| In the design of wireless communication systems, the most important concept to combat fading is diversity. This dissertation addresses advanced diversity techniques. It consists of two major thrusts: (i) Space-time (ST) coded multi-antenna systems; and (ii) Multiuser diversity. As part of the first thrust, a differential space-time-frequency (DSTF) coded orthogonal frequency division multiplexing (OFDM) scheme is proposed, which achieves maximum spatial and multipath diversity over multi-antenna frequency selective fading channels without channel state information (CSI) at the receiver. In an effort to develop low-cost, low-complexity alternatives to capturing the benefits of multi-antenna systems, antenna selection (AS) for multi-antenna systems is also addressed. In the presence of imperfect channel estimation over Rayleigh flat fading channels, the performance of AS for coherent ST coded systems is characterized, where the channel is estimated using multiplexed training and a minimum mean square error (MMSE) criterion. To avoid the drawback of potential training overhead and estimation complications, receiver AS for noncoherent and differential multi-antenna systems that employ unitary ST signals is further proposed in the first thrust for Rayleigh flat fading channels without CSI at the receiver. The results of AS for noncoherent and differential systems over flat fading channels are also extended to frequency selective fading channels.; In the second thrust, practical issues for robust rate adaptation to achieve multiuser diversity with outdated channel feedback are explored, where both single-antenna and multi-antenna systems are addressed. The spectral efficiencies for ST block coding (STBC) and transmit beamforming (BF) with outdated channel feedback are compared for multiuser diversity systems. The results herein can be potentially applied to the next generation cellular systems, wireless local area networks, and fixed/mobile wireless broadband services. |
