A Fast Fourier Transform Approach to Interference Suppression in Direct Sequence Spread Spectrum Signals
DEFENCE RESEARCH ESTABLISHMENT OTTAWA (ONTARIO)
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An FFT algorithm is examined with respect to its utility as an interference suppressor in direct sequence spread spectrum communications signals. An FFT approach is especially attractive because of its computational economy. It is this approach which has been implemented on the TMS32OC30 hardware forming part of the Advanced Communications Electronic Support Measures System ACES and will be implemented on other high-speed hardware forming part of that system. The basic problem to be solved is described, followed by a description of the algorithm. The algorithm consists of power spectrum estimation using an FFT-based routine, interpolation of the power spectrum at equally-spaced points different from those calculated by the FFT, and design of an FIR linear phase filter which filters the data, i.e., suppresses the interference. This technique is feasible so long as the bandwidth of the interference during the observation time over which the FFT is calculated is much less than the bandwidth of the spread spectrum signal. An important result from this brief study is that the interpolation algorithm used can have an effect on the performance and reliability of the suppression filter ultimately designed and that for small order filters, the discrete Fourier transform approach may be better.
- Numerical Mathematics
- Non-Radio Communications