Seamless LTE connectivity in high-speed trains

High-speed train (HST) is revitalizing the train as a preferred mid-range transportation system. The provision of broadband Internet connectivity onboard trains is one of the key challenges in the competition among train operators. Unprecedented spectral efficiency and data rates (up to 100 Mbps in high mobility) of the Universal Mobile Telecommunications System long-term evolution (LTE) are expected to offer the solution for high-speed Internet access onboard in HSTs. Massive wireless access and frequent handovers (HOs) of a large number of users might potentially cause service interruptions, and this, in turn, degrades intolerably the quality of experience (QoE) of users’ onboard Internet access. In this paper, we propose a solution based on distributed antenna system that combines directional and omni-directional antennas as trainto-ground radio-access terminals (T-RATs) and LTE femtocells in each carriage. Directional ntennas are deployed at both ends of the HST to provide multi-cell access by diversifying the HOs over multiple LTE cells. This mechanism virtually elongates the train size by connecting the front and rear carriages’ T-RATs to the faraway eNodeBs and augmenting the number of cells the HST can be simultaneously connected to. An ad hoc distributed load-balancing mechanism that consists in offloading backlogged packets to the on-service T-RATs is mandatorily paired with multi-cell access scheme to tie up with the request of seamless onboard Internet service at high QoE level