Study On Doppler Frequency Shift Estimation Method Of High Speed Railway Wireless Communication System

Rapid development of high speed railway puts forward more strict requirements towireless communication system service quality. How to guarantee to provide high speedmoving train safe and reliable wireless data transmission channel information in real time andprovide convenient and efficient wireless broadband access services has become a hotproblem in the wireless communication system technology research. GSM-R(Global Systemfor Mobile Communications for Railway) is the railway wireless communication systembased on GSM platform, and platform for the speed of500km of high speed railway traincontrol system in the information transmission. In the GSM-R system, doppler frequency shiftgenerated by train fast moving increases the system bit error rate, which has become one ofthe factors affecting the quality of the whole communication system. Although conventionaldoppler frequency shift estimation algorithm owns high accuracy, but its range is not big.Doppler frequency shift of high speed railway GSM-R wireless communication system mayincrease with train running speed, and the range of frequency shift may change by a largemargin. Therefore, at the same time of improving frequency shift estimation precision, how toincrease the range of frequency shift estimation has become a hot research direction indoppler frequency shift estimation algorithm to high speed railway wireless communicationsystem.Based on a problem that conventional doppler frequency shift estimation algorithmunable to achieve a reasonable balance between the frequency shift estimation range andestimation precision, this thesis analyses and researches doppler frequency shift estimationalgorithm to the GSM-R wireless communication system. On the basis of the improved Fitzalgorithm, the thesis adopts a algorithm combined on-board information with improved Fitzalgorithm into doppler frequency shift estimation calculation, improving the frequency shiftestimation precision the frequency shift estimation range.First of all, the thesis introduces general characteristics of the wireless channel, mainlyaimed at small scale fading characteristics including multipath effect and doppler effect. Onthis basis, the thesis analyses the characteristic of wireless channel of high speed railwaycommunication environment.Secondly, the thesis analyses GMSK(Gaussian Minimum Shift Keying) signalcharacteristics in the GSM-R system and frequency shift estimation theory, including theanalysis of characteristics of GMSK signal demodulation technology, how to derivemaximum likelihood function of parameter estimation and the introduction of parameterestimation algorithm performance evaluation standard. And then the thesis analyses differentstatistical characteristics of the doppler effect of high speed railway environment, including the doppler effect under the scenario of the viaduct, tunnels and cutting, the dynamic changeof doppler frequency shift with the train operation and doppler power spectrum shapecharacteristics under common scenarios.Finally, the thesis analyses several kinds of doppler frequency shift estimation algorithmbased on modulation of the linear GMSK signal, including the frequency and phase based onminimum mean square error estimation algorithm, single frequency estimation algorithmbased on the difference, classic Fitz algorithm and the formula derivation, the comparison ofadvantages and disadvantages of improved Fitz algorithm. On the basis of improved Fitzalgorithm, this thesis adopts a joint estimation method combined with on-board informationfor doppler frequency shift estimation calculation, and the simulation analysis of this methodis done. Compared with the classical Fitz algorithm, results show that this method increasingthe frequency shift estimation range, improving the estimation accuracy, and lowing computationcomplexity.