Research On MIMO Channel Modeling For High-Speed Railway

Alter more than a decade of development, the longest mileage of high-speed railway network has been built in China. The high-speed railway technology, with self-owned in-tellectual property right, is maturing and it becomes China’s card in transportation. The safety is essential in train’s operation, which is based on the information interaction of train’s status and train control message. Therefore, the performance of wireless commu-nication system is important. As the coverage of high-speed railway has been improved and more people choose high-speed railway as the travel tool, the information service, such as Internet access, has been on the agenda. However, this raises higher requirements for the wireless communication system, which is not only capable of transmitting control message precisely and reliably, but also provides large amounts of data for passengers. Under this circumstance, new wireless technology is required.MIMO (Multiple-Input Multiple-Output) is the main technology of physical layer in 4G LTE (Long Term Evolution) system and it can provide diversity and multiplexing gains. When MIMO is applied in high-speed railway, the BER (Bit Error Rate) can be reduced and the channel capacity will be improved. The performance of MIMO highly depends on the propagation environment and channel conditions. The special scenario in high-speed railway will show different propagation characteristics. So the previous MIMO channel model cannot be applied in high-speed railway directly. Meanwhile, the current research focuses on channel modeling in high-speed railway, especially the chan-nel spatial and angular characteristics. Based on narrowband single antenna measurement and special scenario analysis in high-speed railway, a semi-deterministic MIMO channel modeling method is adopted to analyze the channel spatial characteristic in this disserta-tion. The impact of antenna array configuration on performance is considered, and the measurement data is used to investigate the time-variability of channel, which can pro-vide some guideline for wireless system simulation and design. The main contributions of the dissertation are summarized as follows.1)For the high speed of the train, the stationarity interval using the correlation of signal amplitude is defined in high-speed railway based on the form of measurement da-ta. The statistical features of stationarity interval in different train’s speeds and different scenarios are obtained. The results are compared with the five MIMO standard chan-nel models, which can provide the guideline for the channel model improvements and wireless system simulation.2)Based on the field trip to Zhengxi railway, two typical scenarios, viaduct and cut-ting are chosen. A semi-deterministic MIMO channel modeling method is used, and the regular sphere channel model is proposed for viaduct scenario. A cluster-based scattering channel model is proposed for cutting scenario. The large scale parameters of model are based on Zhengxi measurement data. The small scale parameters are from scattering and ray-tracing analysis. Finally, the spatial correlation properties of these two scenarios are obtained.3)Depending on the cell coverage in high-speed railway scenario, an antenna array model, which contains different antenna parameters, is used to investigate the effect of antenna array configuration on channel capacity. For the ULA (Uniform Linear Array), the optimal azimuth angle of array is given.4)Depending on the difficulties and constrains of MIMO channel measurement in high-speed railway, the applicability of different MIMO measure methods in high-speed railway has been discussed. Based on the feature of high-speed railway, the moving virtual array method is proposed, which combine the principles of virtual array and switch array schemes. The equivalent number of virtual array is derived. The method is verified by the measurement carried out by a newly-built 1×3 SIMO (Single-Input Multiple-Output) channel sounder.