Group-orthogonal OFDMA in fast time-varying frequency-selective fading environments

This paper presents a group-orthogonal OFDMA (GO-OFDMA) suitable for broadband access systems in a fast time-varying frequency-selective fading environment when channel knowledge is not available at the transmitter. Subcarrier grouping to achieve the diversity gain of a time-domain Rake receiver is discussed and the closed-form expression of its bit-error-rate (BER) performance over a frequency-selective Rayleigh fading channel is derived. The proposed GO-OFDMA scheme uses a split-and-group structure and a maximum-likelihood (ML) multi-user detection (MUD) to increase the number of supportable active users and to reduce the peak-to-average ratio (PAR). Analytical and simulation results are in an excellent agreement. Performance evaluation indicates that the proposed GO-OFDMA provides a lower PAR and similar BER as compared with the group-orthogonal multi-carrier CDMA (GO-MC-CDMA), and outperforms the random-hopping (RH)-OFDMA and matched-filter based MC-CDMA.