational Swedish railway system. We characterize the conditions in terms of usage load, train velocity profiles, and observed throughput and delay as well as the relation between these parameters. Furthermore, we examine the data from an anomaly detection perspective. Based on a changepoint detection method, we examine how the collected metrics varies over the six months. Being able to detect shifts in the metrics over time can help detect anomalous changes in the hardware or environment, and also further helps explain the factors affecting the observed behaviors.