In this paper

a rapid acquisition scheme of Doppler shift is proposed for a LEO satellite spread-spectrum communications system.Based on the use of digital matched filter(DMF)and automatic frequency control(AFC)loop

two characteristics of the DMF are exploited to reduce the mean acquisition time (MAT)of Doppler shift

namely

the rapid acquisition property of PN code and a high sensitivity of maximum correlation value to frequency offset.An expression of the MAT is derived

and a suboptimal decision of acquisition is given out from numerical results.Finally

the performance of the proposed acquisition scheme is compared with the traditional serial scheme

showing a significant improvement achieved.