Abstract This paper presents two group‐based tone diversity schemes, namely, group‐orthogonal tone‐combining‐diversity (GO‐TCD) and group‐optimal tone‐selection‐diversity (GO‐TSD), for orthogonal frequency division multiple access (OFDMA) system in broadband wireless communications. In both schemes, the entire frequency band ofNsub‐carriers is divided intoNG = N/Lfsub‐carrier groups with each havingLfsub‐carriers. When the channel knowledge is not available at the transmitter, GO‐TCD, which has a split‐and‐group structure to reduce the peak‐to‐average ratio (PAR) and employs the multi‐user detection for maximum‐likelihood (ML) estimation to increase the number of active users, is proposed and shown to provide a lower PAR and similar performance as compared with the group‐orthogonal multi‐carrier CDMA, and outperforms the random‐hopping (RH)‐OFDMA and matched‐filter based MC‐CDMA. When the channel knowledge is available at the transmitter, GO‐TSD can be used to select the best sub‐carrier in a given sub‐carrier group for any active user and shown to offer a throughput comparable to the optimal tone selection but with much less complexity. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract This paper considers direct‐sequence code‐division multiple‐access with zero‐correlation zone sequences (ZCZ‐CDMA) and orthogonal frequency‐division multiple‐access (OFDMA) schemes using M‐ary QAM signaling for broadband wireless communications. Their system structures, complexities and performances in both AWGN and multipath frequency‐selective fading channels are evaluated and compared. For ZCZ‐CDMA, joint suppression of the multipath fading interference and multiple‐access interference can be achieved with a reduced family‐size of the spreading sequences. For OFDMA, analytical and simulation results indicate that it has the same performance as ZCZ‐CDMA in fast time‐varying multipath fading channels. In time‐invariant or slowly time‐varying channels, where the channel information can be made available to transmitters, OFDMA outperforms ZCZ‐CDMA, offers a higher capacity and is more flexible for system reconfiguration with a comparable computational complexity. Copyright © 2004 John Wiley & Sons, Ltd.