Performance of a spread spectrum OFDM system in a dispersive fading channel with interference

This paper investigates the use of frequency domain equalization techniques to suppress narrowband interference and combine multiple paths in both direct sequence spread spectrum (DS-SS) and orthogonal frequency division multiplexing (OFDM) spread spectrum (OFDM-SS) systems. The similarities between the two signaling formats are highlighted and it is shown that the same receiver structures can be used for both. Two and four ray channels are considered, including those with delay spreads in excess of the symbol interval, along with tone jamming. The results show that all the equalizers that were evaluated are able to suppress the tone interference while combining the energy in the multiple paths. Additionally, in order to maintain good performance, decision feedback and multiple layers of forward taps are necessary when the delay spread is in excess of a symbol interval.