The Research Of OFDM Technology In High Speed Railway Mobile Channel

The development of high speed railway put forward higher requirement to railway mobile communication system that the railway mobile communication system should be able to meet the real time and reliability requirement of wireless data transmission with high frequency spectrum efficiency under high speed. As the resolve scheme of our country actual railway mobile communication system, GSM-R is able to meet the communication requirement under high speed and has achieved great success. But there are some defect existing in GSM-R, such as the complexity of system implement and defect in the process of hand-off.OFDM technology has a good performance in multi-path delay resilient with high frequency spectrum efficiency, has been widely applied in digital audio broadcast (DAB), digital video broadcast, wireless Local Area Network 802.11a and wireless Metropolitan Area Network. It is has been proven that by the application of OFDM technology in railway mobile communication system, the system can resolve the defect in GSM-R and realize reliability, unsymmetry and high speed data transmission with good performance in interference resilient and high frequency spectrum efficiency.By the introduction of railway mobile communication system based on OFDM, a deeply research in the transmission mode and parameter selection of the system is done. The transmission mode and parameter selection is related to the channel small scale fading. So in the paper, firstly the sorts and modeling method of small scale fading is presented, then the modeling method of high speed railway mobile channel is analysed. By the simulation and analysis of the performance of the four transmission modes in DAB standard under high speed railway mobile channel, it is proven that the third transmission mode performs better than the others. Then the performance of railway mobile communication system based on OFDM is compared with the performance of GSM-R system. Finally, it is proven that the performance of the system can be improved by adding the channel estimation process, changing the modulation or the channel coding method.At last, the baseband process of DAB system is implemented on the DSP platform and the Turbo decoding coprocessor is under debugging.