Frequency Offset And Channel Estimation Research And System Implementation In USRP Of Ultra High Speed Mobile Communication

With the rapid development of civil aviation communication and the increasing number of air mobile terminals,it has become more and more urgent practical needs to construct high-speed,real-time and reliable air ad-hoc networks.Therefore,research on the key technologies of high speed mobile broadband communication is meaningful and significant.The Doppler expansion and the time-varying of wireless channel brought by the high-speed mobile terminal are taken as the starting point in this thesis to focus on research of frequency offset estimation and channel estimation problems in the ultra-high speed mobile communications environment.The main works and achievements are as follows:1.Through the analysis and simulation of several classical frequency offset estimation algorithms,the advantages and disadvantages of the classical frequency offset estimation algorithm are compared.Based on the experimental results and combined with the actual demand under the ultra-high speed moving condition,S&C frequency offset estimation algorithm is used in the high speed mobile communication system.2.In the ultra-high-speed mobile environment,the time-varied characteristic of channel are more obvious.Thus,the channel has changed from the traditional slow time-varying channel to the fast time-varying channel.By analyzing the time-varying channel,the system is modeled by BEM(base expansion model).A new improved method is proposed to overcome Gibbs effect and channel fitting error in the CE-BEM model.The method use second-order offset to reduce the boundary error in channel fitting.The simulation results demonstrate that the new method has characteristics of low error and anti-high frequency offset.3.In order to effectively reduce subcarrier interference effectively,the traditional comb pilot has evolved into clustered pilot.A new pilot improvement scheme is proposed to optimize the pilot structure by fixing the length of the guard pilot for the low efficiency of estimation pilot in the FDKD structure.Simulation results verify the effectiveness and high efficiency of the new pilot structure.4.Load the ultra-high speed wireless communication system into the GNU Radio platform and connect the platforms with the USRP to establish communication between the terminals.The results of experiment illustrate that the system can realize the normal transmission of text files and voice files.