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M. Lerch, P. Svoboda, V. Platzgummer, M. Rupp:
"Analysis of LTE in Two-Path Vehicular Repeater Channels";
Talk: IEEE 90th Vehicular Technology Conference (VTC2019-Fall), Honolulu, USA; 09-22-2019 - 09-25-2019; in: "IEEE 90th Vehicular Technology Conference (VTC2019-Fall)", (2019), ISBN: 978-1-7281-1220-6.

In recent years, many public high-speed trains have been upgraded with active in-train repeaters in order to improve mobile service coverage for train passengers. With a repeater in place, the user equipment perceives a wireless channel with a direct path and an indirect path through the repeater delayed by several micro seconds. In vehicular scenarios, the pick-up antenna experiences a wide range of signal levels. Due to the limited output power of the repeater, the paths may arrive with similar power, which can be a problem for OFDM based systems like LTE. Drive tests in LTE have shown that uplink performance degrades, even if the delay stays within the cyclic prefix. In order to gain a better understanding, we conducted a laboratory experiment to measure, quantify, and analyze the impact of two-path channels, with different delays and power levels, onto a live LTE network. Results show uplink performance degradation and increased transmit power even for delays smaller than the cyclic prefix due to non-optimal time-synchronization. In the system under test this degradation already starts at a path power difference of 15 dB and reaches up to 50% at equal path power levels.

http://dx.doi.org/10.1109/VTCFall.2019.8891353

https://publik.tuwien.ac.at/files/publik_280574.pdf