Adaptive transform domain interference suppression in a hybrid DS/FH-system

We study the performance of a hybrid direct sequence frequency hopping (DS/FH) system with interference suppression in an environment where narrowband (relative to the DS spreading code bandwidth) interference perturbs the signal. In suppressing the narrowband interference, a transform domain approach has been chosen, i.e. the interference suppression takes place, e.g. in the frequency domain. This approach is more practical since the duration of a frequency hop is prohibitive to the use of time domain adaptive filtering. The aim of this paper is to study the relative performance of four different adaptive rules used in determining and suppressing the interfered frequencies in the frequency domain. The interference environment changes from frequency hop to hop but during each hop the interference is considered time-invariant. To avoid spectral leaking of the interfering power, windowing can be performed prior to transformation. The transformations are accomplished with the FFT and the inverse FFT algorithms. After the interference suppression the signal is transformed back to the time domain to be fed to the DS-code matched filter. The criterion used for the performance comparisons is the bit error probability as a function of E₁/N₀ and S/J. The numerical results were obtained by Monte Carlo simulations