Research On Parameter Estimation Of Digital Communication Signals And Jamming Technique

Communication modulation technique and spread spectrum technique have been rapidly developed to accommodate to the increasingly complicated electromagnetic environment, to ensure the correct transmission of information, to utilize the limited frequency resource in reason, consequently to challenge the communication countermeasure field. The communication countermeasure techniques play important role both in military and civilian application, which have been widely used in many aspects: signal detection, spectrum supervision, security surveillance, wireless warning, keeping secret, and etc. The parameter estimation of digital communication signals and the jamming techniques have been arising within recent years.Based on the previous works, associating actual applications of communication reconnaissance and jamming, this paper primarily investigates the modulation parameter estimation of common digital communication signals, the spread- spectrum parameter estimation of Direct Sequence (DS) and hybrid Slow Frequency Hopping & Direct Sequence (SFH/DS) signals along with the jam pattern study for FSK and PSK. The main works can be summarized as follows:1. Aiming at the carrier estimation problem at lower SNRs in spread-spectrum and anti-jamming communication, a method is proposed to estimate signal carrier frequency using a special cyclic cummulants educed by a subclass of the high-order cyclic moments. The special cyclic cumulants of various digital modulation formats: ASK, FSK, PSK, QAM and MSK, are calculated and proved to be nonzero only when the cyclo-frequency equals to the carrier frequency. Thus the accurate carrier estimation of the modulated signals can be implemented by detecting the cyclo-frequency's location. This method can be popularized for the subcarrier estimation of OFDM signals and proved to work well.2. The fact is proved that the power spectrum of the unipolar baseband sequence composed of the coefficient modules of the wavelet transform has discrete spectral lines located at the integer-multiplied symbol rate so that those spectral lines can be used to detect the symbol rate of the digital baseband signals. Associating the physical circumstances of captured signals, methods are given to convert the digital signals, MASK, MFSK, MPSK, MSK and QAM, into unipolar pulse sequences with the same symbol rate. So the symbol rate estimation algorithm based on the wavelet transform is popularized for the bandpass digital signals. The OFDM signals'symbol rate estimation algorithm is proposed by constructing their auxiliary signals associating the symbol rate estimation algorithm of baseband signals based on the wavelet transform.3. Aiming to the parameter estimation problem of DS/SS signals, a method is proposed to estimate the repetition period of the PN code by adopting the cepstrum analysis and the secondary spectrum treatment. The mutual orthogonal eigenvectors can be obtained by the signal subspace decomposition, which are used to determine and reconstruct the PN code combining the principle that the autocorrelation function of the PN code has lower side-lobe energy.4. Aiming at the FH parameter estimation of the hybrid SFH and DS signals, proposed are the following methods: the time-frequency ridge lines are abstracted by calculating signals'time-frequency analysis; the dynamic cluster analysis on signals'time-frequency ridge lines are proposed to determine rough estimation of the hopping frequency set and the frequency seeking range; then the accurate hopping frequencies can be estimated by the special cyclic cumulants algorithm through seeking frequencies within the frequency seeking range obtained above; the time-frequency ridge lines are used to reconstruct the instantaneous carrier curve of the hybrid SFH and DS signals so that the hop rate can be estimated by the digital baseband signals'symbol rate estimation algorithm based on the wavelet transform.5. Aiming at the characteristics that the FSK and PSK signals are respectively frequency and phase keying, knowing form the traditional single frequency and radio frequency (RF) jamming noise, the randomly frequency-hopping noise and the phase-modulated noise by the evenly distributed random code are proposed to be the jamming formats respectively for FSK and PSK signals. System error rate is adopted to measure the communication jamming effect. Under the condition that the timing synchronization has been completed, the error rate formulae of their effect on the communication receiver are deduced in the case respectively of the 2FSK and BPSK signal.