| Spread spectrum communication is one of the most popular topics in thecommunication field. With the increasing requirement for personal communication and the increasing complexity of channel condition, the advantages of spread spectrumcommunication in secrecy and resisting noise has been more and more important. In the spread spectrum communication system, the synchronization of receiver's Persedo-Noise(PN) code to the transmitter's PN code is such an important part that the whole systemcan't work at all without it. But the traditional method to capture the PN code are either too slow or too complicated to satisfy the need of today's communication system.This article works over a mathod named Large Step Fast Acquisition to capture the PN code in the receiver, which was originally put forward for the acquisition andsynchronization of long PN code under the condition of low signal to noise ratio(S/N).The principle of Large Step Fast Acquisition and are disgussed as the emphasis.When analyzing the principle and performance of the LSDLL, circular flowgraph is used. The expression for "penalty" time and mean and variance of the acquisition time is derived from the circular flowgraph of Large Step Acquisition method. And the output components of the despread correlator under the condition of additive white Gaussian noise (AWGN) are analyzed to derive the expressions for the false alarm probability and the detection probability. Using the SIMULINK of MATLAB,this method is simulated.and the theory has been confirmed.The effect of the noise,dopuler frequency-deflection and the compairation of the acquisition time are analyzed. When discussing the digitalization of the LSDLL circuit, some important part of design of the system are charactered,including the PN code generator using CPLD module and so on.Using the flowgraghic chart,the design of floating point opration anddigitalical filter with the microchip TMS320VC5409 are introduced.
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