Broadband Interference Excision in Spread Spectrum Communication Systems Based on Short-Time Fourier Transformation

Abstract

Abstract-An interference excision algorithm in direct-sequence spread spectrum (DS-SS) communication systems is introduced. The proposed excision algorithm is developed for linear frequency modulated (LFM) signals that have broadband frequency characteristics. It is based on the time-frequency analysis of received signals employing short-time Fourier transformation (STFT). To analyze the interference, STFT of the received signal block is evaluated and thresholded. The interference detection is followed by an inverse-STFT computation to estimate the high-power jamming signal. The estimated jammer is then mitigated before demodulation. Simulations present adequate interference estimation results with mean estimation errors less than 0.01%. Various scenarios with different jammer-to-signal ratios (JSRs) and signal-to-noise ratios (SNRs) vs. bit error rates (BERs) are presented for single and multi-component LFM signals. Interference excision algorithms improve the system performance more than an order of magnitude.

Phase Detection With Sub-Nanometer Sensitivity Using Polarization Quadrature Encoding Method in Optical Coherence Tomography

“…Thus, the measured phase sensitivity by this method is as low as 0.23 degree, which allows measurements of pathdifference resolution of 265 pm in a displacement range of 430 nm. It is obvious that our method has better phase stability than the phase sensitivity experiments described in prior literatures [2-4, 6, 8, 12], which used either the Hilbert or Fourier transformation phase decoding method [22]. Besides, our technique which simply acquired optical phase fluctuation by using only the envelope decoding scheme has a reduction of data acquisition (e.g., at least 400 times less than the numerical phase decoding method as compared in Fig.…”

Applications of an Improved Time‐Frequency Filtering Algorithm to Signal Reconstruction

“…Γ is a × diagonal matrix, which is composed of I elements; the shift distance between I and I is . From (8) to (10), we can get the relationship betweeñand̃as…”

“…The time-frequency analysis method is an effective tool for nonstationary signal processing, which has been broadly used in communication, acoustics, mechanical signal processing, medical signal processing, and others [1][2][3][4][5]. Short time Fourier transform time-frequency representation (STFT-TFR) has a rich structure with dependencies along both the time and frequency axes, which is widely applied in speech [6,7], communication [8,9], and others [10,11]. A speech enhancement algorithm employing the STFT-TFR method is presented in [6], which takes advantage of the time and frequency dependencies of speech signals.…”

“…An improved method which can reconstruct the spectral phase of the speech signal is proposed in [7]; the method only depends on the fundamental frequency and the noisy observation from the STFT domain. An interference excision algorithm is proposed for direct-sequence spread spectrum communication systems [8,9], which analyze the interference in STFT timefrequency domain and detect and estimate the high-power jamming signal employing inverse STFT (ISTFT). Abdullah et al apply the STFT-TFR method to analyze the switches faults of three-phase voltage source inverter [10].…”

“…Fractional lower order statistic is applied to extract the evoked potential in [31,32]. In stable distribution environment, the STFT-TFR method in the literature [8][9][10][11] degrades and even fails. Therefore, the corresponding time-frequency filtering method employing the STFT-TFF method in [17][18][19] degenerates.…”