An Application of Digital Filters to Spread Spectrum Communications

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1. We proposed a method to analyze the steady-state performance of a complex coefficient adaptive infinite impulse response (IIR) notch filter which is useful for the rejection of multiple narrow-band interference in quadrature phase shift keying (QPSK) spread spectrum communication systems. The signal-to-noise ratio (SNR) improvement factor has been obtained from which the validity of the use of the notch filter can be concluded.2. We have investigated the problem of narrow-band interference (NBI) suppression in a direct-sequence code-division multiple-access (DS CDMA) communication system using adaptive IIR notch filter algorithms.We first proposed a second-order lattice-based adaptive IIR notch filter with a normalized algorithm. We found out from the convergence analysis that for large NBI power or interference-to-signal power ratio (ISR), the convergence speed of the normalized algorithm is independent of the number of DS CDMA system active users and power of the NBI which is a desirable result.Secondly, we analyzed the performance gain of the DS CDMA system afforded by the proposed second-order lattice-based adaptive IIR notch filter algorithms using SNR improvement factor of the decision variable and bit error rate (BER) as figures of merit. We found out that the SNR improvement factor increases with the power of the NBI and decreases with the number of DS CDMA system active users.3. We proposed a region-of-interest (ROI) image coding based on multiple wavelet transforms. The proposed method can avoid much information loss for non ROI at lower constrained bit rate caused in JPEG-2000, therefore the subjective image quality for whole of restored image will be improved, maintaining the quality of ROI higher than that of non-ROI.