Narrow-band interference rejection in orthogonal multi-carrier spread-spectrum communications

In order to combat strong narrow band interference, different measures called notch-filtering in the time domain (based on LMS algorithm) and in the transform domain (based on FFT) with spread-spectrum (SS) have been analyzed. Another interesting approach is based on orthogonal multi-carrier transmission called the orthogonal-frequency-division-multiple-access (OFDM) technique. This technique permits to achieve a high spectral efficiency and to combat the frequency selective fading and the interference in the channel by switching-off some sub-carriers. The aim of the article is to study the performance of the combination of a spread-spectrum system with OFDM in the presence of narrow-band interference. This combination allows one to use the spectrum in an efficient way, to exploit frequency diversity, to increase the robustness against fading and interference and to retain many advantages of a spread-spectrum system. The interference is considered as narrow-band multi-tone sine interference. A method for evaluating both interference and fading process based on frequency domain analysis is studied. The estimated interference and fading process is used for weighting each received chip before despreading. The results showed that the combination of spread-spectrum/OFDM in the presence of multi-tone narrow-band interference in a frequency/time selective fading channel is a promising approach