Recursive Fourier transform for interference suppression in PN spread spectrum communications

We use recursive short-time Fourier transforms (STFT) for interference excision in PN spread spectrum communication systems. The proposed excision method is based on the attractive localization properties of the impulse responses of the multiple pole filters. These impulse responses have Gaussian-like shapes and decrease in bandwidth with higher pole multiplicities. When used as a data window before Fourier transformation, they result in a large class of computationally efficient STFTs. Localization measures can be applied to determine the proper window (impulse response), which maximally concentrates the jammer in the time-frequency domain. Interference mitigation is then achieved by applying a binary excision to the STFT employing the optimum window for each data bit. We show that this method permits both data-dependent windowing and filtering, and leads to improved BER performance of the DS/SS system.