Research On Link Performance Cognition And Channel Status Information Feedback

People's life has been changed greatly by rapid development of wireless communications.Wireless communications bring revolution into lots of industries. Because railway has substaintial relationship with communication,wireless systems with higher performance become especially important.As a promising method to enhance wireless system performance and making full use of limited wireless resource, cross layer design is becoming more and more focused.The paper lays its point on cross layer design in wireless communications,including key techniques and basic theories. Primary contents and innovations are listed as bellows:Based on current conclusions,whole analysis on cross layer design for wireless communications in the paper indicates that the key points are Link Performance Cognition(LPC) and Channel Status Information(CSI) feedback.Then theoretical analisis on MIMO-OFDM,which is widely used in next generation wireless systems,are presented.Wireless channel model is analyzed and simulated.A general mathematic model of wireless transmissions and detection is generated,in the interest of further analysis and simulations.To the point that LPC lacks of theoretical supports,with the help of Information Theory,Statistical Theory and Signal Detection Principle,a relative complete and effective theoretical model is proposed in this paper to describe LPC.From the view of application,these theories and the proposed model are used to explain and analyze all current algorithms of LPC,including their performance and applied conditions. Moreover these deductions can lead to a novel Enhanced Received Block Information Rate(ERBIR) algorithm,which is of more accuracy and universality for LPC.Link Level Simulation(LLS) validates the proposed theoretical model and ERBIR algorithm.CSI feedback is also theoretically detailed.A rule based on system capacity is proposed to measure the performance of different feedback schemes.Using this measurement,some common feedback schemes are analyzed and compared,and then an optimal layered feedback scheme is deduced,to obtain best performance for close-loop system.Simulation results show that,comparing to current feedback schemes,layered feedback scheme will introduce 1～2dB gain in transmission error performance of precoding MIMO system.Finally,real applications of cross layer design are partly realized in WiMAXⅡ system,and they are analyzed with the conclusions presented in the previous sections. Simulation results show that,the theories proposed in this paper,indicate clear orientations on the usage of cross layer design in real wireless systems,accurately predicting system performance.Following the theories in this paper,ERBIR link evaluation will bring about 10%system capacity gains in link adaptation;Results from System Level Simulation(SLS) show that theories on link evaluation can reduces computational complexity of SLS a lot,and the SLS results are reasonable.