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Co-channel Interference, Fractional Fourier Transform, Minimum Mean-square Error, Speech, Wigner Distribution.

The Fractional Fourier Transform (FrFT) can provide significant interference suppression (IS) over other techniques in real-life non-stationary environments because it can operate with very few samples. However, the optimum rotational parameter ‘a’ must first be estimated. Recently, a new method to estimate ‘a’ based on the value that minimizes the projection of the product of the Wigner Distributions (WDs) of the signal-of-interest (SOI) and interference was proposed. This is more easily calculated by recognizing its equivalency to choosing ‘a’ for which the product of the energies of the SOI and interference in the FrFT domain is minimized, termed the WD-FrFT algorithm. The algorithm was shown to estimate ‘a’ more accurately than minimum mean square error FrFT (MMSE-FrFT) methods and perform far better than MMSE Fast Fourier Transform (MMSE-FFT) methods, which only operate in the frequency domain. The WD-FrFT algorithm significantly improves interference suppression (IS) capability, even at low signal-to-noise ratio (SNR). In this paper, we apply the proposed WD-FrFT technique to recovering a speech signal in non-stationary co-channel interference. Using mean-square error (MSE) between the SOI and its estimate as the performance metric, we show that the technique greatly outperforms the conventional methods, MMSE-FrFT and MMSE-FFT, which fail with just one non-stationary interferer, and continues to perform well in the presence of severe co-channel interference (CCI) consisting of multiple, equal power, non-stationary interferers. This method therefore has great potential for separating co-channel signals in harsh, noisy, non-stationary environments.