Priori Information Based Mimo Limited Feedback Technology For High Speed Rail

With the rapidly development of high-speed railway, the railway communication technology also has to follow the development of communications technology. The key technology of the next generation of wireless communication systems applied to the high-speed rail mobile communication system will be imperative trend. Multiple-input multiple-output (MIMO) is one of the key technologies of LTE system, which can implement space multiplexing and user division, thus increase the transmission rate and robustness of the system. Therefore, the MIMO will be widely used in high speed railway communication in the future. However, the channel state information is needed to feedback during the MIMO system communication, which will take some bandwidth resources and reduces system efficiency. Meanwhile, in the high-speed railway scene, the high moving speed of the train will result in limited feedback information of the MIMO systems invalid or obsolete error etc, and can not achieve high system performance gain. Therefore, the need for an effective way to make the limited feedback MIMO technology is suitable for high-speed rail communication scene.By analyzing the limited feedback MIMO system with linear precoding performance and corresponding user select scheme’s performance under the high mobility scenarios, we conclude that the main factors which affect the limited feedback MIMO transmission rate include the feedback delay caused by the high moving speed, and the number of feedback bits affected the feedback information accuracy.In this thesis, we propose a feedback channel matrix correction scheme with the help of a priori channel matrix, and an adaptive feedback bit scheme based on the position information. The proposed schemes based on the coverage of the high-speed rail are zonal distribution, and the speed and position information of the train are provided by the train control system. It can be seen from the theoretical analysis and simulation, with an effective correction of the feedback information, the system bit error rate (BER) and throughput performance are upgraded. When the moving speed of the train is200km/h, the system’s signal to noise ratio (SNR) is30dB, the throughput performance of the system almost is upgraded almost10.3%, and the BER is almost an order of magnitude lower. What’s more, the schemes can reduce the number of feedback bits in the low SNR region, and upgrade the transmission rate of the system in the high SNR region.Additionally, a two-stage multi-user MIMO feedback scheme is proposed, which is based on the accuracy of channel state information used for user selection. The precoding can be different, namely, the number of feedback bits can be different. Per User Unitary Rate Control (PU2RC) scheme with low number of feedback bits for user selection is used in the first feedback stage, and Zero Forcing Beam Forming (ZFBF) with high number of feedback bits for precoding is used in the second stage. The numerical analysis and simulation show the transmission sum rate performance and feedback overhead. The results also show that the scheme can effectively improve system sum-rate performance at low computational complexity situation. Besides, the scheme applicability under the high speed rail scenario, is provided.