Sensitivity of multiple-access techniques to narrow-band interference

This paper investigates the sensitivity of several multiple-access techniqu es to narrow-band interference. The analysis covers time-division multiple access (TDMA), code-division multiple access (CDMA), and the more recently introduced orthogonal frequency-division multiple access (OFDMA). The study is carried out under the assumption that all considered multiple-access sy stems occupy the same total bandwidth, and the bit rates of all active user s are identical, A major finding of this study is that CDMA with pseudonois e spreading sequences is more sensitive to narrow-hand interference than TD MA. We point out that the signal-to-jammer power ratio at the decision devi ce input is in fact identical for both multiple-access techniques, but the amplitude distribution of the jammer term at the threshold detector input i s more favorable to TDMA, which turns out to be more robust in terms of bit -error rate. Another finding is that in terms of sensitivity to narrow-band interference, orthogonal CDMA (OCDMA) is closer to OFDMA than to CDMA with pseudonoise sequences, because the degradation is not the same for all use rs. Finally, we discuss the relationship of OCDMA and OFDMA and highlight t he superiority, in terms of capacity over the narrow-band interference chan nel, of OFDMA to the other multiple-access techniques considered in this pa per.