The Research Of Fast Acquisition Technology For DSSS Signals Based On Circular Correlation Theory

The Direct Sequence Spread Spectrum Systems (DSSS) can widen the narrow band of the signal needed to sent, by using special spreading functions. This kind of system can achieve the communication process based on the good autocorrelation and cross correlation of pseudo-random code. With the development of the DSSS, the BOC (Binary Offset Carrier) and the TDDM (Time Division Data Modulation) signals all were generated in this spread method. Compared with the traditional PSK (Phase Shift Keying) modulation, the spectral separation would be achieved, and the signal mutual interference would be reduced by BOC modulation. At the same time, its correlation function was steeper than the traditional way-BPSK, and the multipath resolution capability can be enhanced. Compared with the traditional data modulation, the technology with odd point modulated while even point not was adopted, called TDDM, which can improve the tracking accuracy.As a DSSS, the signal acquisition performance of the receiver was pivotal. The acquisition was the precondition of the data processing. There were some traditional signal acquisition methods such as reference signal, matched filter, sequence estimate and sequence search synchronization acquisition, etc. They were all valuable in signal acquisition, while the efficiency of acquisition was relatively low at the cost of the acquisition time and the complexity of hardware. Therefore, they were not propitious to achieve the acquisition of long cycle pseudo-random spreading code signals, BOC signals and TDDM signals. For this reason, the circular correlation was adopted to design the acquisition process in this thesis. Designing with some digital data compression methods, the DSSS could bring out the acquisition result fast, under the condition of low signal noise ratio and the long cycle pseudo-random code signals.The design and simulation had been achieved of the acquisitions about the long cycle pseudo-random spreading code signals and BOC signals, based on the platform of MATLAB7.1, after the disquisition on the methods of codes fast acquisition. Meanwhile, in this thesis, the TDDM-PSK and TDDM-BOC signals also had been designed and simulated, and the characters of circular correlation in rationality, validity and rapidity also can be validated. Above all, on the hardware development platform, the virtex4-sx35 series FPGA (Field Programmable Gate Array) of the Xilinx coroporation, the generation and acquisition processes of the long cycle pseudo-random spreading code,BOC and TDDM signals had been designed, after the MATLAB simulations. Considerding the processes of signals, the design results had been analyzed. At last, the results that the calculation time can be reduced greatly and the fast acquisition can be implemented of the circular correlation by the parameters configured reasonably, can be proved.