Wideband Non-stationary Interference Signal Time-frequency Analysis And Rejection Techniques

Non-stationary wide-band signals are new kind signals which traditional Fourier Transform is insufficient to analylize them. This leads to time-frequency analysis. Time-frequency analysis describes signals in both time and frequency domain. It shows how the signals'spectra vary according to time changes. The purpose of time-frequency analysis is to construct a distribution which shows the signals'power or intensity in both time and frequency domain in order to analylize, process and extract signals'characteristics.There are two kinds of time-frequency presentations: linear and non-linear. Typical linear time-frequency presentations are Short Time Fourier Transform and Fractional Fourier Transform, while typical non-linear presentations are Wigner Ville Distribution, Cohen Class and the like. In this paper, we discuss all these presentations in detail and their usages.Time-frequency analysis is based on signal model. In this paper we use Linear Frequency Modulation signal as a main model to analylize and compare different time-frequency analysis. Besides, we also discuss Non-Linear Frequency Modulation signal analysis using optimized Short Time Fourier Transform. It enhances the time-frequency domain resolution, thus having better ability to extract signal characteristics.Interference and anti-interference are common topics in communication systems. Traditional spectrum spread is efficient in sippressing narrow band interference. But a spectrum spread system's interference immunity depends on spectrum spread gain. As frequency is limited resource, spectrum spread gain can't be too high. Therefore, spectrum spread systems lose efficiency when dealing with wide band interference. If we apply time-frequency analysis in receiver, we can extract interference parameters and filter interference, thus eliminating the interference. Based on Linear Frequency Modulation interference, we simulate system BER performance and prove the efficiency of time-frequency analysis.Moreover, we discuss the Joint Iterative Demodulation and Decoding algorithm. Through exchanging soft information between demodulator and decoder, the demodulation and decoding process runs iteratively. Simulation results shows that applying this algorithm in spectrum spread system will improve Bit Error Rate performance.In the end, after comparing three most common time-frequency analysises, considering both BER performance and complexity, we propose a non-stationary wide band interference suppression scheme in spectrum spread systems.