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Linear equalizers (LEs) have been widely adopted for practical systems due to their low computational complexity. However, it is also well known that LEs provide inferior performance relative to a maximum-likelihood equalizer (MLE) or other near- MLEs, because LEs usually cannot collect the diversity order enabled by the transmitter and at the same time they lose mutual information. More importantly, unlike MLE or near-MLEs, the performance of LEs has not been well quantified. This hinders more general applications of LEs in wireless systems. In this paper, we reveal a fundamental link between a channel parameter-orthogonality deficiency (od) of the channel matrix-and the diversity and capacity of LEs. We identify that when the od of channel matrix has an upper bound strictly less than 1, the same diversity order as that of MLEs is collected by LEs and the outage capacity loss relative to MLEs is also a constant over signal-to-noise ratio (SNR). These results can be applied to designing a framework for hybrid equalizers. Furthermore, by studying the statistical properties of the od and comparing the complexity of different equalizers, we show that hybrid equalizers can trade off between performance and complexity by tuning the channel matrix od. The theoretical analysis is corroborated by computer simulations. [ABSTRACT FROM AUTHOR]

Differential encoding is known to simplify receiver implementation because it by-passes channel estimation. However, over rapidly fading wireless channels, ext!a transceiver modules are necessary to enable differential transmission. Relying on a basis expansion model for time and frequency selective (doubly selective) channels, we derive such a generalized block-differential (BD) codec and prove that it achieves maximum Doppler and multipath diversity gains, while affording low-complexity maximum-likelihood decoding. We further show that existing BD systems over frequency-selective or time-selective channels follow as special cases of our novel system. Simulations using the widely accepted Jakes' model corroborate our theoretical analysis. [ABSTRACT FROM AUTHOR]

We design novel space-time multipath (STM) coded multi-antenna transmissions over frequency-selective Rayleigh fading channels. We develop STM coded systems that guarantee the maximum possible space-multipath diversity, along with large coding gains, and high bandwidth efficiency for any number of transmit-receive antennas. By incorporating subchannel grouping, we also enable desirable tradeoffs between performance and complexity. Our designs rely on digital phase sweeping or block circular delay operations and apply to both single- and multi-carrier systems. Their merits are confirmed by corroborating simulations and comparisons with existing approaches. [ABSTRACT FROM AUTHOR]

Exciting recent developments in wireless multiantenna communications have led to designs aiming mainly at one of two objectives: either high-performance by enabling the diversity provided by multi-input multi-output (MIMO) channels or high-rates by capitalizing on space-time multiplexing gains to realize the high capacity of MIMO fading channels. By concatenating a linear complex-field coder (a.k.a. linear precoder) with a layered space-time mapper, we design systems capable of achieving both goals: full-diversity and full-rate (FDFR), with any number of transmit- and receive-antennas. We develop FDFR designs not only for flat-fading but for frequency-selective, or, time-selective fading MIMO channels as well. Furthermore, we establish the flexibility of our FDFR designs in striking desirable performance-rate-complexity tradeoffs. Our theoretical claims are confirmed by simulations. [ABSTRACT FROM AUTHOR]