Derivation and Calculation of Bit Error Rate due to Doppler Shift in GMSK Modulation

摘要

In the high-speed mobile communication, one of the most important factors that influence the bit error rate is Doppler shift. This thesis, on the basis of GMSK modulation which is used extensively in the mobile communication at present, derives the formula of the bit error rate caused by Doppler shift, and proves the superiority of differential demodulating in reducing the influence of Doppler shift not only by qualitative analysis but also by quantitative calculation. Moreover, we analyze the factors that affect the error probability by simulation. The thesis has five parts: The first part is the foreword, in which we explain the research background of Doppler shift in high speed terrestrial mobile communication and the development in the field. The second part includes the model we work on and the superiority of differential demodulating by calculation. The derivation of the formula of the BER caused by Doppler shift in GMSK modulation and differential demodulation is the third part, and it is also the central content of the thesis. We derived the particular formula with the independent variable, which is the difference of the Doppler shift frequency in a bit's transmission time. Then we make simulation on the basis of the formula in the forth part, and find useful conclusions from it. Finally we make the conclusion that from our research we have proved the superiority of differential demodulation in reducing the influence of Doppler shift, and find the factors that affect the BER.