Abstract :
Performance of Multicarrier DS/SSMA Over Fast Rayleigh Fading Channels With Doppler Diversity The significant loss in performance of multicarrier direct-sequence spread-spectrum multiple-access (DS/SSMA) systems over fast-fading channels is investigated. First, the channel model for individual subchannels is obtained using a canonical decomposition to a wide-sense stationary, uncorrelated scattering channel. Next, a receiver structure, which features both Doppler diversity and frequency diversity, is presented and analyzed. It is found that large Doppler spreads cause the average magnitude of the desired signals to diminish dramatically. Expressions for the bit-error rate are derived for both uncoded and coded systems by applying the standard Gaussian approximation. Numerical results, which show that Doppler diversity is preferable over frequency diversity in fast-fading channels, are provided for different combinations of the diversity orders. Numerical results, which show that the intersymbol and intersubchannel interference can be effectively suppressed, are also provided. It is show that the multiple-access interference tends to degenerate into a wide-sense stationary process with a statistical periodicity destroyed by the fast-fading channel.
