LTE MIMO Performance Measurements on Trains

Abstract: Providing passengers internet on board trains with continuous connectivity at high speeds and over large rural distances is a challenging issue. A promising solution to the problem is to use an on board WI-FI network combined with a cellular radio system connected to the LTE (long term evolution) 900/800MHz networks deployed outside the train. However, in order to reach the data rates that today's business traveller is expecting, \Multiple Input Multiple Output" (MIMO) may be needed. In this project the plausibility of achieving LTE MIMO functionality to moving trains is studied both theoretically and through measurements on a Swedish high speed train in a live LTE 900 network. The measurements were conducted along the main track between Stockholm and Gothenburg. Eight antennas were deployed at 4m height on the roof of a X2000 train that was moving at speeds between 100 and 200km/h. The average distance between the base stations and the track was 2.35km and the average base-station antenna height 45m. The measurement data was recorded using an LTE scanner provided by Rohde&Schwarz (TSMW). The simulations were conducted in Matlab and the above parameters were simulated for typical rural Line of Sight (LOS) radio channels. The simulation results show that MIMO may perform well on trains and reach higher rank in the above described radio channel, given that the inter-element distances are correctly chosen dependent on the base station-to-train distance. In the measurement a 2X2 MIMO system was tested and confirmed the model by showing that the condition number (CN), was less than 15 for 65% of the track covered by LTE. Hence, we find that it is indeed plausible to achieve MIMO functionality in LOS on the roof of a fast moving train. Furthermore, the report concludes that LTE-Advance with 8x8 MIMO functionality and carrier aggregation feature, may be a suitable solution in order to provide the internet capacity needed for all the passengers on board high speed trains.