Bit pattern matched phase interference suppression in a hybrid DS/FH-system

Abstract

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, the transform domain approach has been chosen, i.e. the interference suppression takes place in the frequency domain. This approach is more practical since the duration of a frequency hop may be prohibitive to the use of time domain adaptive filtering. The aim of this paper is to study the relative performance of three different schemes used in determining and suppressing the interfered frequencies in the frequency domain, namely the exciser structure (EXC), phase interference suppressor (PIS) and a novel bit pattern matched phase interference suppressor (BPM-PIS). 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, three different candidate windowing approaches are 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 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 E/sub b//N/sub 0/ and S/J. The numerical results were obtained by Monte Carlo simulations.