Study And Implementation About Carrier Wave Frequency Quisition Of Spread Spectrum Signal Based On FFT

In the part of Tracking and Data Relay Satellite System's (TDRSS) receiver, coherent demodulation and Doppler frequency speed measurement is one of the important tasks and is one of the key functions of the system. The modulated signal format of the TDRSS includes BPSK , QPSK and UQPSK. The demodulation and PN acquisition accurately of received spread spectrum signal are the preconditions of coherent demodulate and speed measurement. The carrier wave frequency acquisition, tracking is the important tache to demodulate accurately.Based on a research institute of electronic technology' project about TDRSS, in this thesis, carrier wave frequency acquisition of spread spectrum signal is studied and implemented.Firstly, based on the study and analysis about spread spectrum signal and its carrier acquisition theory, the carrier acquisition scheme is proposed and implemented. DSP and FPGA is applied for implement this scheme. In the CCS, FFT carrier acquisition arithmetic is programmed, debugged and simulated. On Quartus II, whole acquisition scheme and Direct Digital Synthesizers (DDS) module is implemented.Secondly, nonlinear transform of BPSK/QPSK signal is analyzed.Spread-spectrum BPSK/QPSK is carrier wave signal suppressed. Before FFT calculated, carrier wave must be extracted. In this thesis, BPSK is square nonlinear transform and QPSK is quartic nonlinear transform. These nonlinear transform can result in SNR of spread spectrum signal deteriorated. This study about the square nonlinear transforms and the quartic nonlinear transform is implemented, as the same time, used practical data prove that theoretic value consistent with practical value. The theoretic result offer proof for implement of detector and the analyzing conclusion is applicable to even detector.Finally, the carrier acquisition arithmetic is downloaded in TMS320VC33 to run, and its result is the Doppler frequency. The result is consistent with the practical data. It proves that the carrier acquisition arithmetic proposed in this thesis is availability.