Frequency-domain orthogonal multiuser communications over frequency-selective slowly fading channels

Applying the properties of the frequency-domain approach (Cha´o-Ming Chang and Kwang-Cheng Chen, IEEE Commun. Lett., vol.4, no.11, p.331-3, 2000) to avoid MAI in asynchronous multiuser communications and sharing the rationale behind OFDM systems to mitigate ISI, we propose an asynchronous multiuser communications system over frequency-selective slowly fading channels such that optimal demodulation with similar complexity to point-to-point communications is possible. In addition, by spreading the symbol energies to the whole transmission frequency band, we introduce another asynchronous multiuser communications system to utilize the frequency diversity gain. These proposed systems not only mitigate MAI and ISI efficiently with simple complexity, but also are flexible for variable rate transmission, suggesting their application to practical multimedia services.