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Comparisons of three methods of PN code acquisition under large Doppler shift

Because of its attractive features, direct sequence spread spectrum (DS-SS) technique can be used in telemetering, telecontrol and communications. However, low earth orbit (LEO) satellites channel can experience large Doppler shift which make the acquisition of PN code especially difficult. In this paper, we consider and compare three approaches to the acquisition of direct sequence spread spectrum signal affected by large Doppler frequency shifts. Three sections compose this paper. Section 1 introduces the influence of carrier frequency shifts on the acquisition process of PN code. In section 2, we analyze three measures which can cope with the large Doppler shift of carrier frequency and realize the acquisition of PN code. Computer simulations are performed, which verify the theory analyses. In section 3, contrasts have been done among these three methods mentioned above.