On the Doppler probability density function within a low Earth orbit satellite spot beam and its application to the code acquisition procedure

The probability density function of the Doppler shift in a LEO satellite spot beam has been found for both a circular and elliptical shaped spot beam. The Doppler PDF was used as a priori information in order to achieve better mean acquisition time which is critical in any LEO satellite communication system. It is shown that the Doppler PDF can be very well approximated by a parabola-shaped function. The direct approach is used for the calculation of the mean acquisition time while various searching strategies of the Doppler ambiguity area are analysed and simulated using the parabolic Doppler PDF. The overall analysis shows that the use of the Doppler PDF combined with an appropriate search strategy can reduce the mean acquisition time significantly