Load-Stress Test of Massive Handovers for LTE Two-Hop Architecture in High-Speed Trains

Load-stress test is the experimental performance analysis in extreme traffic and density conditions, routinely required to validate any innovative radio access solution. This article focuses on load-stress test specifically designed for the two-hop architecture that enables the onboard connectivity in HSTs. The load-stress condition of train-to-infrastructure communication for a massive number of onboard UEs is very challenging, as it needs to account for extreme conditions and a complex testing environment. The load-stress method proposed in this article is for a ground network supporting onboard wireless connectivity in HSTs, and is validated for commercial eNBs from LTE cellular networks (Rel-11). The in-lab experimental setup is arranged by virtualizing multiple eNBs serving multiple cells, arranged sequentially along a line to simulate the HST track with a massive number of active onboard UEs. The focus of the experimental load-stress test is the analysis of the impact of Doppler shift and interruptions caused by the frequent HOs of multiple consecutive groups of UEs deployed in HST carriages at the speed of 300 km/h. The HO interruption time is characterized statistically based on the number of active UEe. The consequent impairments on the experienced QoS for high-throughput and low-latency services such as FTP and VoLTE are verified. This article validates experimentally the traffic and HO latency improvements (approximately threefold) in a multi-cell access scheme when the coverage of every single carriage is augmented by fixed directional antennas to offload UEs toward far-away eNBs along the train track.