The Research On Chirp Noise Waveform Based Spread Spectrum Communication System And FPGA Design Of Receiver

In the next generation Ka-band TT&C system, Doppler shift will be over800kHz.However, the traditional direct sequence spread spectrum (DSSS) system sensitive to theDoppler shift, which will greatly extend the acquisition time and increase the complexity ofreceiver.This paper studies the frequency coupling characteristics of Chirp signal which is notsensitive to the Doppler shift, at the same time for its time-frequency characteristicssignificantly and poor security issues, we propose a Chirp noise waveform (CNW) basedSpectrum Communication System, then design and complete the receiver based on FPGAhardware architecture. The main contents of this paper are as follows:First, the performance of existing TT&C acquisition algorithms under high dynamicand low-noise ratio is analyzed. This paper studies the frequency coupling, pulsecompression and other features of Chirp signal, and for its poor security issues, we proposea system adopt CNW as the baseband signal, then analysis theoretically and simulation theDoppler tolerance and LPD/LPI performance of CNW with different phase scale factors.Second, a fast acquisition method with CNW based on dual matched filters ispresented, the receiver could complete signal acquisition and Doppler shift estimation onlyneeds to search for the peak position of the output of matched filters in the time domain.Compared to traditional two-dimensional search method, the acquisition time reduced toless than10ms from about5s, as the complexity of receiver basically unchanged.Third, Chirp Spread Spectrum (CSS) system uses frequency modulation to carryinformation, that’s robust but less information transfer rate and difficult to achieve higherorder modulation. In this paper, a new CCSK higher order modulation method based onCNW is proposed, which effectively improve the information transfer rate and bandwidthefficiency of the system. And for the higher complexity of traditional CCSK higher orderdemodulation used a bank of correlators, we propose an efficient demodulation based ontwo splicing matched filter, otherwise using the way of string and convert to eliminateinter-symbol interference and improve demodulation performance, it also can effectively reduce the consumption of hardware resources.The receiver of CNW based spread spectrum communication system based on FPGAprototype is designed and completed. And the design and implementation of each module iselaborated, including down-conversion, signal acquisition, synchronization and Dopplershift estimation, frequency compensation and CCSK demodulation module. Taking intoaccount the principles of the exchange of FPGA area and rate, both serial and parallelmatched filter implementation modes were designed. Serial mode requires a higher systemclock, but it can effectively reduce consumption of resources.