Spread Spectrum Signal Parameter Estimation And Synchronization Algorithm

Direct-Sequence Spread Spectrum (DS-SS) system has been widely used invarious realms increasingly due to its excellent characteristic of Multiple Access, LowProbability of Interception and Anti-Jamming. Detection and surveillance for this kindof non-cooperative weak communication signals in reconnaissance have been widelyconcerned. Although conventional parameter estimation methods for DS-SS signalcan achieve estimation of primary parameters (carrier frequency, symbol period, chiprate, etc…) in low SNR, more or less they have disadvantage of large amount ofcalculation and inferior robust. Their performances descend while facing DS-SSsignal using Multi-Phase Shift Keying like QPSK. Moreover, mature and effectivemethod for PNS code recovering in low SNR is still lacking. The main task of thisdissertation is to find new approaches to these problems.First of all, we research several conventional parameter estimation methods andtheir performances in low SNR by computer simulation, including correlationdetection, square detection and cyclic spectrum detection.By exploring cumulation arithmetic and character of DS-SS signal, we putforward a parameter estimation method based on symbol cumulation for carrierfrequency and chip rate estimation of DS-SS signal in low SNR. That method canrestraining noise and separate branch components of the QPSK signal withintermediate frequency. Combined with conventional parameter estimation methods,the performances are improved to a certain extent.Several approaches for PNS code recovering including coherent demodulationand eigenanalysis demodulation are discussed in the paper. We achieved therecovering in low SNR with inferior BER by combining cymbol cumulation withthese arithmetics.Synchronization is the week point of symbol cumulation and PNS coderecovering. At the last of this paper we investigate some familiar blindsynchronization method and their effectiveness.